Synergistic Effect of S-Scheme Charge Transfer and Photothermal Conversion in Cs ₃ Bi ₂ Br ₉ /Bi ₂ Se ₃ Heterojunction for Boosted CO ₂ Photoreduction

The escalating anthropogenic CO 2 emissions have triggered severe environmental crises, making the development of efficient photocatalytic CO 2 reduction technologies crucial for carbon neutrality. Herein, an S-scheme heterojunction photocatalyst was successfully constructed by anchoring Cs 3 Bi 2 Br 9 perovskite quantum dots (CBB PQDs) onto Bi 2 Se 3 nanosheets via electrostatic assembly. The S-scheme charge transfer mechanism, verified by Mott–Schottky analysis, ultraviolet photoelectron spectroscopy (UPS), in situ X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) simulations, efficiently suppressed electron-hole recombination while retaining robust redox potentials of photogenerated carriers. Additionally, Bi 2 Se 3 enabled the heterojunction to reach a surface temperature of 131.2 °C within 6 min under ultraviolet-visible-near-infrared (UV-Vis-NIR) irradiation, concomitantly lowering the activation energy barrier for CO 2 reduction. The synergistic effect of S-scheme charge transfer and photothermal conversion in the CBB/Bi 2 Se 3 heterojunction led to boosted CO 2 photoreduction: photocatalytic tests showed that the optimized 50% CBB/Bi 2 Se 3 heterojunction achieved a CO yield rate of 134.93 μmol g –1 h –1 . Furthermore, the reaction pathway was revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This work provides a rational design strategy for perovskite-based photothermal catalysts, highlighting their potential in solar-driven CO 2 conversion to value-added chemicals.