Intentionally Introducing Oxygen Vacancies and Ti³⁺ Defects on the Surface of Bi₄Ti₃O₁₂ Nanosheets for Promoting the Photoreduction of CO₂ to CH₃OH

Using perovskite photocatalytic reduction of CO₂ and H₂O to produce hydrocarbon fuels offers an attractive method to solve the energy crisis and the greenhouse effect. Bi₄Ti₃O₁₂ (BTO) has received much attention in the field of photocatalysis due to its unique layered structure, but it still faces many challenges such as weak photoresponse and severe photogenerated carrier recombination. In this paper, Bi₄Ti₃O₁₂ nanosheets with different concentrations of surface oxygen vacancies (V_O) and Ti³⁺ defect were prepared by the molten salt method and NaBH₄ high-temperature reduction method (HBTO). Surface defects formed obvious carrier traps on the HBTO surface, reduced the recombination rate of photogenerated electrons and holes, and adjusted the band gap structure (from 3.09 to 2.62 eV), which improved the visible light utilization of HBTO. The decrease of photoinduced carrier recombination rate and the improvement of visible light response significantly enhanced the photocatalytic CO₂ reduction activity of HBTO under visible light. The CH₃OH yield with the optimized HBTO-4 (NaBH₄:Bi₄Ti₃O₁₂ = 1:5) was 4.90 μmol·g^-1·h^-1, which was about 3.5 times that of the original BTO. Meanwhile, the band gap structure, electronic density of states (DOS), and work function were calculated by the density functional theory (DFT). This study provided an effective strategy for designing and preparing perovskite photocatalysts rich in surface defects for the efficient conversion of solar energy.