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

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.