ZnO nanocrystals were synthesized by chemical vapor synthesis from two different precursors—diethylzinc and bis(2,2,6,6-tetramethyl-3,5-heptanedionate)zinc—at different temperatures in a tubular hot wall reactor. It is observed that the yield of ZnO nanocrystals is temperature dependent, and it decreases with increasing reactor temperature for both precursors. The nucleation rate was calculated by classical nucleation theory and was correlated with the experimental yield of ZnO nanocrystals.

Self-assembled single-crystalline Si_1−xGe_x nanorings (NRs), as small as 10 nm with narrow distributions of height and diameter, have been fabricated without any specific equipment. Compared to other approaches for nanofabricating the ring-like structures, the smallest Si_1−xGe_x NRs with the highest density were obtained by the mediation of Au nanodots. The process promises the availability of Si_1−xGe_x NRs with a wide range of Ge concentration and size, and can serve as a useful platform for the fundamental understanding and future practical applications of NR devices.

Self-assembly is a versatile approach for the preparation of polymer nanocomposites with prescribed morphologies in the high-technology applications. Here, we use a Brownian dynamics (BD) method to explore the self-assembly of star-polymer-attached nanospheres and propose that a star polymer attached to the nanosphere brings anisotropy and induces the formation of polymer nanocomposites with different morphologies. These morphologies include hollow sphere, porous structure, lamella, perforated lamella with star polymer through nanosphere, and cylinder-like nanosphere, core−shell micelle, gyroid-like network, and star-polymer-formed cylindrical structure, depending on temperature, concentration, and nanosphere size. To give a framework of these mesostructures, a temperature versus concentration phase diagram is presented for each case of nanospheres. In order to better understand the self-assembly of star-polymer-attached nanospheres, we also explore the mechanism of the formation of these morphologies by examining the packing details of star polymers. It is expected that this work would provide useful information for engineering novel polymer nanocomposite materials by means of the mesophase self-assembly.

Very recently, mass spectroscopy of ZnO clusters revealed a hitherto unknown (ZnO)₆₀ magic-number cluster with exceptional stability. Using first-principles approaches, we searched the most stable structures of medium-size (ZnO)_n clusters by considering several possible structural motifs. Instead of the previously nominated nested cage for (ZnO)₆₀, we found a sodalite structure via coalescence of (ZnO)₁₂ cages, which was predicted to be a metastable phase in bulk ZnO solid. Due to the smaller influence of surface reconstruction, this sodalite motif is very competitive for larger (ZnO)_n clusters up to n = 96.

We have prepared silver molybdate glass nanocomposites of compositions xAgI−(1 − x)(yAg₂O−(1 − y)MoO₃) by melting the mixtures of the chemicals AgI, AgNO₃, and MoO₃ and quenching the melts. High-resolution transmission electron micrographs have been employed to detect the α-AgI nanoparticles present in the composites. We have studied relaxation dynamics of silver ions in these nanocomposites as a function of frequency and temperature. It has been observed that the variation of the average size of the α-AgI nanoparticles embedded in these nanocomposites and also the dilation of the glass network with AgI doping are responsible for the variation of the conductivity and hopping frequency with composition. The conductivity spectra have been analyzed using the power law model. We have observed that the power law exponent is almost independent of composition. The variation of the conductivity as well as the crossover frequency depends on the modifier to former ratio. We have estimated the concentration of mobile Ag⁺ ions from the Nernst−Einstein relation, which is found to be almost independent of temperature. We have further observed that only 20−23% of the total Ag⁺ ions contribute to the conduction process.

Electron transfer (ET) in aggregates of cadmium selenide (CdSe) and cadmium telluride (CdTe) nanoparticles (NPs) was studied in aqueous solution by fluorescence quenching. Both steady-state and time-resolved fluorescence measurements were used to quantify how the ET depends on the nature of the NP assemblies. The aggregation of CdSe and CdTe NPs was controlled by the electrostatic attraction of the charged functionalities placed on the NP surface coating. Electron transfer quenching was found to depend on three factors: the interparticle distance, the energetic alignment of the NP bands (hence the size of the NPs), and the direction of the electric field between the NPs, created by their surface charges.

We investigated vacancies, antisites, and nitrogen substitutional defects in ZnO single-walled zigzag and armchair nanotubes using spin-polarized density-functional calculations. We found that all defects introduced defect levels in the band gap. Among the investigated defects, oxygen vacancy had the lowest formation energy under zinc-rich conditions, but induced no magnetism in the tubes. A Zn vacancy induced a magnetic moment of 2.0 μ_B/cell in the tubes, resulting from the oxygen dangling-bond states. On the other hand, while a Zn_O antisite defect induced a magnetic moment of 2.0 μ_B/cell in the zigzag tube, we found no magnetism in the armchair tube. An important prediction is that antisite defects, with high formation energies in bulk, could have relatively low formation energies in ZnO tubes. Finally, we report on the nitrogen-doped ZnO tubes. Most interestingly, we found a magnetic moment of 1.0 μ_B/cell for the N substitution on both the oxygen and zinc sites.

Self-assembled solution micelles prepared from polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP), have been employed as templates to synthesize copper nanocatalysts which are regarded as an excellent catalyst system for 1D nanomaterial synthesis. We have demonstrated that uniform-sized nanoparticles with diameters ranging from 1 to 15 nm have been generated. We have revealed that nanocatalyst size can be rationally tailored by adjusting the interaction between copper precursors and ligands and metal sequestration time. Ordered arrays of copper nanocatalysts derived from depositing a monolayer of solution micelles exhibit excellent thermal stability and do not agglomerate during the thermal treatment at 850 °C, typical growth temperature for 1D nanomaterial using the chemical vapor deposition technique. High-density and aligned single-walled carbon nanotubes with uniform diameter have been synthesized using the chemical vapor deposition technique. The average diameter is 1.4 nm, which is on the same order of catalyst size, around 2.0 nm. The combination of tunable size and spacing with superb thermal stability and outstanding catalytic activity offered by this new copper nanocatalyst system will enable growth of high-yield 1D nanomaterials with controllable diameter and spacing consistently and reproducible properties. It also paves a new path to study the effect of nanocatalyst size on 1D nanomaterial synthesis and their properties.

The loss of electrochemically active surface area (ECSA) causes severe performance degradation over relevant lifetimes of polymer electrolyte fuel cells. Using a simple physical model, we analyze the interrelations between kinetics of platinum nanoparticle dissolution, evolution of the particle size distribution, and ECSA loss with time. The model incorporates the initial particle radius distribution, and it accounts for kinetic processes involving Pt dissolution, Pt−O formation, and Pt−O dissolution. Employing reasonable simplifying assumptions to the governing equations, a full analytical solution was found under potentiostatic conditions. The simplified model predicts the evolution of the particle radius distribution as well as ECSA loss with time, in close agreement with experimental ex situ and in situ studies. The study indicates that the rates of chemical Pt−O dissolution, driven by the particle size dependence of the cohesive energy, may dominate over electrochemical dissolution. Fitting of the model to experimental data provides an effective surface tension and an effective rate constant of Pt−O dissolution. Implications of the model for the development of strategies to reduce ECSA loss are discussed.

The thermal conductivity of single-walled carbon nanotubes (SWCNTs) under axial stress is studied by nonequilibrium molecular dynamics simulation. The thermal conductivity is found to increase and then decrease with the tube elongation changing from an axially compressed state to a stretched state. The phonon density of states of the systems is analyzed to elucidate the variation of heat conduction with respect to the stress in CNTs. The primary peak of the phonon spectrum shows a blue shift or red shift as the SWCNT is compressed or stretched. These shifts correspond to the change of the elasticity coefficient of the CNTs. The variation trend of primary peak height of radial phonon spectra with axial strain is similar to that of the thermal conductivity, which indicates that the radial phonon modes, especially the high-frequency modes, play a dominant role in the heat conduction mechanism of CNTs.

