Bi selectively doped SrTiO_3-x nanosheets enhance photocatalytic CO₂ reduction under visible light

Converting CO₂ into chemical energy by using solar energy is an environmental strategy to achieve carbon neutrality. In this paper, two dimensionality (2D) SrTiO_3-x nanosheets with oxygen vacancies were synthesized successfully. Oxygen vacancies will generate defect levels in the band structure of SrTiO_3-x. So, SrTiO_3-x nanosheets have good photocatalytic CO₂ reduction performance under visible light. In order to further improve its photocatalytic efficiency, Bi was used to dope Sr site and Ti site in SrTiO_3-x nanosheets respectively. It is found that Sr site is the adsorption site of CO₂ molecules. When Bi replaced Sr, CO₂ adsorption on the surface of SrTiO_3-x nanosheets was weakened. When Bi replaced Ti, there has no effect on CO₂ adsorption. Due to the synergistic effect of Bi doping, oxygen vacancies, and Sr active site, the 1.0% Bi-doped Ti site in SrTiO_3-x (1.0% Bi-Ti-STO) had the best photocatalytic performance under visible light (λ ≥ 420 nm). CO and CH₄ yields were 5.58 umol/g/h and 0.36 umol/g/h. Photocatalytic CO₂ reduction path has always been the focus of exploration. The in-situ FTIR spectrum proved the step of photocatalytic CO₂ reduction and COO- and COOH are important intermediates in the photocatalytic CO₂ reaction.