Nanoporous Carbon: Liquid-Free Synthesis and Geometry-Dependent Catalytic Performance
- Ruoyu XuRuoyu XuDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Ruoyu Xu,
- Liqun KangLiqun KangDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Liqun Kang,
- Johannes KnossallaJohannes KnossallaMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, GermanyMore by Johannes Knossalla,
- Jerrik MielbyJerrik MielbyDepartment of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby, DenmarkMore by Jerrik Mielby,
- Qiming WangQiming WangDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Qiming Wang,
- Bolun WangBolun WangDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Bolun Wang,
- Junrun FengJunrun FengDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Junrun Feng,
- Guanjie HeGuanjie HeDepartment of Chemistry, University College London, 20 Gordon Street, Bloomsbury, WC1H 0AJ London, United KingdomMore by Guanjie He,
- Yudao QinYudao QinDepartment of Chemistry, University College London, 20 Gordon Street, Bloomsbury, WC1H 0AJ London, United KingdomMore by Yudao Qin,
- Jijia XieJijia XieDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Jijia Xie,
- Ann-Christin SwertzAnn-Christin SwertzMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, GermanyMore by Ann-Christin Swertz,
- Qian HeQian HeCardiff Catalyst Institute, School of Chemistry, Cardiff University, CF10 3AT Cardiff, United Kingdom)More by Qian He,
- Søren KegnæsSøren KegnæsDepartment of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby, DenmarkMore by Søren Kegnæs,
- Dan J. L. BrettDan J. L. BrettDepartment of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Dan J. L. Brett,
- Ferdi SchüthFerdi SchüthMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, GermanyMore by Ferdi Schüth, and
- Feng Ryan Wang*Feng Ryan Wang*E-mail: [email protected]Department of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United KingdomMore by Feng Ryan Wang
Copyright © 2019 American Chemical Society
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Abstract
Nanostructured carbons with different pore geometries are prepared with a liquid-free nanocasting method. The method uses gases instead of liquid to disperse carbon precursors, leach templates, and remove impurities, minimizing synthetic procedures and the use of chemicals. The method is universal and demonstrated by the synthesis of 12 different porous carbons with various template sources. The effects of pore geometries in catalysis can be isolated and investigated. Two of the resulted materials with different pore geometries are studied as supports for Ru clusters in the hydrogenolysis of 5-hydroxymethylfurfural (HMF) and electrochemical hydrogen evolution (HER). The porous carbon-supported Ru catalysts outperform commercial ones in both reactions. It was found that Ru on bottleneck pore carbon shows a highest yield in hydrogenolysis of HMF to 2,5-dimethylfuran (DMF) due to a better confinement effect. A wide temperature operation window from 110 to 140 °C, with over 75% yield and 98% selectivity of DMF, has been achieved. Tubular pores enable fast charge transfer in electrochemical HER, requiring only 16 mV overpotential to reach current density of 10 mA·cm–2.
Substituting fossil feedstocks with renewable ones calls for efficient processes that convert biomass and green electricity to fuels and chemicals. (1,2) This requires the development of effective catalytic materials beyond the ones that are currently used for petrochemicals. (3,4) The key is to understand (i) the catalytic active-site structure, (ii) the support–active-site chemical interaction, and (iii) the local physical environment of the active site. While the former two are widely studied, the effect of local physical environment, such as pore geometry, has yet to be fully explored and optimized independently. Such an environment strongly influences the catalytic processes, determines the mass transfer efficiency, and provides confinement effects for active species. (5−7)
Nanocasting with hard templates is a well-known method to prepare porous materials. It has been applied to make porous carbon, an important class of materials widely used as supercapacitors, (8,9) effective cathode materials for lithium–sulfur batteries, (10) as well as heterogeneous catalysts. (11−16) In order to study the effects of pore geometries in these carbon materials, precise control of different pore structures via strictly identical synthetic procedures is needed. The synthetic steps and use of chemicals must be minimized to reduce the fluctuation of the chemical properties of the porous materials. However, these are difficult to achieve with the current nanocasting method via wet chemistry, which requires multistep processing, frequent solid–liquid separation, and long operation cycles. (17−20) The low efficiency of complex procedures and the unavoidable large-scale liquid waste containing environmentally unfriendly HF (21−23) or NaOH (24) also limit the potential application of these carbon materials in industrial energy conversion.
In this work, we report a liquid-free synthesis of porous carbon support that leads to carbon materials with the same chemical property but different pore geometry. The synthesis follows hard-templating principles in which the creation of pores stems from an inverse replica of a porous silica template. (25−27) Uniform pore structure can therefore be achieved. Compared to the conventional method, this liquid-free synthesis uses gas for dispersing the carbon precursor, leaching templates, and removing impurities. The synthesis contains only two steps with two chemicals, which is significantly simplified compared with traditional methods. First, chemical vapor deposition (CVD) of ferrocene over a porous SiO2 template forms a SiO2@Fe–carbon composite. Second, porous carbon that is a direct reverse replica of the SiO2 template is obtained by heating the composite with polytetrafluoroethylene (PTFE), in which SiO2 is completely leached into gaseous SiF4 (Figure 1a). The simple and liquid-free operations minimize any chemical differences of the obtained porous carbons.
Figure 1
Figure 1. (a) Schematic of hard template carbon synthesis via liquid-free and conventional methods. (b, c) Transmission electron microscopy (TEM) images of the SiO2@m-SiO2 and SBA-15 templates, respectively. (d, e) Schematic of the bottleneck and tubular pores, respectively. (f, g) TEM images of the Fe/C-SiO2@m-SiO2 and Fe/C-SBA-15 composites, respectively. (h, i) TEM images of C-SiO2@m-SiO2 and C-SBA-15 composites, respectively.
Hydrogenolysis of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) and electrochemical hydrogen evolution reaction (HER) are chosen for evaluating the pore geometry effect in catalysis. These two reactions involve utilizing the dissociative hydrogen atom that is one of the most essential renewable energy carriers. The effect of pore geometry plays an important role in these reactions because mass-transfer limitation and confinement effects are crucial for the transport of molecules and the dispersion of metal clusters. (16) On the basis that (1) uniform pore geometries are achieved via the hard template method, (2) carbon supports have the same chemical properties, and (3) as-prepared Ru clusters have same size distributions and surface oxidation states, the study of the catalytic behaviors resulting from two distinct pore geometries (bottleneck and tubular) is then possible. The Ru/C-SiO2@m-SiO2 catalyst with a bottleneck pore gives an outstanding catalytic performance with a yield of 90% in the hydrogenolysis of HMF to DMF. Such a high DMF yield at the moderate reaction temperature (140 °C) and low Ru/HMF molar ratio (3.5%) substantially exceeds the best reported PtCo catalysts in the literature. (11) For HER, the C-SBA-15 with tubular pores achieves the current density of 10 mA·cm–2 with only 16 mV overpotential, which also outperforms the commercial Pt/carbon. Bottle-neck pores, on the other hand, offer high electrochemical stability due to the confinement of active Ru species.
Finally, we demonstrate that the liquid-free synthesis is universal as it can be applied to at least 10 other types of porous carbons using five commercial zeolites (K-SSZ-13, silicate-1, Na-ZSM-5, Na-zeolite beta, and Na-zeolite Y), two commercial ordered mesoporous silica (KIT-6 and MCM-41), and three in-house made silicas (SiO2@m-SiO2 with half shell thickness and two mesoporous silica spheres) (Figure S1). Our scope of templates includes SSZ-13 and ZSM-5 that have a small pore size of 0.38 and 0.47 nm, respectively, significantly exceeding the pore limit of conventional wet chemistry synthesis. Such synthesis provides a library of hard templating carbon materials, enabling fundamental study on their pore geometry-dependent behaviors in catalysis, energy conversion, and storage.
Results and Discussion
ARTICLE SECTIONS
Ferrocene is used as the carbon source owing to its low sublimation temperature (100 °C) and high carbon-to-hydrogen ratio that provides good carbon yield. (28) The presence of Fe also catalyzes the carbonization. (29) SiO2@m-SiO2 and SBA-15 are used as templates to form porous carbons with bottleneck and tubular pores, respectively. The bottleneck pore origins from the use of octadecyltrimethoxysilane (30) in the ethanol–water mixture as the structure-directing agent, while that of the tubular pore stems from the use of Pluronic P123 with the presence of HCl (Figures 1b–e and S2a,b). The pore size of the SiO2@m-SiO2 and SBA-15 are 3.5 and 4.9 nm, respectively, while the size of the ferrocene molecule is 0.40 nm. The small ferrocene size ensures its diffusion within the pores in both systems. During the pyrolysis step, the ferrocene is oxidized to ferricenium. The strong interaction between the ferricenium and the silanol groups on the intersurface of porous silica leads to the uniformly distribution of pyrolytic carbon clusters on the pore walls of silica templates. (31) Thus, the carbon replica of SiO2@m-SiO2 and SBA-15 can be obtained.
During CVD, ferrocene vapor penetrates the pore systems of the templates and simultaneously decomposes into carbon and iron (Figure. 1f,g). The Fe/C-SiO2@m-SiO2 composite maintains the spherical morphology of the SiO2@m-SiO2 templates, while the tubular pore structures are still visible in the Fe/C-SBA-15 composite (Figures 1f,g and S2c,d). This indicates that ferrocene CVD does not change or affect the structure of the SiO2 template. A comparison of N2 physisorption before and after CVD shows the successful carbon filling of the micropore and mesopore channels in the SiO2 templates (Figure S3). FeOx nanoparticles are found in the composite (Figures 1f,g and S4). The presence of FeOx nanoparticles is important as they catalyze the carbonization reaction and increase the carbon yield. (29) The oxidation state of Fe is between Fe3O4 and Fe2O3 according to X-ray absorption spectroscopy fine structure (XAFS) (Figure S5a,c) and X-ray photoelectron spectroscopy (XPS) (Figure S5e). The pore-filling degree can be calculated by the differences in pore volume (PV) before and after CVD. The filling degrees for SiO2@m-SiO2 and SBA-15 templates are 40% and 54%, respectively (Tables S1). The high filling degree in SBA-15 is due to the tubular channel that boosts the mass transfer during CVD.
The composites are physically mixed with PTFE powder and heated at 900 °C under N2 in order to leach the SiO2 (Figure S6). PTFE first decomposes into several gaseous carbon fluoride compounds which subsequently react with SiO2, forming CO and SiF4. (32) The overall reaction is
This reaction forms only gaseous products and leaves carbon untouched, providing instant separation of carbon during leaching. SiF4 is then reacted with CaCl2 postsynthesis, forming CaF2 and HCl. C-SiO2@m-SiO2 is spherical with hollow voids originating from the solid core in SiO2@m-SiO2. The void diameter 180 ± 8 nm and shell thickness 40 ± 3 nm match those of the SiO2@m-SiO2, showing the perfect replica of the original template (Figures 1h and S2e). The ordered tubular pore structure is obtained in C-SBA15 after leaching at 900 °C, suggesting very good thermal and chemical stability (Figure. 1i). Fe nanoparticles further catalyze the carbon graphitization during PTFE leaching, as indicated in the large graphitic domain in the Raman spectroscopy of C-SiO2@m-SiO2 (Figure S7). In comparison, a smaller graphitic domain is obtained when Fe is removed by HCl prior to the PTFE leaching. After PTFE leaching, Fe nanoparticles cannot be found in the TEM images for both carbons (Figures 1h,i and S2e,f). The XPS and energy-dispersive X-ray spectroscopy (EDS) analysis after PTFE leaching show no obvious presence of Fe (Figures S5 and S8). The XAFS spectra indicates the initial FeOx are reduced to metallic Fe nanoparticles in both carbons (Figure S5b,d). The Fe content is further analyzed by microwave plasma atomic emission spectroscopy (MP-AES), giving 0.97 and 0.42 wt % of Fe for C-SiO2@m-SiO2 and C-SBA-15, respectively (Table S2), which are much smaller than the 30 wt % Fe content in the ferrocene precursor. This indicates the separation between carbon and in situ formed Fe nanoparticles during the PTFE leaching at 900 °C. The thermogravimetric analysis (TGA) shows 93 and 98 wt % weight loss for C-SiO2@m-SiO2 and C-SBA-15 at 800 °C, respectively (Figure S9). Considering that Fe2O3 and SiO2 are the major components in the TGA residue, the calculated SiO2 contents are 5.6 and 1.4 wt % for C-SiO2@m-SiO2 and C-SBA-15, respectively. The porous carbons are the inverse replica of the original silica templates and have different pore geometries (Figures 2a and b). Amounts of 153 mg and 137 mg of C-SiO2@mSiO2 and C-SBA-15 are collected with 650 mg of ferrocene consumed. This gives the carbon yields of 23% and 21% and carbon balances of 37% and 33%, respectively, with our current lab setup. The carbon yields are close to the theoretical carbon yield of 30% that is reported in the literature using sucrose as the carbon precursor. (33) The specific surface areas for C-SiO2@m-SiO2 and C-SBA-15 are 806 and 872 m2·g–1, respectively, which are very similar to each other. The pore size and pore volume of C-SBA-15 are 4.0 nm and 0.72 cm3·g–1, which are higher than those of C-SiO2@m-SiO2 (2.2 nm and 0.56 cm3·g–1) (Figure 2c,d). The smaller pore size of the C-SiO2@m-SiO2 will have a better pore confinement effect than that of C-SBA-15. Such a pore confinement effect for metal clusters will be examined in the hydrogenolysis of 5-HMF to DMF. In addition to ferrocene, the liquid-free synthesis is suitable for a wide range of carbon precursors. C–N–SiO2@m-SiO2 composite (Figure S10a) and C–N–SBA-15 composite are formed during CVD using pyrrole and acetonitrile, respectively, as the carbon precursor. After PTFE leaching, the pure carbon material C–N–SBA-15 is obtained (Figure S10b).
Figure 2
Figure 2. N2-physisorption isotherms of (a) SiO2@m-SiO2 and (b) SBA-15 and their carbon replica. (c, d) Pore size distributions of C-SiO2@m-SiO2 and C-SBA-15, respectively.
Pore Structure–Activity Relationship in HMF Hydrogenolysis
PtCo has been identified as the benchmark for HMF to DMF conversion, suggesting an economical route to produce biofuel (DMF) (11) from a cellulose-derived platform chemical (HMF). (34) Ru is selected as a less expensive alternative to Pt and is loaded into the pore system of the porous carbon via wetness impregnation. Before being loaded with Ru, the C-SiO2@m-SiO2 and C-SBA-15 are washed with HCl solution to remove the residue of Fe and minimize any catalytic influences from those residues (Figure S11). High-angle annular dark-field scanning transmission microscopy (HAADF-STEM) reveals ultrasmall Ru clusters at 1.0 ± 0.2 and 0.9 ± 0.2 nm, evenly distributed through C-SiO2@m-SiO2 and C-SBA-15 support, respectively (Figure 3a,b). Such small clusters have different electronic structures and surface energy compared to that of the nanoparticles (>2 nm), leading to different catalytic behaviors. (35) Therefore, it is very important to avoid the growth of Ru clusters into nanoparticles during catalysis. The surface of Ru clusters on both carbon supports is in the oxidized form, as confirmed by the RuOx signal in the XPS (Figures S12a,c). The carbon XPS of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 also give very similar spectra. The fluorine 1s signal is found in the XPS full elements scan (Figure S11). The binding energy of the F 1s peak is between 686.5 and 687.5 eV. This is in a good agreement with the reported values of fluorinated graphite oxide (687.0 eV) (36) and different from that of PTFE (689.6 eV). (37) The Ru contents, determined by MP-AES element analysis, are 7.52 and 7.46 wt % for Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15, respectively (Table S2). The Fe residues further reduce to 0.24 and 0.09 wt %, respectively. We, therefore conclude that initial Ru clusters in both supports are identical to each other, while the Ru–carbon interactions are also the same. The catalytic properties of materials with different pore geometries are then investigated independently.
Figure 3
Figure 3. Hydrogenolysis of 5-HMF to DMF. (a–c) HAADF-STEM images of Ru/C-SiO2@m-SiO2, Ru/C-SBA-15, and Ru/C-commercial before catalysis. (d–f) HAADF-STEM images of Ru/C-SiO2@m-SiO2, Ru/C-SBA-15, and Ru/C-commercial after catalysis. (g–i) Histogram of Ru particle size before and after catalysis. (j) Hydrogenolysis of HMF to DMF. The main side products are DMTHF and humins. (k) Left: HMF conversion (black), DMF yield (red), DMF selectivity (blue), and DMTHF yield (pink) as a function of the Ru/HMF molar ratio. Reaction conditions: T = 130 °C; P = 10 bar H2; t = 2 h; HMF 0.16 mmol in 3 mL of THF. Right: HMF conversion (black), DMF yield (red), DMF selectivity (blue), and DMTHF yield (pink) as a function of temperature. Reaction conditions: P = 10 bar H2; t = 2 h; HMF 0.16 mmol in 3 mL of THF; Ru/HMF molar ratio 2.6%. The pink zone shows the 30 °C temperature window with over 75% yield of DMF and more than 98% selectivity. The DMF yields using Ru/C-SBA-15 and Ru/C-commercial are marked in purple and green, respectively.
The hydrogenolysis of 5-HMF comprises several steps. First, C═O is converted to C–OH, forming 2,5-hydroxymethylfuran (BHMF). C–O cleavage takes place at the two hydroxyl groups, resulting in DMF. The furan group can overreact with H2, forming cis- and trans-2,5-dimethyltetrahydrofuran (DMTHF) (Figure 3j). Another route to DMF is via the formation of 5-methylfurfural (5-MF). HMF can also undergo polymerization to humins. A major task in this reaction is to avoid ring hydrogenation and humin formation. Ru/C-SiO2@m-SiO2 is studied first to obtain the best operation conditions. The molar ratio between the catalyst and 5-HMF is adjusted to maximize the DMF yield (Figure 3k, left). With a 2.2% molar ratio of Ru to HMF, 79% conversion is achieved with 77% yield and 97% selectivity to DMF at 130 °C (Figure 3k and Table S3), indicating the selective hydrogenation on the formyl group and the hydrogenolysis of the hydroxyl group at low temperature. At 2.6% molar ratio the conversion increases to 84% and the yield of DMF reaches 82%, with only a trace amount of side products. Further increase of the molar ratio to 3.1% and 4.4% causes the formation of DMTHF isomers (Figure S13), and the selectivity of DMF drops to 37% and 4%, whereas the conversion remains at 95%. Kept at a 2.6% molar ratio, the reaction temperature is then varied (Figure 3k, right). The selectivity stays above 98% from 110 to 140 °C, while the conversion increases from 76% to 91%. The drop of selectivity is observed at 160 °C, forming DMTHF. Thus, the highest yield of DMF with Ru/C-SiO2@m-SiO2 is 90%, achieved at 140 °C and 2.6% molar ratio. Ru/C-SBA-15 and commercial Ru/carbon (Ru/C-commercial) give 93% and 86% conversion under the same conditions, but with only 71% and 49% yields of DMF, respectively (Figure 3k, right). The low selectivity toward DMF using Ru/C-SBA-15 and commercial Ru/carbon is due to the incomplete conversion of intermediate species such as BHMF and 5-MF. The 5-HMF hydrolysis was also performed with C-SiO2@mSiO2, C-SBA-15, and commercial activated carbon, giving 34%, 3%, and 6% HMF conversion, respectively. The yields of DMF are only 6%, 0%, and 4% for C-SiO2@m-SiO2, C-SBA-15, and commercial activated carbon, respectively. The difference in HMF conversion among the three carbons comes from the slight higher Fe in the C-SiO2@mSiO2 than that of the others.
