Tomographic Study of Mesopore Formation in Ceria Nanorods

Click to copy article linkArticle link copied!

This article references 61 other publications.

1. 1

   Trovarelli, A.; Llorca, J. Ceria Catalysts at Nanoscale: How Do Crystal Shapes Shape Catalysis?. ACS Catal. 2017, 7, 4716– 4735,  DOI: 10.1021/acscatal.7b01246

   Google Scholar

   1

   Ceria Catalysts at Nanoscale: How Do Crystal Shapes Shape Catalysis?

   Trovarelli, Alessandro; Llorca, Jordi

   ACS Catalysis (2017), 7 (7), 4716-4735CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

   A review. Engineering the shape and size of catalyst particles and the interface between different components of heterogeneous catalysts at the nanometer level can radically alter their performances. This is particularly true with CeO2-based catalysts, where the precise control of surface at. arrangements can modify the reactivity of Ce4+/Ce3+ ions, changing the oxygen release/uptake characteristics of ceria, which, in turn, strongly affects catalytic performance in several reactions like CO, soot, and VOC oxidn., WGS, hydrogenation, acid-base reactions, and so on. Despite the fact that many of these catalysts are polycryst. with rather ill-defined morphologies, exptl. and theor. studies on well-defined nanocrystals have clearly established that the exposure of specific facets can increase/decrease surface oxygen reactivity and metal-support interaction (for supported metal nanoparticles), consequently affecting catalytic reactions. Here, we want to address the most recent developments in this area, showing that shape (and size) modification, surface/face reconstruction, and faceting of ceria at the nanoscale level can offer an important tool to govern activity and stability in several reactions and imagine how this could contribute to future developments.
2. 2

   Montini, T.; Melchionna, M.; Monai, M.; Fornasiero, P. Fundamentals and Catalytic Applications of CeO₂-Based Materials. Chem. Rev. 2016, 116 (10), 5987– 6041,  DOI: 10.1021/acs.chemrev.5b00603

   Google Scholar

   2

   Fundamentals and Catalytic Applications of CeO2-Based Materials

   Montini, Tiziano; Melchionna, Michele; Monai, Matteo; Fornasiero, Paolo

   Chemical Reviews (Washington, DC, United States) (2016), 116 (10), 5987-6041CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

   A review. Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochem. water splitting, and org. reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theor. methods are deepening our understanding of these materials, helping us to predict their behavior and application potential. This review has a wide view on all those aspects related to ceria which promise to produce an important impact on our life, encompassing fundamental knowledge of CeO2 and its properties, characterization toolbox, emerging features, theor. studies, and all the catalytic applications, organized by their degree of establishment on the market.
3. 3

   Karakoti, A. S.; Monteiro-Riviere, N. A.; Aggarwal, R.; Davis, J. P.; Narayan, R. J.; Self, W. T.; McGinnis, J.; Seal, S. Nanoceria as Antioxidant: Synthesis and Biomedical Applications. JOM 2008, 60, 33– 37,  DOI: 10.1007/s11837-008-0029-8

   Google Scholar

   3

   Nanoceria as antioxidant: synthesis and biomedical applications

   Karakoti, A. S.; Monteiro-Riviere, N. A.; Aggarwal, R.; Davis, J. P.; Narayan, R. J.; Self, W. T.; McGinnis, J.; Seal, S.

   JOM (2008), 60 (3), 33-37CODEN: JOMMER; ISSN:1047-4838. (Springer)

   A review. The therapeutic application of nanomaterials has been a focus of numerous studies in the past decade. Due to its unique redox properties, cerium oxide (ceria) is finding widespread use in the treatment of medical disorders caused by the reactive oxygen intermediates (ROI). The radical-scavenging role of ceria nanoparticles (nanoceria) have been established, as well as the autocatalytic ability of nanoceria to regenerate under various environmental conditions. The synthesis of nanoceria in biocompatible media has also been reported along with cell viability in order to det. the potential use of nanoceria in biomedical applications.
4. 4

   Mogensen, M.; Lindegaard, T.; Hansen, U. R.; Mogensen, G. Physical Properties of Mixed Conductor Solid Oxide Fuel Cell Anodes of Doped CeO₂. J. Electrochem. Soc. 1994, 141, 2122,  DOI: 10.1149/1.2055072

   Google Scholar

   4

   Physical properties of mixed conductor solid oxide fuel cell anodes of doped CeO2

   Mogensen, Mogens; Lindegaard, Thomas; Rud Hansen, Uffe

   Journal of the Electrochemical Society (1994), 141 (8), 2122-8CODEN: JESOAN; ISSN:0013-4651.

   Samples of CeO2 doped with oxides such as CaO and Gd2O3 were prepd. Their cond. and expansions on redn. were measured at 1000°, and the thermal expansion coeffs. in the range of 50-1000° were detd. The ionic and electronic cond. were derived from curves of total cond. vs. O partial pressure. For both types of cond. a dependence on dopant valency was obsd. The electronic cond. was independent of dopant radius in contrast to the ionic which was highly dependent. These measured phys. properties are compared with the ideal requirements for solid oxide fuel cell anodes. Not all requirements are fulfilled. Measures to compensate for this are discussed.
5. 5

   Furler, P.; Scheffe, J. R.; Steinfeld, A. Syngas Production by Simultaneous Splitting of H₂O and CO₂ via Ceria Redox Reactions in a High-Temperature Solar Reactor. Energy Environ. Sci. 2012, 5, 6098– 6103,  DOI: 10.1039/C1EE02620H

   Google Scholar

   5

   Syngas production by simultaneous splitting of H2O and CO2 via ceria redox reactions in a high-temperature solar reactor

   Furler, Philipp; Scheffe, Jonathan R.; Steinfeld, Aldo

   Energy & Environmental Science (2012), 5 (3), 6098-6103CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)

   Solar syngas prodn. from H2O and CO2 is exptl. investigated using a two-step thermochem. cycle based on cerium oxide redox reactions. A solar cavity-receiver contg. porous ceria felt is directly exposed to concd. thermal radiation at a mean solar concn. ratio of 2865 suns. In the first endothermic step at 1800 K, ceria is thermally reduced to an oxygen deficient state. In the second exothermic step at 1100 K, syngas is produced by re-oxidizing ceria with a gas mixt. of H2O and CO2. The syngas compn. is exptl. detd. as a function of the molar co-feeding ratio H2O : CO2 in the range of 0.8 to 7.7, yielding syngas with H2 : CO molar ratios from 0.25 to 2.34. Ten consecutive H2O/CO2-splitting cycles performed over an 8 h solar exptl. run are presented.
6. 6

   Vedrine, J. C. Metal Oxides in Heterogeneous Oxidation Catalysis: State of the Art and Challenges for a More Sustainable World. ChemSusChem 2019, 12, 577– 588,  DOI: 10.1002/cssc.201802248

   Google Scholar

   6

   Metal Oxides in Heterogeneous Oxidation Catalysis: State of the Art and Challenges for a More Sustainable World

   Vedrine, Jacques C.

   ChemSusChem (2019), 12 (3), 577-588CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)

   This Review presents current knowledge, recent results, and challenges for the future in heterogeneous oxidn. catalysis in liq. and gaseous phases on solid metal oxide catalysts. Metal oxides that are used as catalysts and their main structures and properties are summarized, as well as their catalytic properties in selective and total oxidn. reactions, which were studied intensively, exptl. and theor., by Professor Jerzy Haber during his scientific life. Some emphasis is placed on the classical and unusual catalyst activation procedures for improving catalytic properties for better efficiency. For a more sustainable world, several examples are given of the oxidn. of biomass derivs. to synthesize valuable chems. and of other applications of metal oxides, such as depollution, photocatalysis, hydrogen prodn. and fuel-cell components. The importance of metal oxide catalysis in environmental and green chem. and sustainability is discussed, and challenges for the future are considered.
7. 7

   Zhou, K.; Wang, X.; Sun, X.; Peng, Q.; Li, Y. Enhanced Catalytic Activity of Ceria Nanorods from Well-Defined Reactive Crystal Planes. J. Catal. 2005, 229 (1), 206– 212,  DOI: 10.1016/j.jcat.2004.11.004

   Google Scholar

   7

   Enhanced catalytic activity of ceria nanorods from well-defined reactive crystal planes

   Zhou, Kebin; Wang, Xun; Sun, Xiaoming; Peng, Qing; Li, Yadong

   Journal of Catalysis (2005), 229 (1), 206-212CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)

   The crystal plane of ceria plays an essential role in detg. its catalytic oxidn. properties. In this study, single-cryst. CeO2 nanorods with well-defined crystal planes have been synthesized by a facile soln.-based hydrothermal method. HRTEM studies reveal that the predominantly exposed planes are the unusually reactive {001} and {110} in the CeO2 nanorods rather than the stable {111} in the irregular nanoparticles. Consequently, it is demonstrated that the CeO2 nanorods are more reactive for CO oxidn. than their counterparts, irregular nanoparticles. The present results indicate that catalysts with well-defined reactive sites may be "designed" because of the recent development of morphol.-controlled synthesis of nanostructured materials.
8. 8

   Ji, Z.; Wang, X.; Zhang, H.; Lin, S.; Meng, H.; Sun, B.; George, S.; Xia, T.; Nel, A. E.; Zink, J. I. Designed Synthesis of CeO₂ Nanorods and Nanowires for Studying Toxicological Effects of High Aspect Ratio Nanomaterials. ACS Nano 2012, 6, 5366,  DOI: 10.1021/nn3012114

   Google Scholar

   8

   Designed Synthesis of CeO2 Nanorods and Nanowires for Studying Toxicological Effects of High Aspect Ratio Nanomaterials

   Ji, Zhaoxia; Wang, Xiang; Zhang, Haiyuan; Lin, Sijie; Meng, Huan; Sun, Bingbing; George, Saji; Xia, Tian; Nel, Andre E.; Zink, Jeffrey I.

