Doping engineering in S-scheme composite for Regulating the selectivity of photocatalytic CO₂ reduction

Regulating product selectivity in photocatalytic CO₂ reduction to enhance the yield of valuable hydrocarbons remains a formidable challenge because of the diversity of reduction products and the competitive reduction of H₂O. Herein, ultrathin Bi₂O₃/ Co-doped SrBi₄Ti₄O₁₅ S-scheme photocatalysts (Co-BS) were synthesized using a hydrothermal method. The Bi₂O₃/Co-doped SrBi₄Ti₄O₁₅ photocatalyst exhibited significantly higher selectivity for CH₄ (62.3 μmolg^-1) and CH₃OH (54.1 μmolg^-1) in CO₂ reduction compared with pure SrBi₄Ti₄O₁₅ (27.2 and 0.8 μmolg^-1) and the Bi₂O₃/SrBi₄Ti₄O₁₅ S-scheme without Co (30.2 and 0 μmolg^-1). The experimental results demonstrated that the inclusion of Co into SrBi₄Ti₄O₁₅ expanded the range of light absorption and generated an internal electric field between Co-doped SrBi₄Ti₄O₁₅ and Bi₂O₃. Density functional theory calculations and other experimental findings confirmed the formation of a new doping energy level in the Bi₂O₃/SrBi₄Ti₄O₁₅ S-scheme heterojunction after Co doping. The valence band electrons of Bi₂O₃/SrBi₄Ti₄O₁₅ transitioned to the Co-doped level because of the interconversion between Co³⁺ and Co²⁺ under the action of the internal electric field. Furthermore, the corresponding characterizations revealed that the adsorption and electron transfer rates of the surface active sites were accelerated after Co doping, enhancing electron involvement in the photocatalytic reaction process. This study presented a metal-doped S-scheme heterojunction approach for CO₂ reduction to produce high-value products, enhancing the conversion of solar energy into energy resources.