Semiconductor Charge Separation and Transfer

The number of electron and hole traps (O2, Ti +, and O ) and the rate of formation of the short-lived hydroxyl radicals OH under UV irradiation were evaluated by EPR. A correlation was suggested among the amount of the charge carrier centers, the rate of formation of OH radicals, and the catalyst photoaclivity 

The use of EPR as a key tool to characterize electronic structure and to reveal the nature of the active sites has been recently considered by Fittipaldi et al. [40], The power of the EPR technique to investigate the local properties is exemplified with C , N , B , and F , as weU as some anion codoped Ti02 and has been summarized, and the limitations and challenges are critically discussed. In particular, complementary techniques in addition to the EPR characterization, such as high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), XRD, Raman spectroscopy, and computational calculations, can improve the general understanding. 

Its intensity is markedly enhanced under visible light irradiation, implying the formation of localized energy states in the TiOj band gap because of anion doping and/or oxygen vacancies. 

EPR has also been used to determine the nature of photoreactive oxygen-centered species. The heterogeneous photocatalytic decomposition of perfluorooctanoic acid (PFOA) by Ti02 under 254 nm UV Hght is one such study [45]. The addition of oxaHc acid as a hole scavenger has been found to significantly accelerate PFOA decomposition under nitrogen atmosphere. EPR measurements confirmed the existence of carboxyl anion radicals (C02 ) in the photocatalytic process as a result 

Product selectivity and yields of cyclohexanol and cyclohexanone formation in the photocatalytic air oxidation of cyclohexane on TiOj irradiated by UV have 

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