Cu₂ZnSnS₄ (CZTS)-ZnO: A noble metal-free hybrid Z-scheme photocatalyst for enhanced solar-spectrum photocatalytic conversion of CO₂ to CH₄

Development of photocatalytic materials for achieving the aspects of cost-effectiveness, improved performance and high stability is a subject of enormous interest among the photocatalysis research society. With the aim of achieving above mentioned features, herein we report a noble metal free, solar-light active, efficient and highly stable hybrid Cu₂ZnSnS₄ (CZTS)-ZnO photocatalyst, synthesized by a simple two-step process. The morphological, crystalline, band alignment, optical and electronic properties of the prepared samples are intensively investigated. Photocatalytic performance is evaluated by measuring, under the simulated solar light, the ability of the photocatalyst to convert CO₂ into hydrocarbon fuels, primarily CH₄. Our optimum CZTS-ZnO photocatalyst sample exhibits a CH₄ yield of 138.90 ppm g^-1 h^-1, a factor of ≈ 31 times greater than the un-sensitized ZnO nanorods, and ≈ 22 times greater than the CZTS nanoparticles; with excellent stability yielding similar CH₄ production up to five test-cycles. The enhanced performance of the hybrid, noble metal-free photocatalyst can be attributed to improved light absorption and efficient separation of the photogenerated charge due to the Z-scheme heterojunction interface.