Tuning Oxygen Vacancies by Construction of a SiO₂@TiO₂ Core−Shell Composite Structure for Boosting Photocatalytic CO₂ Reduction Towards CH₄

Abstract

Controlled photocatalytic conversion of CO₂ into premium fuel such as methane (CH₄) offers a sustainable pathway towards a carbon energy cycle. However, the photocatalytic efficiency and selectivity are still unsatisfactory due to the limited availability of active sites on the current photocatalysts. To resolve this issue, the design of oxygen vacancies (OVs) in metal–oxide semiconductors is an effective option. Herein, in situ deposition of TiO₂ onto SiO₂ nanospheres to construct a SiO₂@TiO₂ core–shell structure was performed to modulate the oxygen vacancy concentrations. Meanwhile, charge redistribution led to the formation of abundant OV-regulated Ti–Ti (Ti–OV–Ti) dual sites. It is revealed that Ti–OV–Ti dual sites served as the key active site for capturing the photogenerated electrons during light-driven CO₂ reduction reaction (CO₂RR). Such electron-rich active sites enabled efficient CO₂ adsorption and activation, thus lowering the energy barrier associated with the rate-determining step. More importantly, the formation of a highly stable *CHO intermediate at Ti–OV–Ti dual sites energetically favored the reaction pathway towards the production of CH₄ rather than CO, thereby facilitating the selective product of CH₄. As a result, SiO₂@TiO₂-50 with an optimized oxygen vacancy concentration of 9.0% showed a remarkable selectivity (90.32%) for CH₄ production with a rate of 13.21 μmol g⁻¹ h⁻¹, which is 17.38-fold higher than that of pristine TiO₂. This study provides a new avenue for engineering superior photocatalysts through a rational methodology towards selective reduction of CO₂.

Keywords

oxygen vacancy / photocatalytic CO₂ methanation / SiO₂@TiO₂ core–shell composite structure / Ti–OV–Ti dual sites

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