Synergistic Photothermal and Photocatalytic Reduction of Carbon Dioxide to Methane via the Integration of Topological Bismuth Selenide and Zinc Indium Sulfide Photocatalysts

Photothermal catalysis is a technique that employs a hybrid photocatalyst to absorb photons and convert them into thermal energy. Light is the energy source in this process, generating electron-hole pairs from the hybrid catalyst. The intense non-radiative relaxation produces heat, increasing the reaction temperature and lowering the activation energy, thereby enhancing the catalytic reaction. This energy conversion pathway improves catalytic efficiency without requiring an additional heat source. Consequently, natural solar-driven synergistic photothermal catalysis for CO₂ reduction is promising for sustainable and efficient CO₂ conversion. In this study, a series of Bi₂Se₃/ZnIn₂S₄ photocatalysts were prepared using the solvothermal method. ZnIn₂S₄, with an appropriate energy level, acts as the primary catalyst to drive the redox reaction in CO₂ photoreduction. Bi₂Se₃, possessing a narrow bandgap (0.3-1.2 eV), exhibits excellent light absorption from ultraviolet to near-infrared. Incorporating Bi₂Se₃ induces the "thermal island" effect in the composite, resulting in a notable increase in bulk temperature under light irradiation. After 15 minutes of halogen lamp irradiation, the temperature of the Bi₂Se₃/ZnIn₂S₄ photocatalyst rises from 27.9°C to 49.1°C, significantly higher than that of bare ZnIn₂S₄ (36.8°C). This temperature increase facilitates the acceleration of the photocatalytic reaction. As expected, 0.10 wt% Bi₂Se₃/ZnIn₂S₄ exhibits the highest activity under simulated sunlight. The production rates of CO₂ to CO and CH₄, are 0.19 and 3.64 μmol/g/h, respectively. The total electron consumption rate of 29.51 μmol/g/h is 134.1 times that of ZnIn₂S₄. The high CH₄ selectivity of up to 95.1% is achieved. Temperature-dependent photoluminescence spectra reveal that Bi₂Se₃/ZnIn₂S₄ photocatalyst has a relatively low exciton binding energy (E_b = 373.7 meV) compared to ZnIn₂S₄ (E_b = 546.6 meV). The thermal effect effectively dissociates excitons into free carriers, enhancing charge transfer and improving photocatalytic activity. Furthermore, we employ photo-assisted Kelvin Probe Force Microscopy (Photo-assisted KPFM) under various wavelength LED light sources, including UV at 365 nm, blue at 470 nm, green at 530 nm, and red at 656 nm to measure the light-induced contact potential difference (CPD) and evaluate the photoresponse. Compared to ZnIn₂S₄, the Bi₂Se₃/ZnIn₂S₄ photocatalyst exhibits a significant potential change due to its broad absorption properties. This further indicates that introducing Bi₂Se₃, with its intrinsic topological surface state, enhances the level of non-radiative relaxation, thereby facilitating the photothermal effect. In summary, this work highlights that the Bi₂Se₃/ZnIn₂S₄ composite material exhibits excellent photothermal effects and high selectivity for photocatalytic CO₂ reduction to CH₄, providing new insights into photothermal conversion.