Engineering Dual-Defective 0D/2D V_N-CNQDs/V_Bi-Bi₄O₅Br₂ S-Scheme Heterostructure for Boosting CO₂ Photoreduction in Air

The direct photocatalytic reduction of CO₂ in air is the future trend of photocatalyst application. Herein, the 0D carbon nitride quantum dots with nitrogen vacancies (V_N-CNQDs) and 2D bismuth-deficient Bi₄O₅Br₂ (V_Bi-Bi₄O₅Br₂) are integrated by hydrothermal method. The S-scheme heterostructure of V_N-CNQDs/V_Bi-Bi₄O₅Br₂ composite promotes the separation rate of photogenerated carriers and enhances the redox capacity. The dual defects provide a large number of adsorption and catalytic sites that enhance the ability to capture and reduce CO₂. The synergistic effect of S-scheme heterostructure and defect engineering enables the efficiency of CO₂ photoreduction to CO with V_N-CNQDs/V_Bi-Bi₄O₅Br₂ to reach 16.89 µmol g^-1 h^-1 in air and 55.69 µmol g^-1 h^-1 in V_CO2: V_Air = 3:1 condition, which is 17 and 21 times higher than that of Bi₄O₅Br₂, respectively. The dual-defective V_N-CNQDs/V_Bi-Bi₄O₅Br₂ exhibits more lower energy barrier for forming ^*CO₂, ^*COOH, and ^*CO and is easier to release CO gas. And it exhibits excellent cycling stability for photocatalytic CO₂ reduction to CO. The photocatalytic reduction mechanism of CO₂ to CO in the V_N-CNQDs/V_Bi-Bi₄O₅Br₂ S-scheme heterostructure is further analyzed. This work provides new perspectives for the design of the photocatalysts with defect engineering for efficient photoconversion at low CO₂ concentrations.