Engineering of 2D/2D CoAl-LDH/Bi2MoO6 S-scheme heterojunction nanoflake films for efficient CO2 photoreduction to CO with high selectivity

Photocatalytically converting CO₂ into renewable fuels or valuable carbon-containing compounds is an effective strategy to ease greenhouse effect and energy crisis. But practical application of powdered catalysts was limited due to their poor recovery. Herein, two-dimensional/two-dimensional (2D/2D) CoAl layered double hydroxides (CoAl-LDH) (CoAl-LDH)/Bi₂MoO₆ S-scheme heterojunction films were synthesized as efficient, visible light-active, and recyclable composite thin-film photocatalysts through two successive liquid phase reactions. The Bi₂MoO₆ nanoflake film was first prepared on fluorine-doped tin oxide (FTO) glass by a solvothermal method, and then the CoAl-LDH nanoflake film was grown on its surface by hydrothermal process. The resulting CoAl-LDH/Bi₂MoO₆ S-scheme heterojunction films offer superior body-plane and interfacial charge transfer capabilities, efficient collection and enrichment of CO₂ molecules, and increased visible light harvesting. There exist short charge transport distance and large interfacial contact area between CoAl-LDH and Bi₂MoO₆ films. As a result, the optimized CoAl-LDH/Bi₂MoO₆ S-scheme heterojunction film achieved a CO yield of 131.1 μmol h⁻¹ m⁻² with nearly 100 % selectivity, which was much higher than those of the control samples. This work provides a valuable approach to developing efficient heterostructure films for photocatalytic applications.