   ACS Nano (2012), 6 (6), 5366-5380CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)

   While it has been shown that high aspect ratio nanomaterials like carbon nanotubes and TiO2 nanowires can induce toxicity by acting as fiber-like substances that damage the lysosome, it is not clear what the crit. lengths and aspect ratios are that induce this type of toxicity. To answer this question, we synthesized a series of cerium oxide (CeO2) nanorods and nanowires with precisely controlled lengths and aspect ratios. Both phosphate and chloride ions were shown to play crit. roles in obtaining these high aspect ratio nanostructures. High-resoln. TEM anal. shows that single-cryst. CeO2 nanorods/nanowires were formed along the direction by an "oriented attachment" mechanism, followed by Ostwald ripening. The successful creation of a comprehensive CeO2 nanorod/nanowire combinatorial library allows, for the first time, the systematic study of the effect of aspect ratio on lysosomal damage, cytotoxicity, and IL-1β prodn. by the human myeloid cell line (THP-1). This in vitro toxicity study demonstrated that, at lengths ≥200 nm and aspect ratios ≥22, CeO2 nanorods induced progressive proinflammatory effects and cytotoxicity. The relatively low "crit." length and aspect ratio were assocd. with small nanorod/nanowire diams. (6-10 nm), which facilitates the formation of stacking bundles due to strong van der Waals and dipole-dipole attractions. Our results suggest that both length and diam. components of aspect ratio should be considered when addressing the cytotoxic effects of high aspect ratio materials.
9. 9

   Yan, L.; Yu, R.; Chen, J.; Xing, X. Template-Free Hydrothermal Synthesis of CeO₂ Nano-Octahedrons and Nanorods: Investigation of the Morphology Evolution. Cryst. Growth Des. 2008, 8, 1474– 1477,  DOI: 10.1021/cg800117v

   Google Scholar

   9

   Template-Free Hydrothermal Synthesis of CeO2 Nano-octahedrons and Nanorods: Investigation of the Morphology Evolution

   Yan, Lai; Yu, Ranbo; Chen, Jun; Xing, Xianran

   Crystal Growth & Design (2008), 8 (5), 1474-1477CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)

   Uniform single-cryst. CeO2 nano-octahedrons and nanorods were synthesized by a facile hydrothermal synthesis process only using Ce(NO3)3·6H2O as cerium resource and Na3PO4·6H2O as mineralizer, into which no surfactant or template was introduced. By tuning the hydrothermal treatment time, the morphol. evolution between the nano-octahedron and nanorod was obsd. Furthermore, the synthesizing mechanism and the morphol. evolution of different shapes were investigated. Unlike traditional hydrothermal synthesis of CeO2 nanostructures using strong base as precipitant, Na3PO4 does not leave any impurity in the hydrothermal reaction system and makes the process very simple to obtain and sep. the octahedral and rodlike morphol.
10. 10

    Florea, I.; Feral-Martin, C.; Majimel, J.; Ihiawakrim, D.; Hirlimann, C.; Ersen, O. Three-Dimensional Tomographic Analyses of CeO₂ Nanoparticles. Cryst. Growth Des. 2013, 13, 1110– 1121,  DOI: 10.1021/cg301445h

    Google Scholar

    10

    Three-Dimensional Tomographic Analyses of CeO2 Nanoparticles

    Florea, Ileana; Feral-Martin, Cedric; Majimel, Jerome; Ihiawakrim, Dris; Hirlimann, Charles; Ersen, Ovidiu

    Crystal Growth & Design (2013), 13 (3), 1110-1121CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)

    Crystal morphol. and structure of CeO2 nanoparticles have been studied using electron tomog. in scanning transmission mode in high angle annular dark field. The nanoparticles were prepd. by a solvothermal synthesis assisted by microwave heating. An adequate choice of the prepn. conditions led to particles with various well-defined morphologies: cubes, octahedrons, and nanorods. In the case of cubic CeO2 nanoparticles, the 3D anal. permitted the anal. calcn. the type and the proportion of the minor facets exposed at the nanoparticle surface. For the CeO2 nanoparticles with an octahedron shape, the ambiguous interpretation of the objects giving triangular views in classical transmission electron microscopy was prevented, and the precise assignment of the external shape, surface crystallog., and type of minor facets was realized. In the case of nanorods, the external shape and the transversal symmetry strongly depended on the nanorod sizes. The presence of a well-defined porosity inside the rods was also evidenced thanks to the ability of the electron tomog. to solve the internal structure of a nano-object.
11. 11

    Liu, X.; Zhou, K.; Wang, L.; Wang, B.; Li, Y. Oxygen Vacancy Clusters Promoting Reducibility and Activity of Ceria Nanorods. J. Am. Chem. Soc. 2009, 131, 3140– 3141,  DOI: 10.1021/ja808433d

    Google Scholar

    11

    Oxygen Vacancy Clusters Promoting Reducibility and Activity of Ceria Nanorods

    Liu, Xiangwen; Zhou, Kebin; Wang, Lei; Wang, Baoyi; Li, Yadong

    Journal of the American Chemical Society (2009), 131 (9), 3140-3141CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    CeO2 is a catalytic material of exceptional technol. importance, and the precise role of oxygen vacancies is crucial to the greater understanding of these oxide materials. Two ceria nanorod samples with different types and distributions of oxygen vacancies were synthesized. A direct relation between the concn. of the larger size oxygen vacancy clusters and the reducibility/reactivity of nanosized ceria was revealed. These results may be an important step in understanding and designing active sites at the surface of metal oxide catalytic materials.
12. 12

    Sakthivel, T.; Das, S.; Kumar, A.; Reid, D. L.; Gupta, A.; Sayle, D. C.; Seal, S. Morphological Phase Diagram of Biocatalytically Active Ceria Nanostructures as a Function of Processing Variables and Their Properties. ChemPlusChem. 2013, 78, 1446– 1455,  DOI: 10.1002/cplu.201300302

    Google Scholar

    12

    Morphological Phase Diagram of Biocatalytically Active Ceria Nanostructures as a Function of Processing Variables and Their Properties

    Sakthivel, Tamilselvan; Das, Soumen; Kumar, Amit; Reid, David L.; Gupta, Ankur; Sayle, Dean C.; Seal, Sudipta

    ChemPlusChem (2013), 78 (12), 1446-1455CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)

    We rationalize how fluorite-structured CeO2, which is crystallog. isotropic, can grow anisotropically (without templates) to form nanoparticles, rods, and cubes. In particular, single-cryst. and monodispersed cubic CeO2 nanoparticles, nanorods, and nanocubes have been selectively synthesized by a very simple, efficient, and economical hydrothermal process using different NaOH concns., and Ce(NO3)3 as the cerium precursor. High-resoln. transmission electron microscopy reveals nanomaterials with differently exposed crystal planes: {111} and {100} for nanoparticles {110} and {100} for nanorods, and {100} for nanocubes. During the prepn. of the CeO2 nanomaterials, the formation of intermediate anisotropic Ce(OH)3 species under basic conditions and their conversion into CeO2 at higher temp. are key factors responsible for the shape evolution. Atomistic computer simulations were used to help rationalize how the synthetic conditions impact upon the morphol. of the nanomaterial. The synthesized CeO2 nanoparticles and nanorods demonstrate higher catalase mimetic activities than the nanocubes.
13. 13

    Sakthivel, T. S.; Reid, D. L.; Bhatta, U. M.; Mobus, G.; Sayle, D. C.; Seal, S. Engineering of Nanoscale Defect Patterns in CeO₂ Nanorods via Ex Situ and in Situ Annealing. Nanoscale 2015, 7, 5169– 5177,  DOI: 10.1039/C4NR07308H

    Google Scholar

    13

    Engineering of nanoscale defect patterns in CeO2 nanorods via ex situ and in situ annealing

    Sakthivel, Tamil Selvan; Reid, David L.; Bhatta, Umananda M.; Mobus, Gunter; Sayle, Dean C.; Seal, Sudipta

    Nanoscale (2015), 7 (12), 5169-5177CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    Single-cryst. ceria nanorods were fabricated using a hydrothermal process and annealed at 325°C-800°C. As-synthesized CeO2 nanorods contain a high concn. of defects, such as oxygen vacancies and high lattice strains. Annealing resulted in an improved lattice cryst. quality along with the evolution of novel cavity-shaped defects in the nanorods with polyhedral morphologies and bound by e.g. {111} and {100} (internal) surfaces, confirmed for both air (ex situ) and vacuum (in situ) heating. We postulate that the cavities evolve via agglomeration of vacancies within the as-synthesized nanorods.
14. 14

    Li, J.; Zhang, Z.; Tian, Z.; Zhou, X.; Zheng, Z.; Ma, Y.; Qu, Y. Low Pressure Induced Porous Nanorods of Ceria with High Reducibility and Large Oxygen Storage Capacity: Synthesis and Catalytic Applications. J. Mater. Chem. A 2014, 2, 16459– 16466,  DOI: 10.1039/C4TA03718A

    Google Scholar

    14

    Low pressure induced porous nanorods of ceria with high reducibility and large oxygen storage capacity: synthesis and catalytic applications

    Li, Jing; Zhang, Zhiyun; Tian, Zhimin; Zhou, Xuemei; Zheng, Zhiping; Ma, Yuanyuan; Qu, Yongquan

    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (39), 16459-16466CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)

    Ceria (CeO2) is finding prolific industrial applications due to its unique redox properties. Such properties, dominated by structural defects that are primarily O vacancies assocd. with the Ce3+/Ce4+ redox couple, can be modulated and optimized by controlling the size and morphol. of the material, in particular those that are nanostructured (nanoceria). The authors report herein a new form of nanoceria prepd. by a 2-step hydrothermal synthesis. In the 1st-step hydrothermal treatment, the low reaction pressure is crit. for the formation of a Ce(OH)3/CeO2 precursor. A subsequent hydrothermal step of dehydration and oxidn. of the precursor nanorods gave porous nanorods of ceria. The porous nanorods of ceria have been found to display enhanced reducibility and capacity for O storage (900.2 μmol O2 per g) as a result of their significantly increased surface area and defects over other forms of nanoceria, including nanoparticles, nonporous nanorods, nanocubes, and nanooctahedra. Their much improved activities have also been demonstrated in a benchmark reaction - catalytic oxidn. of CO. The high catalytic activity of porous nanorods of ceria indicates their potential as the catalysts or supports or promoters for advanced oxidative processes for waste treatment and environmental remediation.
15. 15

    Zhang, S.; Chang, C. R.; Huang, Z. Q.; Li, J.; Wu, Z.; Ma, Y.; Zhang, Z.; Wang, Y.; Qu, Y. High Catalytic Activity and Chemoselectivity of Sub-Nanometric Pd Clusters on Porous Nanorods of CeO₂ for Hydrogenation of Nitroarenes. J. Am. Chem. Soc. 2016, 138, 2629– 2637,  DOI: 10.1021/jacs.5b11413

    Google Scholar

    15

    High Catalytic Activity and Chemoselectivity of Sub-nanometric Pd Clusters on Porous Nanorods of CeO2 for Hydrogenation of Nitroarenes

    Zhang, Sai; Chang, Chun-Ran; Huang, Zheng-Qing; Li, Jing; Wu, Zhemin; Ma, Yuanyuan; Zhang, Zhiyun; Wang, Yong; Qu, Yongquan

    Journal of the American Chemical Society (2016), 138 (8), 2629-2637CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    Sub-nanometric Pd clusters on porous nanorods of CeO2 (PN-CeO2) with a high Pd dispersion of 73.6% exhibit the highest catalytic activity and best chemoselectivity for hydrogenation of nitroarenes to date. For hydrogenation of 4-nitrophenol, the catalysts yield a TOF of ∼44059 h-1 and a chemoselectivity to 4-aminophenol of >99.9%. The superior catalytic performance can be attributed to a cooperative effect between the highly dispersed sub-nanometric Pd clusters for hydrogen activation and unique surface sites of PN-CeO2 with a high concn. of oxygen vacancy for an energetically and geometrically preferential adsorption of nitroarenes via nitro group. The high concn. of surface defects of PN-CeO2 and large Pd dispersion contribute to the enhanced catalytic activity for the hydrogenation reactions. The high chemoselectivity is mainly governed by the high Pd dispersion on the support. The catalysts also deliver high catalytic activity and selectivity for nitroaroms. with various reducible substituents into the corresponding aminoarenes.
16. 16

    Du, N.; Zhang, H.; Chen, B.; Ma, X.; Yang, D. Ligand-Free Self-Assembly of Ceria Nanocrystals into Nanorods by Oriented Attachment at Low Temperature. J. Phys. Chem. C 2007, 111, 12677– 12680,  DOI: 10.1021/jp074011r

    Google Scholar

    16

    Ligand-free Self-Assembly of Ceria Nanocrystals into Nanorods by Oriented Attachment at Low Temperature