The adsorption of Si, Sn, and Li on single-walled boron nitride nanotubes has been studied by density functional theory calculation. Both single Si or Sn atoms and their dimers are able to adsorb on the outer surface of (8,0) BNNT exothermically. The adsorption of dimers is weaker than that of a single atom. With increasing the tube diameter from (8,0) to (16,0), the adsorption energy of a single atom decreases slightly. The adsorption of single Si and Sn atoms induces magnetism whereas dimers do not. None of the single adatoms or dimers is stable inside the (8,0) BNNT. Except for a single Li atom, all other single adatoms and dimers are stable inside (12,0) BNNT with an adsorption energy of less than −0.4 eV. The alloying of a Li atom with Si or Sn further stabilizes the system, showing that BNNTs encapsulated Si or Sn might be a potential Li storage material.

The interaction between silver nanoparticle and calf thymus DNA was studied by UV−visible, fluorescence, and far UV circular dichroism (CD) spectroscopies at a physiologic temperature of 37 °C. By the analysis of UV−visible titration and thermal denaturation studies of DNA, it was found that silver nanoparticle can form a new complex with double-helical DNA and increase the T_m value of DNA. This kind of binding may cause a slight change of the conformation of DNA. The fluorescence emission spectra of intercalated ethidium bromide (EB) with increasing concentration of silver nanoparticle at 37 °C represented a significant reduction of the ethidium intensity and quenching of EB fluorescence. Also, CD results suggested that silver nanoparticle can significantly change the helicity conformation of DNA and then induce the alteration of nonplanar and tilted orientations of DNA bases, resulting in the changes of DNA base stacking, and act as an intercalator. Spectroscopic results represented that binding of silver nanoparticle to DNA resulted in significant changes in the structure and conformation of DNA in a concentration dependent manner and act as an intercalator via increasing stability of DNA by increasing T_m, quenching of EB fluorescence intensity, and alteration of CD spectra. Also, the antitumor property of silver nanoparticle was studied by testing it on human tumor cell line K562. The 50% cytotoxic concentration (Cc₅₀) of silver nanoparticle was determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay after a 24 h incubation time. Results of the present study may provide useful information to design better anticancer compounds using metal nanoparticles with lower side effects in the future.

The nature of observed growth of solid carbon on palladium from ethylene−hydrogen mixtures is consistent with the supposition that the primary source of carbon for growth is homogeneously generated radicals. Evidence includes the lack of growth in the absence of a reacting mixture, sharp maxima as a function of temperature, and dramatic differences in temperature of growth as a function of mixture composition. The finding that the structure of the support strongly influenced the morphology of the solid carbon, and the temperature regime for deposition, is also consistent with this model. Carbon nanofibers were found to form on sputtered palladium films and palladium nanopowder (ca. 700 °C), whereas planar carbon structures deposited on palladium micrometer powder and foil (ca. 600 °C). A radical species growth mechanism is consistent not only with observations made herein but also with data presented in earlier studies.

Without the use of surfactants, a uniform and porous structure zinc oxide film has been synthesized in a chloride electrolyte using a triangular potential waveform. The triangular waveform parameters have been determined based on the findings of the linear sweep voltammetry and the cyclic voltammetry in the chloride electrolyte. The mechanism for producing the porous ZnO film can be attributed to the anodic current that dissolves the metallic zinc grains to form nanosized pores and, more importantly, the Cl⁻ ions in oxidation reactions and the ZnCl⁺ ions in reduction reactions that cyclically function as dynamic templates for the pinning effect and the blocking effect on the zinc oxide film, respectively. The study is of significance not only in successfully developing a promising alternative for synthesizing porous ZnO films but also in understanding the underlying mechanism by the concept of dynamic templates. The findings of the paper also lay down a good foundation for further developing this technique into practical use.

We investigate thermal behavior of transparent film heaters (TFH) made of single-walled carbon nanotubes. We fabricate the TFH by using the spray coating method. We studied the temperature dependence of the electrical resistance of the TFH in terms of Joule and external heating in various gas environments. Test results show that the effect of the electrical current through the TFH on the temperature dependence of the electrical resistance is not important and that the humidity and the degree of vacuum significantly affect the shape of the resistance−temperature curve. We discuss the physical meanings underlying the experimental results and how to make use of these findings. This study improves the understanding of the heating effect on electrical conductance of the TFH made of single-walled carbon nanotubes which could be a good candidate for the heater in many applications requiring both transparency and heating function.

The dramatic enhanced visible light photocatalytic activity and excellent antiphotocorrosion performance of CdS photocatalysts were obtained after hybridized by monolayer polyaniline. The as-prepared PANI-CdS hybrid photocatalysts reveal the outstanding photocatalytic activity and photoelectrical conversion efficiency which can improve about 2.5 and 1.8 times that of the pure CdS, respectively. Significantly, the issue of photocorrosion, a congenital disadvantage of CdS photocatalysts, has been solved completely after hybridization. The mechanisms on enhancement of photocatalytic activity and antiphotocorrosion performance have been emphasized. Under visible light irradiation, photogenerated electrons in LUMO of PANI injected into the conduction band of CdS, photogenerated holes in the valence band of CdS transferred to the photocatalysts surface through HOMO of PANI. The rapid transferring of hole and high separation efficiency of electron−hole pairs lead to the dramatically enhanced photoactivity and completely inhibited photocorrosion.

AgPb₁₀SbTe₁₂ crystals with nanocubic and flower-like morphologies have been successfully fabricated by a facile solution route. The sizes and morphologies of AgPb₁₀SbTe₁₂ were examined in relation to reaction temperature, the molar ratio of KOH/Pb(Ac)₂, polyvinyl pyrrolidone (PVP), and solvents. A surface-protected etching growth mechanism has been proposed to elucidate the formation of nanocubes and flower-like crystals. Furthermore, the electrical conductivities of the samples with nanocubic and flower-like shapes were measured to investigate the possible impact of size and morphology on the electrical conductivity.

Monodisperse Fe nanoparticles with a high saturation magnetization were synthesized by thermal decomposition of a newly developed Fe(CO)_x−oleylamine reacted precursor. The coordinate bond of the Fe(CO)_x−oleylamine reacted precursor is different from conventional Fe(CO)₅, and the CO ligands are partially replaced by oleylamine. The coordinate bond of the Fe(CO)_x−oleylamine reacted precursor had a large influence on the size of the Fe nanoparticles, and as a result, the nanoparticle diameter could be controlled in the range from 2.3 to 10 nm by changing the reaction temperature and time for the precursor. The saturation magnetizations for 10 and 2.3 nm diameter NPs were 192 and 160 emu/g_Fe at 5 K. The high M_S of the Fe NPs was attributed to lesser amounts of impurities, such as C and O.

Real time UV−visible absorption measurements of stopped flows of AgNO₃ and (NH₄)₂S are used to study the nucleation and growth of silver sulfide nanoparticles (Ag₂S NP). Ag₂S NP in the size range of 2 to 10 nm are formed a few seconds after the flow containing the reactants stops. The absorbance near the band edge of the semiconductor nanoparticle is used to monitor the number of particles formed with time and study the nucleation process. Transmission electron microscopy measurements are used to correlate particle size and the indirect band gap energy, determined from the onset of light absorption. A linear relation is established between Ag₂S NP particle size and indirect band gap energy. The nucleation and growth process are not well separated in time. The initial nucleation and growth rates are found to increase with initial [AgNO₃]_o/[(NH₄)₂S]_o ratios larger than 1. Silver-rich sulfides are proposed to be involved in the nucleation stage and growth process of Ag₂S NP. Density functional calculations are consistent with that interpretation: Ag₃S⁺ is found to have a lower energy than the Ag₂S and AgSH molecules or the AgS⁻ and Ag₂SH⁺ ions. The results are discussed in terms of classic nucleation theory and the possible growth mechanisms are discussed.

