Visible-light deposition of CrOx cocatalyst on TiO2: Cr valence regulation for superior photocatalytic CO2 reduction to CH4

Abstract Photodeposition is widely adopted for implanting metal/metal oxide cocatalysts on semiconductors. However, it is prerequisite that the photon energy should be sufficient to excite the host semiconductor. Here, we report a lower-energy irradiation powered deposition strategy for implanting CrOx cocatalyst on TiO2. Excitingly, CrOx-400 implanted under visible-light irradiation significantly promotes the CH4 evolution rate on TiO2 to 8.4 µmol g-1h−1 with selectivity of 98% from photocatalytic CO2 reduction, which is 15 times of that on CrOx-200 implanted under UV–visible-light irradiation. Moreover, CrOx-400 is identified to be composed of higher valence Cr species compared to CrOx-200. This valence states regulation of Cr species is indicated to provide more active sites for CO2 adsorption/activation and to modulate the reaction mechanism from single Cr site to Cr-Cr dual sites, thus endowing the superior CH4 production. This work demonstrates an alternative strategy for constructing efficient metal oxides cocatalysts on wide bandgap semiconductor.