    Du, Ning; Zhang, Hui; Chen, Bingdi; Ma, Xiangyang; Yang, Deren

    Journal of Physical Chemistry C (2007), 111 (34), 12677-12680CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Single-cryst. ceria nanorods were fabricated by self-assembly of ceria nanocrystals via a simple, low-temp., and ligand-free approach. Detailed high-resoln. TEM shows that the nanorods are formed along the [211] or [110] direction by self-organization of truncated octahedral ceria nanocrystals, sharing the {111} or {200} planes with each other, whereas the previous report shows that only the [110] direction exists in ceria nanorods. The nucleation temp. and molar ratio of Ce3+ and OH- also play key roles in the formation of ceria nanorods. Also, the formation mechanism was explained.
17. 17

    Xu, X.; Saghi, Z.; Gay, R.; Möbus, G. Reconstruction of 3D Morphology of Polyhedral Nanoparticles. Nanotechnology 2007, 18, 225501,  DOI: 10.1088/0957-4484/18/22/225501

    Google Scholar

    17

    Reconstruction of 3D morphology of polyhedral nanoparticles

    Xu, Xiaojing; Saghi, Zineb; Gay, Ralph; Mobus, Gunter

    Nanotechnology (2007), 18 (22), 225501/1-225501/8CODEN: NNOTER; ISSN:0957-4484. (Institute of Physics Publishing)

    The three-dimensional (3D) faceting morphol. of ceria nanoparticles is analyzed using transmission electron microscopy (TEM)-based computed tomog. on the nanometer scale. A novel tomog. mode of electron energy loss spectroscopic imaging using a single energy window for inelastically scattered electrons is introduced and found to be reliable and fast for freestanding nanoparticles. To compare the new tomog. method with other methods, we provide the first comprehensive application of three complementary TEM-based imaging techniques, including bright field TEM and annular dark field specific TEM (STEM). Traditional bright-field TEM tomog. is found to be applicable, in spite of obvious artifacts, for cryst. particles of const. compn. However, the safest interpretation is achieved by a combined recording of bright field and spectroscopic images.
18. 18

    Xu, X.; Saghi, Z.; Yang, G.; Hand, R. J.; Möbus, G. Three-Dimensional Structure of CeO₂ Nanodendrites in Glass. Cryst. Growth Des. 2008, 8, 1102– 1105,  DOI: 10.1021/cg700949t

    Google Scholar

    18

    Three-Dimensional Structure of CeO2 Nanodendrites in Glass

    Xu, Xiaojing; Saghi, Zineb; Yang, Guang; Hand, Russell J.; Moebus, Guenter

    Crystal Growth & Design (2008), 8 (4), 1102-1105CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)

    Electron tomog. is used to reconstruct for the first time a nanoscale dendrite pptd. from and embedded in glass in full three dimensions. In combination with electron diffraction, the branching geometry of CeO2 nanodendrites is evaluated in relation to their crystallog. We find that the branches of the dendrite fill a virtual octahedral hull, similar to the surface-morphol. commonly found in free-standing CeO2 nanoparticles. The octahedral facets correspond to {111} planes, while the primary branch growth direction is <100>. Such fluorite-structured ceria ppts. in alkali borosilicate glasses, generated by melting plus annealing, have high relevance for research fields ranging from radionuclide immobilization to glass-ceramic materials and nucleation. Tomog. reconstruction enables apart from qual. morphol. studies quant. evaluation for dendrite fill factors.
19. 19

    Xu, W.; Zhang, Y.; Cheng, G.; Jian, W.; Millett, P. C.; Koch, C. C.; Mathaudhu, S. N.; Zhu, Y. In-Situ Atomic-Scale Observation of Irradiation-Induced Void Formation. Nat. Commun. 2013, 4, 1– 6,  DOI: 10.1038/ncomms3288

    Google Scholar

    There is no corresponding record for this reference.
20. 20

    Esch, F.; Fabris, S.; Zhou, L.; Montini, T.; Africh, C.; Fornasiero, P.; Comelli, G.; Rosey, R. Electron Localization Determines Defect Formation on Ceria Substrates. Science 2005, 309, 752– 755,  DOI: 10.1126/science.1111568

    Google Scholar

    20

    Electron Localization Determines Defect Formation on Ceria Substrates

    Esch, Friedrich; Fabris, Stefano; Zhou, Ling; Montini, Tiziano; Africh, Cristina; Fornasiero, Paolo; Comelli, Giovanni; Rosei, Renzo

    Science (Washington, DC, United States) (2005), 309 (5735), 752-755CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)

    The high performance of ceria (CeO2) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resoln. scanning tunneling microscopy and d. functional calcns. to unravel the local structure of surface and subsurface oxygen vacancies on the (111) surface. Electrons left behind by released oxygen localize on cerium ions. Clusters of more than two vacancies exclusively expose these reduced cerium ions, primarily by including subsurface vacancies, which therefore play a crucial role in the process of vacancy cluster formation. These results have implications for our understanding of oxidn. processes on reducible rare-earth oxides.
21. 21

    Aneggi, E.; Wiater, D.; De Leitenburg, C.; Llorca, J.; Trovarelli, A. Shape-Dependent Activity of Ceria in Soot Combustion. ACS Catal. 2014, 4, 172– 181,  DOI: 10.1021/cs400850r

    Google Scholar

    21

    Shape-Dependent Activity of Ceria in Soot Combustion

    Aneggi, Eleonora; Wiater, Dawid; de Leitenburg, Carla; Llorca, Jordi; Trovarelli, Alessandro

    ACS Catalysis (2014), 4 (1), 172-181CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    In this study, a series of conventional polycryst. ceria and single-cryst. ceria nanorods and nanocubes were prepd. by hydrothermal methods, and their structural, redox, and morphol. properties were investigated using XRD, SEM, HRTEM, BET, temp.-programmed redn., and oxygen storage capacity measurements. According to HRTEM, they are characterized by exposure of different surfaces: {100} surface for nanocubes; {100}, {110}, and in part {111} for nanorods; and mainly {111} for conventional polycryst. ceria, with a morphol. dominated by {111}-enclosed octahedral particles. The presence of more-reactive exposed surfaces affects the reaction of soot oxidn. pos., with an increase in activity in nanoshaped materials compared with conventional ceria. Thermal aging, although detrimental for surface area, is shown to affect morphol. by promoting irregular truncation of edges and corners and development of more reactive surface combinations in all crystal shapes. It is likely that thermal treatment, starting from either cubes or octahedral particles, induces the formation of a similar particle geometry whose activity is dependent on the type of plane exposed and by the no. an extension of edge and corners, thus linking reactivity of octahedral particles in conventional ceria powders with that of cubes in nanoshaped materials. The results indicate that soot oxidn. is also a surface-dependent reaction, and catalyst design for this purpose should allow for surface structure morphol. and its evolution against temp.
22. 22

    Desaunay, T.; Bonura, G.; Chiodo, V.; Freni, S.; Couzinie, J.-P.; Bourgon, J.; Ringuede, A.; Labat, F.; Adamo, C.; Cassir, M. Surface-Dependent Oxidation of H2 on CeO₂ Surfaces. J. Catal. 2013, 297, 193– 201,  DOI: 10.1016/j.jcat.2012.10.011

    Google Scholar

    22

    Surface-dependent oxidation of H2 on CeO2 surfaces

    Desaunay, T.; Bonura, G.; Chiodo, V.; Freni, S.; Couzinie, J.-P.; Bourgon, J.; Ringuede, A.; Labat, F.; Adamo, C.; Cassir, M.

    Journal of Catalysis (2013), 297 (), 193-201CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)

    Ceria nanoparticles with well-defined surface states were prepd. to enable the study of different ceria surfaces, independently. Ceria nanocubes were shown to expose only (100) surfaces, ceria nanooctahedra only (111) surfaces, and ceria nanorods are more complex, with at least 50% of (110) surfaces, as shown by high-resoln. transmission electron microscopy. Temp.-programmed redn. (TPR) by hydrogen performed on these powders shows the following order of reaction temps.: cubes < rods < octahedra. Moreover, activation energies assocd. with the first surface redn. in each sample show a similar trend. Ceria (100) surface is the most reactive toward hydrogen oxidn., while (111) surface is the less reactive, and (110) surface has likely an intermediate behavior. These results confirm that hydrogen oxidn. is highly surface-dependent and that a strong attention must be paid to the surface state of the catalyst in these devices.
23. 23

    Han, W.-Q.; Wu, L. J.; Klie, R. F.; Zhu, Y. M. Enhanced Optical Absorption Induced by Dense Nanocavities inside Titania Nanorods. Adv. Mater. 2007, 19, 2525– 2529,  DOI: 10.1002/adma.200700540

    Google Scholar

    23

    Enhanced optical absorption induced by dense nanocavities inside titania nanorods

    Han, Wei-Qiang; Wu, Lijun; Klie, Robert F.; Zhu, Yimei

    Advanced Materials (Weinheim, Germany) (2007), 19 (18), 2525-2529CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Dense polyhedral nanocavities inside single-cryst. anatase TiO2 nanorods are successfully synthesized by simply heating H2Ti3O7 nanorods. The size of the nanocavities is typically about 10 nm. The surfaces of the nanocavity polyhedron are detd. to be the crystallog. low-index planes of the TiO2 crystal.
24. 24

    Zhu, H.; Tao, J.; Dong, X. Preparation and Photoelectrochemical Activity of Cr-Doped TiO₂ Nanorods with Nanocavities. J. Phys. Chem. C 2010, 114, 2873– 2879,  DOI: 10.1021/jp9085987

    Google Scholar

    24

    Preparation and photoelectrochemical activity of Cr-doped TiO2 nanorods with nanocavities

    Zhu, Hong; Tao, Jie; Dong, Xiang

    Journal of Physical Chemistry C (2010), 114 (7), 2873-2879CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Cr-doped TiO2 nanorods with nanocavities were synthesized by a facile hydrothermal treatment and heating in air. The samples were characterized resp. by means of X-ray diffraction (XRD), high-resoln. transmission electron microscopy (HRTEM), and XPS. XRD patterns indicated that all the samples were anatase cryst. HRTEM results and the electron diffraction patterns illustrated that the TiO2 nanorods possessed the single-cryst. structure. TEM images confirmed that there were different types of nanocavities inside the nanorods, such as a circle, hexagon, and rectangle. XPS results suggested that Cr elements were successfully doped into the TiO2 nanorods after hydrothermal and most Cr congregated on the surface in the form of Cr2O3 after heating. The optical properties of the samples were studied with a UV-vis spectrometer. The photoelectrochem. activity of the Cr-doped TiO2 nanorods thin film was better than that of the com. anatase TiO2 particulate thin film. The high photoelectrochem. activity of the synthesized Cr-doped TiO2 nanorods could be attributed to three factors: the doped Cr, one-dimensional nanostructure of the nanorod, and the increased light-harvesting abilities.
25. 25

    Gao, W.; Zhang, Z.; Li, J.; Ma, Y.; Qu, Y. Surface Engineering on CeO₂ Nanorods by Chemical Redox Etching and Their Enhanced Catalytic Activity for CO Oxidation. Nanoscale 2015, 7, 11686– 11691,  DOI: 10.1039/C5NR01846C

    Google Scholar

    25

    Surface engineering on CeO2 nanorods by chemical redox etching and their enhanced catalytic activity for CO oxidation

    Gao, Wei; Zhang, Zhiyun; Li, Jing; Ma, Yuanyuan; Qu, Yongquan

    Nanoscale (2015), 7 (27), 11686-11691CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    Controllable surface properties of nanocerias are desired for various catalytic processes. There is a lack of efficient approaches to adjust the surface properties of ceria to date. Herein, a redox chem. etching method was developed to controllably engineer the surface properties of ceria nanorods. Ascorbic acid and hydrogen peroxide were used to perform the redox chem. etching process, resulting in a rough surface and/or pores on the surface of ceria nanorods. Increasing the etching cycles induced a steady increase of the sp. surface area, oxygen vacancies and surface Ce3+ fractions. As a result, the etched nanorods delivered enhanced catalytic activity for CO oxidn., compared to the non-etched ceria nanorods. Our method provides a novel and facile approach to continuously adjust the surface properties of ceria for practical applications.
26. 26