We report a one-pot synthesis protocol for highly efficient and stable covalent binding of both the fluorescent drug doxorubicin (DOX) and the biocompatible polymer poly(ethylene glycol) (PEG) to the surface of superparamagnetic iron oxide nanoparticles (SPIONs). The final aim is to obtain a biocompatible, injectable nanosystem combining anticancer activity (magnetically targeted drug delivery) and nondestructive imaging of the treated cancer cells and tissues by means of fluorescence and magnetic resonance imaging (MRI). Our protocol employs silane and epoxide chemistry, which could also be useful to bind other molecules possessing a primary or secondary amine group, such as drugs, proteins, and fluorescent labels. The suspensions of SPIONs-DOX-PEG (iron concentration of 17 mg/L) obtained in this study are stable at physiological pH values. This stability coupled with the PEG surface neutrality makes these nanoparticles compatible with their application in vivo, via systemic administration. Efficient binding of DOX to the SPIONs surface via the amine group of the sugar moiety of the drug, i.e., outside of the aromatic pharmacophore−fluorophore, preserves the fluorescence activity of DOX. Confocal fluorescence spectral imaging of treated MCF7 cancer cells indicates that, in spite of the accumulation of SPIONs-DOX-PEG in the cytosol, only a minor fraction of the drug reaches the nucleus in 24 h. As a result, no in vitro cytotoxicity against MCF7 cancer cells was detected (the highest iron and drug concentrations were 2.7 mg/L and 8.1 μM, respectively). Interestingly, SPIONs-DOX particles noncoated with PEG were cytotoxic. We conclude that cellular enzymes can cleave the amine drug−particle linkage, but the PEG shell hinders the cleavage, possibly by sterical repulsion. Therefore, the developed chemistry is useful for stable coating of SPIONs with polymers and fluorescent labels, while an alternative strategy will be needed for more efficient drug release.

We report the formation of two- and three-component porous supramolecular networks from combinations of uracil, PTCDI, and melamine. The structures, which are formed on Au(111) in ultra-high vacuum (UHV) and studied by scanning tunneling microscopy (STM), are stabilized by hydrogen bonds. We show that two bimolecular networks comprising uracil and PTCDI can be formed, one of which contains two pore geometries and is composed of 28 molecules per unit cell. In addition, we observe two different ordered structures from mixtures of melamine and uracil. By combining all three of these species, we demonstrate the formation of a single ternary structure that contains 33 molecules per unit cell. Our results demonstrate the capacity of hydrogen bonding to produce highly complex structures, and open up the possibility of forming a wide range of new structures from combinations of nucleic bases and other small organic molecules.

Well-crystalline SnO₂ nanorods were first synthesized via a continuous and scalable iron-assisted flame approach with production rate up to 50 g/h in laboratory-scale. The as-prepared SnO₂ nanorods with uniform length up to 200 nm and diameter around 20 nm are smooth and single crystal rutile structures, growing along the [001] direction. Iron dopant is incorporated into the SnO₂ lattice and selectively effects a specific SnO₂ crystal plane, promoting the further crystal oriented growth into nanorods. Meanwhile, the photoluminescence (PL) spectrum of such SnO₂ nanorods exhibits a broad, stronger orange-emission peak around 620 nm, suggesting potential applications in optoelectronics. It is noteworthy that this dopant-assisted flame approach provides a new strategy for sequentially engineering one-dimensional nanomaterials.

A new approach for the synthesis of freely dispersible one-dimensional (1D) lanthanum telluride nanowires (La₂Te₃ NWs) in the solution phase is reported. The process involves a reaction between tellurium nanowires (Te NWs) and lanthanum nitrate (La(NO₃)₃) at room-temperature. Te NWs act as templates for the formation of La₂Te₃ NWs. The aspect ratio of the as prepared La₂Te₃ NWs is the same as the parent Te NWs. Various microscopic and spectroscopic tools such as HRTEM, SEM, EDAX, XRD, XPS, Raman, UV−visible, and fluorescence were used for the characterization of the NWs. A new surface enhanced Raman active substrate was synthesized by doping silver in La₂Te₃ NWs. Surface enhanced Raman spectra were studied using crystal violet (CV) as the analyte. Raman features have been observed up to a concentration of 10⁻⁸ M of CV. Different concentrations of Ag in Ag-doped La₂Te₃ NWs were investigated. The monodispersity, homogeneity, and Raman enhancement properties of the NWs, synthesized through a simple solution phase protocol, are expected to motivate further studies on this material.

Electron relaxation dynamics in CdS−Ag₂S nanorods have been measured as a function of the relative fraction of the two semiconductors, which can be tuned via cation exchange between Cd²⁺ and Ag⁺. The transient bleach of the first excitonic state of the CdS nanorods is characterized by a biexponential decay corresponding to fast relaxation of the excited electrons into trap states. This signal completely disappears when the nanorods are converted to Ag₂S but is fully recovered after a second exchange to convert them back to CdS, demonstrating annealing of the nonradiative trap centers probed and the robustness of the cation exchange reaction. Partial cation exchange produces heterostructures with embedded regions of Ag₂S within the CdS nanorods. Transient bleaching of the CdS first excitonic state shows that increasing the fraction of Ag₂S produces a greater contribution from the fast component of the biexponential bleach recovery, indicating that new midgap relaxation pathways are created by the Ag₂S material. Transient absorption with a mid-infrared probe further confirms the presence of states that preferentially trap electrons on a time scale of 1 ps, 2 orders of magnitude faster than that of the parent CdS nanorods. These results suggest that the Ag₂S regions within the heterostucture provide an efficient relaxation pathway for excited electrons in the CdS conduction band.

Adsorption of carbon monoxide on Pt (335) and (112) stepped surfaces has been investigated by the extended LEPS (London-Eryring-Polanyi-Sato) method which is constructed by the 5-parameter Morse Potential. The calculated results show there have common characteristics of CO adsorption on the two surfaces. On both Pt (335) and (112) stepped surfaces, CO molecules adsorb on the step top site initially. With the coverage increasing, CO molecules diffuse from the step top sites to the stable terrace bridge sites and the terrace top sites sequentially. However, the step bridge site only corresponds to a transition state on the two surfaces. The predictions for vibrational frequency are in good agreement with the experimental results.

Understanding and quantifying the principles governing surface-to-adsorbate charge transfer is of utmost importance because excess electrons in n-type oxides alter significantly surface binding and reactivity. We performed a systematic study using density functional theory (DFT) of the role of excess electrons in rutile TiO_2, which can result from point defects such as oxygen vacancies, bridging row hydroxyls, and interstitial Ti species. These defects create excess electrons within the Ti sublattice which can perform redox chemistry on adsorbates. We show the similarity of these defects in their ability to donate electrons to surface adsorbates, indicating that experimentally distinguishing the nature of the defects may be difficult. We examined the adsorption and reactivity of O₂ in detail and also present a generalization of these findings for a variety of species. A characterization of the redox properties of the surface/adsorbate complex indicates that when the electronegativity of the adsorbate is greater than the surface electronegativity, significant charge transfer from the reduced surface to the absorbate occurs. Surface defects do not participate in significant charge transfer for adsorbates with low electronegativity. Through variations of the U parameter in the DFT+U theory we modulated the position of the defect states in the band gap. Increased stability of the defect states leads to more difficult charge transfer to the adsorbates and a decrease in the adsorption energy. The present study offers insights on requirements with regard to modeling reduced TiO₂ using electronic structure methods and an understanding of how to control the surface reactivity through degree of reduction or defect state location.

