EDITORIAL pubs.acs.org/JPCL
Dominance of Metal Oxides in the Era of Nanotechnology Chart 1. TiO2-Related Papers Published in The Journal of Physical Chemistry A/B/C/Letters during the Period of 20012010 (Source: ISI Web of Science)
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he abundance and stability of metal oxides have rendered them convenient materials in catalytic applications, either as a participant or as a support in heterogeneous catalysis. In this era of nanotechnology, metal oxides continue to play a dominant role. Shape- and size-controlled synthesis, new tools to understand the surface properties, and ease of chemical modification to tailor their surface properties have given many of these oxides prominence in recent years. Take, for example, a familiar oxide, titanium dioxide, which has become an integral part of our lifestyle. From nondairy coffee creamers to cosmetics, from powdered donuts to paints, and toothpaste to self-cleaning glass, TiO2 is widely used in everyday applications. In 1966, the U.S. Food and Drug Administration (US-FDA) approved TiO2 as a food color additive (up to 1% of total weight) (http://www.fda.gov/forindustry/coloradditives/ coloradditiveinventories/ucm115641.htm). Since then, many packaged foods and household products routinely include TiO2 as a whitener or as a desiccant. The nontoxic nature, proven stability in acidic and alkaline media, and wide-band-gap semiconducting properties have made TiO2 the most popular material in light energy conversion and storage.1,2 During the past decade, we have seen continuous growth of the scientific literature related to TiO2 and its impact on physical chemistry research. The Journal of Physical Chemistry A/B/C and Letters have published more than 2400 papers on TiO2-related research from 2001 to 2010 (Chart 1) and have gathered 55000þ citations (or 22.5 cites per published paper) during the same period.
Vanadium oxide (VOx) is another important catalyst material with wide practical importance. For example, discontinuous jumps in electrical conductivity and optical transmittance of VO2 enable the design of thermoelectric sensors and energyefficient smart windows. Banerjee and co-workers present mechanistic insight into the nature of metalinsulator phase transitions of VO2 in their Perspective.8 Elucidation of the electronic and structural aspects of such materials are crucial to establish the microscopic mechanisms of the phase transition.911 Synthesis of well-defined, variable nuclearity VOx surface structures by organometallic grafting is also being attempted to obtain mechanistic understanding of the role of oxide surface centers in catalytic reactions.12 Another emerging area is endohedral metallofullerenes, which readily undergo electron transfer, resulting in population/depopulation of the fullerene-based molecular orbitals. In their Perspective, Popov and Dunsch present the electrochemical redox activity of endohedral metallofullerenes and the physics of electron transfer through the carbon cage.13 Recent experimental and theoretical studies are discussed to identify their endohedral redox activity. In particular, they highlight the merits of EPR spectroscopy, which has been found to be a valuable tool in probing the electrochemical electron transfer through spin charge separation and spin flow phenomena. In another study, Turro and co-workers14,15 succeeded in encapsulating a hydrogen molecule in the fullerene (C60) cage and explored the interactions of the endohedral H2 within the cage or with the outside world. A basic understanding of the structural aspects of new nanomaterials is important to establishing their catalytic or sensing properties.