C-SiO2@m-SiO2, C-SBA-15, and C-commercial have bottleneck (2.2 nm) and tubular (4.0 nm) pores and micropores (<1 nm), respectively. The strength of the pore confinement effect to Ru clusters at 1 nm is in the order C-SiO2@m-SiO2 > C-SBA-15 > C-commercial (Figure 3a–c). As a result, the size of Ru clusters grows from 1.0 ± 0.2, 0.9 ± 0.2, 1.1 ± 0.5 nm to 1.2 ± 0.2, 1.5 ± 0.5, 2.0 ± 1.0 nm over C-SiO2@m-SiO2, C-SBA-15, C-commercial, respectively, after catalysis (Figure 3a–i). The slight increase of Ru sizes in Ru/C-SBA-15 and Ru/C-commercial during catalysis leads to the change of surface electronic structures, a decrease of the active surface, and thus the loss of activity. Cluster aggregations are found for both Ru/C-SBA-15 and Ru/C-commercial, suggesting that Ru clusters are more mobile on those supports than that of Ru/C-SiO2@m-SiO2 (Figures 3d–f and S14–16). The cluster aggregation on Ru/C-commercial is more severe than that on Ru/C-SBA-15, leading to a lower DMF yield of 49% than the 71% yield using the Ru/C-SBA-15 catalyst. This clearly indicates the importance of bottleneck pores in confining active Ru clusters during catalysis, showing a wide operation window from 110 to 140 °C, with over 75% yield and 98% selectivity of DMF. The temperature range of the window is the lowest compared to those reported in the literature. (38−41) Our result significantly outperforms the benchmark PtCo catalyst, which gives only 5% DMF yield at 120 °C under the same conditions and requires at least 160 °C to achieve a substantial DMF yield (Table S4). (11) These results show the superior activity of sub-nanometer Ru clusters in the hydrogenolysis of 5-HMF and, thus, the significant importance of confinement effects from the bottleneck pores that prevent the growth of the clusters.
The recycled Ru/C-SiO2@m-SiO2 shows 72% conversion, 68% yield, and 94% selectivity to DMF at 130 °C (Table S3, entry 9). The XPS spectrum reveals nonsignificant changes for both Ru and carbon (Figure S12b and Table S5 and S6). A slight increase of the metallic Ru crystalline domain is found in X-ray diffraction (Figure S17). This is in good agreement with X-ray absorption near-edge spectroscopy (XANES), showing the reduction of the average Ru oxidation state (Figure 4a). The Ru K absorption edge position shifts to lower energy (Figure S18), and the coordination number of the first-shell Ru–Ru scattering (2.69 Å) increases from 0.7 ± 0.4 to 3.9 ± 0.8, while the Ru–O scattering coordination number decreases (Figure 4c,d and Table S7). This is due to the partial reduction of Ru by H2 during the reaction.
Figure 4
Figure 4. (a) XANES and (b) k2-weighted R space extended X-ray absorption fine structure (EXAFS) of Ru foil (purple), Ru/C-SiO2@m-SiO2 before (red), after catalysis (blue), RuO2 (black). Experimental and fitted results of Ru/C-SiO2@m-SiO2 in R-space EXAFS (c) before and (d) after catalysis (SBA-15), respectively.
Pore Structure–Activity Relationship in Electrochemical H2 Evolution
Electrochemical HER produces CO-free H2 for fuel cells and ammonia synthesis, where low porosity resistance (42) and efficient charge transfer (43,44) are the keys to achieving high activity. Here, the HER activities in bottleneck and tubular mesopores are studied. The same Ru clusters described above are selected as the active species due to their lower price and similar H2 bond strength compared to that of Pt in alkaline media. (45,46) Ru/C-SBA-15 exhibits a negligible overpotential (16 mV) at a current density of 10 mA cm–2, which is only one-third that of Ru/C-SiO2@m-SiO2 (42 mV) and commercial Pt/C (42 mV) (Figure 5a). Such low overpotential is the key indicator of high HER activity. Electrochemical impedance spectroscopy (EIS) is performed to understand their differences in porosity resistance and charge-transfer efficiency during HER reaction (Figure 5b). Here, the high-frequency semicircle (at lower Z′) represents the resistance in the formation of the electrical double layer within the pore, while the low-frequency one (at higher Z′) corresponds to the charge-transfer resistance. (47) Thanks to the tubular pore geometry, Ru/C-SBA-15 has much smaller porosity resistance than that of bottleneck pores in Ru/C-SiO2@m-SiO2. (42) The charge transfer in the Ru/C-SBA-15 is also higher than that in Ru/C-SiO2@m-SiO2, suggesting a favored transfer mechanism in tubular pore system. We hypothesize that this is due to the diffusion of as formed H2. The H2 can quickly diffuse through the tubular pore and thus leave the catalytic center. In the bottom-neck pore, H2 will be trapped inside the pore and thus block the active sites. The superior performance of the Ru/C-SBA-15 compared to that of commercial Pt/C suggests the potential of practical applications of those Ru-based catalysts in the conversion of green electricity to energy.
Figure 5
Figure 5. (a) HER polarization curves of the Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 compared with a commercial Pt/C catalyst in 1 M KOH. (b) EIS Nyquist plots of the of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 records at −100 mV vs RHE from 100 kHz to 100 mHz. (c) Tafel plots derived from Figure 5a. (d) Time-dependent voltage curve of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 under a current density of 10 mA cm–1 for 24 h.
The fitting of the linear portions of the Tafel plots accordingly gives Tafel slopes. (48) The slopes suggest a difference in the rate-determining step for the tubular and bottleneck pores. Ru/C-SBA-15 gives a slope of 56 mV dec–1, suggesting a major rate determining step following the Heyrovsky reaction (H2O + e– + H* → H2 + OH–) in the tubular pore. (45) The slope for Ru/C-SiO2@m-SiO2 is 83 mV dec–1, indicating that in addition to the Heyrovsky reaction, the Volmer reaction (H2O + e– → H* + OH–) is also the rate-determining step in the bottleneck pore (Figure 5c). The tubular pore system provides fast charge transfer of sufficient electrons for the Volmer reaction and and efficient OH– diffusion pathway, shifting the rate-determining step to solely the Heyrovsky reaction. The stability of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 catalysts are measured galvanostatically at a current density of 10 mA·cm–2 (Figure 5d). Within 24 h, the overpotential for Ru/C-SBA-15 increases by 39 mV, while that of Ru/C-SiO2@m-SiO2 only increases by 4 mV. Such a drop in stability is due to the growth and aggregation of Ru clusters in C-SBA-15 during HER. The high Ru cluster stability in HER in the bottleneck pore systems is in good agreement with that in the hydrogenolysis of 5-HMF to DMF.
Universal Liquid-Free Synthesis of Porous Carbon Materials
The catalytic behaviors of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 in 5-HMF hydrogenolysis and HER clear show the important role of pore geometry in catalysis and energy conversions. Thanks to the liquid-free carbon synthesis method, a range of carbon materials with the same chemical composition but different pore geometries can be prepared. The broad application of such a method is further verified in 10 additional silica supports, which are chosen as the representative templates according to their pore size, volume, and surface area. They are K-SSZ-13, silicate-1, Na-ZSM-5, Na-zeolite beta, Na-zeolite Y, MCM-41, KIT-6, 200 nm mesoporous silica sphere (mSiO2-200), 30 nm mesoporous silica sphere (mSiO2-30), and SiO2@m-SiO2 with half-shell thickness (SiO2@h-mSiO2) (Figure S1). The pore sizes start from 0.38 nm for K-SSZ-13 and increase to to 5.9 nm for KIT-6 (Figure S19). The size of ferrocene is 0.33 nm between the two cyclopentadienyl groups (Cp–) and 0.4 nm for the Cp–. Therefore, K-SSZ-13 represents the template with the smallest pores that can be used for ferrocene CVD.
Most porous carbons keep the original morphology of the SiO2 template (Figure 6), except for K-SSZ-13, in which the cuboid shape is slightly distorted. The diffusion of ferrocene into the zeolite framework is limited, resulting in a quasi-hollow structure where more carbons are formed at the peripheral part than at the center (Figure 6f–j). Even with silicate-1, which has the smallest particle size of 129 ± 19 nm, a clear shell with a thickness of 12 ± 3 nm is found (Figure 6h). The diffusion limitation is also found in zeolite catalysis systems, where reactions only take place within several nanometers of the zeolite surface. (49) Similar to C-SBA-15, 3D-ordered mesoporous C-KIT-6 is also obtained (Figure 6v). Unlike C-SBA-15 and C-KIT-6, the C-MCM-41 is disordered (Figure 6u), possibly due to the small pore size of MCM-41 template that leads very thin carbon walls, which are not stable at high temperature. C-mSiO2-200, C-mSiO2-30, and C-SiO2@h-mSiO2 retain the spherical morphology of the original silica template (Figure 6w–y). The diameters are 208 ± 20, 35 ± 3, and 170 ± 7 nm, respectively, corresponding well with that of the original SiO2 templates. Trace amounts of Fe and Al are found in the C-Na-zeolite-Y, giving 0.30 and 1.54 wt % from MP-AES analysis, respectively (Table S2). All porous carbons are the inverse replica of the original silica templates and have different pore geometries (Figure 6). Hysteresis between 0.4 and 0.9 P/P0 is found for all five zeolite-templated carbons, showing the formation of mesopores inside the carbon cuboid. The mesopores are also found in all mesopore silica templated carbons. The well-controlled synthesis of carbon materials with different pore structures enables a fundamental understanding of pore geometry effects in chemical reactions.
Figure 6
Figure 6. TEM images of 10 carbon–silica composites obtained after CVD: (a) Fe/C-SSZ-13; (b) Fe/C-ZSM-5; (c) Fe/C-silicate-1; (d) Fe/C-zeolite beta; (e) Fe/C-zeolite Y; (p) Fe/C-MCM-41; (q) Fe/C-KIT-6; (r) Fe/C-mSiO2-200; (s) Fe/C-mSiO2-30; and (t) Fe/C-SiO2@mSiO2. TEM images of 10 porous carbons obtained after PTFE leaching: (f) C-SSZ-13; (g) C-ZSM-5; (h) C-silicate-1; (i) C-zeolite beta; (j) C-zeolite Y; (u) C-MCM-41; (v) C-KIT-6; (w) C-mSiO2-200; (x) C-mSiO2-30; and (y) C-SiO2@h-mSiO2. (k–o, z–ad) Comparison of corresponding N2 sorption between the SiO2 templates and porous carbons. For K-SSZ-13, although the kinetic diameter of N2 (0.36 nm) is lower than the pore aperture of SSZ-13 (3.8 Å), the low polarizability and electric quadrupole moment of N2 result in a rather low energy of interaction when K+ presents in the framework (Figure. 6k), showing a very low N2 uptake.
Conclusions
ARTICLE SECTIONS
Ru clusters in bottleneck and tubular carbon pores are studied in the 5-HMF hydrogenolysis and HER. Bottleneck pores successfully confine the Ru clusters size around 1 nm during catalysis, showing twice the DMF yield of unconfined clusters and better stability in HER. The tubular pore has low porosity resistance and provides efficient charge transfer in HER, requiring only 16 mV overpotential to reach current density of 10 mA·cm–2. The difference in catalytic activity is mainly pore geometry dependent, while the chemical properties of Ru clusters and carbon support are kept the same. The fast and liquid-free synthesis of carbon support with different pore geometry is general applicable, with 10 additional syntheses of porous carbon templated from commercial zeolite and mesoporous silica. The use of gas for dispersing chemicals, leaching templates, and removing impurities is advantageous in the material innovations that are important for catalysis, energy conversion, and storage applications.
Experimental Methods
ARTICLE SECTIONS
Synthesis of SiO2@m-SiO2 and SiO2@h-mSiO2 Templates
To obtain a solid SiO2 core, ethanol (552.3 g), H2O (132.53 mL), NH3 (28–30%, 12.83 mL) and tetraethyl orthosilicate (TEOS, 27.77 mL) were mixed in a 1000 mL round-bottom flask. The mixture was stirred for 12 h at room temperature. To synthesize the mesoporous SiO2 shell, TEOS (19.72 mL) and octadecyltrimethoxysilane (OTMS, 7.78 mL) were then added to the aforementioned mixture. The mixture was then stirred for another 12 h. Half amounts of TEOS (9.86 mL) and OTMS (3.89 mL) were used to synthesize the half-shell template. The product was collected by centrifugation and placed in an oven to dry. Approximately, 8.5 g of white product was obtained in each batch. The sample was calcined at 550 °C for 1.5 h with a heating rate of 1.5 °C min–1 for the removal of the alkyl chains contained in OTMS.
Synthesis of mSiO2-30
A 7.675 g portion of ethyltrimethylammonium bromide (CTAB) was dissolved in 500 mL of deionized water in a polypropylene bottle. The suspension was stirred for 5 min and subsequently sonicated for 20 min. Afterward, the solution was placed in an oven at 100 °C for 10 min. Then 1.545 mL of triethanolamine was added, and the solution was stirred at 80 °C for 1 h. Then 77.55 mL of TEOS was rapidly added to the stirring solution, which was subsequently stirred at 80 °C for 2 h. The product was collected by centrifugation and placed in an oven to dry. The sample was calcined at 550 °C for 1.5 h with a heating rate of 1.5 °C min–1 for the removal of the alkyl chains contained in CTAB and TEOS.
Synthesis of mSiO2-200
A 0.8 g portion of CTAB and 4.8 mL of 30% ammonia–water were dissolved in 118 mL of deionized water in a 500 mL round-bottom flask. The suspension was stirred for 5 min. The mixture of TOES (4 mL) and hexane (16 mL) was added into the solution dropwise, and the solution was stirred for 12 h. The product was collected by centrifugation and placed in an oven to dry. The sample was calcined at 550 °C for 1.5 h with a heating rate of 1.5 °C min–1 for the removal of the alkyl chains contained in CTAB and TEOS.
Synthesis of Porous Carbon Materials via Various Templates
The porous carbon materials were prepared by using the CVD method with different zeolites and SiO2 as the templates and ferrocene as the carbon source. Ferrocene (2 g) and zeolite/SiO2 (500 mg) were placed in different heating zones within the two-stage tubular furnace. The sublimation and the pyrolysis of the ferrocene were conducted in 56 mL min–1 argon flow at 120 and 550 °C, respectively, for 2 h. The weight loss for ferrocene during CVD is 650 mg. The as-prepared [email protected]2 composite (500 mg) was mixed with PTFE (4 g) and heated under 1 L min–1 nitrogen flow at 900 °C for 4 h to subsequently leach silica.
Synthesis of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15
Before loading of Ru, the carbon material, C-SiO2@m-SiO2, was washed with HCl solution. RuCl3 (Ru 38%, 137 mg, 0.52 mmol) was dissolved in water (0.22 mL) and then impregnated into the C-SiO2@m-SiO2 powder (470 mg) under stirring until it was mixed uniformly and then dried at 60 °C. The mixture was heated at 220 °C under 15% hydrogen/argon for 3 h. The same method was used to prepared Ru/C-SBA-15
Hydrogenolysis of 5-Hydroxymethylfurfural
For a typical experiment, HMF (20 mg, 0.16 mmol), tetrahydrofuran (THF, 3 mL), dodecane (1.37 mg, 0.008 mmol), and different amounts of catalyst were added into a Teflon inset, transferred into a stainless-steel autoclave reactor, and then sealed and purged with hydrogen three times. The reaction was performed at the target temperature with 10 bar of initial hydrogen pressure under 400 rpm stirring. After the desired reaction time, the reactor was cooled to room temperature. The solution was filtered and analyzed by gas chromatography–mass spectrometry (GC–MS). The catalysts were collected by centrifugation, washed with THF several times, and then reduced by hydrogen again before recycling.
Electrochemical Measurement
All of the tests were carried out using an Autolab (Metrohm PGSTAT302N) electrochemical station by a three-electrode method with a glassy carbon rotating disk as the working electrode and carbon rod and Ag/AgCl/saturated KCl as counter and reference electrode in alkaline electrolyte (1 M KOH) at room temperature. All of the measurements were carried out with a fixed catalyst deposition of ∼0.28 mg cm–2 on a 3 mm in diameter (or area of 0.0707 cm2) glassy carbon disk electrode. The catalyst was prepared as follows: 2 mg of sample was dispersed in a total of 540 μL of solution consisting 500 μL of 4:1 v/v water/ethanol and 40 μL of Nafion (5% solution) under sonication. The sonication was carried out up to 1 h to obtain uniform catalyst dispersion ink, of which 5 μL was micropipetted and dropped on to a GCDE followed by drying at 60 °C in the oven prior to the electrochemical tests. All of the electrochemical test results were reported with respect to the reference, Ag/AgCl. The HER liner sweep voltammetry (LSV) curves were measured at disk rotating speeds of 1600 rpm. Stability tests were carried under a current of 0.707 mA for 24 h. EIS was taken from 100k Hz to 100m Hz at −100 mV vs RHE.
