Self-Assembled Zn_1–xO/TiO₂ Nanocomposite as a Novel p–n Heterojunction for Selective CO₂-to-CO Photoreduction

Selective CO 2 photoreduction to valuable chemicals is promising for a carbon-neutral future and still remains a challenge. Herein, Zn vacancy-rich ZnO (Zn 1– x O) nanoparticles were used as cocatalyst to construct a Zn 1– x O/TiO 2 nanostructure via the self-assembly process. The existence of Zn vacancies triggered the intimate contact between Zn 1– x O and TiO 2 through the Ti–O–Zn bonds. Theoretical and experimental results show that the hybridization of Zn 1– x O and TiO 2 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 Zn 1– x O/TiO 2 nanocomposite exhibited nearly 100% selectivity of CO 2 -to-CO photoreduction, and the productivity was 4.2 times higher than that of pristine TiO 2 . In situ Fourier transform infrared spectra along with theoretical calculations were also conducted to investigate the mechanism of the selective photocatalytic CO 2 -to-CO process. It is concluded that the charge depletion on the TiO 2 surface induced by the charge transfer from Zn 1– x O to TiO 2 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 CO 2 conversion through intermediate modulation.