Self-Assembled Zn1–xO/TiO2 Nanocomposite as a Novel p–n Heterojunction for Selective CO2-to-CO Photoreduction

Selective CO2 photoreduction to valuable chemicals is promising for a carbon-neutral future and still remains a challenge. Herein, Zn vacancy-rich ZnO (Zn1–xO) nanoparticles were used as cocatalyst to construct a Zn1–xO/TiO2 nanostructure via the self-assembly process. The existence of Zn vacancies triggered the intimate contact between Zn1–xO and TiO2 through the Ti–O–Zn bonds. Theoretical and experimental results show that the hybridization of Zn1–xO and TiO2 resulted in the formation of a p–n heterojunction, leading to the enhanced separation efficiency of photoinduced electron–hole pairs. As a result, the optimized Zn1–xO/TiO2 nanocomposite exhibited nearly 100% selectivity of CO2-to-CO photoreduction, and the productivity was 4.2 times higher than that of pristine TiO2. In situ Fourier transform infrared spectra along with theoretical calculations were also conducted to investigate the mechanism of the selective photocatalytic CO2-to-CO process. It is concluded that the charge depletion on the TiO2 surface induced by the charge transfer from Zn1–xO to TiO2 can lower the energy barrier of CO* desorption and convert the endothermic CO* desorption process into an exothermic reaction step, thus triggering selective CO production. This work provides a new perspective on the rational fabrication of nanostructures for efficient and selective photocatalytic CO2 conversion through intermediate modulation.