Nitrogen-stabilized oxygen vacancies in TiO2 for site-selective loading of Pt and CoOx cocatalysts toward enhanced photoreduction of CO2 to CH4

Abstract

Photocatalysis provides an attractive approach to convert CO2 into valuable fuels, which yet highly relies on a well-designed photocatalyst with good selectivity and high CO2 reduction ability. Herein, we report a mild synthesis of mesoporous spherical N-doped TiO2 photocatalyst with site-selective deposition of redox cocatalysts. Theoretical calculations prove that nitrogen doping favors the formation of oxygen vacancies (VO) in TiO2 and stabilizes them as well. The combination of ESR characterization, theoretical calculation and photocatalytic tests confirms VO-induced site-selective loading of the redox cocatalysts (Pt, CoOx). The designed composite shows a maximal CH4-yielding rate of 409.17 μmol g−1, which is 180 times higher than that of pure TiO2. Photoelectrochemical and optical measurements indicate that Pt is the key active center for CO2 adsorption and activation, while CoOx is responsible for H2O oxidization and proton transfer. The separation of reaction site and accelerated mass transfer on the catalyst surface largely enhance the conversion efficiency of CO2. This work provides a strategy to selectively deposit dual cocatalysts on semiconductor surface through introduction of oxygen vacancies for substantially improved photocatalytic reduction of CO2.