Characterization
TEM was performed using a JEOL JEM-2100 microscope equipped with an Oxford Instruments EDS detector at 200 kV. Particle size distributions were estimated through measurement of 100 particles. Scanning electron microscopy (SEM) imaging was performed on a JEOL JSM-7401F SEM. Scanning transmission electron microscopy (STEM) was performed using a probe corrected (CEOS) JEM ARM 200CF (JEOL, Japan) equipped with detectors for bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging at 200 kV. X-ray diffraction (XRD) measurements were performed using a StadiP diffractometer from STOE, a voltage of 40 kV, at 30 mA, with a Cu source with Kα1 = 1.540562 Å and Kα2 = 1.544398 Å. The signal from Kα2 was removed for analysis. XPS) analyses were performed on a Thermoscientific XPS K-α surface analysis machine using an Al source. Analysis was performed on the Casa XPS software. Elemental analysis was performed using an Agilent 4100 microwave plasma-atomic emission spectrometer. Solid samples were digested in aqua regia. Each sample was measured three times to ensure reliable results. The results show the average of the measurements recorded. Thermogravimetric analysis was carried by PerkinElmer Pyris 1 TGA in nitrogen flow from 30 to 900 °C. Nitrogen adsorption–desorption isotherms were recorded at 77 K using a Micromeritics 3Flex surface characterization analyzer. The samples were degassed at 300 °C overnight. Specific surface areas were determined according to the BET model, with pore diameters, volumes, and distributions determined through the BJH method. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis of the Ru K edge (22.117 keV) and the Fe K edge (7.112 keV) were carried out at 3.0 GeV with a beam current of 300 mA on the Beamline B18 of the Diamond Light Source (UK). Samples were diluted by cellulose and pressed into a 0.8 cm diameter pellets for measurement.). Ru foil, RuO2, Fe foil, FeO (wüstite), Fe2O3 (hematite), and Fe3O4 (magnetite) were measured as the standard for energy shift calibration. The XAFS spectra of all samples were measured in transmission mode in an energy range of 21.9–23.2 keV for Ru K edge and 6.91 to 7.66 keV for Fe K edge with a beam size of 200 μm (H) × 250 μm (V). The spectrum of each sample was measured five times and merged to improve the signal-to-noise ratio. Athena software was used for data extraction and XANES analysis. Artemis software was used to fit the k2-weighted EXAFS data in real space with 3.4 Å–1 < k < 13.5 Å–1 and 1.0 Å < R < 3.0 Å. (50,51) Raman spectra were recorded on a Renishaw InVia Raman spectrometer in a backscattered confocal configuration using 647 nm laser excitation.
Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.8b09399.
TEM and SEM images, N2-physisorption isotherms, XPS spectra, Raman spectra, XAFS spectra and fittings, XRD patterns, and catalytic results (Figures S1–S19 and Tables S1–S7) (PDF)
Terms & Conditions
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Author Information
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- Feng Ryan Wang - Department of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United Kingdom;
http://orcid.org/0000-0002-2475-606X;
- Liqun Kang - Department of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United Kingdom;http://orcid.org/0000-0003-2100-4310
- Johannes Knossalla - Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany;http://orcid.org/0000-0002-2220-6670
- Jerrik Mielby - Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark;http://orcid.org/0000-0001-6588-2495
- Yudao Qin - Department of Chemistry, University College London, 20 Gordon Street, Bloomsbury, WC1H 0AJ London, United Kingdom;http://orcid.org/0000-0002-3623-2319
- Jijia Xie - Department of Chemical Engineering, University College London, Torrington Place, WC1E 7JE London, United Kingdom;http://orcid.org/0000-0003-4609-8915
- Søren Kegnæs - Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark;http://orcid.org/0000-0002-6933-6931
Acknowledgments
ARTICLE SECTIONS
This work was conducted with the support from EPSRC First Grant project (EP/P02467X/1, EP/S018204/1), Royal Society research grant (RG160661), and Royal Society International Exchange (IES\R3\170097). We acknowledge Diamond Light Source and the UK Catalysis Hub block allocation for beamtime (SP15151, SP206191), the rapid access beamtime (EM21370), the B18 and E01 beamline scientists Diego Gianolio, Giannantonio Cibin, and Mohsen Danaie for their help. The UK Catalysis Hub is kindly thanked for resources and support provided via our membership in the UK Catalysis Hub Consortium and funded by EPSRC (portfolio grants EP/K014706/1, EP/K014668/1, EP/K014854/1, EP/K014714/1, and EP/I019693/1). We are grateful for the funding provided by the Max-Planck-Institut für Kohlenforschung, the Cluster of Excellence TMFB, and the Danish Council for Independent Research (Grant No. 5054-00119). R.X thanks the China Scholarship Council (CSC) for the Ph.D. funding. B.W. thanks the Newton International Fellowship (NF170761) for funding support.
References
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- 11Wang, G. H.; Hilgert, J.; Richter, F. H.; Wang, F.; Bongard, H. J.; Spliethoff, B.; Weidenthaler, C.; Schuth, F. Platinum-Cobalt Bimetallic Nanoparticles in Hollow Carbon Nanospheres for Hydrogenolysis of 5-Hydroxymethylfurfural. Nat. Mater. 2014, 13, 293– 300, DOI: 10.1038/nmat3872[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXislCltbs%253D&md5=6e38a80e6a3dfe01109e9e990f79b985Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfuralWang, Guang-Hui; Hilgert, Jakob; Richter, Felix Herrmann; Wang, Feng; Bongard, Hans-Josef; Spliethoff, Bernd; Weidenthaler, Claudia; Schueth, FerdiNature Materials (2014), 13 (3), 293-300CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diams. of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres.
- 12Arnal, P. M.; Comotti, M.; Schuth, F. High-Temperature-Stable Catalysts by Hollow Sphere Encapsulation. Angew. Chem., Int. Ed. 2006, 45, 8224– 8227, DOI: 10.1002/anie.200603507[Crossref], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtlGns7rP&md5=d4579293d22560f28494336f955e7ed7High-temperature-stable catalysts by hollow sphere encapsulationArnal, Pablo M.; Comotti, Massimiliano; Schueth, FerdiAngewandte Chemie, International Edition (2006), 45 (48), 8224-8227CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Hollow ZrO2 shells each contg. one Au nano-particle are stable to sintering and can be used as heterogeneous catalysts in reactions, e.g., CO oxidn. in air. The performance of Au in ZrO2 shells is unaffected by calcination at 800°.
- 13Baldizzone, C.; Mezzavilla, S.; Carvalho, H. W. P.; Meier, J. C.; Schuppert, A. K.; Heggen, M.; Galeano, C.; Grunwaldt, J. D.; Schuth, F.; Mayrhofer, K. J. J. Confined-Space Alloying of Nanoparticles for the Synthesis of Efficient PtNi Fuel-Cell Catalysts. Angew. Chem., Int. Ed. 2014, 53, 14250– 14254, DOI: 10.1002/anie.201406812[Crossref], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVGmu7bF&md5=7547a8dd9cd7e9011f08815cc6afd4eaConfined-Space Alloying of Nanoparticles for the Synthesis of Efficient PtNi Fuel-Cell CatalystsBaldizzone, Claudio; Mezzavilla, Stefano; Carvalho, Hudson W. P.; Meier, Josef Christian; Schuppert, Anna K.; Heggen, Marc; Galeano, Carolina; Grunwaldt, Jan-Dierk; Schueth, Ferdi; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2014), 53 (51), 14250-14254CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, i.e., its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen redn. reaction assocd. with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 A mgPt-1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined-space alloying of the nanoparticles in a controlled manner in the pores of the support.
- 14Ortac, I.; Simberg, D.; Yeh, Y.-s.; Yang, J.; Messmer, B.; Trogler, W. C.; Tsien, R. Y.; Esener, S. Dual-Porosity Hollow Nanoparticles for the Immunoprotection and Delivery of Nonhuman Enzymes. Nano Lett. 2014, 14, 3023– 3032, DOI: 10.1021/nl404360k[ACS Full Text], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht12lsLs%253D&md5=48718181a990e5abe16228754ac3f021Dual-Porosity Hollow Nanoparticles for the Immunoprotection and Delivery of Nonhuman EnzymesOrtac, Inanc; Simberg, Dmitri; Yeh, Ya-san; Yang, Jian; Messmer, Bradley; Trogler, William C.; Tsien, Roger Y.; Esener, SadikNano Letters (2014), 14 (6), 3023-3032CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Although enzymes of nonhuman origin have been studied for a variety of therapeutic and diagnostic applications, their use has been limited by the immune responses generated against them. The described dual-porosity hollow nanoparticle platform obviates immune attack on nonhuman enzymes paving the way to in vivo applications, including enzyme-prodrug therapies and enzymic depletion of tumor nutrients. This platform is manufd. with a versatile, scalable, and robust fabrication method. It efficiently encapsulates macromol. cargos filled through mesopores into a hollow interior, shielding them from antibodies and proteases once the mesopores are sealed with nanoporous material. The nanoporous shell allows small mol. diffusion allowing interaction with the large macromol. payload in the hollow center. The approach has been validated in vivo using L-asparaginase to achieve L-asparagine depletion in the presence of neutralizing antibodies.
- 15Lee, J.; Kim, S. M.; Lee, I. S. Functionalization of Hollow Nanoparticles for Nanoreactor Applications. Nano Today 2014, 9, 631– 667, DOI: 10.1016/j.nantod.2014.09.003[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFyrtbrI&md5=d5c948b233503ee3a023d0a755c2bc4eFunctionalization of hollow nanoparticles for nanoreactor applicationsLee, Jihwan; Kim, Soo Min; Lee, In SuNano Today (2014), 9 (5), 631-667CODEN: NTAOCG; ISSN:1748-0132. (Elsevier Ltd.)A review. The hollow nanoparticles, which contain catalytic species inside the cavity enclosed by a porous nanoshell, are considered an ideal framework for the nanoreactor that efficiently catalyzes the transformation of the selectively transferred substrate mols. with little loss of activity and surface area of entrapped catalysts even in harsh reaction conditions or during the recycling process. In the performance of the hollow nanoreactor, the selectively functionalized interior cavity is the most vital component which allows chem. reactions to occur within the confines of the protected cavity. Therefore, selective and differential functionalization of the internal space of the hollow nanoshell is the important and challenging topic which is demanded for fully exploiting the potential of the hollow nanoparticle in the nanoreactor application. In this context, this review paper intends to make a survey on the synthetic strategies of functionalizing the interior cavity of the hollow nanoparticles and their employment as nanoreactor systems which catalyze the chem. reactions and template the growth of nanocrystals.
- 16Prieto, G.; Tuysuz, H.; Duyckaerts, N.; Knossalla, J.; Wang, G. H.; Schuth, F. Hollow Nano- and Microstructures as Catalysts. Chem. Rev. 2016, 116, 14056– 14119, DOI: 10.1021/acs.chemrev.6b00374[ACS Full Text], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1aju7nM&md5=a269c05df7f789532583d991b2b82b73Hollow Nano- and Microstructures as CatalystsPrieto, Gonzalo; Tueysuez, Harun; Duyckaerts, Nicolas; Knossalla, Johannes; Wang, Guang-Hui; Schueth, FerdiChemical Reviews (Washington, DC, United States) (2016), 116 (22), 14056-14119CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)Catalysis is at the core of almost every established and emerging chem. process and also plays a central role in the quest for novel technologies for the sustainable prodn. and conversion of energy. Particularly since the early 2000s, a great surge of interest exists in the design and application of micro- and nanometer-sized materials with hollow interiors as solid catalysts. This review provides an updated and crit. survey of the ever-expanding material architectures and applications of hollow structures in all branches of catalysis, including bio-, electro-, and photocatalysis. First, the main synthesis strategies toward hollow materials are succinctly summarized, with emphasis on the (regioselective) incorporation of various types of catalytic functionalities within their different subunits. The principles underlying the scientific and technol. interest in hollow materials as solid catalysts, or catalyst carriers, are then comprehensively reviewed. Aspects covered include the stabilization of catalysts by encapsulation, the introduction of mol. sieving or stimuli-responsive "auxiliary" functionalities, as well as the single-particle, spatial compartmentalization of various catalytic functions to create multifunctional (bio)catalysts. Examples are also given on the applications which hollow structures find in the emerging fields of electro- and photocatalysis, particularly in the context of the sustainable prodn. of chem. energy carriers. Finally, a crit. perspective is provided on the plausible evolution lines for this thriving scientific field, as well as the main practical challenges relevant to the reproducible and scalable synthesis and utilization of hollow micro- and nanostructures as solid catalysts.
- 17Wu, S. H.; Tseng, C. T.; Lin, Y. S.; Lin, C. H.; Hung, Y.; Mou, C. Y. Catalytic Nano-Rattle of [email protected] Silica: Towards a Poison-Resistant Nanocatalyst. J. Mater. Chem. 2011, 21, 789– 794, DOI: 10.1039/C0JM02012E[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhs1WjtLrP&md5=cbc39dfc851587f01e8d53ec427cbad8Catalytic nano-rattle of [email protected] silica: Towards a poison-resistant nanocatalystWu, Si-Han; Tseng, Chih-Ta; Lin, Yu-Shen; Lin, Cheng-Han; Hung, Yann; Mou, Chung-YuanJournal of Materials Chemistry (2011), 21 (3), 789-794CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)In this work, size-controlled gold nanocatalysts (2.8 to 4.5 nm) inside monodisperse hollow silica nanospheres, [email protected], have been prepd. by using a water-in-oil microemulsion as a template. The size of gold nanocatalysts can be easily controlled based on the gold precursor and the chloroauric acid concn. used during synthesis. These [email protected] nanocatalysts were characterized by transmission electron microscopy, SEM, N2 adsorption-desorption isotherms, powder X-ray diffraction, and UV-vis spectrometer. Furthermore, we demonstrate their catalytic capability with respect to the 4-nitrophenol redn. reaction in the absence and presence of a thiol compd., meso-2,3-dimercaptosuccinic acid. The results show that the [email protected] display highly catalytic activity and resistance to other strongly adsorbing mols. in reaction solns.
- 18Li, Y. Q.; Bastakoti, B. P.; Imura, M.; Tang, J.; Aldalbahi, A.; Torad, N. L.; Yamauchi, Y. Dual Soft-Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica Nanoparticles. Chem. - Eur. J. 2015, 21, 6375– 6380, DOI: 10.1002/chem.201406137[Crossref], [PubMed], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXkvVCjtr4%253D&md5=9d0501e8d9d4bc21900ebc345ee39b53Dual Soft-Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica NanoparticlesLi, Yunqi; Bastakoti, Bishnu Prasad; Imura, Masataka; Tang, Jing; Aldalbahi, Ali; Torad, Nagy L.; Yamauchi, YusukeChemistry - A European Journal (2015), 21 (17), 6375-6380CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)A new dual soft-template system comprising the asym. triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to synthesize hollow mesoporous silica (HMS) nanoparticles with a center void of around 17 nm. The stable PS-b-P2VP-b-PEO polymeric micelle serves as a template to form the hollow interior, while the CTAB surfactant serves as a template to form mesopores in the shells. The P2VP blocks on the polymeric micelles can interact with pos. charged CTA+ ions via neg. charged hydrolyzed silica species. Thus, dual soft-templates clearly have different roles for the prepn. of the HMS nanoparticles. Interestingly, the thicknesses of the mesoporous shell are tunable by varying the amts. of TEOS and CTAB. This study provides new insight on the prepn. of mesoporous materials based on colloidal chem.
- 19Lim, J.; Um, J. H.; Ahn, J.; Yu, S. H.; Sung, Y. E.; Lee, J. K. Soft Template Strategy to Synthesize Iron Oxide-Titania Yolk-Shell Nanoparticles as High-Performance Anode Materials for Lithium-Ion Battery Applications. Chem. - Eur. J. 2015, 21, 7954– 7961, DOI: 10.1002/chem.201406667[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlvVeltrg%253D&md5=d0e6f1dcf87fc5469867b7d0e688ed1cSoft Template Strategy to Synthesize Iron Oxide-Titania Yolk-Shell Nanoparticles as High-Performance Anode Materials for Lithium-Ion Battery ApplicationsLim, Joohyun; Um, Ji Hyun; Ahn, Jihoon; Yu, Seung-Ho; Sung, Yung-Eun; Lee, Jin-KyuChemistry - A European Journal (2015), 21 (21), 7954-7961CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)Yolk-shell-structured nanoparticles with iron oxide core, void, and titania shell configuration are prepd. by a simple soft template method and used as the anode material for lithium ion batteries. The iron oxide-titania yolk-shell nanoparticles ([email protected]@TNPs) exhibit a higher and more stable capacity than simply mixed nanoparticles of iron oxide and hollow titania because of the unique structure obtained by the perfect sepn. between iron oxide nanoparticles, in combination with the adequate internal void space provided by stable titania shells. Moreover, the structural effect of [email protected]@TNPs clearly demonstrates that the capacity retention value after 50 cycles is approx. 4 times that for iron oxide nanoparticles under harsh operating conditions, i.e., when the temp. is increased to 80°.
- 20Deng, X. H.; Chen, K.; Tuysuz, H. Protocol for the Nanocasting Method: Preparation of Ordered Mesoporous Metal Oxides. Chem. Mater. 2017, 29, 40– 52, DOI: 10.1021/acs.chemmater.6b02645[ACS Full Text], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVKrsb%252FE&md5=edaaac8c55b0311775d45fc8615bb430Protocol for the Nanocasting Method: Preparation of Ordered Mesoporous Metal OxidesDeng, Xiaohui; Chen, Kun; Tueysuez, HarunChemistry of Materials (2017), 29 (1), 40-52CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Ordered mesoporous transition metal oxides have attracted considerable research attention due to their unique properties and wide applications. The prepn. of these materials has been reported in the literature using soft and hard templating pathways. Compared with soft templating, hard templating, namely, nanocasting, is advantageous for synthesizing rigid mesostructures with high crystallinity and has already been applied to numerous transition metal oxides such as Co3O4, NiO, Fe2O3, and Mn3O4. However, nanocasting is often complicated by the multiple steps involved: first, the prepn. of ordered mesoporous silica as the hard template, then infiltration of the metal precursor into the pores, and finally, formation of the metal oxide and removal of the hard template. In this paper, we provide a complete protocol that covers the prepn. of most widely used ordered mesoporous silica templates (MCM-41, KIT-6, SBA-15) and the nanocasting process for obtaining ordered mesoporous metal oxides, with emphasizing cobalt oxide as an example. Characterization of the products is presented, and the factors that can potentially affect the process are discussed.