The adsorption of aniline on SWCNTs has been investigated using three different DFT methods, PW91LYP, the hybrid m-GGA MPWB1K, and the dispersion-corrected BP86-D functionals. The BSSE-corrected adsorption energies for top orientation of aniline to the nanotube surface are E_ads = 9.7 kcal mol⁻¹ and E_ads = 1.4 kcal mol⁻¹ with BP86-D/SVP and MPWB1K/6-311+G(d), respectively. Results validated that the adsorption energy of aniline depends on the diameter of the nanotube with a pronounced manner, especially for small diameters. The TDDFT calculations of UV/vis spectra predict two electronic transitions resulting from nanotube excitations in the visible spectra (>500 nm) and one imperceptible aniline → SWCNT excitation at ca. 1200 nm. Inclusion of solvent effects (MeOH) by explicit solvent molecules leads to a pronounced red shift of the weak longest wavelength aniline → nanotube transition, whereas the strong intratube excitations are only a little influenced. Fluorescence excitation spectra (λ_em = 586 nm) of SWCNTs in aniline yield a broad structured absorption in the range of 22 000−18 000 cm⁻¹, which is insensitive to the addition of methanol as cosolvent.

A modified boron-doped diamond (BDD) electrode was prepared by evenly assembling Sb-doped SnO₂ nanoparticles on the BDD surface, which possesses excellent electrocatalytic performance and is more suitable to degrade the pollutants. The growth of Sb-doped SnO₂−NPs was controlled using micelles of the block copolymer surfactant and homogeneous precipitation approaches. SEM and HRTEM confirmed that BDD still can be fully exposed after modification of Sb-doped SnO₂−NPs. The prepared Sb-doped SnO₂−NPs/BDD electrode maintained high oxygen evolution potential (2.3 V vs SCE); meanwhile, its conductivity is greatly improved when the resistance decreases to 1.2 from 60.8 kΩ and the reaction activation energy also reduces from 8.02 to 4.93 kJ mol⁻¹, owing to the excellent electrocatalytic performance. Moreover, Sb-doped SnO₂−NPs/BDD has higher oxidation ability. The reaction rate constant of 2,4-D on the Sb-doped SnO₂−NPs/BDD is 2 times and mineralization current efficiency at 30 min on the Sb-doped SnO₂−NPs/BDD is 1.6 times that on the BDD. The time for complete removal of the total organic carbon (TOC) is 240 min on the Sb-doped SnO₂−NPs/BDD electrode, while it is beyond 360 min on the BDD. Energy consumption on the BDD is 1.3 times that on the Sb-doped SnO₂−NPs/BDD for the TOC total removal. The generation and further oxidation of the intermediates further approved the high efficiency of the Sb-doped SnO₂−NPs/BDD.

Operando X-ray absorption spectroscopy (XAS) has been used to study the adsorbates and structural changes and their dependence on potential, existing during the ethanol oxidation reaction (EOR) on carbon-supported Pt, PtRu, and PtSn anode catalysts. Conventional EXAFS was applied to identify nanoparticle structure and particle size. The Δμ-XANES technique was used to investigate adsorbed species with potential. On pure Pt, an overall increase in Δμ amplitude exists under EOR compared to that existing during the methanol oxidation reaction (MOR). This increased amplitude was attributed mainly to the C₁ species on the surface during the EOR; these C₁ species and CO become oxidized when O(H) come down on the surface. On PtRu catalysts, the O(H) formation and C-species oxidation begins at lower potentials compared to Pt. The ligand effect from oxidized RuO_x islands is operative in PtRu and responsible for the performance enhancement. On PtSn, we observe O(H) at nearly all potentials, which may be explained by a very strong ligand effect involving SnO_x. The operando Δμ and EXAFS results enable the determination of relative active surface areas, particle structure, and adsorbate coverages with potential of C species, OH, and O providing new insights into the role of OH in the EOR.

In this article, cactus-like hierarchical structures were fabricated via click chemistry of azide−alkyne 1,3-dipolar Huisgen cycloaddition reaction. It is convenient to control the size of hierarchical particulates and to tune their surface roughness by adjusting the cycles of the click reaction. Dual-sized surface roughness, which biomimics the surface topology of sticky superhydrophobic gecko feet, originates from well-defined silica-based cactus-like particulates that are covalently bonded to an alkynyl-treated substrate. After surface modification with fluorinated azobenzene, the resulting hairy hierarchical structure coatings show the static water contact angle as high as 151.6 ± 1.5°, high adhesion to water, and outstanding chemical stability. We believe that the densely packed nanoscale aggregates are the key contributors to the observed high adhesion, presumably by generating large van der Waals’ forces from the large surface area in very close contact with water.

A DFT model of the Fe(100) surface was used to study the dissociation process of H₂. The dissociation of H₂ was considered on a clean surface as well as CO- and C-precovered surfaces. The presence of CO and C is shown to block several sites for hydrogen adsorption, as well as increasing various hydrogen dissociation barriers. At CO and C coverages up to 0.25 ML the main contributor to the barrier increase is the CO−H and C−H repulsion. In these cases, off-symmetry sites will play an important role in the dissociation of the approaching hydrogen molecules. At coverages of 0.5 ML of CO and C, adsorption site blocking occurred, and the dissociation barriers increased to more than 3 times larger values than that of the clean surface. This increase in the barriers will result in a significant decrease in the rate constant of the dissociative H₂ adsorption process.

Ordered vanadosilicate mesoporous material with large (∼15 nm), uniform, novel cage-like mesopores was synthesized under acidic aqueous conditions from tetraethyl orthosilicate in the presence of ammonia vanadiate, using P₁₂₃ with CTAB as cotemplate and TMB as a swelling agent. The catalysts were extensively characterized by a combination of different techniques (N₂ adsorption, small-angle X-ray scattering (SAXS), transmission electron microscope (TEM), UV Raman, and UV−vis spectra) in relation to their performance for oxidation dehydrogenation of propane. SAXS and TEM analysis showed that the as-synthesized vanadosilicate samples have a uniform, well-defined cage-like mesostructure. UV Raman and UV−vis spectra revealed that the vanadium species was isolated and presented as a highly dispersed state in the framework of the vanadosilicate samples. Significantly enhanced catalytic activity was observed for the vanadosilicate catalysts, as compared with the 1.0 V-SBA-15 prepared by conventional impregnation. The enhanced catalytic activity of the vanadosilicate catalyst was attributed to the beneficial presence of a larger amount of isolated and highly dispersed V-species, as well as the cage-like mesoporous structure.

Thermoresponsive polymer brushes on 20 nm colloidal gold were formed through atom transfer free radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) in aqueous media. In this approach, the “grafting-from” technique was used with atom transfer radical polymerization (ATRP) to grow polymer chains from the surface of gold nanoparticles (∼20 nm). “Grafting from” using the ATRP technique enables dense, uniform, and homogeneous coverage of polymer chains on the surface of gold nanoparticles. Other advantages of ATRP are the growth of polymer chains without appreciable chain termination or chain transfer and that the presence of an active initiator site at the end of the growing polymer chain facilitates synthesis of surface grafted block copolymers. In the present work, pNIPAAm was grown from the surface of nanoparticles with the help of 2-bromopropionyl bromide as the initiator. The polymerization reaction was carried out at room temperature under inert atmosphere and aqueous conditions. The system was found to exhibit thermoresponsive behavior above and below the LCST. This behavior could be exploited to develop aggregation based assays for making drug delivery systems, detection assays, and bioseparations. The hybrid polymer−gold nanoparticle system was characterized using optical absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). These analytical techniques confirmed the growth of polymer chains in the reaction scheme yielding the final product and a qualitative estimate of polymer chain thickness grafted onto the surface of the nanoparticles.