    Nandi, P.; Das, D. Photocatalytic Degradation of Rhodamine-B Dye by Stable ZnO Nanostructures with Different Calcination Temperature Induced Defects. Appl. Surf. Sci. 2019, 465, 546– 556,  DOI: 10.1016/j.apsusc.2018.09.193

    Google Scholar

    26

    Photocatalytic degradation of Rhodamine-B dye by stable ZnO nanostructures with different calcination temperature induced defects

    Nandi, Prami; Das, Debajyoti

    Applied Surface Science (2019), 465 (), 546-556CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)

    For developing ZnO as an efficient photocatalyst it needs to embrace a suitable architecture to promote simultaneous max. photon absorption and min. charge carrier recombination. In this regard, presently ZnO nanoparticle and nanorod morphologies with embedded pit like structures possessing enriched surface defects, as demonstrated by X-ray diffraction as well as electron microscopic studies, have been prepd. using a rapid one-pot co-pptn. technique. Further characterization by ESR (EPR), Raman and PL spectroscopy reveal the origin of bulk and surface defects within the nanostructures. Prominent EPR signals with different g-factors e.g., g = 1.93, 1.97, 2.01 etc., indicate EPR-active defect regions on the bulk and surface of the material. These defect states lower the fast recombination of electron and hole, increase charge transport and accelerate the photocatalytic activity. In the present study most efficient ZnO nanostructures have been obtained at calcination temp. (TC) ∼500 °C. Formation of metallic zinc through surface redn. of Zn2+ centers promotes narrowing of the optical band gap and endorses efficient absorption of light, addnl. via enhanced surface area of the pitted structures. These surface defects reduce recombination of the photogenerated charge carriers and enhance photo-degrdn. efficiency to ∼97.75% and rate const. to ∼0.042 min-1 under the exposure of UV light.
27. 27

    Castell, M. R. Wulff Shape of Microscopic Voids in UO2 Crystals. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 68, 235411,  DOI: 10.1103/PhysRevB.68.235411

    Google Scholar

    27

    Wulff shape of microscopic voids in UO2 crystals

    Castell, Martin R.

    Physical Review B: Condensed Matter and Materials Physics (2003), 68 (23), 235411/1-235411/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)

    UO2 single crystals with a size of around 1 cm3 are created in a process involving a period of spectacular grain growth. (111) cleavage cross sections through these crystals expose voids that are typically of μm dimensions. Low voltage SEM of the voids reveals that they are bound by {111} and {001} facets, and some appear to have reached their thermodn. equil. shape (Wulff shape). An anal. of the facet areas shows that the smaller voids are closer to the Wulff shape, and have a surface energy ratio .vepsiln.001/.vepsiln.111=1.42±0.05. The larger voids show step bunching at the facet intersections which typically gives rise to ordered step structures of 10s of nm periodicity and produces nanoscale staircases and amphitheatres. Evidence of void ripening by way of connecting channels is also obsd.
28. 28

    Galvin, C. O. T.; Rushton, M. J. D.; Cooper, M. W. D.; Andersson, D. A.; Burr, P. A.; Grimes, R. W. The Predicted Shapes of Voids and Xe Bubbles in UO2. J. Nucl. Mater. 2021, 543, 152622,  DOI: 10.1016/j.jnucmat.2020.152622

    Google Scholar

    28

    The predicted shapes of voids and Xe bubbles in UO2

    Galvin, C. O. T.; Rushton, M. J. D.; Cooper, M. W. D.; Andersson, D. A.; Burr, P. A.; Grimes, R. W.

    Journal of Nuclear Materials (2021), 543 (), 152622CODEN: JNUMAM; ISSN:0022-3115. (Elsevier B.V.)

    Morphol. is a fundamental attribute when investigating voids and bubbles in UO2. This study uses mol. dynamics and Monte Carlo simulations to predict the lowest energy shapes for voids and bubbles in UO2. The energies of the {100},{110} and {111} surfaces have been calcd. and used to predict the equil. void shape from Wulff construction. This equil. shape is compared to low energy faceted voids exhibiting different relative proportions of each family of terminating surfaces. It is found that the equil. Wulff shape does not represent the lowest energy morphol. for nm void sizes at temps. between 300 K and 1200 K. Furthermore, the lowest energy faceted voids are slightly more energetically favorable than spherical voids, and as Xe is added, and bubble pressure increases, the faceted morphol. becomes even more favorable than the spherical shape.
29. 29

    Levitz, P.; Ehret, G.; Sinha, S. K.; Drake, J. M. Porous Vycor Glass: The Microstructure as Probed by Electron Microscopy, Direct Energy Transfer, Small Angle Scattering, and Molecular Adsorption. J. Chem. Phys. 1991, 95, 6151– 6161,  DOI: 10.1063/1.461583

    Google Scholar

    29

    Porous Vycor glass: the microstructure as probed by electron microscopy, direct energy transfer, small-angle scattering, and molecular adsorption

    Levitz, P.; Ehret, G.; Sinha, S. K.; Drake, J. M.

    Journal of Chemical Physics (1991), 95 (8), 6151-61CODEN: JCPSA6; ISSN:0021-9606.

    A comprehensive anal. is provided for the microstructure of the porous glass, Vycor. Using transmission electron microscopy, small-angle x-ray scattering, mol. adsorption, and the dynamic process of direct energy transfer, a consistent picture of the mass, pore, and interfacial features of this material is presented. From a transmission-electron-microscopy image of an ultrathin section of Vycor the material appears to have a homogeneous distribution of mass with no hierarchical organization. The pore interface exhibits a roughness which is probed by both small-angle x-ray scattering and mol. adsorption. The roughness has an upper cutoff of <20 Å which is not resolved in the transmission-electron-microscopy image and is shown to be unimportant to the dynamics of the direct energy transfer process. The dimensionality probed by direct energy transfer is shown to be related to interfacial geometrical crossover from two dimensional to three dimensional, which is characterized by a persistent length of the interface of 45 Å.
30. 30

    Shelekhin, A. B.; Pien, S.; Ma, Y. H. Permeability, Surface Area, Pore Volume and Pore Size of Vycor Glass Membrane Heat-Treated at High Temperatures. J. Membr. Sci. 1995, 103 (1–2), 39– 43,  DOI: 10.1016/0376-7388(94)00304-H

    Google Scholar

    30

    Permeability, surface area, pore volume and pore size of Vycor glass membrane heat-treated at high temperatures

    Shelekhin, A. B.; Pien, S.; Ma, Y. H.

    Journal of Membrane Science (1995), 103 (1-2), 39-43CODEN: JMESDO; ISSN:0376-7388. (Elsevier)

    Vycor glass porous membranes can be used for high temp. gas sepn. processes operating at temps. ≤850°. At temps. >925°, collapse of the membrane porous structure occurred and irreversibly decreased the membrane permeability. No gas permeability was obsd. in membranes heat treated at >1000°. The pore size in the porous Vycor glass membranes did not change as a result of heat treatment. The pore diam. was 47 Å for pretreatment temps. <1000°. Before use in high temp. applications, the porous Vycor glass membranes should be pretreated at temps. higher than the operation temp. of the process to avoid shrinkage of the membrane and resulting stress.
31. 31

    Snyder, J.; Livi, K.; Erlebacher, J. Dealloying Silver/Gold Alloys in Neutral Silver Nitrate Solution: Porosity Evolution, Surface Composition, and Surface Oxides. J. Electrochem. Soc. 2008, 155, C464,  DOI: 10.1149/1.2940319

    Google Scholar

    31

    Dealloying Silver/Gold Alloys in Neutral Silver Nitrate Solution: Porosity Evolution, Surface Composition, and Surface Oxides

    Snyder, J.; Livi, K.; Erlebacher, J.

    Journal of the Electrochemical Society (2008), 155 (8), C464-C473CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)

    The electrochem. of dealloying Ag/Au alloys in neutral pH Ag nitrate soln. to form nanoporous Au (NPG) is discussed. At pH 7, porosity evolution occurs at high potentials, above that required for oxygen evolution, and within the nominal domain of the Pourbaix diagram where Ag would be expected to form a passivating oxide. Electron microscopy shows that a small pore (∼5 nm) NPG is formed over a potential regime of 1.3-2.0 V vs. normal H electrode, but electrochem. measurements show that the specific capacitance of samples over the same voltage range rises nearly 3-fold. The observations are explained in terms of residual surface oxides passivating the pores behind the dissoln. front, which is itself acidified (and thus corrosive) due to an accumulation of protons assocd. with oxide formation and H2O dissocn. A model is proposed that is consistent with the electrochem. and microscopy results. This method of fabricating NPG has advantages of simplicity and safety, and the porosity formation mechanism may be extended to other systems.
32. 32

    Saghi, Z.; Xu, X.; Möbus, G. Transition from Quantitative to Geometric Tomography. J. Phys. Conf. Ser. 2008, 126, 012063,  DOI: 10.1088/1742-6596/126/1/012063

    Google Scholar

    There is no corresponding record for this reference.
33. 33

    Saghi, Z.; Xu, X.; Möbus, G. Electron Tomography of Regularly Shaped Nanostructures under Non-Linear Image Acquisition. J. Microsc. 2008, 232, 186– 195,  DOI: 10.1111/j.1365-2818.2008.02084.x

    Google Scholar

    33

    Electron tomography of regularly shaped nanostructures under non-linear image acquisition

    Saghi Z; Xu X; Mobus G

    Journal of microscopy (2008), 232 (1), 186-95 ISSN:.

    Electron tomography allows the 3D quantitative characterization of nanostructures, provided a monotonic relationship is fulfilled between the projected signal and the atomic number and thickness of the specimen. This requirement is not satisfied if the micrographs are affected by (i) diffraction contrast, (ii) detector saturation or (iii) contrast inversion due to absorption (high-angle scattering) at high thickness. Artefacts related to the non-monotonic tomography acquisition are examined using computer simulations and experimental tilt series of tungsten tips and CeO(2) nanoparticles. Conditions are derived under which in spite of the non-linear artefacts the information is sufficient for reconstructing the 3D morphology of convex objects by geometric tomography.
34. 34

    Gardner, R. J. Geometric Tomography; Cambridge University Press: Cambridge, 2006.