- 21Bottger-Hiller, F.; Kempe, P.; Cox, G.; Panchenko, A.; Janssen, N.; Petzold, A.; Thurn-Albrecht, T.; Borchardt, L.; Rose, M.; Kaskel, S.; Georgi, C.; Lang, H.; Spange, S. Twin Polymerization at Spherical Hard Templates: an Approach to Size-Adjustable Carbon Hollow Spheres with Micro- or Mesoporous Shells. Angew. Chem., Int. Ed. 2013, 52, 6088– 6091, DOI: 10.1002/anie.201209849
- 22Yoon, S. B.; Sohn, K.; Kim, J. Y.; Shin, C. H.; Yu, J. S.; Hyeon, T. Fabrication of Carbon Capsules with Hollow Macroporous Core/Mesoporous Shell Structures. Adv. Mater. 2002, 14, 19– 21, DOI: 10.1002/1521-4095(20020104)14:1<19::AID-ADMA19>3.0.CO;2-X[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xmt12qtw%253D%253D&md5=728f4a736d1dbc2204749320607d76c5Fabrication of carbon capsules with hollow macroporous core/mesoporous shell structuresYoon, Suk Bon; Sohn, Kwonnam; Kim, Jeong Yeon; Shin, Chae-Ho; Yu, Jong-Sung; Hyeon, TaeghwanAdvanced Materials (Weinheim, Germany) (2002), 14 (1), 19-21CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH)A solid core/mesoporous shell (SCMS) silica sphere was used as template to prep. carbon capsules with hollow core mesoporous shell (HCMS). Most particles of the HCMS carbon capsules were uniform and spherical with particle diams. of 30 nm and some particles were deformed. The TEM image of the carbon material showed hollow cores of 220 nm in diam. and mesoporous shells with thickness of 55 nm. The structure of the HCMS carbon capsules is an inverse replica of the SCMS silica sphere templates. Due to uniform, hollow macroscopic core and mesopores of the bimodal pore systems in the shell, HCMS carbon capsules could have a wide range of applications, including catalysts, adsorbents, sensors, electrode materials, and advanced storage materials.
- 23Valle-Vigon, P.; Sevilla, M.; Fuertes, A. B. Synthesis of Uniform Mesoporous Carbon Capsules by Carbonization of Organosilica Nanospheres. Chem. Mater. 2010, 22, 2526– 2533, DOI: 10.1021/cm100190a[ACS Full Text], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjvFCjt7g%253D&md5=f12864285a159c628709ef997659001fSynthesis of Uniform Mesoporous Carbon Capsules by Carbonization of Organosilica NanospheresValle-Vigon, Patricia; Sevilla, Marta; Fuertes, Antonio B.Chemistry of Materials (2010), 22 (8), 2526-2533CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A synthetic method to produce uniform mesoporous hollow carbon nanospheres with a large surface area and uniform mesoporosity has been developed by employing, as carbon source, an org. moiety used as porogen agent to synthesize spherical organosilica nanoparticles with a [email protected] (org.-inorg.) structure. The conversion of the org. moiety to carbon is achieved by means of sulfuric acid which considerably increases the carbon yield via dehydration and sulfonation reactions. The carbon capsules exhibit a uniform morphol. (a diam. of ∼440 nm and a shell thickness of ∼50 nm), a high Brunauer-Emmett-Teller (BET) surface area (1620 m2.g-1), a large pore vol. (2.3 cm3.g-1), and a porosity made up of mesopores centered at around 4.3 nm. Iron oxide magnetic nanoparticles were incorporated into the pores of the porous shell of the carbon capsules. The magnetic hollow nanoparticles were then used as support for the immobilization of cytochrome C. A large amt. of enzyme is stored in this magnetic nanocomposite (∼500 mg Cyt·g-1 support) which suggests that a significant fraction of enzyme is accommodated in the hollow core of the capsules.
- 24Li, J. J.; Liang, Y.; Dou, B. J.; Ma, C. Y.; Lu, R. J.; Hao, Z. P.; Xie, Q.; Luan, Z. Q.; Li, K. Nanocasting Synthesis of Graphitized Ordered Mesoporous Carbon Using Fe-Coated SBA-15 Template. Mater. Chem. Phys. 2013, 138, 484– 489, DOI: 10.1016/j.matchemphys.2012.12.003[Crossref], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvFSntrrF&md5=23b86d4a85f131c489b13c7a74afc84fNanocasting synthesis of graphitized ordered mesoporous carbon using Fe-coated SBA-15 templateLi, Jinjun; Liang, Yan; Dou, Baojuan; Ma, Chunyan; Lu, Renjie; Hao, Zhengping; Xie, Qiang; Luan, Zhiqiang; Li, KaiMaterials Chemistry and Physics (2013), 138 (2-3), 484-489CODEN: MCHPDR; ISSN:0254-0584. (Elsevier B.V.)Ordered mesoporous carbons with high porosities and graphitized structures were synthesized by a template-catalysis method using low-mol.-wt. phenolic resin as carbon precursor and Fe-coated SBA-15 as both template and catalyst. The synthesis route involves the following steps: (a) the synthesis of mesoporous Fe-coated SBA-15 through a one-pot method, (b) the infiltration of a low-mol.-wt. phenolic resin into the porosity of the Fe-coated SBA-15, (c) the carbonization and catalytic graphitization of the infiltrated phenolic resin at 900 °C, and (d) the removal of the Fe-coated SBA-15 template. The X-ray diffraction, nitrogen sorption, transmission electron microscopy and SEM were used to characterize the materials, and the results indicate that the prepd. carbon materials have well-ordered mesoporous structures replicated from the templates, and graphitized structures can be obsd. on the carbon frameworks, depending on the iron content in the templates.
- 25Lu, A. H.; Schüth, F. Nanocasting: a Versatile Strategy for Creating Nanostructured Porous Materials. Adv. Mater. 2006, 18, 1793– 1805, DOI: 10.1002/adma.200600148[Crossref], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xot1Kktr0%253D&md5=ceb160f9820c4a9e03648204d57db7d1Nanocasting: a versatile strategy for creating nanostructured porous materialsLu, An-Hui; Schueth, FerdiAdvanced Materials (Weinheim, Germany) (2006), 18 (14), 1793-1805CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Nanocasting is a powerful method for creating materials that are more difficult to synthesize by conventional processes. We summarize recent developments in the synthesis of various structured porous solids, covering silica, carbon, and other nonsiliceous solids that are created by a nanocasting pathway. Structure replication on the nanometer length scale allows materials' properties to be manipulated in a controlled manner, such as tunable compn., controllable structure and morphol., and specific functionality. The nanocasting pathway with hard templates opens the door to the design of highly porous solids with multifunctional properties and interesting application perspectives.
- 26Lou, X. W. D.; Archer, L. A.; Yang, Z. Hollow Micro-/Nanostructures: Synthesis and Applications. Adv. Mater. 2008, 20, 3987– 4019, DOI: 10.1002/adma.200800854[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsVartbnK&md5=06f1f33dc2ccfe8627f5e0b1cb4322dcHollow micro-/nanostructures: synthesis and applicationsLou, Xiong Wen; Archer, Lynden A.; Yang, ZichaoAdvanced Materials (Weinheim, Germany) (2008), 20 (21), 3987-4019CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Hollow micro-/nanostructures are of great interest in many current and emerging areas of technol. Perhaps the best-known example of the former is the use of fly-ash hollow particles generated from coal power plants as partial replacement for Portland cement to produce concrete with enhanced strength and durability. This review is devoted to the progress made in the last decade in synthesis and applications of hollow micro-/nanostructures. We present a comprehensive overview of synthetic strategies for hollow structures. These strategies are broadly categorized into four themes which include well-established approaches such as conventional hard-templating and soft-templating methods, as well as newly emerging methods based on sacrificial templating and template-free synthesis. Success in each has inspired multiple variations that continue to drive the rapid evolution of the field. This review therefore focuses on the fundamentals of each process, pointing out advantages and disadvantages where appropriate. Strategies for generating more complex hollow structures, such as rattle-type and nonspherical hollow structures, are also discussed. Applications of hollow structures in lithium batteries, catalysis and sensing, and biomedical applications are reviewed.
- 27Xia, Y.; Mokaya, R. Hollow Spheres of Crystalline Porous Metal Oxides: A Generalized Synthesis Route via Nanocasting with Mesoporous Carbon Hollow Shells. J. Mater. Chem. 2005, 15, 3126– 3131, DOI: 10.1039/b502558c
- 28Andrews, R.; Jacques, D.; Rao, A. M.; Derbyshire, F.; Qian, D.; Fan, X.; Dickey, E. C.; Chen, J. Continuous Production of Aligned Carbon Nanotubes: a Step Closer to Commercial Realization. Chem. Phys. Lett. 1999, 303, 467– 474, DOI: 10.1016/S0009-2614(99)00282-1[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXisFCktrg%253D&md5=93b5c1a11d9e1194426c5af6ccb30690Continuous production of aligned carbon nanotubes: a step closer to commercial realizationAndrews, R.; Jacques, D.; Rao, A. M.; Derbyshire, F.; Qian, D.; Fan, X.; Dickey, E. C.; Chen, J.Chemical Physics Letters (1999), 303 (5,6), 467-474CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)High-purity aligned multi-walled carbon nanotubes (MWNTs) were synthesized through the catalytic decompn. of a ferrocene-xylene mixt. at ∼675°C in a quartz tube reactor and over quartz substrates, with a conversion of ∼25% of the total hydrocarbon feedstock. Under the exptl. conditions used, scanning electron microscope images reveal that the MWNT array grows perpendicular to the quartz substrates at an av. growth rate of ∼25 μm/h. A process of this nature which does not require preformed substrates, and which operates at atm. pressure and moderate temps., could be scaled up for continuous or semi-continuous prodn. of MWNTs.
- 29Sevilla, M.; Sanchis, C.; Valdes-Solis, T.; Morallon, E.; Fuertes, A. B. Synthesis of Graphitic Carbon Nanostructures from Sawdust and Their Application as Electrocatalyst Supports. J. Phys. Chem. C 2007, 111, 9749– 9756, DOI: 10.1021/jp072246x[ACS Full Text], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmt1artrw%253D&md5=2008f8569cb6b35070080e27fa205e54Synthesis of Graphitic Carbon Nanostructures from Sawdust and Their Application as Electrocatalyst SupportsSevilla, M.; Sanchis, C.; Valdes-Solis, T.; Morallon, E.; Fuertes, A. B.Journal of Physical Chemistry C (2007), 111 (27), 9749-9756CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The authors present a novel and facile synthetic method for fabricating graphitic C nanostructures (GCNs) from sawdust. This method is based on the use of catalysts (Fe or Ni) that allows the direct conversion of sawdust into highly graphitized C material. The following procedure was used to obtain these graphitic nanoparticles: (a) impregnation of the sawdust particles with Fe or Ni salts, (b) carbonization of the impregnated material at a temp. of 900 or 1000°, and (c) selective removal of the nongraphitized C (amorphous C) by an oxidant (KMnO4). The resulting C is made up of nanosized graphitic structures (i.e., nanocapsules, nanocoils, nanoribbons), which have a high crystallinity, as evidenced by TEM/SAED, XRD and Raman anal. These GCNs were used as supports for Pt nanoparticles. Such prepd. electrocatalysts show an electrocatalytical surface area close to 90 m2 g-1 Pt, and they present a similar or higher electrocatalytic activity toward MeOH electrooxidn. than the Pt/Vulcan electrocatalyst prepd. in the same conditions.
- 30Galeano, C.; Meier, J. C.; Peinecke, V.; Bongard, H.; Katsounaros, I.; Topalov, A. A.; Lu, A. H.; Mayrhofer, K. J. J.; Schuth, F. Toward Highly Stable Electrocatalysts via Nanoparticle Pore Confinement. J. Am. Chem. Soc. 2012, 134, 20457– 20465, DOI: 10.1021/ja308570c[ACS Full Text], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslCgsbjL&md5=a5dfa149688bf886ac5acb0f2d1d1908Toward Highly Stable Electrocatalysts via Nanoparticle Pore ConfinementGaleano, Carolina; Meier, Josef C.; Peinecke, Volker; Bongard, Hans; Katsounaros, Ioannis; Topalov, Angel A.; Lu, Anhui; Mayrhofer, Karl J. J.; Schueth, FerdiJournal of the American Chemical Society (2012), 134 (50), 20457-20465CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A mesostructured graphitic carbon support, called Hollow Graphitic Spheres (HGS), with sp. surface area >1000 m2/g and precisely controlled pore structure, was specifically developed to overcome long-term fuel cell catalyst degrdn., esp. for the oxygen redn. reaction, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles (∼3 to 4 nm size) encapsulated in the HGS pore structure that are stable at 850°C and, more importantly, during simulated accelerated electrochem. aging. The high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochem. cycling, the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degrdn. mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support.
- 31Schnitzler, M. C.; Mangrich, A. S.; Macedo, W. A. A.; Ardisson, J. D.; Zarbin, A. J. G. Incorporation, Oxidation and Pyrolysis of Ferrocene into Porous Silica Glass: a Route to Different Silica/Carbon and Silica/Iron Oxide Nanocomposites. Inorg. Chem. 2006, 45, 10642– 10650, DOI: 10.1021/ic061312r
- 32Singh, D. K.; Krishna, K. S.; Harish, S.; Sampath, S.; Eswaramoorthy, M. No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance. Angew. Chem., Int. Ed. 2016, 55, 2032– 2036, DOI: 10.1002/anie.201509054[Crossref], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktlShug%253D%253D&md5=3d2f61da65b10393eadc92141a5f83d1No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor PerformanceSingh, Dheeraj Kumar; Krishna, Katla Sai; Harish, Srinivasan; Sampath, Srinivasan; Eswaramoorthy, MuthusamyAngewandte Chemie, International Edition (2016), 55 (6), 2032-2036CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)An innovative technique to obtain high-surface-area mesostructured C (2545 m2 g-1) with significant microporosity uses Teflon as the SiO2 template removal agent. This method not only shortens synthesis time by combining SiO2 removal and carbonization in a single step, but also assists in ultrafast removal of the template (in 10 min) with complete elimination of toxic HF usage. The obtained C material (JNC-1) displays excellent CO2 capture ability (∼26.2% at 0° under 0.88 bar CO2 pressure), which is twice that of CMK-3 obtained by the HF etching method (13.0%). JNC-1 demonstrated higher H2 adsorption capacity (2.8%) compared to CMK-3 (1.2%) at -196° under 1.0 bar H2 pressure. The bimodal pore architecture of JNC-1 led to superior supercapacitor performance, with a specific capacitance of 292 F g-1 and 182 F g-1 at a drain rate of 1 A g-1 and 50 A g-1, resp., in 1 M H2SO4 compared to CMK-3 and activated C.
- 33Shin, H. J.; Ryoo, R.; Kruk, M.; Jaroniec, M. Modification of SBA-15 Pore Connectivity by High-Temperature Calcination Investigated by Carbon Inverse Replication. Chem. Commun. 2001, 349– 350, DOI: 10.1039/b009762o[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhtFamtb4%253D&md5=7a755742957a26d755e4fb20df9d915fModification of SBA-15 pore connectivity by high-temperature calcination investigated by carbon inverse replicationShin, Hyun June; Ryoo, Ryong; Kruk, Michal; Jaroniec, MietekChemical Communications (Cambridge, United Kingdom) (2001), (4), 349-350CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Two-dimensional hexagonally ordered CMK-3 carbons were synthesized using SBA-15 templates calcined at a temp. of 1153 K, whereas a disordered carbon was obtained using SBA-15 calcined at 1243 K. the results demonstrate that the pores connecting ordered mesopores in SBA-15 silica persist up to ca. 1153 K, but are eliminated at temps. close to 1243 K.
- 34Artz, J.; Mallmann, S.; Palkovits, R. Selective Aerobic Oxidation of HMF to 2,5-Diformylfuran on Covalent Triazine Frameworks-Supported Ru Catalysts. ChemSusChem 2015, 8, 672– 679, DOI: 10.1002/cssc.201403078[Crossref], [PubMed], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosFGltg%253D%253D&md5=9ebb642e793ced794138f3d891aad3f3Selective Aerobic Oxidation of HMF to 2,5-Diformylfuran on Covalent Triazine Frameworks-Supported Ru CatalystsArtz, Jens; Mallmann, Sabrina; Palkovits, ReginaChemSusChem (2015), 8 (4), 672-679CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)The selective aerobic oxidn. of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran has been performed under mild conditions at 80 °C and 20 bar of synthetic air in Me t-Bu ether. Ru clusters supported on covalent triazine frameworks (CTFs) allowed excellent selectivity and superior catalytic activity compared to other support materials such as activated carbon, γ-Al2O3, hydrotalcite, or MgO. CTFs with varying pore size, sp. surface area, and N content could be prepd. from different monomers. The structural properties of the CTF materials influence the catalytic activity of Ru/CTF significantly in the aerobic oxidn. of HMF, which emphasizes the superior activity of mesoporous CTFs. Recycling of the catalysts is challenging, but promising methods to maintain high catalytic activity were developed that facilitate only minor deactivation in five consecutive recycling expts.
- 35Zhang, H. B.; Liu, G. G.; Shi, L.; Ye, J. H. Single-Atom Catalysts: Emerging Multifunctional Materials in Heterogeneous Catalysis. Adv. Energy Mater. 2018, 8, 1701343, DOI: 10.1002/aenm.201701343
- 36Jankovsky, O.; Simek, P.; Sedmidubsky, D.; Matejkova, S.; Janousek, Z.; Sembera, F.; Pumera, M.; Sofer, Z. Water-Soluble Highly Fluorinated Graphite Oxide. RSC Adv. 2014, 4, 1378– 1387, DOI: 10.1039/C3RA45183F[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvVKhtL7M&md5=ec4b37eb164e387100c352c387085c5eWater-soluble highly fluorinated graphite oxideJankovsky, Ondrej; Simek, Petr; Sedmidubsky, David; Matejkova, Stanislava; Janousek, Zbynek; Sembera, Filip; Pumera, Martin; Sofer, ZdenekRSC Advances (2014), 4 (3), 1378-1387CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Water-sol. highly fluorinated graphite oxide is a promising candidate for applications in biosensing and for fluorescent probes due to its variable fluorescence properties. We report on a simple process for the prepn. of a fluorinated graphite oxide (FGO). This process is based on fluorination of graphite oxide (GO) in a fluorine atm. at an elevated temp. and pressure. We used two different GO precursors, which were prepd. by Staudenmaier and Hummers methods. The method of GO synthesis has a strong influence on the concn. of fluorine in the obtained product. The mechanism of GO fluorination is assocd. with the presence of reactive groups, mostly epoxides, and is accompanied by etching of graphite oxide. Our analyses highlighted that the FGO prepd. by Hummers method contains a significantly higher amt. of bounded fluorine and can be used as a starting material for the synthesis of chem. reduced fluorine doped graphene. Water sol. fluorinated graphene can be easily processed in aq. solns. to create hydrophilic particles and films with tunable fluorescence properties.
