Visible-light-driven selective oxidation of alcohols using a dye-sensitized TiO2-polyoxometalate catalyst

This study demonstrated a dye-sensitized TiO2-polyoxometalate system (denoted TiO2-(PW12-TH) 8, where PW12 = PW12O403 and TH = thionine) for selective oxidation of alcohols under visible light. The results showed that various substituted alcohols were transformed into their corresponding aldehydes with high selectivity. Due to more efficient electrons transfer, large surface area, and enhanced visible light absorption, the photocatalytic activity of TiO2-(PW12-TH) 8 was superior to any other dyesensitized system reported to date. The response in the photocurrent-time curves over several on/off cycles of intermittent irradiation showed good reproducibility. The photocurrent response of TiO2(PW12-TH) 8 was much higher than that of TiO2/TH (physical mixture of TiO2 and TH), SiO2-(PW12-TH) 8 or P25-(PW12-TH) 8 (P25 = Degussa P25), attributed to the more efficient transfer and longer lifetime of photoexcited electrons. This photocatalytic process confirmed that efficient electron transfer during photocatalytic oxidation plays a vital role in determining the reaction conversion and obtaining good selectivity. Electron paramagnetic resonance (EPR) spectra and radical scavenging experiments proved that superoxide radicals and electrons were the main reactive species in the proposed system, the absence of hydroxyl radicals and holes is demonstrated to be the key of high reaction selectivity. (C) 2017 Elsevier Inc. All rights reserved.