The Journal of Physical Chemistry A/B/C and Letters have published more than 2400 papers on TiO2related research from 2001 to 2010 and have gathered 55000þ citations. Yang and co-workers, in their Perspective, focus on the theoretical simulations and exploration of the unusual properties of anatase TiO2 with highly reactive facets.3 The breakthrough in synthesizing TiO2 with exposed (001) facets has enabled the researchers to explore its role in photocatalytic remediation, water splitting reaction, and dye-sensitized solar cells. Recent theoretical and experimental studies also highlight the surface property of TiO2 and the reactivity of different facets in dictating catalytic activity.46 The reactive (001) facet provides a different platform than the commonly used TiO2(110) surface to probe the photoinduced reactivity of adsorbed acceptor or donor molecules. Chemisorbed O2 species have also been directly imaged recently on reduced TiO2(110) at 50 K with highresolution scanning tunneling microscopy (STM).7 r 2011 American Chemical Society
Prashant V. Kamat Deputy Editor University of Notre Dame
Published: April 07, 2011 839
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The Journal of Physical Chemistry Letters
EDITORIAL
’ REFERENCES (1) Mora-Sero, I.; Bisquert, J. Breakthroughs in the Development of Semiconductor-Sensitized Solar Cells. J. Phys. Chem. Lett. 2010, 1, 3046–3052. (2) Miyasaka, T. Toward Printable Sensitized Mesoscopic Solar Cells: Light-Harvesting Management with Thin TiO2 Films. J. Phys. Chem. Lett. 2011, 2, 262–269. (3) Gong, X. Q.; Fang, W. Q.; Yang, H. G. On the Unusual Properties of Anatase TiO2 Exposed by Highly Reactive Facets. J. Phys. Chem. Lett. 2011, 2, 725–734. (4) Zhang, Z.; Yates, J. T. Effect of Adsorbed Donor and Acceptor Molecules on Electron Stimulated Desorption: O2/TiO2(110). J. Phys. Chem. Lett. 2010, 1, 2185–2188. (5) Petrik, N. G.; Kimmel, G. A. Off-Normal CO2 Desorption from the Photooxidation of CO on Reduced TiO2(110). J. Phys. Chem. Lett. 2010, 1, 2508–2513. (6) Petrik, N. G.; Kimmel, G. A. Photoinduced Dissociation of O2 on Rutile TiO2(110). J. Phys. Chem. Lett. 2010, 1, 1758–1762. (7) Wang, Z.-T.; Du, Y.; Dohnalek, Z.; Lyubinetsky, I. Direct Observation of Site-Specific Molecular Chemisorption of O2 on TiO2(110). J. Phys. Chem. Lett. 2010, 1, 3524–3529. (8) Whittaker, L.; Patridge, C. J.; Banerjee, S. A Microscopic and Nanoscale Perspective of the MetalInsulator Phase Transitions of VO2: Some New Twists to an Old Tale. J. Phys. Chem. Lett. 2011, 2, 745–758. (9) Wu, C.; Feng, F.; Feng, J.; Dai, J.; Yang, J.; Xie, Y. Ultrafast SolidState Transformation Pathway from New-Phased Goethite VOOH to Paramontroseite VO2 to Rutile VO2(R). J. Phys. Chem. C 2011, 115, 791–799. (10) Kang, L.; Gao, Y.; Zhang, Z.; Du, J.; Cao, C.; Chen, Z.; Luo, H. Effects of Annealing Parameters on Optical Properties of Thermochromic VO2 Films Prepared in Aqueous Solution. J. Phys. Chem. C 2010, 114, 1901–1911. (11) Baik, J. M.; Kim, M. H.; Larson, C.; Wodtke, A. M.; Moskovits, M. Nanostructure-Dependent MetalInsulator Transitions in Vanadium-Oxide Nanowires. J. Phys. Chem. C 2008, 112, 13328–13331. (12) Wegener, S. L.; Kim, H.; Marks, T. J.; Stair, P. C. Precursor Nuclearity Effects in Supported Vanadium Oxides Prepared by Organometallic Grafting. J. Phys. Chem. Lett. 2011, 2, 170–175. (13) Popov, A.; Dunsch, L. Electrochemistry In Cavea: Endohedral Redox Reactions of Encaged Species in Fullerenes. J. Phys. Chem. Lett. 2011, 2, 786–794. (14) Frunzi, M.; Lei, X.; Murata, Y.; Komatsu, K.; Iwamatsu, S.-I.; Murata, S.; Lawler, R. G.; Turro, N. J. Magnetic Interaction of SolutionState Paramagnets with Encapsulated H2O and H2. J. Phys. Chem. Lett. 2010, 1, 1420–1422. (15) Li, Y.; Lei, X.; Lawler, R. G.; Murata, Y.; Komatsu, K.; Turro, N. J. Distance-Dependent Paramagnet-Enhanced Nuclear Spin Relaxation of H2@C60 Derivatives Covalently Linked to a Nitroxide Radical. J. Phys. Chem. Lett. 2010, 1, 2135–2138.
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