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Synergistic Integration of AuCu Co-Catalyst with Oxygen Vacancies on TiO2 for Efficient Photocatalytic Conversion of CO2 to CH4.

Photocatalytic reduction of CO2 toward eight-electron CH4 product with simultaneously high conversion efficiency and selectivity remains great challenging owing to the sluggish charge separation and transfer kinetics and lack of active sites for the adsorption and activation of reactants. Herein, a defective TiO2 nanosheet photocatalyst simultaneously equipped with AuCu alloy co-catalyst and oxygen vacancies (AuCu-TiO2-x NSs) was rationally designed and fabricated for the selective conversion of CO2 into CH4. The experimental results demonstrated that the AuCu alloy co-catalyst not only effectively promotes the separation of photogenerated electron-hole pairs but also acts as synergistic active sites for the reduction of CO2. The oxygen vacancies in TiO2 contribute to the separation of charge carriers and, more importantly, promote the oxidation of H2O, thus providing rich protons to promote the deep reduction of CO2 to CH4. Consequently, the optimal AuCu-TiO2-x nanosheets (NSs) photocatalyst achieves a CO2 reduction selectivity toward CH4 up to 90.55%, significantly higher than those of TiO2-x NSs (31.82%), Au-TiO2-x NSs (38.74%), and Cu-TiO2-x NSs (66.11%). Furthermore, the CH4 evolution rate over the AuCu-TiO2-x NSs reaches 22.47 μmol·g-1·h-1, which is nearly twice that of AuCu-TiO2 NSs (12.10 μmol·g-1·h-1). This research presents a unique insight into the design and synthesis of photocatalyst with oxygen vacancies and alloy metals as the co-catalyst for the highly selective deep reduction of CO2.