Hydrogen adsorption properties of a superactived carbon (AX-21) doped with Pt nanoparticles by using plasma reduction were studied and were compared with that by using traditional H₂ reduction. The hydrogen storage capacity was significantly increased by plasma reduction. The H₂ storage capacity on Pt-doped AX-21 at 298 K and 10 MPa was increased from 1.19 wt % (by H₂ reduction) to 1.46 wt % on the sample obtained by plasma reduction. The plasma-reduced sample produced 1.5−3 nm Pt particles that were highly dispersed on carbon, and most interestingly, the metal particles were recessed into the carbon substrate. Both isosteric heats of adsorption and the activation energies for spillover were decreased by plasma reduction, which was evidence that the energy barrier for H spillover was lowered by plasma treatment, resulting in faster rates as well as higher spillover capacities. Mechanisms for plasma reduction and for edge recession of the metal particles into carbon are proposed.

The location of extra-framework cations in low-silica zeolites is determined from in-house X-ray powder diffraction pattern by a successful implementation of a newly developed methodology. The method combines reciprocal and direct space methods plus a cost function that accounts for simultaneous fit of the chemical composition and the X-ray diffractogram. We demonstrated that the iterative combination of relaxation methods (Monte Carlo exploration and lattice energy minimization) helps to improve the structural refinement. The methodology is successfully applied to the study of natural clinoptilolite samples enriched with Ni and Co; in both cases, two different cation sites were found octahedrally coordinated to water molecules. The most populated site is located in the center of the A channel, while the second one is found in the window of the B channel. This result was validated using XANES and EXAFS spectroscopies.

Two-layer ONIOM calculations were carried out to study initial reactions of catalytic cracking of 1-butene to produce propene and ethene on HZSM-5 and HFAU zeolites. Direct cracking and dimerization cracking mechanisms were evaluated. The calculated data indicate that the dimerization cracking is more favorable than the direct cracking based on both kinetic and thermodynamic considerations. HZSM-5 is catalytically more effective than HFAU for the cracking reactions. ONIOM energy analysis shows that the effectiveness of zeolite is due to long-range van der Waals interaction energies that stabilize all reaction intermediates, and short-range interaction between the zeolite and the reacting species that reduce the activation energies. For the dimerization process, stepwise and concerted mechanisms are similar in energy changes. Generally speaking, dimerizations appear to be exothermic reactions with modest activation energies. The activation energies for isomerization, β-scission, and deprotonation are lower for larger molecular fragments than for smaller ones.

Homogeneous Au−Ag alloy nanoparticles have been synthesized in the cavity of horse spleen apoferritin (HSAF) by a diffusion technique. The Au−Ag nanoparticle cores are 5.6−6.3 nm in diameter with narrow size distribution (≤1.0 nm), and their average diameter was gradually increased with an increase in the Ag content. The core formation ratios of Au−Ag−HASF samples are higher than 80%. These series of nanoparticles were applied for the reduction of 4-nitrophenol in the presence of NaBH₄. As the Au content was increased in the Au−Ag−HSAF nanoparticles, the rate constant of the reduction was exponentially increased from 1.3 × 10⁻³ s⁻¹ (pure Ag−HSAF) to 7.58 × 10⁻² s⁻¹ (pure Au−HSAF). These synthesized Au−Ag nanoparticles with different compositions will be further applicable in catalysis, sensing, and biomedical areas.

The surface properties of YSZ (111) have been investigated by X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), temperature programmed desorption (TPD) of adsorbed formate, and computational studies using the ReaxFF reactive force field approach. XPS and computer simulations showed enrichment of the surface with yttria. STM studies indicated that a high density of step edges are readily formed with ∼35% of the surface sites located at steps. Step edges are identified as the primary adsorption sites for formate. The formate oxidizes in a dehydration reaction producing carbon monoxide and water at ∼600 K. This is contrasted to the reaction of formate on pure zirconia where formate reacts by both dehydration and dehydrogenation reactions. This shift in the selectivity between pure zirconia and yttria-doped zirconia is attributed to the modification of the active step edge sites by yttria segregation. Therefore, the modification of active sites by minority species in a mixed oxide can control the chemical surface functionality.

The performance of existing force-field models for the calcium carbonate - water system has been critically assessed with particular reference to the thermodynamic consequences. It is demonstrated that all currently available parametrizations fail to describe the calcite-aragonite phase transition, and the free energies of solvation for the calcium cation are also considerably in error leading to a poor description of the dissolution enthalpy for calcite. A new force-field, based on rigid carbonate ions, has been developed that corrects these deficiencies and accurately describes the thermodynamics of the aqueous calcium carbonate system within molecular dynamics simulations. Not only does this new model lead to quantitative changes in the properties of the calcite (101̅4) surface in contact with water, but also significant qualitative differences. With this more accurate model it is found that calcium ions do not adsorb at the pristine basal plane of calcite, while carbonate ions only weakly bind. Carbonate diffusion across the surface is found to occur only when the anion is solvent separated from the underlying surface, with there being an equal tendency to readsorb or migrate into the bulk liquid.

The formation, potential-dependent structural change, and reduction of adsorbed nitrite at a platinum electrode were examined in 0.1 M HClO₄ and 0.1 M NaClO₄ by surface-enhanced infrared absorption spectroscopy (SEIRAS). The band assigned to the symmetric NO₂ stretch of the nitro form of nitrite appeared at around 1300 cm⁻¹ in both solutions. The potential dependence of the spectra revealed that this adsorbed nitrite is converted to NO adsorbed at on-top, bridge, and defect sites via IR-inactive surface nitrite species. In 0.1 M HClO₄, these three adsorbed NO species were also formed during the adsorption process from the solution NO formed by the disproportionation of nitrite. In addition to the reduction via the IR-inactive surface nitrite species, a direct conversion from adsorbed nitrite to adsorbed NO was also suggested in 0.1 M HClO₄.

We have investigated the relative efficiency of Pt and Pd catalysts, in the structural formats of nanoporous solids and planar metallic surfaces, for the electro-oxidation of methanol and ethanol in acidic and basic aqueous solutions. There are two issues of primary concern in this comparison. These are the surface area of the two catalyst structures and the crystalline morphology of the metals. We find that the nanoporous solids of Pt and Pd afford greater electro-oxidation efficiency and increased catalytic stability relative to the corresponding planar metallic surface for methanol and ethanol. The increase in current density for the Pt nanoporous solid was greater for basic conditions than for acidic conditions. Although both metals provided increased catalytic activity relative to that of the corresponding planar metal, the reactivity of Pt was greater for methanol, while Pd exhibited greater reactivity for ethanol. Our data point to the utility of nanoporous solids for use as catalytic media.

In this work we present a study on the adsorption of linear alkyl aldehydes physisorbed from their bulk liquid onto a graphite substrate combining calorimetry for all homologues from C6 to C13, with more detailed diffraction, incoherent neutron scattering, and scanning tunneling microscopy techniques for one (C12) representative member. We identify solid monolayer formation for some of these species for alkyl chain lengths of 6 to 13 carbons at high surface coverages. The C12 monolayer structure is determined to be most likely Pgg and this structure is discussed in terms of the importance of dipolar interactions.