    Google Scholar

    There is no corresponding record for this reference.
35. 35

    Mai, H. X.; Sun, L. D.; Zhang, Y. W.; Si, R.; Feng, W.; Zhang, H. P.; Liu, H. C.; Yan, C. H. Shape-Selective Synthesis and Oxygen Storage Behavior of Ceria Nanopolyhedra, Nanorods, and Nanocubes. J. Phys. Chem. B 2005, 109, 24380– 24385,  DOI: 10.1021/jp055584b

    Google Scholar

    35

    Shape-Selective Synthesis and Oxygen Storage Behavior of Ceria Nanopolyhedra, Nanorods, and Nanocubes

    Mai, Hao-Xin; Sun, Ling-Dong; Zhang, Ya-Wen; Si, Rui; Feng, Wei; Zhang, Hong-Peng; Liu, Hai-Chao; Yan, Chun-Hua

    Journal of Physical Chemistry B (2005), 109 (51), 24380-24385CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)

    Single-cryst. and uniform nanopolyhedra, nanorods, and nanocubes of cubic CeO2 were selectively prepd. by a hydrothermal method at temps. in the range of 100-180 °C under different NaOH concns., using Ce(NO3)3 as the cerium source. According to high-resoln. transmission electron microscopy, they have different exposed crystal planes: {111} and {100} for polyhedra, {110} and {100} for rods, and {100} for cubes. During the synthesis, the formation of hexagonal Ce(OH)3 intermediate species and their transformation into CeO2 at elevated temp., together with the base concn., have been demonstrated as the key factors responsible for the shape evolution. Oxygen storage capacity (OSC) measurements at 400 °C revealed that the oxygen storage takes place both at the surface and in the bulk for the as-obtained CeO2 nanorods and nanocubes, but is restricted at the surface for the nanopolyhedra just like the bulk one, because the {100}/{110}-dominated surface structures are more reactive for CO oxidn. than the {111}-dominated one. This result suggests that high OSC materials might be designed and obtained by shape-selective synthetic strategy.
36. 36

    Huang, P. X.; Wu, F.; Zhu, B. L.; Gao, X. P.; Zhu, H. Y.; Yan, T. Y.; Huang, W. P.; Wu, S. H.; Song, D. Y. CeO₂ Nanorods and Gold Nanocrystals Supported on CeO₂ Nanorods as Catalyst. J. Phys. Chem. B 2005, 109, 19169– 19174,  DOI: 10.1021/jp052978u

    Google Scholar

    36

    CeO2 Nanorods and Gold Nanocrystals Supported on CeO2 Nanorods as Catalyst

    Huang, P. X.; Wu, F.; Zhu, B. L.; Gao, X. P.; Zhu, H. Y.; Yan, T. Y.; Huang, W. P.; Wu, S. H.; Song, D. Y.

    Journal of Physical Chemistry B (2005), 109 (41), 19169-19174CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)

    The formation mechanism of uniform CeO2 structure at the nanometer scale via a wet-chem. reaction is of great interest in fundamental study as well as a variety of applications. In this work, large-scale well-crystd. CeO2 nanorods with uniform diams. in the range of 20-30 nm and lengths up to tens of micrometers are first synthesized through a hydrothermal synthetic route in 5 M KOH soln. at 180 °C for 45 h without any templates and surfactants. The nanorod formation involves dehydration of CeO2 nanoparticles and orientation growth along the 〈110〉 direction in KOH soln. Subsequently, gold nanoparticles with crystallite sizes between 10 and 20 nm are loaded on the surface of CeO2 nanorods using HAuCl4 soln. as the gold source and NaBH4 soln. as a reducing agent. The synthesized Au/CeO2 nanorods demonstrate a higher catalytic activity in CO oxidn. than the pure CeO2 nanorods.
37. 37

    Zhang, R.; Lu, K.; Zong, L.; Tong, S.; Wang, X.; Feng, G. Gold Supported on Ceria Nanotubes for CO Oxidation. Appl. Surf. Sci. 2017, 416, 183– 190,  DOI: 10.1016/j.apsusc.2017.04.158

    Google Scholar

    37

    Gold supported on ceria nanotubes for CO oxidation

    Zhang, Rongbin; Lu, Kun; Zong, Lijuan; Tong, Sai; Wang, Xuewen; Feng, Gang

    Applied Surface Science (2017), 416 (), 183-190CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)

    CeO2 is a typical of fluorite structure, semiconductor material, has high oxygen storage capability as well as unique redox property, which is widely used as catalysts supports in catalysis. Ceria nanotubes and nanocubes are prepd. via hydrothermal method in the present work, and Au/CeO2 catalysts are prepd. using deposition-pptn. technique with HAuCl4 as gold precursor. The prepd. samples were used as catalysts for the CO oxidn. reaction using a fix-bed reactor at 50-130 °C and characterized by XRD, BET, SEM, TEM, XPS, TPR and ICP. It is found that CeO2-NT and CeO2-NC expose different surface planes. The XPS and H2-TPR results illustrates that the {110} surface exposed by CeO2-NT has stronger interaction with gold particles, which benefits the electron and oxygen transfer between Au and ceria. All these characters of the Au/CeO2-NT(3%) result in the better activity and stability than the Au/CeO2-NC(3%).
38. 38

    Tang, Z.-R.; Zhang, Y.; Xu, Y.-J. A Facile and High-Yield Approach to Synthesize One-Dimensional CeO₂ Nanotubes with Well-Shaped Hollow Interior as a Photocatalyst for Degradation of Toxic Pollutants. RSC Adv. 2011, 1, 1772,  DOI: 10.1039/c1ra00518a

    Google Scholar

    38

    A facile and high-yield approach to synthesize one-dimensional CeO2 nanotubes with well-shaped hollow interior as a photocatalyst for degradation of toxic pollutants

    Tang, Zi-Rong; Zhang, Yanhui; Xu, Yi-Jun

    RSC Advances (2011), 1 (9), 1772-1777CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)

    A facile, template-free and high-yield synthesis of single-cryst. cerium dioxide nanotubes (CeO2-NT) has been reported via a "casually-modified" approach based on the hydrothermal treatment of Ce(OH)CO3 precursors with alkali soln. in an aq. phase. This simple modification in synthesis procedures not only improves the yield of CeO2-NT remarkably, but also gives rise to the formation of CeO2-NT featuring excellent nanotubular open-ended structure with a well-shaped hollow interior. The collection techniques of BET, UV/visible diffuse reflectance spectra (DRS), SEM, and transmission electron microscopy (TEM) anal. have been employed to characterize the morphol. and optical properties of the as-prepd. CeO2-NT. Significantly, we demonstrate that CeO2-NT exhibits a markedly enhanced photocatalytic activity and stability as compared with its counterpart of CeO2 nanoparticles and com. TiO2 (P25) toward the degrdn. of arom. benzene, a well-known toxic pollutant that commonly occurs in urban ambient air and is of significant concern regarding environmental health because of its toxic, mutagenic, or carcinogenic properties. This represents a first example to demonstrate the advantage of CeO2 nanotubes as photocatalyst as compared to its counterpart of CeO2 nanoparticles, clearly suggesting the morphol./shape-dependent photocatalytic behavior of CeO2 materials. Therefore, our current work not only offers a simple approach for fabrication of open-ended CeO2-NT with well-shaped hollow interior, but also demonstrates the promising potential of the applications of CeO2-NT, CeO2-NT-based and other metal oxide nanotube-based materials in the area of photocatalysis, which will inevitably enrich the intriguing chem. of morphol./shape-dependent heterogeneous photocatalysis and thermal catalysis.
39. 39

    Möbus, G.; Inkson, B. J. Three-Dimensional Reconstruction of Buried Nanoparticles by Element-Sensitive Tomography Based on Inelastically Scattered Electrons. Appl. Phys. Lett. 2001, 79, 1369– 1371,  DOI: 10.1063/1.1400080

    Google Scholar

    39

    Three-dimensional reconstruction of buried nanoparticles by element-sensitive tomography based on inelastically scattered electrons

    Mobus, G.; Inkson, B. J.

    Applied Physics Letters (2001), 79 (9), 1369-1371CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)

    Energy-filtered transmission electron microscopy is used to image the nanocomposite FeAl+Y2O3, an oxide-dispersion-strengthened intermetallic alloy, over a tilt range of ±60° using inelastically scattered electrons only. The properties of electron spectroscopic imaging are exploited to recover a projection relationship between the three-dimensional chem. concn. distribution and the micrographs. This allows recovery of the full information on vol. shape, distribution, and homogeneity of the buried nanoparticles by back-projection. Restrictions to low at. no., common in bio-objects, are here overcome at the expense of higher electron exposures.
40. 40

    Midgley, P. A.; Weyland, M. 3D Electron Microscopy in the Physical Sciences: The Development of Z-Contrast and EFTEM Tomography. Ultramicroscopy 2003, 96, 413– 431,  DOI: 10.1016/S0304-3991(03)00105-0

    Google Scholar

    40

    3D electron microscopy in the physical sciences: the development of Z-contrast and EFTEM tomography

    Midgley, P. A.; Weyland, M.

    Ultramicroscopy (2003), 96 (3-4), 413-431CODEN: ULTRD6; ISSN:0304-3991. (Elsevier Science B.V.)

    A review. The rapid advances in nanotechnol. and the ever decreasing size of features in the microelectronics industry brings with it the need for advanced characterization with high spatial resoln. in two and three dimensions. Stereo microscopy allows some insight into the three-dimensional nature of an object but for true quant. anal., one has to turn to tomog. as a way to reconstruct a three-dimensional object from two-dimensional projections (images). X-ray tomog. allow structures to be imaged at relatively large length scales, atom probe tomog. at the at. level. Electron tomog. offers an intermediate resoln. (of ∼1 nm) with a field of view of hundreds of nm making it ideal for the characterization of many nanoscale devices. While electron tomog. was used in the biol. sciences for >30 yr, it is only now being applied to the phys. sciences. The authors review the status of electron tomog., describe the basis behind the technique and some of the practicalities of recording and analyzing data for tomog. reconstruction, particularly in regard to solving three-dimensional problems that are encountered in materials science at the nanometer level. The authors present examples of how STEM dark-field imaging and energy-filtered TEM can be used successfully to examine nearly all types of specimens likely to be encountered by the phys. scientist.
41. 41

    Ishikawa, Y.; Takeda, M.; Tsukimoto, S.; Nakayama, K. S.; Asao, N. Cerium Oxide Nanorods with Unprecedented Low-Temperature Oxygen Storage Capacity. Adv. Mater. 2016, 28, 1467– 1471,  DOI: 10.1002/adma.201504101

    Google Scholar

    41

    Cerium Oxide Nanorods with Unprecedented Low-Temperature Oxygen Storage Capacity

    Ishikawa, Yoshifumi; Takeda, Maiki; Tsukimoto, Susumu; Nakayama, Koji S.; Asao, Naoki

    Advanced Materials (Weinheim, Germany) (2016), 28 (7), 1467-1471CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)

    Ce oxide nanorods were prepd. by corrosion of Ce6Al94 alloy in alk. soln. The presence of Ce3Al11 nanocrystals in the alloy leads to the nanorod formation. The sp. surface area is 218 m2/g. The nanorods are formed only on the surface of the alloy, leaving Al behind. Theses nanorods could be used as catalysts.
42. 42

    Das, S.; Singh, S.; Dowding, J. M.; Oommen, S.; Kumar, A.; Sayle, T. X. T.; Saraf, S.; Patra, C. R.; Vlahakis, N. E.; Sayle, D. C. The Induction of Angiogenesis by Cerium Oxide Nanoparticles through the Modulation of Oxygen in Intracellular Environments. Biomaterials 2012, 33, 7746– 7755,  DOI: 10.1016/j.biomaterials.2012.07.019

    Google Scholar

    42

    The induction of angiogenesis by cerium oxide nanoparticles through the modulation of oxygen in intracellular environments

    Das, Soumen; Singh, Sanjay; Dowding, Janet M.; Oommen, Saji; Kumar, Amit; Sayle, Thi X. T.; Saraf, Shashank; Patra, Chitta R.; Vlahakis, Nicholas E.; Sayle, Dean C.; Self, William T.; Seal, Sudipta

    Biomaterials (2012), 33 (31), 7746-7755CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)

    Angiogenesis is the formation of new blood vessels from existing blood vessels and is crit. for many physiol. and pathophysiol. processes. In this study we have shown the unique property of cerium oxide nanoparticles (CNPs) to induce angiogenesis, obsd. using both in vitro and in vivo model systems. In particular, CNPs trigger angiogenesis by modulating the intracellular oxygen environment and stabilizing hypoxia inducing factor 1α endogenously. Furthermore, correlations between angiogenesis induction and CNPs physicochem. properties including: surface Ce3+/Ce4+ ratio, surface charge, size, and shape were also explored. High surface area and increased Ce3+/Ce4+ ratio make CNPs more catalytically active towards regulating intracellular oxygen, which in turn led to more robust induction of angiogenesis. Atomistic simulation was also used, in partnership with in vitro and in vivo experimentation, to reveal that the surface reactivity of CNPs and facile oxygen transport promotes pro-angiogenesis.
43. 43

    Aryanpour, M.; Khetan, A.; Pitsch, H. Activity Descriptor for Catalytic Reactions on Doped Cerium Oxide. ACS Catal. 2013, 3, 1253– 1262,  DOI: 10.1021/cs400034c

    Google Scholar

    43

    Activity Descriptor for Catalytic Reactions on Doped Cerium Oxide

    Aryanpour, M.; Khetan, A.; Pitsch, H.

