Selective Aerobic Oxidation Mediated by TiO2 Photocatalysis

TiO2 is one of the most studied metal oxide photocatalysts and has unparalleled 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 H-2 and O-2, 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)(-)) 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 O-2 mediated by TiO2 photocatalysis. The transfer of O-atoms from O-2 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)(-) of TiO2 In contribution to the oxidation products. These findings imply that O-2 plays a unique role in its transfer into the products rather than independent role of e(cb)(-) scavenger. More importantly, e(cb)(-) 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 O-2. To this end, efficient selective oxidation of organic substrates such as alcohols, amines, and aromatic alkanes with O-2 mediated by TiO2 photocatalysis under visible light irradiation has been achieved. In summary, the concerted effect of h(vb)(+) and e(cb)(-) to implement one oxidation event could pave the way for selective oxofunctionalization of organic substrates with O-2 by metal oxide photocatalysis. Furthermore, it could also deepen our understanding on the role of O-2 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.