Enhancement effect of oxygen vacancy on photocatalytic CO2 reduction

Abstract

BiOBr was manufactured with various concentrations of oxygen vacancies via a solvothermal method using various alcohols as reducing agents. The reductive alcohol resulted in the fracture of the Bi–O bond, thus producing oxygen vacancies. The less polar solvent and extension of the hydroxyl carbon chain of the alcohol facilitate the generation of oxygen vacancies. Theoretical calculations and experiments demonstrated that oxygen vacancies could act as trapping sites to improve the separation efficiency of photogenerated carriers, accompanied by a decrease in the band gap energy to increase the absorption capacity for visible light. The enriched electrons in the defect band could generate more “hot electrons” that were transported to CO₂ molecules adsorbed onto unsaturated coordination centers, lowering the reaction barrier and promoting the activation of CO₂via the surface plasmon resonance effect. The resulting catalyst prepared with ethylene glycol exhibited a remarkable CO yield of 122.38 μmol g⁻¹ h⁻¹, which is nearly 7.2 times over that of the catalyst prepared with pure water. The enhanced photocatalytic performance corresponded to changes in oxygen vacancy concentration. Therefore, the change in the band gap structure arising from the variation in the content of oxygen vacancies is the cause of enhanced photocatalytic CO₂ reduction.