To improve the energy conversion of solar irradiation, a photocatalyst with high reactivity under visible light is required. Using density functional theory, the structural and electronic properties of iodine cation-doped rutile TiO₂ are studied. The total energy calculations show that iodine substituting for titanium sites in TiO₂ matrix is energetically favorable. The electronic structure calculations reveal that iodine doping induces a delocalized band consisting of I 5s states and O 2p states at the top of the valence band of TiO₂. Due to this delocalized state, the band gap is markedly narrowed by about 0.4 eV, the optical absorption is extended to the visible light region, and the excited electron−hole pairs are expected to have better mobility. Moreover, the conduction band edge is raised above the reduction level of H₂/H₂O by I-doping, which enables the achievement of high photocatalytic efficiency of I-doped rutile TiO₂.

A computational study based on B3LYP calculations was carried out to investigate the kinetic and mechanistic aspects of the selective oxidation of methanol to formaldehyde using titania-supported vanadate as a catalyst model. A complete picture of the possible mechanisms to obtain formaldehyde is given. Statistical mechanics as well as transition state theory (TST) were utilized to determine the rate coefficients and equilibrium constants of the most plausible mechanism. A tetrahedral vanadia containing a methoxy species is found to be the most stable intermediate. The rate-limiting step in the most commonly accepted mechanism is the hydrogen transfer from the tetrahedral methoxy intermediate to the catalyst sites V−O−Ti (46.4 kcal/mol) or V═O (41.0 kcal/mol) via a spin-crossing process. The transition states associated to these steps are biradicaloid. The simultaneous formation of H₂ and formaldehyde can be discarded because it proceeds with a higher energetic barrier of 57.0 kcal/mol. The plausibility of a more reactive site involving fivefold coordinated vanadium species along a H-transfer process with a energetic barrier of 20.1 kcal/mol is discussed. Finally, the dependence of the calculated values of energy barriers for the rate-limiting step on the functional used is analyzed.

We had, in a previous study, found that flat cold-rolled Ni₃Al foil is spontaneously activated during the initial stage of catalytic methanol decomposition, and further, this is accompanied by the gradual formation of fine Ni particles. In this study, we investigate the evolution of the foil surface structure at the beginning of the spontaneous activation by using hard X-ray (hν = 5.95 keV) photoelectron spectroscopy. The core level spectra of Ni 2p, Ni 3p, Al 2p, O 1s, Al 1s, and C 1s have been analyzed in detail. Ni in the Ni₃Al foil remained in the metallic state during the reaction, and neither Ni oxide nor Ni hydroxide was formed. In contrast, Al was found to react with the gaseous products of methanol decomposition to form two compounds in succession. At the beginning of the reaction, Al was oxidized to form an Al₂O₃ layer on the surface. The outer surface of the Al₂O₃ layer then hydroxylated to Al(OH)₃, thereby forming an Al(OH)₃/Al₂O₃ two-layer structure. Thus, it was found that an Al(OH)₃/Al₂O₃ two-layer structure with metallic Ni particles evolves during the initial stage of catalytic methanol decomposition.

We report a systematic density functional theory (DFT) computational investigation of Ru(II) sensitizer/TiO₂ systems relevant to dye-sensitized solar cells (DSSCs). Focusing on the prototypical N719 and the recently introduced YE05 sensitizers, and considering large slab and cluster models for TiO₂, we have systematically studied the influence of the molecular adsorption geometry, counterions, and surface protonation on the electronic structure of the dye/semiconductor systems by means of Car−Parrinello molecular dynamics combined with single-point hybrid functional calculations of the electronic properties. Our results show that the homoleptic N719 and YE05 dyes, both bearing two bipyridine ligands functionalized with four carboxylic groups, adsorb onto the TiO₂ surface by exploiting three carboxylic groups. The bulky TBA counterions employed in N719 cause a modest energy down-shift of the TiO₂ conduction band, whereas the smaller Na⁺ counterions, which can access the surface more closely, lead to a larger conduction band energy perturbation. Our results also confirm that the surface protonation plays a fundamental role in determining the DSSC efficiency, with a strong impact on both short-circuit photocurrent and open-circuit potential. Altogether, our study provides evidence that adsorption of the sensitizer via “three anchoring sites” is a key requisite to obtain high open-circuit potentials when employed in DSSC devices, thus paving the route to the design of new and more efficient sensitizers.

We present a detailed, in situ study of photoluminescence of ultrathin perylene films on a Cu(110) surface. Temperature-dependent measurement has been correlated to the surface phase transition process. Different components of the fluorescence emission have been assigned to excimer, defect states, and monomer excitons. Most importantly, a coverage-dependent measurement has allowed us to identify that only emission from the first layer of the perylene is quenched by the metal substrate.

Exciton recurrence motions in double-ring molecular aggregates are investigated using the quantum master equation approach. The rotatory and oscillatory recurrence behaviors are found to be controlled by changing the relative direction of the circular polarization of an incident two-mode laser field. These dynamics are understood by the relative phases among off-diagonal exciton density matrices, the feature of which is determined by the interaction between the circular-polarized field and the degenerate states of the double-ring structure. The results of exciton relaxation effects caused by the exciton−phonon coupling and static disorder also demonstrate the robustness of the exciton recurrence motions in double-ring molecular aggregates.

Nonlinear optical (NLO) activity of a molecule in general is connected to fundamental issues like charge transfer, conjugation, polarization, and recently suggested and less investigated diradical character. Extensively studied molecules for negative second order hyperpolarizabilities are the centrosymmetric squaraine derivatives (SQ) which have absorption in the region greater than 600 nm. These have no formal electronic structure but can be represented as a mixture of zwitterionic and diradicaloid valence bond resonance structures. In this work we have designed and synthesized arylamino SQ, 1−10, which bias the valence bond resonance picture completely to the zwitterionic type and totally eliminates the diradicaloid contribution (estimated using computational studies to be zero). Due to this, the lowest energy transitions are blue-shifted to the region less than 500 nm. We have carried out degenerate four wave mixing (DFWM) studies for estimation of γ values of these molecules using a 800 nm wavelength laser. The γ values are measured under nonresonant conditions and also at intensities where two photon absorption does not play any role. Nonlinear absorption properties of these molecules are studied through Z scan technique. The γ values, though smaller than the SQ having absorption in the red region, are reasonably large and range from −1.2 to −6.9 × 10⁻³³ esu. High level computational techniques and model molecules have been utilized to understand the transition and the NLO activity in these molecules.

Phosphorescence has rarely been observed in pure organic chromophore systems at room temperature. We herein report efficient phosphorescence from the crystals of benzophenone and its derivatives with a general formula of (X-C₆H₄)₂C═O (X = F, Cl, Br) as well as methyl 4-bromobenzoate and 4,4′-dibromobiphenyl under ambient conditions. These luminogens are all nonemissive when they are dissolved in good solvents, adsorbed on TLC plates, and doped into polymer films, because active intramolecular motions such as rotations and vibrations under these conditions effectively annihilate their triplet excitons via nonradiative relaxation channels. In the crystalline state, the intramolecular motions are restricted by the crystal lattices and intermolecular interactions, particularly C−H···O, N−H···O, C−H···X (X = F, Cl, Br), C−Br···Br−C, and C−H···π hydrogen bonding. The physical constraints and multiple intermolecular interactions collectively lock the conformations of the luminogen molecules. This structural rigidification effect makes the luminogens highly phosphorescent in the crystalline state at room temperature.

Here we demonstrate the preparation and improved hydrogen monitoring properties based on p-NiO/n-SnO₂ heterojunction composite nanofibers via the electrospinning technique and calcination procedure. NiO/SnO₂ heterojuction composite nanofibers were spin-coated on the ceramic tube with a pair of Au electrodes for the detection of hydrogen. Extremely fast response−recovery behavior (∼3s) has been obtained at the operable temperature of 320 °C, based on our gas sensor, with the detection limit of approximate 5 ppm H₂. The role of the addition of NiO into the SnO₂ nanofibers and the sensing mechanism has also been discussed in this work.

