Vacancy pair induced surface chemistry reconstruction of Cs2AgBiBr6/Bi2WO6 heterojunction to enhance photocatalytic CO2 reduction

Cs2AgBiBr6/Bi-O vacancy pair Bi2WO6 (Cs2AgBiBr6/VBi-OBi2WO6) heterojunction was synthesised for photocatalytic CO2 reduction under visible light irradiation. The characterisation results show that the Bi-O vacancy pairs can reconstruct the surface electronic states of the heterojunction. The optimal 10%Cs2AgBiBr6/VBi-OBi2WO6 heterojunction exhibited a substantial CO yield of 48.5 μmol/g, approximately 22 times higher than that of Bi2WO6, exceeding the performance of most of the Bi-based photocatalysts reported to date. The enhanced activity of 10%Cs2AgBiBr6/VBi-OBi2WO6 was due to exposed Bi sites that facilitate the chemisorption and activation of CO2 and the lower reaction energy barrier for the protonation of CO2 to CO via the formation of COOH* intermediates with the cooperation of surface four-coordinated H2O molecules. Furthermore, charge migration from Cs2AgBiBr6 to VBi-OBi2WO6 and space-charge distribution in the heterojunction under visible light irradiation were demonstrated. This work reveals defective heterojunction catalysts that facilitate the transformation of reactive molecules in surface/interfacial reactions.