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Photochemical Mechanism of Size-Quantized Vanadium-Doped TiO_2 Particles

Martin, Scot T. and Morrison, Colin L. and Hoffmann, Michael R. (1994) Photochemical Mechanism of Size-Quantized Vanadium-Doped TiO_2 Particles. Journal of Physical Chemistry, 98 (51). pp. 13695-13704. ISSN 0022-3654.

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Transition metal ions doped into TiO_2 can increase the quantum efficiency of the heterogeneous photooxidation of chlorinated hydrocarbons. In this regard, a single dopant (vanadium) has been selected for a detailed investigation to elucidate the mechanism of the dopant action on the photoreactivity of TiO_2. Large polycrystalline (1-4 nm) TiO_2 particles (50 μm) that show size quantization effects due to the individual crystallites are synthesized. Doping (1 at. % ) of the TiO_2 crystals with vanadium reduces the photooxidation rates of 4-chlorophenol (4-CP) compared to the undoped aggregates. Under ambient conditions (25 °C), vanadium is found to be present primarily on TiO_2 surfaces as >VO_2^+ (~90%) (">" denotes a surficial moiety) and secondarily as interstitial V^(4+) (~10% ). Sintering at higher temperatures (200-400 °C) results in the formation of surficial islands of V_2O_5 on TiO_2 while sintering at 600 and 800 °C produces nonstoichiometric solid solutions of V_xTi_1-xO_2. Vanadium appears to reduce the photoreactivity of TiO_2-25 by promoting charge-carrier recombination with electron trapping at > VO_2^+ whereas V (IV) impurities in surficial V_2O_5 islands on TiO_2-200/400 promote charge-carrier recombination by hole trapping. Substitutional V(IV) in the lattice of TiO_2-600/800 appears to act primarily as a charge-carrier recombination center that shunts charge carriers away from the solid-solution interface with a net reduction in photoreactivity. The complexities of the physical and electronic effects of vanadium doping are expected to be present in the mechanisms of other transition metal ions doped into TiO_2.

Item Type:Article
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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1994 American Chemical Society. Received: July 25, I994; In Final Form: October 1, 1994. We are grateful to ARPA and ONR {NAV 5 HFMN N0001492J1901} for financial support. S. Martin is supported by a National Defense Science and Engineering Graduate Fellowship. C. Morrison thanks the Bobst foundation for an American University of Beirut Faculty development grant. Wonyong Choi, Peter Green, Nicole Peill, Ronald Siefert, and Dr. Andreas Termin provided valuable support and stimulating discussion.
Funding AgencyGrant Number
Advanced Research Projects Agency (ARPA)UNSPECIFIED
Office of Naval Research (ONR)NAV 5 HFMN N0001492J1901
National Defense Science and Engineering Graduate (NDSEG) FellowshipUNSPECIFIED
Bobst FoundationUNSPECIFIED
Issue or Number:51
Record Number:CaltechAUTHORS:20150810-083413078
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Official Citation:Photochemical Mechanism of Size-Quantized Vanadium-Doped TiO2 Particles Scot T. Martin, Colin L. Morrison, and Michael R. Hoffmann The Journal of Physical Chemistry 1994 98 (51), 13695-13704 DOI: 10.1021/j100102a041
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59338
Deposited By: Ruth Sustaita
Deposited On:10 Aug 2015 16:57
Last Modified:03 Mar 2020 13:01

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