- 37Girardeaux, C.; Pireaux, J.-J. Analysis of Poly(tetrafluoroethylene) (PTFE) by XPS. Surf. Sci. Spectra 1996, 4, 138– 141, DOI: 10.1116/1.1247814[Crossref], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXit1artw%253D%253D&md5=cca37af54a807f9ebe45bacc22ace6abAnalysis of poly(tetrafluoroethylene) (PTFE) by XPSGirardeaux, Christophe; Pireaux, Jean-JacquesSurface Science Spectra (1997), 4 (2), 138-141CODEN: SSSPEN; ISSN:1055-5269. (American Institute of Physics)X-ray photoemission spectra of poly(tetrafluoroethylene) (PTFE) is reported. XPS spectra were measured with the SSI, SSX-100 model, using monochromated A1 Ka x-rays. The survey spectrum (binding energy range of 0-1000 eV) and narrow scans of C 1s and F 1s is presented. The polymer is used as a ref. to study the influence of PTFE surface modification by an excimer UV laser (λ = 193 nm).
- 38Zhu, Y. F.; Kong, X.; Zheng, H. Y.; Ding, G. Q.; Zhu, Y. L.; Li, Y. W. Efficient Synthesis of 2,5-Dihydroxymethylfuran and 2,5-Dimethylfuran from 5-Hydroxymethylfurfural Using Mineral-Derived Cu Catalysts as Versatile Catalysts. Catal. Sci. Technol. 2015, 5, 4208– 4217, DOI: 10.1039/C5CY00700C[Crossref], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVWqsbnF&md5=b9308c72d653b7897c260ea9b4e8a3e0Efficient synthesis of 2,5-dihydroxymethylfuran and 2,5-dimethylfuran from 5-hydroxymethylfurfural using mineral-derived Cu catalysts as versatile catalystsZhu, Yifeng; Kong, Xiao; Zheng, Hongyan; Ding, Guoqiang; Zhu, Yulei; Li, Yong-WangCatalysis Science & Technology (2015), 5 (8), 4208-4217CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)Selective conversion of 5-hydroxymethylfurfural (HMF) can produce sustainable fuels and chems. Herein, Cu-ZnO catalysts derived from minerals (malachite, rosasite and aurichalcite) were employed for selective hydrogenation of HMF for the first time. High yields of 2,5-dihydroxymethylfuran (∼99.1%) and 2,5-dimethylfuran (∼91.8%) were obtained tunably over the catalyst with a Cu/Zn molar ratio of 2, due to the well-dispersed metal sites tailored by mineral precursors, well-controlled surface sites and optimized reaction conditions. The relationship between catalytic performance and catalyst properties was elucidated by characterization based on the compn. and the structural and surface properties, and catalytic tests. The catalyst can also be extended to selective hydrogenation of other bio-derived mols. (furfural and 5-methylfurfural) to target products. The construction of mineral-derived Cu-ZnO catalysts and the revelation of the structure-performance relationship can be applied to further rational design and functionalization of non-noble Cu catalysts for selective conversion of bio-derived compds.
- 39Hu, L.; Tang, X.; Xu, J. X.; Wu, Z.; Lin, L.; Liu, S. J. Selective Transformation of 5-Hydroxymethylfurfural into the Liquid Fuel 2,5-Dimethylfuran over Carbon-Supported Ruthenium. Ind. Eng. Chem. Res. 2014, 53, 3056– 3064, DOI: 10.1021/ie404441a[ACS Full Text], [CAS], Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1Ggs7Y%253D&md5=47c99c2c4c472d10ed6a3ca600029946Selective Transformation of 5-Hydroxymethylfurfural into the Liquid Fuel 2,5-Dimethylfuran over Carbon-Supported RutheniumHu, Lei; Tang, Xing; Xu, Jiaxing; Wu, Zhen; Lin, Lu; Liu, ShijieIndustrial & Engineering Chemistry Research (2014), 53 (8), 3056-3064CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)A simple and efficient process was presented for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) into the high-quality liq. fuel 2,5-dimethylfuran (DMF) in the presence of THF. Among the employed metal catalysts, the relatively inexpensive C-supported Ru (Ru/C) displayed the highest catalytic performance, which led to 94.7% DMF yield with 100% HMF conversion at a relatively mild reaction temp. of 200° for only 2 h. Although Ru/C had a little loss in the catalytic activity when it was used for 5 successive reaction runs, the partially deactivated Ru/C could be easily regenerated by heating at a mixed flow of H2 and N2. Also, the plausible mechanism involving an aldehyde group, a hydroxyl group, and a furan ring for the selective hydrogenation of HMF into DMF was also proposed. Subsequently, DMF was sepd. from the crude hydrogenation mixt. according to their various b.ps. by the combination of atm. distn. and vacuum distn., and then, the chem. structures and phys. properties of the sepd. DMF are consistent with the authentic DMF. More gratifyingly, Ru/C and THF also are a good combination for the direct hydrogenation of carbohydrate-derived HMF into DMF, which is very important for the practical prodn. of DMF from a variety of biomass-derived carbohydrates such as fructose, glucose, sucrose, maltose, cellobiose, starch, and cellulose.
- 40Zu, Y. H.; Yang, P. P.; Wang, J. J.; Liu, X. H.; Ren, J. W.; Lu, G. Z.; Wang, Y. Q. Efficient Production of the Liquid Fuel 2,5-Dimethylfuran from 5-Hydroxymethylfurfural over Ru/Co3O4 Catalyst. Appl. Catal., B 2014, 146, 244– 248, DOI: 10.1016/j.apcatb.2013.04.026[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXotl2gt7w%253D&md5=05e96e5d5695c508fcce0322658dc4dcEfficient production of the liquid fuel 2,5-dimethylfuran from 5-hydroxymethylfurfural over Ru/Co3O4 catalystZu, Yanhong; Yang, Panpan; Wang, Jianjian; Liu, Xiaohui; Ren, Jiawen; Lu, Guanzhong; Wang, YanqinApplied Catalysis, B: Environmental (2014), 146 (), 244-248CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Ru/Co3O4 catalyst prepd. by a simple copptn. method, was used to catalyze the conversion of 5-hydroxymethylfurfural into 2,5-dimethylfuran and exhibited excellent catalytic performance. Yield of 93.4% of 2,5-dimethylfuran was achieved at relatively low reaction temp. and H2 pressure (130°, 0.7 MPa). Further studies showed that Ru is responsible for hydrogenation, while CoOx species played important role in the hydrogenolysis of hydroxyl groups. This catalyst also displayed a good reusability and can be used for 5 times without loss of the activity.
- 41Saha, B.; Bohn, C. M.; Abu-Omar, M. M. Zinc-Assisted Hydrodeoxygenation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-Dimethylfuran. ChemSusChem 2014, 7, 3095– 3101, DOI: 10.1002/cssc.201402530[Crossref], [PubMed], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVyrs7fE&md5=c3e0795ecbb13e172976fcbc9cf078fcZinc-Assisted Hydrodeoxygenation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-DimethylfuranSaha, Basudeb; Bohn, Christine M.; Abu-Omar, Mahdi M.ChemSusChem (2014), 7 (11), 3095-3101CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)2,5-Dimethylfuran (DMF), a promising cellulosic biofuel candidate from biomass derived intermediates, has received significant attention because of its low oxygen content, high energy d., and high octane value. A bimetallic catalyst combination contg. a Lewis-acidic ZnII and Pd/C components is effective for 5-hydroxymethylfurfural (HMF) hydrodeoxygenation (HDO) to DMF with high conversion (99 %) and selectivity (85 % DMF). Control expts. for evaluating the roles of zinc and palladium revealed that ZnCl2 alone did not catalyze the reaction, whereas Pd/C produced 60 % less DMF than the combination of both metals. The presence of Lewis acidic component (Zn) was also found to be beneficial for HMF HDO with Ru/C catalyst, but the synergistic effect between the two metal components is more pronounced for the Pd/Zn system than the Ru/Zn. A comparative anal. of the Pd/Zn/C catalyst to previously reported catalytic systems show that the Pd/Zn system contg. at least four times less precious metal than the reported catalysts gives comparable or better DMF yields. The catalyst shows excellent recyclability up to 4 cycles, followed by a deactivation, which could be due to coke formation on the catalyst surface. The effectiveness of this combined bimetallic catalyst has also been tested for one-pot conversion of fructose to DMF.
- 42Chen, Z. X.; Leng, K.; Zhao, X. X.; Malkhandi, S.; Tang, W.; Tian, B. B.; Dong, L.; Zheng, L. R.; Lin, M.; Yeo, B. S.; Loh, K. P. Interface Confined Hydrogen Evolution Reaction in Zero Valent Metal Nanoparticles-Intercalated Molybdenum Disulfide. Nat. Commun. 2017, 8, 14548, DOI: 10.1038/ncomms14548[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjsVCrsLw%253D&md5=75770a186992a5df64443219266c4dffInterface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfideChen, Zhongxin; Leng, Kai; Zhao, Xiaoxu; Malkhandi, Souradip; Tang, Wei; Tian, Bingbing; Dong, Lei; Zheng, Lirong; Lin, Ming; Yeo, Boon Siang; Loh, Kian PingNature Communications (2017), 8 (), 14548CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Interface confined reactions, which can modulate the bonding of reactants with catalytic centers and influence the rate of the mass transport from bulk soln., have emerged as a viable strategy for achieving highly stable and selective catalysis. Here we demonstrate that 1T'-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ redn. of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. In particular, the inner platinum surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral mols. This points a way forward for using bulk intercalated compds. for energy related applications.
- 43Wang, L.; Xia, M.; Wang, H.; Huang, K.; Qian, C.; Maravelias, C. T.; Ozin, G. A. Greening Ammonia toward the Solar Ammonia Refinery. Joule 2018, 2, 1055– 1074, DOI: 10.1016/j.joule.2018.04.017[Crossref], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFyntbvK&md5=2f5f9d5bf388046edc086cdfd61aa1aeGreening Ammonia toward the Solar Ammonia RefineryWang, Lu; Xia, Meikun; Wang, Hong; Huang, Kefeng; Qian, Chenxi; Maravelias, Christos T.; Ozin, Geoffrey A.Joule (2018), 2 (6), 1055-1074CODEN: JOULBR; ISSN:2542-4351. (Cell Press)In light of the targets set out by the Paris Climate Agreement and the global energy sector's ongoing transition from fossil fuels to renewables, the chem. industry is searching for innovative ways of reducing greenhouse gas emissions assocd. with the prodn. of ammonia. To address this need, research and development is under way around the world to replace the century-old Haber-Bosch process for manufg. ammonia from N2 and H2, powered by renewable electricity. This involves replacing H2 obtained from steam-reformed CH4 to H2 that is instead obtained from electrolyzed H2O. This transition will enable the changeover from the Haber-Bosch prodn. of NH3 to electrochem., plasma chem., thermochem., and photochem. generation of NH3. If ammonia can eventually be produced directly from N2 and H2O powered by just sunlight, at a technol. significant scale, efficiency, and cost, in a "solar ammonia refinery," green ammonia can change the world!
- 44Turner, J. A. Sustainable Hydrogen Production. Science 2004, 305, 972– 974, DOI: 10.1126/science.1103197[Crossref], [PubMed], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXmsVGmt7w%253D&md5=a54b69353584dccce736af47070665a4Sustainable Hydrogen ProductionTurner, John A.Science (Washington, DC, United States) (2004), 305 (5686), 972-974CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. Identifying and building a sustainable energy system are perhaps 2 of the most crit. issues that today's society must address. Replacing the current energy carrier mix with a sustainable fuel is one of the key pieces in that system. H as an energy carrier, primarily derived from H2O, can address issues of sustainability, environmental emissions, and energy security. Issues relating to H prodn. pathways are addressed here. Future energy systems require money and energy to build. Given that the United States has a finite supply of both, decisions must be made about the way forward.
- 45Wang, J.; Wei, Z. Z.; Mao, S. J.; Li, H. R.; Wang, Y. Highly Uniform Ru Nanoparticles over N-doped Carbon: pH and Temperature-Universal Hydrogen Release from Water Reduction. Energy Environ. Sci. 2018, 11, 800– 806, DOI: 10.1039/C7EE03345A[Crossref], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXivVCrtLo%253D&md5=9a27e0968ec7b54b757e44633cdeb889Highly uniform Ru nanoparticles over N-doped carbon: pH and temperature-universal hydrogen release from water reductionWang, Jing; Wei, Zhongzhe; Mao, Shanjun; Li, Haoran; Wang, YongEnergy & Environmental Science (2018), 11 (4), 800-806CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Highly uniform ruthenium (Ru) nanoparticles over N-doped carbon ([email protected]) was designed and confirmed as a promising candidate for the hydrogen evolution reaction (HER) over a wide pH range. In particular, outstanding catalytic activity with an overpotential of 32 mV at 10 mA cm-2 was achieved in basic media. Moreover, [email protected] holds promise for hydrogen prodn. from 0 °C to 60 °C, greatly broadening its applicability.
- 46Xu, J.; Liu, T.; Li, J.; Li, B.; Liu, Y.; Zhang, B.; Xiong, D.; Amorim, I.; Li, W.; Liu, L. Boosting the Hydrogen Evolution Performance of Ruthenium Clusters Through Synergistic Coupling with Cobalt Phosphide. Energy Environ. Sci. 2018, 11, 1819– 1827, DOI: 10.1039/C7EE03603E[Crossref], [CAS], Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntlCnsr4%253D&md5=9b5fdddc4145db34257df7750a160e58Boosting the hydrogen evolution performance of ruthenium clusters through synergistic coupling with cobalt phosphideXu, Junyuan; Liu, Tianfu; Li, Junjie; Li, Bo; Liu, Yuefeng; Zhang, Bingsen; Xiong, Dehua; Amorim, Isilda; Li, Wei; Liu, LifengEnergy & Environmental Science (2018), 11 (7), 1819-1827CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)In this article, we for the first time report the synthesis and electrocatalytic properties of ruthenium cobalt phosphide hybrid clusters for the hydrogen evolution reaction (HER). Two types of catalysts are investigated: wet chem. redn. of Ru3+ on pre-formed cobalt phosphide (CoP) nanoparticles results in ruthenium-cobalt phosphide side-by-side structures (Ru/CoP); while phosphorizing chem. reduced RuCo alloy leads to the formation of hybrid ruthenium cobalt phosphide (RuCoP) clusters. Compared to pristine Ru clusters, both Ru/CoP and RuCoP show significantly improved HER performance in both acidic and alk. solns. In particular, the hybrid RuCoP clusters demonstrate a considerably low overpotential (η10) of 11 mV at -10 mA cm-2 and a high turnover frequency (TOF) of 10.95 s-1 at η = 100 mV in 0.5 M H2SO4. Even in 1.0 M KOH the excellent HER activity of the RuCoP clusters remains, with a very low η10 of 23 mV and exceptionally high TOF value of 7.26 s-1 at η = 100 mV. Moreover, the RuCoP catalysts can sustain galvanostatic electrolysis in both acidic and alk. solns. at -10 mA cm-2 for 150 h with little degrdn., showing better catalytic stability than the state-of-the-art com. Pt/C catalysts. Our d. functional theory (DFT) calcns. indicate that the RuCoP hybrid exhibits a hydrogen adsorption energy very close to that of Pt and water and -OH adsorption energies distinct from pristine Ru, which reasonably explain the exptl. obsd. excellent HER activities and highlight the importance of synergistic coupling with cobalt phosphide to boost the HER performance of ruthenium.
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Abstract
Figure 1
Figure 1. (a) Schematic of hard template carbon synthesis via liquid-free and conventional methods. (b, c) Transmission electron microscopy (TEM) images of the SiO2@m-SiO2 and SBA-15 templates, respectively. (d, e) Schematic of the bottleneck and tubular pores, respectively. (f, g) TEM images of the Fe/C-SiO2@m-SiO2 and Fe/C-SBA-15 composites, respectively. (h, i) TEM images of C-SiO2@m-SiO2 and C-SBA-15 composites, respectively.
Figure 2
Figure 2. N2-physisorption isotherms of (a) SiO2@m-SiO2 and (b) SBA-15 and their carbon replica. (c, d) Pore size distributions of C-SiO2@m-SiO2 and C-SBA-15, respectively.
Figure 3
Figure 3. Hydrogenolysis of 5-HMF to DMF. (a–c) HAADF-STEM images of Ru/C-SiO2@m-SiO2, Ru/C-SBA-15, and Ru/C-commercial before catalysis. (d–f) HAADF-STEM images of Ru/C-SiO2@m-SiO2, Ru/C-SBA-15, and Ru/C-commercial after catalysis. (g–i) Histogram of Ru particle size before and after catalysis. (j) Hydrogenolysis of HMF to DMF. The main side products are DMTHF and humins. (k) Left: HMF conversion (black), DMF yield (red), DMF selectivity (blue), and DMTHF yield (pink) as a function of the Ru/HMF molar ratio. Reaction conditions: T = 130 °C; P = 10 bar H2; t = 2 h; HMF 0.16 mmol in 3 mL of THF. Right: HMF conversion (black), DMF yield (red), DMF selectivity (blue), and DMTHF yield (pink) as a function of temperature. Reaction conditions: P = 10 bar H2; t = 2 h; HMF 0.16 mmol in 3 mL of THF; Ru/HMF molar ratio 2.6%. The pink zone shows the 30 °C temperature window with over 75% yield of DMF and more than 98% selectivity. The DMF yields using Ru/C-SBA-15 and Ru/C-commercial are marked in purple and green, respectively.
Figure 4
Figure 4. (a) XANES and (b) k2-weighted R space extended X-ray absorption fine structure (EXAFS) of Ru foil (purple), Ru/C-SiO2@m-SiO2 before (red), after catalysis (blue), RuO2 (black). Experimental and fitted results of Ru/C-SiO2@m-SiO2 in R-space EXAFS (c) before and (d) after catalysis (SBA-15), respectively.
Figure 5
Figure 5. (a) HER polarization curves of the Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 compared with a commercial Pt/C catalyst in 1 M KOH. (b) EIS Nyquist plots of the of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 records at −100 mV vs RHE from 100 kHz to 100 mHz. (c) Tafel plots derived from Figure 5a. (d) Time-dependent voltage curve of Ru/C-SiO2@m-SiO2 and Ru/C-SBA-15 under a current density of 10 mA cm–1 for 24 h.
