Photogenerated Defects in Shape-Controlled TiO2 Anatase Nanocrystals: A Probe To Evaluate the Role of Crystal Facets in Photocatalytic Processes

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• 作者：Massimiliano D鈥橝rienzo ; Jaime Carbajo ; Ana Bahamonde ; Maurizio Crippa ; Stefano Polizzi ; Roberto Scotti ; Laura Wahba ; Franca Morazzoni
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：November 9, 2011
• 年：2011
• 卷：133
• 期：44
• 页码：17652-17661
• 全文大小：1249K
• 年卷期：v.133,no.44(November 9, 2011)
• ISSN：1520-5126

文摘

The promising properties of anatase TiO₂ nanocrystals exposing specific surfaces have been investigated in depth both theoretically and experimentally. However, a clear assessment of the role of the crystal faces in photocatalytic processes is still under debate. In order to clarify this issue, we have comprehensively explored the properties of the photogenerated defects and in particular their dependence on the exposed crystal faces in shape-controlled anatase. Nanocrystals were synthesized by solvothermal reaction of titanium butoxide in the presence of oleic acid and oleylamine as morphology-directing agents, and their photocatalytic performances were evaluated in the phenol mineralization in aqueous media, using O₂ as the oxidizing agent. The charge-trapping centers, Ti³⁺, O^{鈥?/sup>, and O₂鈥?/sup>, formed by UV irradiation of the catalyst were detected by electron spin resonance, and their abundance and reactivity were related to the exposed crystal faces and to the photoefficiency of the nanocrystals. In vacuum conditions, the concentration of trapped holes (O鈥?/sup> centers) increases with increasing {001} surface area and photoactivity, while the amount of Ti3+ centers increases with the specific surface area of {101} facets, and the highest value occurs for the sample with the worst photooxidative efficacy. These results suggest that {001} surfaces can be considered essentially as oxidation sites with a key role in the photoxidation, while {101} surfaces provide reductive sites which do not directly assist the oxidative processes. Photoexcitation experiments in O₂ atmosphere led to the formation of Ti4+鈥揙₂鈥?/sup> oxidant species mainly located on {101} faces, confirming the indirect contribution of these surfaces to the photooxidative processes. Although this work focuses on the properties of TiO₂, we expect that the presented quantitative investigation may provide a new methodological tool for a more effective evaluation of the role of metal oxide crystal faces in photocatalytic processes.}