Selective photocatalytic CO₂ reduction to methane over CTAB-stabilized two-dimensional CsPbBr₃ nanosheets with gold...

Photocatalytic carbon dioxide (CO₂) reduction offers a sustainable route for converting solar energy into chemical fuels. However, achieving selective deep hydrogenation beyond CO remains challenging due to inefficient charge separation and rapid carrier recombination. In particular, selective conversion of CO₂ to methane (CH₄) requires sustained multi-electron transfer and stable reaction interfaces under continuous illumination. Herein, we report a cetyltrimethylammonium bromide (CTAB)-stabilized two-dimensional (2D) CsPbBr₃ nanosheet photocatalyst decorated with size-controlled gold (Au) cocatalysts for the selective photocatalytic reduction of CO₂ to CH₄. The introduction of CTAB enables uniform growth of 2D nanosheets and substantially improves the preservation of their quantum-confined optical characteristics during storage compared with the corresponding CTAB-free nanosheets. Photodeposited Au cocatalysts form a Schottky junction with CsPbBr₃, which promotes directional charge separation and suppresses charge recombination. By optimizing the Au loading, an optimal cocatalyst configuration is identified that maximizes charge-carrier lifetime without inducing excessive lattice distortion. As a result, the Au-decorated CsPbBr₃ nanosheets exhibit a pronounced enhancement in CH₄ selectivity, increasing from 31.16% for pristine CsPbBr₃ to 96.88% after Au cocatalyst deposition. This work clarifies the synergistic roles of dimensional engineering, ligand stabilization, and cocatalyst optimization in perovskite-based photocatalysts for enabling the selective deep hydrogenation of CO₂.