    ACS Catalysis (2013), 3 (6), 1253-1262CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    It is well-known that ceria enhances chem. activity and catalyst durability in several important catalytic reactions, including CO oxidn. and NOx redn. Of great practical value is then having a theor. model to predict the effect of doping on the ceria activity before the actual synthesis of its compds. Such a model is developed in the present work on the basis of exptl. obsd. data, where we verify our hypothesis that the energy for oxygen vacancy formation is a simple yet powerful activity descriptor for this class of materials. We further benchmark and use our DFT + U computations to est. this descriptor and to suggest a few transition metals that would increase the activity of ceria toward redox reactions. This new activity descriptor might be an important factor in similar systems because it does not require any knowledge about the exact chem. or mechanism of catalysis.
44. 44

    Sayle, T. X. T.; Cantoni, M.; Bhatta, U. M.; Parker, S. C.; Hall, S. R.; Möbus, G.; Molinari, M.; Reid, D.; Seal, S.; Sayle, D. C. Strain and Architecture-Tuned Reactivity in Ceria Nanostructures; Enhanced Catalytic Oxidation of CO to CO₂. Chem. Mater. 2012, 24, 1811– 1821,  DOI: 10.1021/cm3003436

    Google Scholar

    44

    Strain and Architecture-Tuned Reactivity in Ceria Nanostructures; Enhanced Catalytic Oxidation of CO to CO2

    Sayle, Thi X. T.; Cantoni, Michelle; Bhatta, Umananda M.; Parker, Stephen C.; Hall, Simon R.; Mobus, Gunter; Molinari, Marco; Reid, David; Seal, Sudipta; Sayle, Dean C.

    Chemistry of Materials (2012), 24 (10), 1811-1821CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)

    Atomistic simulations reveal that the chem. reactivity of ceria nanorods is increased when tensioned and reduced when compressed promising strain-tunable reactivity; the reactivity is detd. by calcg. the energy required to oxidize CO to CO2 by extg. oxygen from the surface of the nanorod. Visual reactivity "fingerprints", where surface oxygens are colored according to calcd. chem. reactivity, are presented for ceria nanomaterials including: nanoparticles, nanorods, and mesoporous architectures. The images reveal directly how the nanoarchitecture (size, shape, channel curvature, morphol.) and microstructure (dislocations, grain-boundaries) influences chem. reactivity. We show the generality of the approach, and its relevance to a variety of important processes and applications, by using the method to help understand: TiO2 nanoparticles (photocatalysis), mesoporous ZnS (semiconductor band gap engineering), MgO (catalysis), CeO2/YSZ interfaces (strained thin films; solid oxide fuel cells/nanoionics), and Li-MnO2 (lithiation induced strain; energy storage).
45. 45

    Bhatta, U. M.; Reid, D.; Sakthivel, T.; Sayle, T. X. T.; Sayle, D.; Molinari, M.; Parker, S. C.; Ross, I. M.; Seal, S.; Mobus, G. Morphology and Surface Analysis of Pure and Doped Cuboidal Ceria Nanoparticles. J. Phys. Chem. C 2013, 117, 24561– 24569,  DOI: 10.1021/jp405993v

    Google Scholar

    45

    Morphology and Surface Analysis of Pure and Doped Cuboidal Ceria Nanoparticles

    Bhatta, Umananda M.; Reid, David; Sakthivel, Tamilselvan; Sayle, Thi X. T.; Sayle, Dean; Molinari, Marco; Parker, Stephen C.; Ross, Ian M.; Seal, Sudipta; Mobus, Gunter

    Journal of Physical Chemistry C (2013), 117 (46), 24561-24569CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    Cuboidal nanoparticles of ceria are examd. by high resoln. imaging and anal. to explore their local morphol. of faces, edges, and corners. Synthesized with and without Sm doping using a hydrothermal process, we find a high fraction of particles enclosed by {100} facets, which are normally energy-penalized compared to octahedral {111} facets. Electron tomog. conducted at high magnification with lattice resolved imaging is combined with electron energy loss spectroscopy revealing oxidn. states of Ce ions. It is found that extended {100} faces exist predominantly without local nanofaceting, except for {111} corner caps and subfacets on {110} edges. Reduced Ce is found on all {100} surfaces, while Sm doping does not lower the reduced Ce concn. Mol. dynamics simulations are used to complement the microscopy, including the formation of {111} subfacets on {110} edges, formation of a {111} corner facet, and also the fact that reduced Ce ions prefer low coordinated positions like steps and corners along with more active {100} faces.
46. 46

    Yang, C.; Yu, X.; Heißler, S.; Nefedov, A.; Colussi, S.; Llorca, J.; Trovarelli, A.; Wang, Y.; Woll, C. Surface Faceting and Reconstruction of Ceria Nanoparticles. Angew. Chem., Int. Ed. 2017, 56, 375– 379,  DOI: 10.1002/anie.201609179

    Google Scholar

    46

    Surface Faceting and Reconstruction of Ceria Nanoparticles

    Yang, Chengwu; Yu, Xiaojuan; Heissler, Stefan; Nefedov, Alexei; Colussi, Sara; Llorca, Jordi; Trovarelli, Alessandro; Wang, Yuemin; Woell, Christof

    Angewandte Chemie, International Edition (2017), 56 (1), 375-379CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)

    The surface at. arrangement of metal oxides dets. their phys. and chem. properties, and the ability to control and optimize structural parameters is of crucial importance for many applications, in particular in heterogeneous catalysis and photocatalysis. Whereas the structures of macroscopic single crystals can be detd. with established methods, for nanoparticles (NPs), this is a challenging task. Herein, we describe the use of CO as a probe mol. to det. the structure of the surfaces exposed by rod-shaped ceria NPs. After calibrating the CO stretching frequencies using results obtained for different ceria single-crystal surfaces, we found that the rod-shaped NPs actually restructure and expose {111} nanofacets. This finding has important consequences for understanding the controversial surface chem. of these catalytically highly active ceria NPs and paves the way for the predictive, rational design of catalytic materials at the nanoscale.
47. 47

    Lawrence, N. J.; Brewer, J. R.; Wang, L.; Wu, T.-S.; Wells-Kingsbury, J.; Ihrig, M. M.; Wang, G.; Soo, Y.-L.; Mei, W.-N.; Cheung, C. L. Defect Engineering in Cubic Cerium Oxide Nanostructures for Catalytic Oxidation. Nano Lett. 2011, 11, 2666– 2671,  DOI: 10.1021/nl200722z

    Google Scholar

    47

    Defect Engineering in Cubic Cerium Oxide Nanostructures for Catalytic Oxidation

    Lawrence, Neil J.; Brewer, Joseph R.; Wang, Lu; Wu, Tai-Sing; Wells-Kingsbury, Jamie; Ihrig, Marcella M.; Wang, Gonghua; Soo, Yun-Liang; Mei, Wai-Ning; Cheung, Chin Li

    Nano Letters (2011), 11 (7), 2666-2671CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)

    Traditional nanostructured design of cerium oxide catalysts typically focuses on their shape, size, and elemental compn. We report a different approach to enhance the catalytic activity of cerium oxide nanostructures through engineering high d. of oxygen vacancy defects in these catalysts without dopants. The defect engineering was accomplished by a low pressure thermal activation process that exploits the nanosize effect of decreased oxygen storage capacity in nanostructured cerium oxides.
48. 48

    MessaoudiI, C.; Boudier, T.; Sorzano, C.; Marco, S. TomoJ: Tomography Software for Three-Dimensional Reconstruction in Transmission Electron Microscopy. BMC Bioinf. 2007, 8, 288,  DOI: 10.1186/1471-2105-8-288

    Google Scholar

    48

    TomoJ: tomography software for three-dimensional reconstruction in transmission electron microscopy

    Messaoudii Cedric; Boudier Thomas; Sanchez Sorzano Carlos Oscar; Marco Sergio

    BMC bioinformatics (2007), 8 (), 288 ISSN:.

    BACKGROUND: Transmission electron tomography is an increasingly common three-dimensional electron microscopy approach that can provide new insights into the structure of subcellular components. Transmission electron tomography fills the gap between high resolution structural methods (X-ray diffraction or nuclear magnetic resonance) and optical microscopy. We developed new software for transmission electron tomography, TomoJ. TomoJ is a plug-in for the now standard image analysis and processing software for optical microscopy, ImageJ. RESULTS: TomoJ provides a user-friendly interface for alignment, reconstruction, and combination of multiple tomographic volumes and includes the most recent algorithms for volume reconstructions used in three-dimensional electron microscopy (the algebraic reconstruction technique and simultaneous iterative reconstruction technique) as well as the commonly used approach of weighted back-projection. CONCLUSION: The software presented in this work is specifically designed for electron tomography. It has been written in Java as a plug-in for ImageJ and is distributed as freeware.
49. 49

    Pettersen, E. F.; Goddard, T. D.; Huang, C. C.; Couch, G. S.; Greenblatt, D. M.; Meng, E. C.; Ferrin, T. E. UCSF Chimera: A Visualization System for Exploratory Research and Analysis. J. Comput. Chem. 2004, 25, 1605– 1612,  DOI: 10.1002/jcc.20084

    Google Scholar

    49

    UCSF Chimera-A visualization system for exploratory research and analysis

    Pettersen, Eric F.; Goddard, Thomas D.; Huang, Conrad C.; Couch, Gregory S.; Greenblatt, Daniel M.; Meng, Elaine C.; Ferrin, Thomas E.

    Journal of Computational Chemistry (2004), 25 (13), 1605-1612CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)

    The design, implementation, and capabilities of an extensible visualization system, UCSF Chimera, are discussed. Chimera is segmented into a core that provides basic services and visualization, and extensions that provide most higher level functionality. This architecture ensures that the extension mechanism satisfies the demands of outside developers who wish to incorporate new features. Two unusual extensions are presented: Multiscale, which adds the ability to visualize large-scale mol. assemblies such as viral coats, and Collab., which allows researchers to share a Chimera session interactively despite being at sep. locales. Other extensions include Multalign Viewer, for showing multiple sequence alignments and assocd. structures; ViewDock, for screening docked ligand orientations; Movie, for replaying mol. dynamics trajectories; and Vol. Viewer, for display and anal. of volumetric data. A discussion of the usage of Chimera in real-world situations is given, along with anticipated future directions. Chimera includes full user documentation, is free to academic and nonprofit users, and is available for Microsoft Windows, Linux, Apple Mac OS X, SGI IRIX, and HP Tru64 Unix from http://www.cgl.ucsf.edu/chimera/.
50. 50

    Kresse, G.; Hafner, J. Ab Initio Molecular-Dynamics Simulation of the Liquid-Metal-Amorphous-Semiconductor Transition in Germanium. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 14251– 14269,  DOI: 10.1103/PhysRevB.49.14251

    Google Scholar

    50

    Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium

    Kresse, G.; Hafner, J.

