Selective Aerobic Oxidation Mediated by TiO2 Photocatalysis

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• 作者：Xianjun Lang ; Wanhong Ma ; Chuncheng Chen ; Hongwei Ji ; Jincai Zhao
• 刊名：Accounts of Chemical Research
• 出版年：2014
• 出版时间：February 18, 2014
• 年：2014
• 卷：47
• 期：2
• 页码：355-363
• 全文大小：471K
• ISSN：1520-4898

文摘

TiO₂ is one of the most studied metal oxide photocatalysts and has unparal-leled efficiency and stability. This cheap, abundant, and non-toxic material has the potential to address future environmental and energy concerns. Understanding about the photoinduced interfacial redox events on TiO₂ could have profound effect on the degradation of organic pollutants, splitting of H₂O into H₂ and O₂, and selective redox organic transformations. Scientists traditionally accept that for a semiconductor photocatalyst such as TiO₂ under the illumination of light with energy larger than its band gap, two photocarriers will be created to carry out their independent reduction and oxidation processes. However, our recent discoveries indicate that it is the concerted rather than independent effect of both photocarriers of valence band hole (h_vb⁺) and conduction band electron (e_cb^{鈥?/sup>) that dictate the product formation during interfacial oxidation event mediated by TiO₂ photocatalysis.
In this Account, we describe our recent findings on the selective oxidation of organic substrates with O₂ mediated by TiO₂ photocatalysis. The transfer of O-atoms from O₂ to the corresponding products dominates the selective oxidation of alcohols, amines, and alkanes mediated by TiO₂ photocatalysis. We ascribe this to the concerted effect of both h_vb+ and e_cb鈥?/sup> of TiO₂ in contribution to the oxidation products. These findings imply that O₂ plays a unique role in its transfer into the products rather than independent role of e_cb鈥?/sup> scavenger. More importantly, e_cb鈥?/sup> plays a crucial role to ensure the high selectivity for the oxygenation of organic substrates. We can also use the half reactions such as those of the conduction band electron of TiO₂ for efficient oxidation reactions with O₂. To this end, efficient selective oxidation of organic substrates such as alcohols, amines, and aromatic alkanes with O₂ mediated by TiO₂ photocatalysis under visible light irradiation has been achieved.
In summary, the concerted effect of h_vb+ and e_cb鈥?/sup> to implement one oxidation event could pave the way for selective oxofunctionalization of organic substrates with O₂ by metal oxide photocatalysis. Furthermore, it could also deepen our understanding on the role of O₂ and the elusive nature of oxygen species at the interface of TiO₂, which, in turn, could shed new light on avant-garde photocatalytic selective redox processes in addressing the energy and environmental challenges of the future.}