CQD-Modified SrTiO₃ for Enhanced Photocatalytic CO₂ Reduction to Methane

SrTiO₃ has attracted considerable attention owing to its favorable electronic structure and chemical stability among various semiconductor photocatalysts. However, its practical application is hindered by a wide bandgap and rapid recombination of photogenerated charge carriers. Herein, we report the fabrication of a SrTiO₃/carbon quantum dot (CQD) heterojunction via a two-step hydrothermal method for efficient CO₂-to-CH₄ photocatalysis, a strategy that circumvents the need for high-temperature treatment and noble metals. TEM images revealed well-defined lattice fringes and intimate interfacial contact between SrTiO₃ and CQDs, suggesting efficient charge transfer pathways. Optical measurements confirmed that CQD modification extends the visible-light absorption range of SrTiO₃ to 420 nm while significantly enhancing charge separation efficiency. The SrTiO₃/CQDs composite with 10 wt% CQD loading exhibited optimal activity, achieving a CH₄ evolution rate of 1.16 μmol·g^-1·h^-1-16.3 times higher than that of pristine SrTiO₃. Mechanistic investigations demonstrate that CQDs serve as efficient electron reservoirs, facilitating interfacial charge transfer and suppressing the recombination of photogenerated charge carriers. The catalyst maintained stable performance over four consecutive cycles, confirming its structural robustness and reusability. This work demonstrates that CQD modification effectively enhances the visible-light response and charge separation efficiency of SrTiO₃, offering a viable strategy for designing high-performance photocatalysts toward solar fuel production.