In this article, we employ a systematic approach to the computational quantum chemical study of the two-photon absorption (2PA) properties of 161 representative molecules containing a symmetrically substituted fluorene unit. The molecules studied contain meta- or para-substituted phenyl groups, five- and six-membered heterocycles, and benzo derivatives of five-membered heterocycles. The computational procedure employed to calculate the 2PA parameters was previously described [Chem. Mater. 2008, 20, 4142] and is based on semiempirical electronic structure methods: the RM1 model to optimize the molecular geometry and the INDO/S method to calculate the spectroscopic properties of the molecules. We further advance a new, simplified expression employed to calculate an approximate three-level contribution of the imaginary part of the negative component of the second hyperpolarizability. We then show that, in order to rationalize the 2PA cross sections for the substituted fluorenes, the three-level approximation has to be adapted to include a fourth state. That done, we advance that the parameter most responsible for the large observed variation in the calculated values of the 2PA cross sections for the substituted fluorenes is the effective transition dipole moment between the 1PA-active state and the two 2PA-active states. Based on our results, we discuss three structural effects that can contribute to the value of the 2PA cross section and show how they can be tuned. We conclude by propositioning novel putative molecules with potentially large values of 2PA cross sections, such as 2,2′-(9,9-dialkyl-9H-fluorene-2,7-diyl)dibenzo[d]oxazole.

In this paper a polymethacrylate with pendent azobenzothiazole (pBAMA) was synthesized via free radical polymerization, and the polymer exhibited good solubility and thermal stability. Films of pBAMA sandwiched between bottom indium−tin oxide (ITO) or Pt electrode and top Al electrodes show the excellent FLASH memory behaviors or write once read many times (WORM) behaviors according to the film thickness. Particularly, the charge transport processes during the OFF to ON states were precisely discussed to reveal the physical mechanism which is still a topic of active debate in any given device structure. One metal islands layer was confirmed lying in the pBAMA films, and this layer decided the memory characteristics of different device structures. The fabricated devices show the excellent memory characteristics as the highest ON/OFF ratio up to 10⁷, and enduring 10⁸ read cycles under −1 V pulse voltages, these properties promised that the memory device based on pBAMA has a potential application for the future advanced computers and digital electronics.

In this work the photochromic behaviors of four Reversacol compounds from James Robinson Ltd., previously investigated in solution, have been studied in a microcrystalline solid phase and embedded in a poly(methyl methacrylate) matrix (PMMA). The compounds studied belong to the classes of spirooxazines and naphthopyrans. In solution, they showed photocoloration and thermocoloration. Embedded into polymeric films, as well as in the microcrystalline phase, they have maintained their photochromic and thermochromic behavior. The photocoloration quantum yields in PMMA were determined and found to be fairly high. Compared to solution, the kinetic and thermodynamic activation parameters of thermal bleaching significantly changed. The solid environment has the effect of slowing down the bleaching rates in films as well in the pure crystalline phase and introduces multiexponential terms in the photocoloration and thermal bleaching kinetics. Activation enthalpy and entropy decrease, compared to solution, leaving the activation free energy substantially unchanged. Thermochromism was characterized through the equilibrium constant and the thermodynamic standard parameters, ΔH⁰, ΔS⁰, and ΔG⁰, of the thermal reactions. Time-dependent processes were also analyzed according to the maximum entropy method (MEM). Based on the data from the least-squares and MEM treatments, the occurrence of multiexponential kinetics in polymers was attributed to the effects of the inhomogeneous distribution of free volume in the matrix.

Thermotropic ionic liquid crystals (ILCs), 1,1′-dialkyl-4,4′-bipyridinium bis(triflimide)s have been used as binders to fabricate new carbon composite electrodes. ILC compounds possess an ordered molecular orientation, and upon mixing with graphite, ILCs retain their liquid crystal characteristics and thus their ordered arrangement. The electrochemical performances of these composite electrodes were evaluated by using different electrochemical probes. The resulting electrodes offer high electrochemical reactivity, low background current, improved signal-to-noise ratio, greater stability, excellent mechanical strength, and very good antifouling effects. It is believed that the higher conductivity of ILCs as well as the ordered orientation of these thermotropic ILCs which cause an increase in the edge-plane sites of these composite electrodes are responsible for the promotion of their electrocatalytic activities and antifouling effects. Such characteristics make these composite electrodes ideal for use in different electrochemical and biosensing applications.

Herein is presented systematic analysis of air-stable, ambipolar heterojunction-based organic light-emitting field-effect transistors (OLEFETs). Top-contact OLEFETs with multidigitated, long channel-width geometry were produced by the successive deposition of electron-transporting N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) and hole-transporting tetracene layers, using the neutral cluster beam deposition (NCBD) method. The morphological, structural, and photoluminescence properties of the untreated and thermally post-treated P13/tetracene active layers were examined by atomic force microscopy, X-ray diffraction, and laser scanning confocal microscopy. From the comparative analysis of the NCBD thin films, the neutral cluster beams led to the preparation of smooth, uniform bilayer films consisting of well-packed grain crystallites. The OLEFETs demonstrated good field-effect characteristics, stress-free operational stability, and electroluminescence under ambient conditions. The operating conduction mechanism that accounts for the observed light emission is also discussed.

Nonlinear optical and optical limiting properties of a range of single-walled carbon nanotube dispersions prepared in N-methyl-2-pyrrolidinone (NMP) were studied using the open aperture Z-scan technique at 532 nm. As the appropriate thermodynamic properties of the solvents are much more important than the bundle size of nanotubes for improving the optical limiting performance, the solvent parameters were controlled by either changing the temperature of the dispersions or blending a secondary solvent. While the optical limiting performance can be varied freely by increasing or decreasing the temperature from room temperature to 100 °C, the reduction of temperature below the freezing point of NMP and then down as far as −80 °C has little influence on the limiting performance. As a result of adding a small amount of organic solvent into the NMP dispersions, the nonlinear optical responses were enhanced significantly due to the reduction of surface tension and other parameters. By contrast, the addition of water leads to a decrease in the optical limiting response. Nanotube dispersions in water/surfactant exhibit a similar limiting performance to the nanotubes in NMP. Our results reveal that the optical limiting performance of the nanotube dispersions can be engineered by adjusting the solvent properties. Because the carbon nanotube dispersions are typical of the thermally induced light scattering dominated optical limiting materials, we believe the conclusions fit not only the nanotubes but also other nanomaterials with the similar limiting mechanism.

NaNbO₃ rods modified by In₂O₃ nanoparticles (In₂O₃/NaNbO₃) were successfully synthesized by an improved coprecipitation method, and they were found to be advantageous for photocatalytic H₂ evolution under visible light irradiation and pure water splitting under ultraviolet light irradiation. The composites were characterized by X-ray diffraction, UV−vis diffuse reflectance spectrometry, Brunauer−Emmett−Teller measurement, scanning electron microscopy, energy-dispersive spectrometry, and transmission electron microscopy. With use of the electrochemical and valence band X-ray photoelectron spectroscopy analysis, the improvement of the photocatalytic activity was attributed to the promoted transportation of photoexcited holes in the composite.

