TiO2 Facet-dependent reconstruction and photocatalysis of CuOx/TiO2 photocatalysts in CO2 photoreduction

A series of CuOx/TiO2 photocatalysts with different TiO2 nanocrystals as the supports were prepared to explore the effect of CuOx-TiO2 interaction on the reconstruction and photocatalysis in CO2 photoreduction with water as the reducing agent. The CuOx-TiO2 interaction was observed to be strongest in CuOx/TiO2-{0 0 1} photocatalysts. Under Xe light irradiation, supported CuO species on TiO2-{0 0 1} is photo-reduced to stable supported Cu2O species beneficial for photocatalytic CO2 reduction to CH4, while supported CuOx species on TiO2-{1 0 0} and TiO2-{1 0 1} is photo-reduced to supported Cu0 species unfavorable for photocatalytic CO2 reduction to CH4. The photo-induced reduction of supported CuOx to Cu0 becomes more severe under Hg light irradiation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) results demonstrate that photocatalytic CO2 reduction to CH4 occurs via the bicarbonate and carboxyl intermediates over all CuOx/TiO2 photocatalysts and via the additional CO2– and formate intermediates over CuOx/TiO2-{1 0 0} and CuOx/TiO2-{1 0 1} photocatalysts. These results deepen the fundamental understanding of Cu-based photocatalysts for photocatalytic CO2 reduction and exemplify the facet effect of TiO2 nanocrystals in TiO2-related photocatalysis.