    Physical Review B: Condensed Matter and Materials Physics (1994), 49 (20), 14251-69CODEN: PRBMDO; ISSN:0163-1829.

    The authors present ab initio quantum-mech. mol.-dynamics simulations of the liq.-metal-amorphous-semiconductor transition in Ge. The simulations are based on (a) finite-temp. d.-functional theory of the 1-electron states, (b) exact energy minimization and hence calcn. of the exact Hellmann-Feynman forces after each mol.-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nose' dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows the authors to perform simulations over >30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liq. and amorphous Ge in very good agreement with expt.. The simulation allows the authors to study in detail the changes in the structure-property relation through the metal-semiconductor transition. The authors report a detailed anal. of the local structural properties and their changes induced by an annealing process. The geometrical, bounding, and spectral properties of defects in the disordered tetrahedral network are studied and compared with expt.
51. 51

    Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169– 11186,  DOI: 10.1103/PhysRevB.54.11169

    Google Scholar

    51

    Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set

    Kresse, G.; Furthmueller, J.

    Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)

    The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
52. 52

    Molinari, M.; Parker, S. C.; Sayle, D. C.; Islam, M. S. Water Adsorption and its Effect on the Stability of Low Index Stoichiometric and Reduced Surfaces of Ceria. J. Phys. Chem. C 2012, 116, 7073– 7082,  DOI: 10.1021/jp300576b

    Google Scholar

    52

    Water Adsorption and Its Effect on the Stability of Low Index Stoichiometric and Reduced Surfaces of Ceria

    Molinari, Marco; Parker, Stephen C.; Sayle, Dean C.; Islam, M. Saiful

    Journal of Physical Chemistry C (2012), 116 (12), 7073-7082CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)

    The influence of H2O on the redox properties of ceria is pivotal to its widespread exploitation spanning a variety of applications. Ab initio simulation techniques based on DFT-GGA+U are used to study the H2O-ceria system including associative (H2O) and dissociative (-OH) adsorption/desorption of H2O and the formation of oxygen vacancies in the presence of H2O vapor on the stoichiometric and reduced low index surfaces of ceria at different H2O coverages. Calcns. address the controversy concerning the adsorption of H2O on the CeO2{111}, and new results are reported for the CeO2{110} and {100} surfaces. The simulations reveal strong H2O coverage dependence for dissociatively (-OH) adsorbed H2O on stoichiometric surfaces which becomes progressively destabilized at high coverage, while associative (H2O) adsorption depends weakly on the coverage due to weaker interactions between the adsorbed mols. Anal. of the adsorption geometries suggests that the surface Ce atom coordination controls the strong adhesion of H2O as the av. distance Ce-OW is always 10% greater than the Ce-O distance in the bulk, while the hydrogen bonding network dictates the orientation of the mols. The adsorption energy is predicted to increase on reduced surfaces because oxygen vacancies act as active sites for H2O dissocn. Crucially, by calcg. the heat of redn. of dry and wet surfaces, also H2O promotes further redn. of ceria surfaces and is therefore central to its redox chem. Finally, these simulation approaches can be used to evaluate H2O desorption as a function of temp. and pressure which accords well with exptl. data for CeO2{111}. The authors predict desorption temps. (TD) for CeO2{110} and CeO2{100} surfaces, where exptl. data are not yet available. Such an understanding will help expt. interpret the complex surface/interface redox processes of ceria, which will, inevitably, include H2O.
53. 53

    Molinari, M.; Symington, A. R.; Sayle, D. C.; Sakthivel, T. S.; Seal, S.; Parker, S. C. Computer-Aided Design of Nanoceria Structures as Enzyme Mimetic Agents: The Role of Bodily Electrolytes on Maximizing Their Activity. ACS Appl. Bio Mater. 2019, 2, 1098– 1106,  DOI: 10.1021/acsabm.8b00709

    Google Scholar

    53

    Computer-Aided Design of Nanoceria Structures as Enzyme Mimetic Agents: The Role of Bodily Electrolytes on Maximizing Their Activity

    Molinari, Marco; Symington, Adam R.; Sayle, Dean C.; Sakthivel, Tamil S.; Seal, Sudipta; Parker, Stephen C.

    ACS Applied Bio Materials (2019), 2 (3), 1098-1106CODEN: AABMCB; ISSN:2576-6422. (American Chemical Society)

    Nanoceria, typically used for "clean-air" catalytic converter technologies because of its ability to capture, store, and release oxygen, is the same material that has the potential to be used in nanomedicine. Specifically, nanoceria can be used to control oxygen content in cellular environments; as a "nanozyme", nanoceria mimics enzymes by acting as an antioxidant agent. The computational design procedures for predicting active materials for catalytic converters can therefore be used to design active ceria nanozymes. Crucially, the ceria nanomedicine is not a mol.; rather, it is a crystal and exploits its unique crystal properties. Here, we use ab initio and classical computer modeling, together with the expt., to design structures for nanoceria that maximize its nanozymetic activity. We predict that the optimum nanoparticle shape is either a (truncated) polyhedral or a nanocube to expose (active) CeO2{100} surfaces. It should also contain oxygen vacancies and surface hydroxyl species. We also show that the surface structures strongly affect the biol. activity of nanoceria. Analogous to catalyst poisoning, phosphorus "poisoning", the interaction of nanoceria with phosphate, a common bodily electrolyte, emanates from phosphate ions binding strongly to CeO2{100} surfaces, inhibiting oxygen capture and release and hence its ability to act as a nanozyme. Conversely, the phosphate interaction with {111} surfaces is weak, and therefore, these surfaces protect the nanozyme against poisoning. The atom-level understanding presented here also illuminates catalytic processes and poisoning in "clean-air" or fuel-cell technologies because the mechanism underpinning and exploited in each technol., oxygen capture, storage, and release, is identical.
54. 54

    Todorov, I. T.; Smith, W.; Trachenko, K.; Dove, M. T. DL_POLY_3: New Dimensions in Molecular Dynamics Simulations via Massive Parallelism. J. Mater. Chem. 2006, 16, 1911,  DOI: 10.1039/b517931a

    Google Scholar

    54

    DL_POLY_3: new dimensions in molecular dynamics simulations via massive parallelism

    Todorov, Ilian T.; Smith, William; Trachenko, Kostya; Dove, Martin T.

    Journal of Materials Chemistry (2006), 16 (20), 1911-1918CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)

    DL_POLY_3 is a general-purpose massively parallel mol. dynamics simulation package embedding a highly efficient set of methods and algorithms such as: Domain Decompn. (DD), Linked Cells (LC), Daresbury Advanced Fourier Transform (DAFT), Trotter derived Velocity Verlet (VV) integration and RATTLE. Written to support academic research, it has a wide range of applications and can run on a wide range of computers; from single processor workstations to multi-processor computers. The code development has placed particular emphasis on the efficient utilization of multi-processor power by optimized memory workload and distribution, which makes it possible to simulate systems of the order of tens of millions of particles and beyond. We discuss the new DL_POLY_3 design, and report on the performance, capability and scalability. We also discuss new features implemented to simulate highly non-equil. processes of radiation damage and analyze the structural damage during such processes.
55. 55

    Minervini, L.; Zacate, M.; Grimes, R. Defect Cluster Formation in M2O3-Doped CeO₂. Solid State Ionics 1999, 116, 339– 349,  DOI: 10.1016/S0167-2738(98)00359-2

    Google Scholar

    55

    Defect cluster formation in M2O3-doped CeO2

    Minervini, Licia; Zacate, Matthew O.; Grimes, Robin W.

    Solid State Ionics (1999), 116 (3,4), 339-349CODEN: SSIOD3; ISSN:0167-2738. (Elsevier Science B.V.)

    Atomistic simulation calcns. based on energy minimization techniques were used to study the energetics assocd. with M2O3 soln. in CeO2. The binding energy of an O vacancy to one or two substitutional cations is a strong function of dopant cation radius; small dopant ions prefer to occupy 1st neighbor sites, large dopant ions prefer 2nd neighbor sites. The crossover occurs at approx. Gd3+, which also exhibits the smallest binding energy. These results were used to predict lattice parameter as a function of defect concn. and comparison is made to exptl. values.
56. 56

    Sayle, D. C.; Feng, X.; Ding, Y.; Wang, Z. L.; Sayle, T. X. T. Simulating Synthesis”: Ceria Nanosphere Self-Assembly into Nanorods and Framework Architectures. J. Am. Chem. Soc. 2007, 129, 7924– 7935,  DOI: 10.1021/ja070893w

    Google Scholar

    56

    "Simulating Synthesis": Ceria Nanosphere Self-Assembly into Nanorods and Framework Architectures

    Sayle, Dean C.; Feng, Xiangdong; Ding, Yong; Wang, Zhong Lin; Sayle, Thi X. T.

    Journal of the American Chemical Society (2007), 129 (25), 7924-7935CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    The authors predict, from computer modeling and simulation in partnership with expt., a general strategy for synthesizing spherical oxide nanocrystals via crystn. from melt. In particular the authors simulate synthesis to generate full atomistic models of undoped and Ti-doped CeO2 nanoparticles, nanorods, and nanoporous framework architectures. The authors' simulations demonstrate, in quant. agreement with expt. [Science 2006, 312, 1504], that Ti (dopant) ions change the shape of CeO2 nanocrystals from polyhedral to spherical. The authors rationalize this morphol. change by elucidating, at the atomistic level, the mechanism underpinning its synthesis. In particular, CeO2 nanocrystals can be synthesized via crystn. from melt: as a molten (undoped) CeO2 nanoparticle is cooled, nucleating seeds spontaneously evolve at the surface and express energetically stable {111} facets to minimize the energy. As crystn. proceeds, the {111} facets grow, thus facilitating a polyhedral shape. Conversely, when doped with Ti, a (predominantly) TiO2 shell encapsulates the inner CeO2 core. This shell inhibits the evolution of nucleating seeds at the surface thus rendering it amorphous during cooling. Accordingly, crystn. is forced to proceed via the evolution of a nucleating seed in the bulk CeO2 region of the nanoparticle, and as this seed grows, it remains surrounded by amorphous ions, which wrap around the core so that the energies for high-index facets are drastically reduced; these amorphous ions adopt a spherical shape to minimize the surface energy. Crystn. emanates radially from the nucleating seed, and because it is encapsulated by an amorphous shell, the crystn. front is not compelled to express energetically favorable surfaces. Accordingly, after the nanoparticle has crystd. it retains this spherical shape. A typical animation showing the crystn. (with atomistic detail) is available as Supporting Information. The authors predict that spherical oxide nanocrystals can be synthesized via crystn. from melt in general by suppressing nucleating seed evolution at the surface thus forcing the nucleating seed to spontaneously evolve in the bulk. Nanospheres can, similar to zeolitic classifications, constitute Secondary Building Units (SBUs) and can aggregate to form nanorods and nanoporous framework architectures. Here the authors have attempted to simulate this process to generate models for CeO2 and Ti-doped CeO2 nanorods and framework architectures. In particular, the authors predict that Ti doping will smooth the surfaces:hexagonal prism shaped CeO2 nanorods with {111} and {100} surfaces become cylindrical, and framework architectures change from facetted pores and channels with well-defined {111} and {100} surfaces to smooth pores and channels (expressing both concave and convex curvatures). Such structures are difficult to characterize using, for example, Miller indexes; rather probably these new structural materials are better described using minimal surfaces.
57. 57