Figure 6
Figure 6. TEM images of 10 carbon–silica composites obtained after CVD: (a) Fe/C-SSZ-13; (b) Fe/C-ZSM-5; (c) Fe/C-silicate-1; (d) Fe/C-zeolite beta; (e) Fe/C-zeolite Y; (p) Fe/C-MCM-41; (q) Fe/C-KIT-6; (r) Fe/C-mSiO2-200; (s) Fe/C-mSiO2-30; and (t) Fe/C-SiO2@mSiO2. TEM images of 10 porous carbons obtained after PTFE leaching: (f) C-SSZ-13; (g) C-ZSM-5; (h) C-silicate-1; (i) C-zeolite beta; (j) C-zeolite Y; (u) C-MCM-41; (v) C-KIT-6; (w) C-mSiO2-200; (x) C-mSiO2-30; and (y) C-SiO2@h-mSiO2. (k–o, z–ad) Comparison of corresponding N2 sorption between the SiO2 templates and porous carbons. For K-SSZ-13, although the kinetic diameter of N2 (0.36 nm) is lower than the pore aperture of SSZ-13 (3.8 Å), the low polarizability and electric quadrupole moment of N2 result in a rather low energy of interaction when K+ presents in the framework (Figure. 6k), showing a very low N2 uptake.
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- 10Ji, X. L.; Lee, K. T.; Nazar, L. F. A Highly Ordered Nanostructured Carbon-Sulphur Cathode for Lithium-Sulphur Batteries. Nat. Mater. 2009, 8, 500– 506, DOI: 10.1038/nmat2460[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmtFenu7Y%253D&md5=35c8dc5d874d37a9c008882fbfcdf3f7A highly ordered nanostructured carbon-sulphur cathode for lithium-sulphur batteriesJi, Xiulei; Lee, Kyu Tae; Nazar, Linda F.Nature Materials (2009), 8 (6), 500-506CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The Li-S batteries have been studied for over 2 decades, as it offers the possibility of high gravimetric capacities and theor. energy densities ranging up to a factor of 5 beyond conventional Li-ion systems. The feasibility to approach such capacities by creating highly ordered interwoven composites was studied. The conductive mesoporous C framework constrains S nanofiller growth within its channels and generates essential elec. contact to the insulating S. The structure provides access to Li+ ingress/egress for reactivity with the S. It is possible that the kinetic inhibition to diffusion within the framework and the sorption properties of the C aid in trapping the polysulfides formed during redox. Polymer modification of the C surface further provides a chem. gradient that retards diffusion of these large anions out of the electrode, thus facilitating more complete reaction. Reversible capacities up to 1320 mA-h/g are attained. The assembly process is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.
- 11Wang, G. H.; Hilgert, J.; Richter, F. H.; Wang, F.; Bongard, H. J.; Spliethoff, B.; Weidenthaler, C.; Schuth, F. Platinum-Cobalt Bimetallic Nanoparticles in Hollow Carbon Nanospheres for Hydrogenolysis of 5-Hydroxymethylfurfural. Nat. Mater. 2014, 13, 293– 300, DOI: 10.1038/nmat3872[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXislCltbs%253D&md5=6e38a80e6a3dfe01109e9e990f79b985Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfuralWang, Guang-Hui; Hilgert, Jakob; Richter, Felix Herrmann; Wang, Feng; Bongard, Hans-Josef; Spliethoff, Bernd; Weidenthaler, Claudia; Schueth, FerdiNature Materials (2014), 13 (3), 293-300CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diams. of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres.
- 12Arnal, P. M.; Comotti, M.; Schuth, F. High-Temperature-Stable Catalysts by Hollow Sphere Encapsulation. Angew. Chem., Int. Ed. 2006, 45, 8224– 8227, DOI: 10.1002/anie.200603507[Crossref], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtlGns7rP&md5=d4579293d22560f28494336f955e7ed7High-temperature-stable catalysts by hollow sphere encapsulationArnal, Pablo M.; Comotti, Massimiliano; Schueth, FerdiAngewandte Chemie, International Edition (2006), 45 (48), 8224-8227CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Hollow ZrO2 shells each contg. one Au nano-particle are stable to sintering and can be used as heterogeneous catalysts in reactions, e.g., CO oxidn. in air. The performance of Au in ZrO2 shells is unaffected by calcination at 800°.
- 13Baldizzone, C.; Mezzavilla, S.; Carvalho, H. W. P.; Meier, J. C.; Schuppert, A. K.; Heggen, M.; Galeano, C.; Grunwaldt, J. D.; Schuth, F.; Mayrhofer, K. J. J. Confined-Space Alloying of Nanoparticles for the Synthesis of Efficient PtNi Fuel-Cell Catalysts. Angew. Chem., Int. Ed. 2014, 53, 14250– 14254, DOI: 10.1002/anie.201406812[Crossref], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVGmu7bF&md5=7547a8dd9cd7e9011f08815cc6afd4eaConfined-Space Alloying of Nanoparticles for the Synthesis of Efficient PtNi Fuel-Cell CatalystsBaldizzone, Claudio; Mezzavilla, Stefano; Carvalho, Hudson W. P.; Meier, Josef Christian; Schuppert, Anna K.; Heggen, Marc; Galeano, Carolina; Grunwaldt, Jan-Dierk; Schueth, Ferdi; Mayrhofer, Karl J. J.Angewandte Chemie, International Edition (2014), 53 (51), 14250-14254CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, i.e., its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen redn. reaction assocd. with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 A mgPt-1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined-space alloying of the nanoparticles in a controlled manner in the pores of the support.
- 14Ortac, I.; Simberg, D.; Yeh, Y.-s.; Yang, J.; Messmer, B.; Trogler, W. C.; Tsien, R. Y.; Esener, S. Dual-Porosity Hollow Nanoparticles for the Immunoprotection and Delivery of Nonhuman Enzymes. Nano Lett. 2014, 14, 3023– 3032, DOI: 10.1021/nl404360k[ACS Full Text], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht12lsLs%253D&md5=48718181a990e5abe16228754ac3f021Dual-Porosity Hollow Nanoparticles for the Immunoprotection and Delivery of Nonhuman EnzymesOrtac, Inanc; Simberg, Dmitri; Yeh, Ya-san; Yang, Jian; Messmer, Bradley; Trogler, William C.; Tsien, Roger Y.; Esener, SadikNano Letters (2014), 14 (6), 3023-3032CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Although enzymes of nonhuman origin have been studied for a variety of therapeutic and diagnostic applications, their use has been limited by the immune responses generated against them. The described dual-porosity hollow nanoparticle platform obviates immune attack on nonhuman enzymes paving the way to in vivo applications, including enzyme-prodrug therapies and enzymic depletion of tumor nutrients. This platform is manufd. with a versatile, scalable, and robust fabrication method. It efficiently encapsulates macromol. cargos filled through mesopores into a hollow interior, shielding them from antibodies and proteases once the mesopores are sealed with nanoporous material. The nanoporous shell allows small mol. diffusion allowing interaction with the large macromol. payload in the hollow center. The approach has been validated in vivo using L-asparaginase to achieve L-asparagine depletion in the presence of neutralizing antibodies.
- 15Lee, J.; Kim, S. M.; Lee, I. S. Functionalization of Hollow Nanoparticles for Nanoreactor Applications. Nano Today 2014, 9, 631– 667, DOI: 10.1016/j.nantod.2014.09.003[Crossref], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFyrtbrI&md5=d5c948b233503ee3a023d0a755c2bc4eFunctionalization of hollow nanoparticles for nanoreactor applicationsLee, Jihwan; Kim, Soo Min; Lee, In SuNano Today (2014), 9 (5), 631-667CODEN: NTAOCG; ISSN:1748-0132. (Elsevier Ltd.)A review. The hollow nanoparticles, which contain catalytic species inside the cavity enclosed by a porous nanoshell, are considered an ideal framework for the nanoreactor that efficiently catalyzes the transformation of the selectively transferred substrate mols. with little loss of activity and surface area of entrapped catalysts even in harsh reaction conditions or during the recycling process. In the performance of the hollow nanoreactor, the selectively functionalized interior cavity is the most vital component which allows chem. reactions to occur within the confines of the protected cavity. Therefore, selective and differential functionalization of the internal space of the hollow nanoshell is the important and challenging topic which is demanded for fully exploiting the potential of the hollow nanoparticle in the nanoreactor application. In this context, this review paper intends to make a survey on the synthetic strategies of functionalizing the interior cavity of the hollow nanoparticles and their employment as nanoreactor systems which catalyze the chem. reactions and template the growth of nanocrystals.
- 16Prieto, G.; Tuysuz, H.; Duyckaerts, N.; Knossalla, J.; Wang, G. H.; Schuth, F. Hollow Nano- and Microstructures as Catalysts. Chem. Rev. 2016, 116, 14056– 14119, DOI: 10.1021/acs.chemrev.6b00374[ACS Full Text], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1aju7nM&md5=a269c05df7f789532583d991b2b82b73Hollow Nano- and Microstructures as CatalystsPrieto, Gonzalo; Tueysuez, Harun; Duyckaerts, Nicolas; Knossalla, Johannes; Wang, Guang-Hui; Schueth, FerdiChemical Reviews (Washington, DC, United States) (2016), 116 (22), 14056-14119CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)Catalysis is at the core of almost every established and emerging chem. process and also plays a central role in the quest for novel technologies for the sustainable prodn. and conversion of energy. Particularly since the early 2000s, a great surge of interest exists in the design and application of micro- and nanometer-sized materials with hollow interiors as solid catalysts. This review provides an updated and crit. survey of the ever-expanding material architectures and applications of hollow structures in all branches of catalysis, including bio-, electro-, and photocatalysis. First, the main synthesis strategies toward hollow materials are succinctly summarized, with emphasis on the (regioselective) incorporation of various types of catalytic functionalities within their different subunits. The principles underlying the scientific and technol. interest in hollow materials as solid catalysts, or catalyst carriers, are then comprehensively reviewed. Aspects covered include the stabilization of catalysts by encapsulation, the introduction of mol. sieving or stimuli-responsive "auxiliary" functionalities, as well as the single-particle, spatial compartmentalization of various catalytic functions to create multifunctional (bio)catalysts. Examples are also given on the applications which hollow structures find in the emerging fields of electro- and photocatalysis, particularly in the context of the sustainable prodn. of chem. energy carriers. Finally, a crit. perspective is provided on the plausible evolution lines for this thriving scientific field, as well as the main practical challenges relevant to the reproducible and scalable synthesis and utilization of hollow micro- and nanostructures as solid catalysts.
- 17Wu, S. H.; Tseng, C. T.; Lin, Y. S.; Lin, C. H.; Hung, Y.; Mou, C. Y. Catalytic Nano-Rattle of [email protected] Silica: Towards a Poison-Resistant Nanocatalyst. J. Mater. Chem. 2011, 21, 789– 794, DOI: 10.1039/C0JM02012E[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhs1WjtLrP&md5=cbc39dfc851587f01e8d53ec427cbad8Catalytic nano-rattle of [email protected] silica: Towards a poison-resistant nanocatalystWu, Si-Han; Tseng, Chih-Ta; Lin, Yu-Shen; Lin, Cheng-Han; Hung, Yann; Mou, Chung-YuanJournal of Materials Chemistry (2011), 21 (3), 789-794CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)In this work, size-controlled gold nanocatalysts (2.8 to 4.5 nm) inside monodisperse hollow silica nanospheres, [email protected], have been prepd. by using a water-in-oil microemulsion as a template. The size of gold nanocatalysts can be easily controlled based on the gold precursor and the chloroauric acid concn. used during synthesis. These [email protected] nanocatalysts were characterized by transmission electron microscopy, SEM, N2 adsorption-desorption isotherms, powder X-ray diffraction, and UV-vis spectrometer. Furthermore, we demonstrate their catalytic capability with respect to the 4-nitrophenol redn. reaction in the absence and presence of a thiol compd., meso-2,3-dimercaptosuccinic acid. The results show that the [email protected] display highly catalytic activity and resistance to other strongly adsorbing mols. in reaction solns.
- 18Li, Y. Q.; Bastakoti, B. P.; Imura, M.; Tang, J.; Aldalbahi, A.; Torad, N. L.; Yamauchi, Y. Dual Soft-Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica Nanoparticles. Chem. - Eur. J. 2015, 21, 6375– 6380, DOI: 10.1002/chem.201406137[Crossref], [PubMed], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXkvVCjtr4%253D&md5=9d0501e8d9d4bc21900ebc345ee39b53Dual Soft-Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica NanoparticlesLi, Yunqi; Bastakoti, Bishnu Prasad; Imura, Masataka; Tang, Jing; Aldalbahi, Ali; Torad, Nagy L.; Yamauchi, YusukeChemistry - A European Journal (2015), 21 (17), 6375-6380CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)A new dual soft-template system comprising the asym. triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to synthesize hollow mesoporous silica (HMS) nanoparticles with a center void of around 17 nm. The stable PS-b-P2VP-b-PEO polymeric micelle serves as a template to form the hollow interior, while the CTAB surfactant serves as a template to form mesopores in the shells. The P2VP blocks on the polymeric micelles can interact with pos. charged CTA+ ions via neg. charged hydrolyzed silica species. Thus, dual soft-templates clearly have different roles for the prepn. of the HMS nanoparticles. Interestingly, the thicknesses of the mesoporous shell are tunable by varying the amts. of TEOS and CTAB. This study provides new insight on the prepn. of mesoporous materials based on colloidal chem.
- 19Lim, J.; Um, J. H.; Ahn, J.; Yu, S. H.; Sung, Y. E.; Lee, J. K. Soft Template Strategy to Synthesize Iron Oxide-Titania Yolk-Shell Nanoparticles as High-Performance Anode Materials for Lithium-Ion Battery Applications. Chem. - Eur. J. 2015, 21, 7954– 7961, DOI: 10.1002/chem.201406667[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlvVeltrg%253D&md5=d0e6f1dcf87fc5469867b7d0e688ed1cSoft Template Strategy to Synthesize Iron Oxide-Titania Yolk-Shell Nanoparticles as High-Performance Anode Materials for Lithium-Ion Battery ApplicationsLim, Joohyun; Um, Ji Hyun; Ahn, Jihoon; Yu, Seung-Ho; Sung, Yung-Eun; Lee, Jin-KyuChemistry - A European Journal (2015), 21 (21), 7954-7961CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)Yolk-shell-structured nanoparticles with iron oxide core, void, and titania shell configuration are prepd. by a simple soft template method and used as the anode material for lithium ion batteries. The iron oxide-titania yolk-shell nanoparticles ([email protected]@TNPs) exhibit a higher and more stable capacity than simply mixed nanoparticles of iron oxide and hollow titania because of the unique structure obtained by the perfect sepn. between iron oxide nanoparticles, in combination with the adequate internal void space provided by stable titania shells. Moreover, the structural effect of [email protected]@TNPs clearly demonstrates that the capacity retention value after 50 cycles is approx. 4 times that for iron oxide nanoparticles under harsh operating conditions, i.e., when the temp. is increased to 80°.
- 20Deng, X. H.; Chen, K.; Tuysuz, H. Protocol for the Nanocasting Method: Preparation of Ordered Mesoporous Metal Oxides. Chem. Mater. 2017, 29, 40– 52, DOI: 10.1021/acs.chemmater.6b02645[ACS Full Text], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVKrsb%252FE&md5=edaaac8c55b0311775d45fc8615bb430Protocol for the Nanocasting Method: Preparation of Ordered Mesoporous Metal OxidesDeng, Xiaohui; Chen, Kun; Tueysuez, HarunChemistry of Materials (2017), 29 (1), 40-52CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)Ordered mesoporous transition metal oxides have attracted considerable research attention due to their unique properties and wide applications. The prepn. of these materials has been reported in the literature using soft and hard templating pathways. Compared with soft templating, hard templating, namely, nanocasting, is advantageous for synthesizing rigid mesostructures with high crystallinity and has already been applied to numerous transition metal oxides such as Co3O4, NiO, Fe2O3, and Mn3O4. However, nanocasting is often complicated by the multiple steps involved: first, the prepn. of ordered mesoporous silica as the hard template, then infiltration of the metal precursor into the pores, and finally, formation of the metal oxide and removal of the hard template. In this paper, we provide a complete protocol that covers the prepn. of most widely used ordered mesoporous silica templates (MCM-41, KIT-6, SBA-15) and the nanocasting process for obtaining ordered mesoporous metal oxides, with emphasizing cobalt oxide as an example. Characterization of the products is presented, and the factors that can potentially affect the process are discussed.
- 21Bottger-Hiller, F.; Kempe, P.; Cox, G.; Panchenko, A.; Janssen, N.; Petzold, A.; Thurn-Albrecht, T.; Borchardt, L.; Rose, M.; Kaskel, S.; Georgi, C.; Lang, H.; Spange, S. Twin Polymerization at Spherical Hard Templates: an Approach to Size-Adjustable Carbon Hollow Spheres with Micro- or Mesoporous Shells. Angew. Chem., Int. Ed. 2013, 52, 6088– 6091, DOI: 10.1002/anie.201209849
- 22Yoon, S. B.; Sohn, K.; Kim, J. Y.; Shin, C. H.; Yu, J. S.; Hyeon, T. Fabrication of Carbon Capsules with Hollow Macroporous Core/Mesoporous Shell Structures. Adv. Mater. 2002, 14, 19– 21, DOI: 10.1002/1521-4095(20020104)14:1<19::AID-ADMA19>3.0.CO;2-X[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xmt12qtw%253D%253D&md5=728f4a736d1dbc2204749320607d76c5Fabrication of carbon capsules with hollow macroporous core/mesoporous shell structuresYoon, Suk Bon; Sohn, Kwonnam; Kim, Jeong Yeon; Shin, Chae-Ho; Yu, Jong-Sung; Hyeon, TaeghwanAdvanced Materials (Weinheim, Germany) (2002), 14 (1), 19-21CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH)A solid core/mesoporous shell (SCMS) silica sphere was used as template to prep. carbon capsules with hollow core mesoporous shell (HCMS). Most particles of the HCMS carbon capsules were uniform and spherical with particle diams. of 30 nm and some particles were deformed. The TEM image of the carbon material showed hollow cores of 220 nm in diam. and mesoporous shells with thickness of 55 nm. The structure of the HCMS carbon capsules is an inverse replica of the SCMS silica sphere templates. Due to uniform, hollow macroscopic core and mesopores of the bimodal pore systems in the shell, HCMS carbon capsules could have a wide range of applications, including catalysts, adsorbents, sensors, electrode materials, and advanced storage materials.