Lithium borohydride (LiBH₄) is a promising material for hydrogen storage, with a gravimetric hydrogen content of 18.5%. However, the thermodynamics and kinetics of its hydrogen release and uptake need to be improved before it can meet the requirements for mobile applications. In this study, we investigate the confinement of LiBH₄ in ordered mesoporous SiO₂ and its effect on the hydrogen sorption properties. We demonstrate that, only under hydrogen pressure, melt infiltration is an effective method for the synthesis of LiBH₄/SBA-15 nanocomposites. Our work clearly shows that formation of lithium silicates from LiBH₄ and SiO₂ can effectively be suppressed by hydrogen. Thus, under hydrogen pressure, LiBH₄ can fully fill the mesopores of SBA-15 while the long-range order of the mesopores is maintained. The confined LiBH₄ has enhanced hydrogen desorption properties, with desorption starting at 150 °C. However, upon dehydrogenation, SiO₂ and decomposition products of LiBH₄ react to form Li₂SiO₃ and Li₄SiO₄, leading to irreversible hydrogen loss.

We have studied the electrocatalytic effects of polythiophene-based conducting polymers toward the redox reactions of the dilithium salt of the thiadiazole-based dithiol compound 2,5-dimercapto-1,3,4-thiodiazole (DMcT-2Li) via cyclic voltammetry (CV), rotating-disk electrode voltammetry, and electrochemical impedance spectroscopy (EIS). We have found that the electrocatalytic activity of the conducting polymers is strongly influenced by the potential range over which the polymers are electrically conductive (i.e., window of conductivity), which was tuned by employing different electron-donating groups at the 3- or 3,4-positions of polythiophene (PTh). Both poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), whose windows of conductivity exhibited a good overlap with the formal potential for the dimerization process of DMcT-2Li; E⁰′_d (−0.54 V versus Ag/Ag⁺) exhibited electrocatalytic activity toward both the oxidation and reduction processes of DMcT-2Li. On the other hand, PTh, poly(3-methylthiophene) (PMTh), and poly(3,4-dimethoxythiophene) (PDMTh), whose windows of conductivity did not overlap with E⁰′_d, did not exhibit electrocatalytic activity. The standard charge transfer rate constants for the dimerization process of DMcT-2Li at PEDOT, PProDOT, and PDMTh film-modified glassy carbon electrodes (GCEs) were estimated to be 7.4 × 10⁻⁴, 3.2 × 10⁻⁴, and 6.9 × 10⁻⁵ cm/s while the rate constant was 6.3 × 10⁻⁵ cm/s at an unmodified GCE. Moreover, EIS studies for PEDOT, PProDOT, and PDMTh film-modified GCEs indicated the smallest charge transfer resistance for a PEDOT film and highest for a PDMTh film at E⁰′_d, indicating that the higher the electrical conductivity of a film at E⁰′_d the higher the electrocatalytic activity toward the redox reactions of DMcT-2Li. These results clearly indicate that in order to accelerate the redox reactions of DMcT-2Li (and likely of other organosulfur compounds) the window of conductivity of a conducting polymer needs to overlap the formal potentials of the organosulfur compounds and, thus, support our previous observations that the electrocatalytic reactions proceed via electron exchange reactions between DMcT-2Li and conducting polymers such as PEDOT. Additional computational results for oligomers of PEDOT, ProDOT, and PDMTh showed that substituents at the 3,4-positions of the thiophene ring influence the window of conductivity via steric and electronic effects. This study provides important insights toward rational design of novel conducting-polymer-based electrocatalysts to enable organosulfur compounds to be of practical use as cathode materials for lithium-ion rechargeable batteries.

We investigate the temperature dependence of the O−H stretch band in the infrared absorbance spectra of the proton-conducting hydrated perovskites BaIn_xZr_1−xO_3−x/2 (x = 0.10−0.75) over the temperature range −160 to 350 °C. Upon increasing temperature from −160 to 30 °C, we show that there is a redistribution of protons from nonsymmetrical structural configurations, such as Zr-OH-In and Zr-OH-Zr-vacancy, where the degree of hydrogen bonding between the protons and neighboring oxygens is strong, to symmetrical configurations, such as Zr-OH-Zr and In-OH-In, where hydrogen bonding is weaker. Spectra measured at elevated temperatures, 30−350 °C, indicate preferential desorption of protons in sites where the degree of hydrogen bonding is strong, and show that the materials gradually dehydrate with increasing temperature. The dehydration rate is found to be highest in the temperature range 275−325 °C. Furthermore, the spectroscopic results indicate that strong hydrogen bonding, caused by dopant-induced short-range structural distortions, is favorable for high proton mobility and that the rate-limiting step in the conduction mechanism is the proton transfer between neighboring oxygens.

Propylene carbonate (PC) in electrolytes is generally believed to lead to graphite exfoliation due to intensive cointercalation and ceaseless decomposition reactions. This paper reports the formation of an effective solid electrolyte interface (SEI) film on a natural graphite surface through decomposition of PC in the presence of a quaternary ammonium ionic liquid. With an ionic liquid content of at least 60%, the PC molecules are reduced in the first charge, effectively passivating the graphite anode and allowing the formation of LiC₆ with high capacity and good reversibility. In the electrolyte containing 20 vol % PC, the natural graphite anode attains a discharge capacity of 322.8 mAh/g and 76.5% coulombic efficiency on the first cycle. A stable discharge capacity of around 330 mAh/g was obtained in the initial 20 cycles without any noticeable capacity loss. This result compares favorably with using 20 vol % ethylene carbonate (EC) as the film-forming additive in the electrolyte. SEM and FTIR studies demonstrate the formation of a thin, homogeneous SEI layer on the graphite-electrode surface through the reduction of PC molecules. Raman spectroscopy studies show a significant decrease of the interaction between the Li ion and PC molecules in the presence of the quaternary ammonium ionic liquid. The competition for Li ions between PC and the ionic liquid reduces the solvation of PC molecules for Li ions, which in turn limits the intercalation of PC into the graphene layers during Li intercalation, an event that typically leads to exfoliation. Instead, the loosely bound PC is reduced at the graphite/electrolyte interface, forming a stable SEI.

Ni-decorated activated-carbon film is deposited directly onto the stainless steel substrate by using electrophoretic deposition (EPD) in the activated-carbon suspension containing nickel nitrate additive. The adsorption of nickel ions on the external surface and interior pores of activated carbons considerably increases the measured zeta potential and consequently favors the dispersion and EPD of activated carbons. More importantly, when an activated carbon arrives at the substrate in the EPD process, nickel ions adsorbed on the activated carbon are reduced electrochemically to a form metallic nickel layer. The deposited nickel layer plays an important role in improving the adhesion, wettability, and electrochemical reaction of the Ni-decorated activated-carbon film. Therefore, the Ni-decorated activated-carbon film exhibits an excellent capacitive behavior compared with the bare activated-carbon film.

Hybrid photovoltaic devices based on poly(3-hexylthiophene) (P3HT) and an ordered electrospun ZnO nanofibrous network have been investigated. The diameters of the ZnO nanofibers have been controlled within 30−150 nm. The performance of the P3HT/ZnO hybrid solar cell is dependent on fabrication conditions, especially the thickness of the nanofibrous film. It has been found that the lifetime of carriers is lower in the device consisting of thicker ZnO nanofibrous films due to the higher density of surface traps in the ZnO nanofibers. The device with optimum fabrication conditions exhibits a power conversion efficiency of 0.51%.

The phase behavior and thermal properties of ternary ionic liquid−lithium salt (IL−IL−LiX) mixtures intended for use as electrolytes for lithium batteries are reported here. It is shown that the addition of small amounts of N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (PY₁₃FSI) to N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PY₁₄TFSI)−lithium salt (LiTFSI or LiPF₆) mixtures greatly hinders the ability of the samples to crystallize. This results in a much improved subambient temperature conductivity for the mixtures relative to the binary IL−LiX electrolytes at low temperature. The thermal stability of the mixtures is reduced by the addition of PY₁₃FSI but remains acceptable for Li battery applications.