    Castanet, U.; Feral-Martin, C.; Demourgues, A.; Neale, R. L.; Sayle, D. C.; Caddeo, F.; Flitcroft, J. M.; Caygill, R.; Pointon, B. J.; Molinari, M. J. Controlling the {111}/{110} Surface Ratio of Cuboidal Ceria Nanoparticles. ACS Appl. Mater. Interfaces 2019, 11, 11384– 11390,  DOI: 10.1021/acsami.8b21667

    Google Scholar

    57

    Controlling surface ratio of cuboidal ceria nanoparticles

    Castanet, Uli; Feral-Martin, Cedric; Demourgues, Alain; Neale, Rachel L.; Sayle, Dean C.; Caddeo, Francesco; Flitcroft, Joseph M.; Caygill, Robert; Pointon, Ben J.; Molinari, Marco; Majimel, Jerome

    ACS Applied Materials & Interfaces (2019), 11 (12), 11384-11390CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)

    The ability to control the size and morphol. is crucial in optimizing nanoceria catalytic activity as this is governed by the atomistic arrangement of species and structural features at the surfaces. Here, we show that cuboidal cerium oxide nanoparticles can be obtained via microwave-assisted hydrothermal synthesis in highly alk. media. High-resoln. transmission electron microscopy (HRTEM) revealed that the cube edges were truncated by CeO2{110} surfaces and the cube corners were truncated by CeO2{111} surfaces. When adjusting synthesis conditions by increasing NaOH concn., the av. particle size increased. Although this was accompanied by an increase of the cube faces, CeO2{100}, the cube edges, CeO2{110}, and cube corners, CeO2{111}, remained of const. size. Mol. dynamics (MD) was used to rationalize this behavior and revealed that energetically, the corners and edges cannot be atomically sharp, rather they are truncated by {111} and {110} surfaces, resp., to stabilize the nanocube; both the expt. and simulation showed agreement regarding the min. size of ∼1.6 nm assocd. with this truncation. Moreover, HRTEM and MD revealed {111}/{110} faceting of the {110} edges, which balances the surface energy assocd. with the exposed surfaces, which follows {111} > {110} > {100}, although only the {110} surface facets because of the ease of extg. oxygen from its surface and follows {111} > {100} > {110}. Finally, MD revealed that the {100} surfaces are "liq.-like" with a surface oxygen mobility 5 orders of magnitude higher than that on the {111} surfaces; this arises from the flexibility of the surface species network that can access many different surface arrangements because of very small energy differences. This finding has implications for understanding the surface chem. of nanoceria and provides avenues to rationalize the design of catalytically active materials at the nanoscale.
58. 58

    Sayle, T. X. T.; Molinari, M.; Das, S.; Bhatta, U. M.; Mobus, G.; Parker, S. C.; Seal, S.; Sayle, D. C. Environment-Mediated Structure, Surface Redox Activity and Reactivity of Ceria Nanoparticles. Nanoscale 2013, 5, 6063,  DOI: 10.1039/c3nr00917c

    Google Scholar

    58

    Environment-mediated structure, surface redox activity and reactivity of ceria nanoparticles

    Sayle, Thi X. T.; Molinari, Marco; Das, Soumen; Bhatta, Umananda M.; Moebus, Guenter; Parker, Stephen C.; Seal, Sudipta; Sayle, Dean C.

    Nanoscale (2013), 5 (13), 6063-6073CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    Nanomaterials, with potential application as bio-medicinal agents, exploit the chem. properties of a solid, with the ability to be transported (like a mol.) to a variety of bodily compartments. However, the chem. environment can change significantly the structure and hence properties of a nanomaterial. Accordingly, its surface reactivity is critically dependent upon the nature of the (biol.) environment in which it resides. Here, we use Mol. Dynamics (MD) simulation, D. Functional Theory (DFT) and aberration cor. TEM to predict and rationalise differences in structure and hence surface reactivity of ceria nanoparticles in different environments. In particular we calc. reactivity fingerprints' for unreduced and reduced ceria nanoparticles immersed in water and in vacuum. Our simulations predict higher activities of ceria nanoparticles, towards oxygen release, when immersed in water because the water quenches the coordinative unsatn. of surface ions. Conversely, in vacuum, surface ions relax into the body of the nanoparticle to relieve coordinative unsatn., which increases the energy barriers assocd. with oxygen release. Our simulations also reveal that reduced ceria nanoparticles are more active towards surface oxygen release compared to unreduced nanoceria. In parallel, expt. is used to explore the activities of ceria nanoparticles that have suffered a change in environment. In particular, we compare the ability of ceria nanoparticles, in an aq. environment, to scavenge superoxide radicals compared to the same batch of nanoparticles, which have first been dried and then rehydrated. The latter show a distinct redn. in activity, which we correlate to a change in the redox chem. assocd. with moving between different environments. The reactivity of ceria nanoparticles is therefore not only environment dependent, but is also influenced by the transport pathway or history required to reach the particular environment in which its reactivity is to be exploited.
59. 59

    Sayle, T. X. T.; Inkson, B. J.; Karakoti, A.; Kumar, A.; Molinari, M.; Möbus, G.; Parker, S. C.; Seal, S.; Sayle, D. C. Mechanical Properties of Ceria Nanorods and Nanochains; the Effect of Dislocations, Grain-Boundaries and Oriented Attachment. Nanoscale 2011, 3, 1823,  DOI: 10.1039/c0nr00980f

    Google Scholar

    59

    Mechanical properties of ceria nanorods and nanochains; the effect of dislocations, grain-boundaries and oriented attachment

    Sayle, Thi X. T.; Inkson, Beverley J.; Karakoti, Ajay; Kumar, Amit; Molinari, Marco; Mobus, Gunter; Parker, Stephen C.; Seal, Sudipta; Sayle, Dean C.

    Nanoscale (2011), 3 (4), 1823-1837CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)

    It is predict that the presence of extended defects can reduce the mech. strength of a ceria nanorod by 70%. Conversely, the pristine material can deform near its theor. strength limit. Specifically, atomistic models of ceria nanorods were generated with full microstructure, including: growth direction, morphol., surface roughening (steps, edges, corners), point defects, dislocations and grain-boundaries. The models were then used to calc. the mech. strength as a function of microstructure. The compressive yield strengths of ceria nanorods, ca. 10 nm in diam. and without extended defects, are 46 and 36 GPa for rods oriented along [211] and [110] resp., which represents almost 10% of the bulk elastic modulus and are assocd. with yield strains of ≈0.09. Tensile yield strengths were calcd. to be ≈50% lower with assocd. yield strains of about 0.06. For both nanorods, plastic deformation was found to proceed via slip in the {001} plane with direction 〈110〉 - a primary slip system for crystals with the fluorite structure. Dislocation evolution for the nanorod oriented along [110] was nucleated via a cerium vacancy present at the surface. A nanorod oriented along [321] and comprising twin-grain boundaries with {111} interfacial planes was calcd. to have a yield strength of about 10 GPa (compression and tension) with the grain boundary providing the vehicle for plastic deformation, which slipped in the plane of the grain boundary, with an assocd. 〈110〉 slip direction. Using a combination of atomistic simulation and DFT it was also predicted, that rutile-structured ceria is feasible when the crystal is placed under tension. The mech. properties of nanochains, comprising individual ceria nanoparticles with oriented attachment and generated using simulated self-assembly, were found to be similar to those of the nanorod with grain-boundary. Images of the atom positions during tension and compression are shown, together with animations, revealing the mechanisms underpinning plastic deformation. For the nanochain, the simulations help further understanding of how a crystg. ice front can be used to "sculpt" ceria nanoparticles into nanorods via oriented attachment.
60. 60

    Humphrey, W.; Dalke, A.; Schulten, K. VMD: Visual Molecular Dynamics. J. Mol. Graphics 1996, 14, 33– 38,  DOI: 10.1016/0263-7855(96)00018-5

    Google Scholar

    60

    VDM: visual molecular dynamics

    Humphrey, William; Dalke, Andrew; Schulten, Klaus

    Journal of Molecular Graphics (1996), 14 (1), 33-8, plates, 27-28CODEN: JMGRDV; ISSN:0263-7855. (Elsevier)

    VMD is a mol. graphics program designed for the display and anal. of mol. assemblies, in particular, biopolymers such as proteins and nucleic acids. VMD can simultaneously display any no. of structures using a wide variety of rendering styles and coloring methods. Mols. are displayed as one or more "representations," in which each representation embodies a particular rendering method and coloring scheme for a selected subset of atoms. The atoms displayed in each representation are chosen using an extensive atom selection syntax, which includes Boolean operators and regular expressions. VMD provides a complete graphical user interface for program control, as well as a text interface using the Tcl embeddable parser to allow for complex scripts with variable substitution, control loops, and function calls. Full session logging is supported, which produces a VMD command script for later playback. High-resoln. raster images of displayed mols. may be produced by generating input scripts for use by a no. of photorealistic image-rendering applications. VMD has also been expressly designed with the ability to animate mol. dynamics (MD) simulation trajectories, imported either from files or from a direct connection to a running MD simulation. VMD is the visualization component of MDScope, a set of tools for interactive problem solving in structural biol., which also includes the parallel MD program NAMD, and the MDCOMM software used to connect the visualization and simulation programs, VMD is written in C++, using an object-oriented design; the program, including source code and extensive documentation, is freely available via anonymous ftp and through the World Wide Web.
61. 61

    Watson, G. W.; Kelsey, E. T.; de Leeuw, N. H.; Harris, D. J.; Parker, S. C. Atomistic Simulation of Dislocations, Surfaces and Interfaces in MgO. J. J. Chem. Soc., Faraday Trans. 1996, 92, 433– 438,  DOI: 10.1039/ft9969200433

    Google Scholar

    61

    Atomistic simulation of dislocations, surfaces and interfaces in MgO

    Watson, Graeme W.; Kelsey, E. Toby; de Leeuw, Nora H.; Harris, Duncan J.; Parker, Stephen C.

    Journal of the Chemical Society, Faraday Transactions (1996), 92 (3), 433-8CODEN: JCFTEV; ISSN:0956-5000. (Royal Society of Chemistry)

    A new simulation code for modeling extended defects e.g. linear (dislocations) and planar (surfaces and grain boundaries) at the atomistic level is introduced. One of the key components is the ability to calc. the Coulombic potential of a solid with 1-dimensional periodicity. This approach was applied to screw dislocations in MgO and the structure (including core size) and stability of the 〈100〉 and 1/2〈110〉 screw dislocations were evaluated. The 1/2〈110〉 dislocation, which has the shortest Burgers vector, is more stable, as predicted by elasticity theory, although the simulations show that elasticity theory underests. the energy difference. By using this new computer simulation code METADISE, following the approach of Tasker, the structure and energetics of surfaces and interfaces can be calcd. This method was applied to modeling microfaceting, and microfaceted {110} and {111} surfaces of MgO are the most stable forms of these surfaces. The formation energy of tilt grain boundaries in MgO ({h10} and {h20}) as a function of misorientation angle was also studied and for the {h10} series the formation energy is proportional to the interfacial bond d. while no such pattern can be found for the {h20} series.