- 23Valle-Vigon, P.; Sevilla, M.; Fuertes, A. B. Synthesis of Uniform Mesoporous Carbon Capsules by Carbonization of Organosilica Nanospheres. Chem. Mater. 2010, 22, 2526– 2533, DOI: 10.1021/cm100190a[ACS Full Text], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXjvFCjt7g%253D&md5=f12864285a159c628709ef997659001fSynthesis of Uniform Mesoporous Carbon Capsules by Carbonization of Organosilica NanospheresValle-Vigon, Patricia; Sevilla, Marta; Fuertes, Antonio B.Chemistry of Materials (2010), 22 (8), 2526-2533CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A synthetic method to produce uniform mesoporous hollow carbon nanospheres with a large surface area and uniform mesoporosity has been developed by employing, as carbon source, an org. moiety used as porogen agent to synthesize spherical organosilica nanoparticles with a [email protected] (org.-inorg.) structure. The conversion of the org. moiety to carbon is achieved by means of sulfuric acid which considerably increases the carbon yield via dehydration and sulfonation reactions. The carbon capsules exhibit a uniform morphol. (a diam. of ∼440 nm and a shell thickness of ∼50 nm), a high Brunauer-Emmett-Teller (BET) surface area (1620 m2.g-1), a large pore vol. (2.3 cm3.g-1), and a porosity made up of mesopores centered at around 4.3 nm. Iron oxide magnetic nanoparticles were incorporated into the pores of the porous shell of the carbon capsules. The magnetic hollow nanoparticles were then used as support for the immobilization of cytochrome C. A large amt. of enzyme is stored in this magnetic nanocomposite (∼500 mg Cyt·g-1 support) which suggests that a significant fraction of enzyme is accommodated in the hollow core of the capsules.
- 24Li, J. J.; Liang, Y.; Dou, B. J.; Ma, C. Y.; Lu, R. J.; Hao, Z. P.; Xie, Q.; Luan, Z. Q.; Li, K. Nanocasting Synthesis of Graphitized Ordered Mesoporous Carbon Using Fe-Coated SBA-15 Template. Mater. Chem. Phys. 2013, 138, 484– 489, DOI: 10.1016/j.matchemphys.2012.12.003[Crossref], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvFSntrrF&md5=23b86d4a85f131c489b13c7a74afc84fNanocasting synthesis of graphitized ordered mesoporous carbon using Fe-coated SBA-15 templateLi, Jinjun; Liang, Yan; Dou, Baojuan; Ma, Chunyan; Lu, Renjie; Hao, Zhengping; Xie, Qiang; Luan, Zhiqiang; Li, KaiMaterials Chemistry and Physics (2013), 138 (2-3), 484-489CODEN: MCHPDR; ISSN:0254-0584. (Elsevier B.V.)Ordered mesoporous carbons with high porosities and graphitized structures were synthesized by a template-catalysis method using low-mol.-wt. phenolic resin as carbon precursor and Fe-coated SBA-15 as both template and catalyst. The synthesis route involves the following steps: (a) the synthesis of mesoporous Fe-coated SBA-15 through a one-pot method, (b) the infiltration of a low-mol.-wt. phenolic resin into the porosity of the Fe-coated SBA-15, (c) the carbonization and catalytic graphitization of the infiltrated phenolic resin at 900 °C, and (d) the removal of the Fe-coated SBA-15 template. The X-ray diffraction, nitrogen sorption, transmission electron microscopy and SEM were used to characterize the materials, and the results indicate that the prepd. carbon materials have well-ordered mesoporous structures replicated from the templates, and graphitized structures can be obsd. on the carbon frameworks, depending on the iron content in the templates.
- 25Lu, A. H.; Schüth, F. Nanocasting: a Versatile Strategy for Creating Nanostructured Porous Materials. Adv. Mater. 2006, 18, 1793– 1805, DOI: 10.1002/adma.200600148[Crossref], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xot1Kktr0%253D&md5=ceb160f9820c4a9e03648204d57db7d1Nanocasting: a versatile strategy for creating nanostructured porous materialsLu, An-Hui; Schueth, FerdiAdvanced Materials (Weinheim, Germany) (2006), 18 (14), 1793-1805CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Nanocasting is a powerful method for creating materials that are more difficult to synthesize by conventional processes. We summarize recent developments in the synthesis of various structured porous solids, covering silica, carbon, and other nonsiliceous solids that are created by a nanocasting pathway. Structure replication on the nanometer length scale allows materials' properties to be manipulated in a controlled manner, such as tunable compn., controllable structure and morphol., and specific functionality. The nanocasting pathway with hard templates opens the door to the design of highly porous solids with multifunctional properties and interesting application perspectives.
- 26Lou, X. W. D.; Archer, L. A.; Yang, Z. Hollow Micro-/Nanostructures: Synthesis and Applications. Adv. Mater. 2008, 20, 3987– 4019, DOI: 10.1002/adma.200800854[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsVartbnK&md5=06f1f33dc2ccfe8627f5e0b1cb4322dcHollow micro-/nanostructures: synthesis and applicationsLou, Xiong Wen; Archer, Lynden A.; Yang, ZichaoAdvanced Materials (Weinheim, Germany) (2008), 20 (21), 3987-4019CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Hollow micro-/nanostructures are of great interest in many current and emerging areas of technol. Perhaps the best-known example of the former is the use of fly-ash hollow particles generated from coal power plants as partial replacement for Portland cement to produce concrete with enhanced strength and durability. This review is devoted to the progress made in the last decade in synthesis and applications of hollow micro-/nanostructures. We present a comprehensive overview of synthetic strategies for hollow structures. These strategies are broadly categorized into four themes which include well-established approaches such as conventional hard-templating and soft-templating methods, as well as newly emerging methods based on sacrificial templating and template-free synthesis. Success in each has inspired multiple variations that continue to drive the rapid evolution of the field. This review therefore focuses on the fundamentals of each process, pointing out advantages and disadvantages where appropriate. Strategies for generating more complex hollow structures, such as rattle-type and nonspherical hollow structures, are also discussed. Applications of hollow structures in lithium batteries, catalysis and sensing, and biomedical applications are reviewed.
- 27Xia, Y.; Mokaya, R. Hollow Spheres of Crystalline Porous Metal Oxides: A Generalized Synthesis Route via Nanocasting with Mesoporous Carbon Hollow Shells. J. Mater. Chem. 2005, 15, 3126– 3131, DOI: 10.1039/b502558c
- 28Andrews, R.; Jacques, D.; Rao, A. M.; Derbyshire, F.; Qian, D.; Fan, X.; Dickey, E. C.; Chen, J. Continuous Production of Aligned Carbon Nanotubes: a Step Closer to Commercial Realization. Chem. Phys. Lett. 1999, 303, 467– 474, DOI: 10.1016/S0009-2614(99)00282-1[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXisFCktrg%253D&md5=93b5c1a11d9e1194426c5af6ccb30690Continuous production of aligned carbon nanotubes: a step closer to commercial realizationAndrews, R.; Jacques, D.; Rao, A. M.; Derbyshire, F.; Qian, D.; Fan, X.; Dickey, E. C.; Chen, J.Chemical Physics Letters (1999), 303 (5,6), 467-474CODEN: CHPLBC; ISSN:0009-2614. (Elsevier Science B.V.)High-purity aligned multi-walled carbon nanotubes (MWNTs) were synthesized through the catalytic decompn. of a ferrocene-xylene mixt. at ∼675°C in a quartz tube reactor and over quartz substrates, with a conversion of ∼25% of the total hydrocarbon feedstock. Under the exptl. conditions used, scanning electron microscope images reveal that the MWNT array grows perpendicular to the quartz substrates at an av. growth rate of ∼25 μm/h. A process of this nature which does not require preformed substrates, and which operates at atm. pressure and moderate temps., could be scaled up for continuous or semi-continuous prodn. of MWNTs.
- 29Sevilla, M.; Sanchis, C.; Valdes-Solis, T.; Morallon, E.; Fuertes, A. B. Synthesis of Graphitic Carbon Nanostructures from Sawdust and Their Application as Electrocatalyst Supports. J. Phys. Chem. C 2007, 111, 9749– 9756, DOI: 10.1021/jp072246x[ACS Full Text], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmt1artrw%253D&md5=2008f8569cb6b35070080e27fa205e54Synthesis of Graphitic Carbon Nanostructures from Sawdust and Their Application as Electrocatalyst SupportsSevilla, M.; Sanchis, C.; Valdes-Solis, T.; Morallon, E.; Fuertes, A. B.Journal of Physical Chemistry C (2007), 111 (27), 9749-9756CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The authors present a novel and facile synthetic method for fabricating graphitic C nanostructures (GCNs) from sawdust. This method is based on the use of catalysts (Fe or Ni) that allows the direct conversion of sawdust into highly graphitized C material. The following procedure was used to obtain these graphitic nanoparticles: (a) impregnation of the sawdust particles with Fe or Ni salts, (b) carbonization of the impregnated material at a temp. of 900 or 1000°, and (c) selective removal of the nongraphitized C (amorphous C) by an oxidant (KMnO4). The resulting C is made up of nanosized graphitic structures (i.e., nanocapsules, nanocoils, nanoribbons), which have a high crystallinity, as evidenced by TEM/SAED, XRD and Raman anal. These GCNs were used as supports for Pt nanoparticles. Such prepd. electrocatalysts show an electrocatalytical surface area close to 90 m2 g-1 Pt, and they present a similar or higher electrocatalytic activity toward MeOH electrooxidn. than the Pt/Vulcan electrocatalyst prepd. in the same conditions.
- 30Galeano, C.; Meier, J. C.; Peinecke, V.; Bongard, H.; Katsounaros, I.; Topalov, A. A.; Lu, A. H.; Mayrhofer, K. J. J.; Schuth, F. Toward Highly Stable Electrocatalysts via Nanoparticle Pore Confinement. J. Am. Chem. Soc. 2012, 134, 20457– 20465, DOI: 10.1021/ja308570c[ACS Full Text], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslCgsbjL&md5=a5dfa149688bf886ac5acb0f2d1d1908Toward Highly Stable Electrocatalysts via Nanoparticle Pore ConfinementGaleano, Carolina; Meier, Josef C.; Peinecke, Volker; Bongard, Hans; Katsounaros, Ioannis; Topalov, Angel A.; Lu, Anhui; Mayrhofer, Karl J. J.; Schueth, FerdiJournal of the American Chemical Society (2012), 134 (50), 20457-20465CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A mesostructured graphitic carbon support, called Hollow Graphitic Spheres (HGS), with sp. surface area >1000 m2/g and precisely controlled pore structure, was specifically developed to overcome long-term fuel cell catalyst degrdn., esp. for the oxygen redn. reaction, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles (∼3 to 4 nm size) encapsulated in the HGS pore structure that are stable at 850°C and, more importantly, during simulated accelerated electrochem. aging. The high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochem. cycling, the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degrdn. mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support.
- 31Schnitzler, M. C.; Mangrich, A. S.; Macedo, W. A. A.; Ardisson, J. D.; Zarbin, A. J. G. Incorporation, Oxidation and Pyrolysis of Ferrocene into Porous Silica Glass: a Route to Different Silica/Carbon and Silica/Iron Oxide Nanocomposites. Inorg. Chem. 2006, 45, 10642– 10650, DOI: 10.1021/ic061312r
- 32Singh, D. K.; Krishna, K. S.; Harish, S.; Sampath, S.; Eswaramoorthy, M. No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance. Angew. Chem., Int. Ed. 2016, 55, 2032– 2036, DOI: 10.1002/anie.201509054[Crossref], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktlShug%253D%253D&md5=3d2f61da65b10393eadc92141a5f83d1No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor PerformanceSingh, Dheeraj Kumar; Krishna, Katla Sai; Harish, Srinivasan; Sampath, Srinivasan; Eswaramoorthy, MuthusamyAngewandte Chemie, International Edition (2016), 55 (6), 2032-2036CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)An innovative technique to obtain high-surface-area mesostructured C (2545 m2 g-1) with significant microporosity uses Teflon as the SiO2 template removal agent. This method not only shortens synthesis time by combining SiO2 removal and carbonization in a single step, but also assists in ultrafast removal of the template (in 10 min) with complete elimination of toxic HF usage. The obtained C material (JNC-1) displays excellent CO2 capture ability (∼26.2% at 0° under 0.88 bar CO2 pressure), which is twice that of CMK-3 obtained by the HF etching method (13.0%). JNC-1 demonstrated higher H2 adsorption capacity (2.8%) compared to CMK-3 (1.2%) at -196° under 1.0 bar H2 pressure. The bimodal pore architecture of JNC-1 led to superior supercapacitor performance, with a specific capacitance of 292 F g-1 and 182 F g-1 at a drain rate of 1 A g-1 and 50 A g-1, resp., in 1 M H2SO4 compared to CMK-3 and activated C.
- 33Shin, H. J.; Ryoo, R.; Kruk, M.; Jaroniec, M. Modification of SBA-15 Pore Connectivity by High-Temperature Calcination Investigated by Carbon Inverse Replication. Chem. Commun. 2001, 349– 350, DOI: 10.1039/b009762o[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhtFamtb4%253D&md5=7a755742957a26d755e4fb20df9d915fModification of SBA-15 pore connectivity by high-temperature calcination investigated by carbon inverse replicationShin, Hyun June; Ryoo, Ryong; Kruk, Michal; Jaroniec, MietekChemical Communications (Cambridge, United Kingdom) (2001), (4), 349-350CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Two-dimensional hexagonally ordered CMK-3 carbons were synthesized using SBA-15 templates calcined at a temp. of 1153 K, whereas a disordered carbon was obtained using SBA-15 calcined at 1243 K. the results demonstrate that the pores connecting ordered mesopores in SBA-15 silica persist up to ca. 1153 K, but are eliminated at temps. close to 1243 K.
- 34Artz, J.; Mallmann, S.; Palkovits, R. Selective Aerobic Oxidation of HMF to 2,5-Diformylfuran on Covalent Triazine Frameworks-Supported Ru Catalysts. ChemSusChem 2015, 8, 672– 679, DOI: 10.1002/cssc.201403078[Crossref], [PubMed], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXosFGltg%253D%253D&md5=9ebb642e793ced794138f3d891aad3f3Selective Aerobic Oxidation of HMF to 2,5-Diformylfuran on Covalent Triazine Frameworks-Supported Ru CatalystsArtz, Jens; Mallmann, Sabrina; Palkovits, ReginaChemSusChem (2015), 8 (4), 672-679CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)The selective aerobic oxidn. of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran has been performed under mild conditions at 80 °C and 20 bar of synthetic air in Me t-Bu ether. Ru clusters supported on covalent triazine frameworks (CTFs) allowed excellent selectivity and superior catalytic activity compared to other support materials such as activated carbon, γ-Al2O3, hydrotalcite, or MgO. CTFs with varying pore size, sp. surface area, and N content could be prepd. from different monomers. The structural properties of the CTF materials influence the catalytic activity of Ru/CTF significantly in the aerobic oxidn. of HMF, which emphasizes the superior activity of mesoporous CTFs. Recycling of the catalysts is challenging, but promising methods to maintain high catalytic activity were developed that facilitate only minor deactivation in five consecutive recycling expts.
- 35Zhang, H. B.; Liu, G. G.; Shi, L.; Ye, J. H. Single-Atom Catalysts: Emerging Multifunctional Materials in Heterogeneous Catalysis. Adv. Energy Mater. 2018, 8, 1701343, DOI: 10.1002/aenm.201701343
- 36Jankovsky, O.; Simek, P.; Sedmidubsky, D.; Matejkova, S.; Janousek, Z.; Sembera, F.; Pumera, M.; Sofer, Z. Water-Soluble Highly Fluorinated Graphite Oxide. RSC Adv. 2014, 4, 1378– 1387, DOI: 10.1039/C3RA45183F[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvVKhtL7M&md5=ec4b37eb164e387100c352c387085c5eWater-soluble highly fluorinated graphite oxideJankovsky, Ondrej; Simek, Petr; Sedmidubsky, David; Matejkova, Stanislava; Janousek, Zbynek; Sembera, Filip; Pumera, Martin; Sofer, ZdenekRSC Advances (2014), 4 (3), 1378-1387CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Water-sol. highly fluorinated graphite oxide is a promising candidate for applications in biosensing and for fluorescent probes due to its variable fluorescence properties. We report on a simple process for the prepn. of a fluorinated graphite oxide (FGO). This process is based on fluorination of graphite oxide (GO) in a fluorine atm. at an elevated temp. and pressure. We used two different GO precursors, which were prepd. by Staudenmaier and Hummers methods. The method of GO synthesis has a strong influence on the concn. of fluorine in the obtained product. The mechanism of GO fluorination is assocd. with the presence of reactive groups, mostly epoxides, and is accompanied by etching of graphite oxide. Our analyses highlighted that the FGO prepd. by Hummers method contains a significantly higher amt. of bounded fluorine and can be used as a starting material for the synthesis of chem. reduced fluorine doped graphene. Water sol. fluorinated graphene can be easily processed in aq. solns. to create hydrophilic particles and films with tunable fluorescence properties.
- 37Girardeaux, C.; Pireaux, J.-J. Analysis of Poly(tetrafluoroethylene) (PTFE) by XPS. Surf. Sci. Spectra 1996, 4, 138– 141, DOI: 10.1116/1.1247814[Crossref], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXit1artw%253D%253D&md5=cca37af54a807f9ebe45bacc22ace6abAnalysis of poly(tetrafluoroethylene) (PTFE) by XPSGirardeaux, Christophe; Pireaux, Jean-JacquesSurface Science Spectra (1997), 4 (2), 138-141CODEN: SSSPEN; ISSN:1055-5269. (American Institute of Physics)X-ray photoemission spectra of poly(tetrafluoroethylene) (PTFE) is reported. XPS spectra were measured with the SSI, SSX-100 model, using monochromated A1 Ka x-rays. The survey spectrum (binding energy range of 0-1000 eV) and narrow scans of C 1s and F 1s is presented. The polymer is used as a ref. to study the influence of PTFE surface modification by an excimer UV laser (λ = 193 nm).
