Simple preparation of nitrogen-doped TiO2 and its performance in selective oxidation of benzyl alcohol and benzylamine under visible light

Abstract N-doped TiO2, denoted as T_400, was prepared simply by the facile thermal hydrolysis of TiOSO4 using NH4OH as both a precipitating agent and a nitrogen source. Compared to TiO2 without nitrogen doping, T_400 provides superior photocatalytic activity toward the selective oxidation of benzyl alcohol and benzylamine under visible light irradiation, with >85% conversion and >95% selectivity to benzaldehyde and N-benzylidenebenzylamine products, respectively. The increased photoactivity of T_400 is ascribed to enhanced visible-light absorption and efficient photogenerated charge transfer and separation as supported by UV-vis DRS, photoelectrochemical and VB-XPS results. The catalyst can tolerate the presence of substituent groups in benzyl alcohol and benzelamine molecules as > 80% conversion and > 95% selectivity are still achieved, which expands the scope of substrates and catalyst utilization. Band energy level of N-doped TiO2 compared to that of undoped TiO2 is determined using Mott-Schottky and UV-vis DRS measurements. Possible mechanisms for the formation of benzaldehyde and N-benzylidenebenzylamine over N-doped TiO2 are proposed. This work presents a simple synthesis of N-doped TiO2, using a low-cost and easily handled inorganic titanium salt instead of air/moisture-sensitive alkoxide precursors and reveals its potential application toward photocatalytic synthesis of organic fine chemicals under visible light.