Applied Catalysis B: Environmental, Vol.243, 760-770, 2019
TiO22-x/CoOx photocatalyst sparkles in photothermocatalytic reduction of CO2 with H2O steam
Solar photocatalytic production of fuels from CO2 and H2O remains a challenging goal. Herein we report a strategy to co-modify TiO2 with oxygen vacancies and CoOx nanoclusters for enhanced photothermocatalytic reduction of CO2. The TiO2-x/CoOx material exhibits prominently enhanced activity for the yield of CH4 and CO under ultraviolet irradiation at elevated temperature of 393 K, which is 111.3- and 13.2-times greater yield of CH4 and CO, respectively than the conventional photocatalytic process at 298 K, and 175.1- and 2.9-times greater yield of CH4 and CO, respectively than the pristine TiO2 under the same photothermocatalytic conditions. Control experiments over singly modified TiO2 and doubly modified TiO2 by different preparation history, together with high-resolution transmission electron microscope (HRTEM), electron spin resonance (ESR), and transient photovoltage measurements reveal the synergistic effect of oxygen vacancies and surface-grafted CoOx on the photothermocatalytic reduction of CO2 to CH4, i.e. oxygen vacancies at TiO2 surface facilitate the adsorption and reduction of CO2 and the dispersion of CoOx nanoclusters, whereas surface-grafted CoOx clusters facilitate the hole trapping and the oxidation of H2O. Thereby the coexistence of oxygen vacancies and CoOx nanoclusters at TiO2 surface promote the separation of photogenerated electrons and holes, and remarkably enhance the eight-electron reduction of CO2 to CH4 under photothermocatalytic conditions. This study shows the great potential of photo-thermal synergy on CO2 reduction and provides a promising means to design photo-thermocatalysts for solar photocatalytic reduction of CO2 to fuel.