- 38Zhu, Y. F.; Kong, X.; Zheng, H. Y.; Ding, G. Q.; Zhu, Y. L.; Li, Y. W. Efficient Synthesis of 2,5-Dihydroxymethylfuran and 2,5-Dimethylfuran from 5-Hydroxymethylfurfural Using Mineral-Derived Cu Catalysts as Versatile Catalysts. Catal. Sci. Technol. 2015, 5, 4208– 4217, DOI: 10.1039/C5CY00700C[Crossref], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtVWqsbnF&md5=b9308c72d653b7897c260ea9b4e8a3e0Efficient synthesis of 2,5-dihydroxymethylfuran and 2,5-dimethylfuran from 5-hydroxymethylfurfural using mineral-derived Cu catalysts as versatile catalystsZhu, Yifeng; Kong, Xiao; Zheng, Hongyan; Ding, Guoqiang; Zhu, Yulei; Li, Yong-WangCatalysis Science & Technology (2015), 5 (8), 4208-4217CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)Selective conversion of 5-hydroxymethylfurfural (HMF) can produce sustainable fuels and chems. Herein, Cu-ZnO catalysts derived from minerals (malachite, rosasite and aurichalcite) were employed for selective hydrogenation of HMF for the first time. High yields of 2,5-dihydroxymethylfuran (∼99.1%) and 2,5-dimethylfuran (∼91.8%) were obtained tunably over the catalyst with a Cu/Zn molar ratio of 2, due to the well-dispersed metal sites tailored by mineral precursors, well-controlled surface sites and optimized reaction conditions. The relationship between catalytic performance and catalyst properties was elucidated by characterization based on the compn. and the structural and surface properties, and catalytic tests. The catalyst can also be extended to selective hydrogenation of other bio-derived mols. (furfural and 5-methylfurfural) to target products. The construction of mineral-derived Cu-ZnO catalysts and the revelation of the structure-performance relationship can be applied to further rational design and functionalization of non-noble Cu catalysts for selective conversion of bio-derived compds.
- 39Hu, L.; Tang, X.; Xu, J. X.; Wu, Z.; Lin, L.; Liu, S. J. Selective Transformation of 5-Hydroxymethylfurfural into the Liquid Fuel 2,5-Dimethylfuran over Carbon-Supported Ruthenium. Ind. Eng. Chem. Res. 2014, 53, 3056– 3064, DOI: 10.1021/ie404441a[ACS Full Text], [CAS], Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1Ggs7Y%253D&md5=47c99c2c4c472d10ed6a3ca600029946Selective Transformation of 5-Hydroxymethylfurfural into the Liquid Fuel 2,5-Dimethylfuran over Carbon-Supported RutheniumHu, Lei; Tang, Xing; Xu, Jiaxing; Wu, Zhen; Lin, Lu; Liu, ShijieIndustrial & Engineering Chemistry Research (2014), 53 (8), 3056-3064CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)A simple and efficient process was presented for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) into the high-quality liq. fuel 2,5-dimethylfuran (DMF) in the presence of THF. Among the employed metal catalysts, the relatively inexpensive C-supported Ru (Ru/C) displayed the highest catalytic performance, which led to 94.7% DMF yield with 100% HMF conversion at a relatively mild reaction temp. of 200° for only 2 h. Although Ru/C had a little loss in the catalytic activity when it was used for 5 successive reaction runs, the partially deactivated Ru/C could be easily regenerated by heating at a mixed flow of H2 and N2. Also, the plausible mechanism involving an aldehyde group, a hydroxyl group, and a furan ring for the selective hydrogenation of HMF into DMF was also proposed. Subsequently, DMF was sepd. from the crude hydrogenation mixt. according to their various b.ps. by the combination of atm. distn. and vacuum distn., and then, the chem. structures and phys. properties of the sepd. DMF are consistent with the authentic DMF. More gratifyingly, Ru/C and THF also are a good combination for the direct hydrogenation of carbohydrate-derived HMF into DMF, which is very important for the practical prodn. of DMF from a variety of biomass-derived carbohydrates such as fructose, glucose, sucrose, maltose, cellobiose, starch, and cellulose.
- 40Zu, Y. H.; Yang, P. P.; Wang, J. J.; Liu, X. H.; Ren, J. W.; Lu, G. Z.; Wang, Y. Q. Efficient Production of the Liquid Fuel 2,5-Dimethylfuran from 5-Hydroxymethylfurfural over Ru/Co3O4 Catalyst. Appl. Catal., B 2014, 146, 244– 248, DOI: 10.1016/j.apcatb.2013.04.026[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXotl2gt7w%253D&md5=05e96e5d5695c508fcce0322658dc4dcEfficient production of the liquid fuel 2,5-dimethylfuran from 5-hydroxymethylfurfural over Ru/Co3O4 catalystZu, Yanhong; Yang, Panpan; Wang, Jianjian; Liu, Xiaohui; Ren, Jiawen; Lu, Guanzhong; Wang, YanqinApplied Catalysis, B: Environmental (2014), 146 (), 244-248CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)Ru/Co3O4 catalyst prepd. by a simple copptn. method, was used to catalyze the conversion of 5-hydroxymethylfurfural into 2,5-dimethylfuran and exhibited excellent catalytic performance. Yield of 93.4% of 2,5-dimethylfuran was achieved at relatively low reaction temp. and H2 pressure (130°, 0.7 MPa). Further studies showed that Ru is responsible for hydrogenation, while CoOx species played important role in the hydrogenolysis of hydroxyl groups. This catalyst also displayed a good reusability and can be used for 5 times without loss of the activity.
- 41Saha, B.; Bohn, C. M.; Abu-Omar, M. M. Zinc-Assisted Hydrodeoxygenation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-Dimethylfuran. ChemSusChem 2014, 7, 3095– 3101, DOI: 10.1002/cssc.201402530[Crossref], [PubMed], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVyrs7fE&md5=c3e0795ecbb13e172976fcbc9cf078fcZinc-Assisted Hydrodeoxygenation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-DimethylfuranSaha, Basudeb; Bohn, Christine M.; Abu-Omar, Mahdi M.ChemSusChem (2014), 7 (11), 3095-3101CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)2,5-Dimethylfuran (DMF), a promising cellulosic biofuel candidate from biomass derived intermediates, has received significant attention because of its low oxygen content, high energy d., and high octane value. A bimetallic catalyst combination contg. a Lewis-acidic ZnII and Pd/C components is effective for 5-hydroxymethylfurfural (HMF) hydrodeoxygenation (HDO) to DMF with high conversion (99 %) and selectivity (85 % DMF). Control expts. for evaluating the roles of zinc and palladium revealed that ZnCl2 alone did not catalyze the reaction, whereas Pd/C produced 60 % less DMF than the combination of both metals. The presence of Lewis acidic component (Zn) was also found to be beneficial for HMF HDO with Ru/C catalyst, but the synergistic effect between the two metal components is more pronounced for the Pd/Zn system than the Ru/Zn. A comparative anal. of the Pd/Zn/C catalyst to previously reported catalytic systems show that the Pd/Zn system contg. at least four times less precious metal than the reported catalysts gives comparable or better DMF yields. The catalyst shows excellent recyclability up to 4 cycles, followed by a deactivation, which could be due to coke formation on the catalyst surface. The effectiveness of this combined bimetallic catalyst has also been tested for one-pot conversion of fructose to DMF.
- 42Chen, Z. X.; Leng, K.; Zhao, X. X.; Malkhandi, S.; Tang, W.; Tian, B. B.; Dong, L.; Zheng, L. R.; Lin, M.; Yeo, B. S.; Loh, K. P. Interface Confined Hydrogen Evolution Reaction in Zero Valent Metal Nanoparticles-Intercalated Molybdenum Disulfide. Nat. Commun. 2017, 8, 14548, DOI: 10.1038/ncomms14548[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjsVCrsLw%253D&md5=75770a186992a5df64443219266c4dffInterface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfideChen, Zhongxin; Leng, Kai; Zhao, Xiaoxu; Malkhandi, Souradip; Tang, Wei; Tian, Bingbing; Dong, Lei; Zheng, Lirong; Lin, Ming; Yeo, Boon Siang; Loh, Kian PingNature Communications (2017), 8 (), 14548CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Interface confined reactions, which can modulate the bonding of reactants with catalytic centers and influence the rate of the mass transport from bulk soln., have emerged as a viable strategy for achieving highly stable and selective catalysis. Here we demonstrate that 1T'-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ redn. of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. In particular, the inner platinum surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral mols. This points a way forward for using bulk intercalated compds. for energy related applications.
- 43Wang, L.; Xia, M.; Wang, H.; Huang, K.; Qian, C.; Maravelias, C. T.; Ozin, G. A. Greening Ammonia toward the Solar Ammonia Refinery. Joule 2018, 2, 1055– 1074, DOI: 10.1016/j.joule.2018.04.017[Crossref], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFyntbvK&md5=2f5f9d5bf388046edc086cdfd61aa1aeGreening Ammonia toward the Solar Ammonia RefineryWang, Lu; Xia, Meikun; Wang, Hong; Huang, Kefeng; Qian, Chenxi; Maravelias, Christos T.; Ozin, Geoffrey A.Joule (2018), 2 (6), 1055-1074CODEN: JOULBR; ISSN:2542-4351. (Cell Press)In light of the targets set out by the Paris Climate Agreement and the global energy sector's ongoing transition from fossil fuels to renewables, the chem. industry is searching for innovative ways of reducing greenhouse gas emissions assocd. with the prodn. of ammonia. To address this need, research and development is under way around the world to replace the century-old Haber-Bosch process for manufg. ammonia from N2 and H2, powered by renewable electricity. This involves replacing H2 obtained from steam-reformed CH4 to H2 that is instead obtained from electrolyzed H2O. This transition will enable the changeover from the Haber-Bosch prodn. of NH3 to electrochem., plasma chem., thermochem., and photochem. generation of NH3. If ammonia can eventually be produced directly from N2 and H2O powered by just sunlight, at a technol. significant scale, efficiency, and cost, in a "solar ammonia refinery," green ammonia can change the world!
- 44Turner, J. A. Sustainable Hydrogen Production. Science 2004, 305, 972– 974, DOI: 10.1126/science.1103197[Crossref], [PubMed], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXmsVGmt7w%253D&md5=a54b69353584dccce736af47070665a4Sustainable Hydrogen ProductionTurner, John A.Science (Washington, DC, United States) (2004), 305 (5686), 972-974CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review. Identifying and building a sustainable energy system are perhaps 2 of the most crit. issues that today's society must address. Replacing the current energy carrier mix with a sustainable fuel is one of the key pieces in that system. H as an energy carrier, primarily derived from H2O, can address issues of sustainability, environmental emissions, and energy security. Issues relating to H prodn. pathways are addressed here. Future energy systems require money and energy to build. Given that the United States has a finite supply of both, decisions must be made about the way forward.
- 45Wang, J.; Wei, Z. Z.; Mao, S. J.; Li, H. R.; Wang, Y. Highly Uniform Ru Nanoparticles over N-doped Carbon: pH and Temperature-Universal Hydrogen Release from Water Reduction. Energy Environ. Sci. 2018, 11, 800– 806, DOI: 10.1039/C7EE03345A[Crossref], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXivVCrtLo%253D&md5=9a27e0968ec7b54b757e44633cdeb889Highly uniform Ru nanoparticles over N-doped carbon: pH and temperature-universal hydrogen release from water reductionWang, Jing; Wei, Zhongzhe; Mao, Shanjun; Li, Haoran; Wang, YongEnergy & Environmental Science (2018), 11 (4), 800-806CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Highly uniform ruthenium (Ru) nanoparticles over N-doped carbon ([email protected]) was designed and confirmed as a promising candidate for the hydrogen evolution reaction (HER) over a wide pH range. In particular, outstanding catalytic activity with an overpotential of 32 mV at 10 mA cm-2 was achieved in basic media. Moreover, [email protected] holds promise for hydrogen prodn. from 0 °C to 60 °C, greatly broadening its applicability.
- 46Xu, J.; Liu, T.; Li, J.; Li, B.; Liu, Y.; Zhang, B.; Xiong, D.; Amorim, I.; Li, W.; Liu, L. Boosting the Hydrogen Evolution Performance of Ruthenium Clusters Through Synergistic Coupling with Cobalt Phosphide. Energy Environ. Sci. 2018, 11, 1819– 1827, DOI: 10.1039/C7EE03603E[Crossref], [CAS], Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntlCnsr4%253D&md5=9b5fdddc4145db34257df7750a160e58Boosting the hydrogen evolution performance of ruthenium clusters through synergistic coupling with cobalt phosphideXu, Junyuan; Liu, Tianfu; Li, Junjie; Li, Bo; Liu, Yuefeng; Zhang, Bingsen; Xiong, Dehua; Amorim, Isilda; Li, Wei; Liu, LifengEnergy & Environmental Science (2018), 11 (7), 1819-1827CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)In this article, we for the first time report the synthesis and electrocatalytic properties of ruthenium cobalt phosphide hybrid clusters for the hydrogen evolution reaction (HER). Two types of catalysts are investigated: wet chem. redn. of Ru3+ on pre-formed cobalt phosphide (CoP) nanoparticles results in ruthenium-cobalt phosphide side-by-side structures (Ru/CoP); while phosphorizing chem. reduced RuCo alloy leads to the formation of hybrid ruthenium cobalt phosphide (RuCoP) clusters. Compared to pristine Ru clusters, both Ru/CoP and RuCoP show significantly improved HER performance in both acidic and alk. solns. In particular, the hybrid RuCoP clusters demonstrate a considerably low overpotential (η10) of 11 mV at -10 mA cm-2 and a high turnover frequency (TOF) of 10.95 s-1 at η = 100 mV in 0.5 M H2SO4. Even in 1.0 M KOH the excellent HER activity of the RuCoP clusters remains, with a very low η10 of 23 mV and exceptionally high TOF value of 7.26 s-1 at η = 100 mV. Moreover, the RuCoP catalysts can sustain galvanostatic electrolysis in both acidic and alk. solns. at -10 mA cm-2 for 150 h with little degrdn., showing better catalytic stability than the state-of-the-art com. Pt/C catalysts. Our d. functional theory (DFT) calcns. indicate that the RuCoP hybrid exhibits a hydrogen adsorption energy very close to that of Pt and water and -OH adsorption energies distinct from pristine Ru, which reasonably explain the exptl. obsd. excellent HER activities and highlight the importance of synergistic coupling with cobalt phosphide to boost the HER performance of ruthenium.
- 47Hitz, C.; Lasia, A. Experimental Study and Modeling of Impedance of the HER on Porous Ni Electrodes. J. Electroanal. Chem. 2001, 500, 213– 222, DOI: 10.1016/S0022-0728(00)00317-X[Crossref], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhslelsLw%253D&md5=3f33684b285bfb575dfd3a30c63b3cc9Experimental study and modeling of impedance of the her on porous Ni electrodesHitz, C.; Lasia, A.Journal of Electroanalytical Chemistry (2001), 500 (1-2), 213-222CODEN: JECHES ISSN:. (Elsevier Science S.A.)The electrochem. activity towards the hydrogen evolution reaction (her) of pressed powder electrodes (Ni-Zn and Ni-Al) was studied in alk. solns. after leaching out the more active element. These electrodes displayed porous character, and electrochem. impedance spectroscopy was used to characterize surface porosity. The influence of overpotential, temp., poisons, electrode compn. and electrolyte concn. was studied and distinction criteria between faradaic and geometrical effects were formulated. Digital simulations of impedance values in different pore geometries were also carried out. The kinetic parameters of hydrogen evolution were detd. The main factor influencing the electrode activity seems to be the real surface area.
- 48Yang, Y.; Fei, H. L.; Ruan, G. D.; Tour, J. M. Porous Cobalt-Based Thin Film as a Bifunctional Catalyst for Hydrogen Generation and Oxygen Generation. Adv. Mater. 2015, 27, 3175– 3180, DOI: 10.1002/adma.201500894[Crossref], [PubMed], [CAS], Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmsFyrsLo%253D&md5=00da6dccea8dd4f48e27ca76e31b4fcfPorous Cobalt-Based Thin Film as a Bifunctional Catalyst for Hydrogen Generation and Oxygen GenerationYang, Yang; Fei, Huilong; Ruan, Gedeng; Tour, James M.Advanced Materials (Weinheim, Germany) (2015), 27 (20), 3175-3180CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A mixed-phased porous thin film of Co phosphide/Co phosphate was directly fabricated through reaction of phosphorus vapor with anodized Co oxide porous films. The porous films can directly work as electrodes for catalytic H2 and O2 evolution reactions and they show superior activity to the state-of-the-art catalysts. The mixed phases in such porous films give a dual ability to deliver both efficient H2 and O2 generation in a single electrolyzer through an alternating sequence. Thus, with a.c. inputs renewable energy device platforms that are wind or solar based could be used to generate both H2 and O2 as a fuel source.
- 49Meirer, F.; Kalirai, S.; Morris, D.; Soparawalla, S.; Liu, Y. J.; Mesu, G.; Andrews, J. C.; Weckhuysen, B. M. Life and Death of a Single Catalytic Cracking Particle. Science Advances 2015, 1, e1400199 DOI: 10.1126/sciadv.1400199
- 50Dent, A.; Cibin, G.; Ramos, S.; Parry, S.; Gianolio, D.; Smith, A.; Scott, S.; Varandas, L.; Patel, S.; Pearson, M. In Performance of B18, the Core EXAFS Bending Magnet Beamline at Diamond. J. Phys.: Conf. Ser. 2013, 430, 012023, DOI: 10.1088/1742-6596/430/1/012023[Crossref], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlsVeisb4%253D&md5=5f25e8c1fdad8f56d9b7598e072c7ffbPerformance of B18, the Core EXAFS bending magnet beamline at diamondDent, A. J.; Cibin, G.; Ramos, S.; Parry, S. A.; Gianolio, D.; Smith, A. D.; Scott, S. M.; Varandas, L.; Patel, S.; Pearson, M. R.; Hudson, L.; Krumpa, N. A.; Marsch, A. S.; Robbins, P. E.Journal of Physics: Conference Series (2013), 430 (15th International Conference on X-Ray Absorption Fine Structure, 2012), 012023/1-012023/7CODEN: JPCSDZ; ISSN:1742-6588. (IOP Publishing Ltd.)A review. B18 has been operational since Apr. 2010 and has hosted a total of 63 EXAFS user expts. up to Jan 2012. B18 is contributing to research programs across a wide range of scientific disciplines, e.g. solid state physics and materials, catalysis, chem., soft matter, surfaces and biomaterials. We present a review of its present performance and capabilities.
- 51Dent, A.; Cibin, G.; Ramos, S.; Smith, A.; Scott, S.; Varandas, L.; Pearson, M.; Krumpa, N.; Jones, C.; Robbins, P. In B18: A Core XAS Spectroscopy Beamline for Diamond. J.Phys.: Conf. Ser. 2009, 190, 012039, DOI: 10.1088/1742-6596/190/1/012039
Supporting Information
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ARTICLE SECTIONSThe Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.8b09399.
TEM and SEM images, N2-physisorption isotherms, XPS spectra, Raman spectra, XAFS spectra and fittings, XRD patterns, and catalytic results (Figures S1–S19 and Tables S1–S7) (PDF)
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