Synthesis of a Hexagonal Phase ZnS Photocatalyst for High CO Selectivity in CO₂ Reduction Reactions

ZnS materials exhibit very negative potential of the conduction band, which is promising in photocatalytic reduction reactions. Unfortunately, previously reported ZnS materials for photocatalysis are mainly in the cubic phase, which produce high activity for H2 evolutions and low activity toward CO2 reductions. Herein, a hexagonal phase ZnS photocatalyst is fabricated for highly efficient CO2 reduction reactions. The hexagonal ZnS nanoplates with the pure phase and well crystallization are synthesized via three-step solvothermal methods. In photocatalytic CO2 reduction reactions under an aqueous solution environment, the hexagonal ZnS produces a CO selectivity of 21%, which is distinctly higher than that of 0.2% for commonly used cubic ZnS. The energy band study suggests that hexagonal ZnS possesses a slightly more negative conduction band and wider bandgap than cubic ZnS. Theoretical calculations reveal that the hexagonal ZnS possesses increased electron density around Zn atoms as that of cubic ZnS. Furthermore, hexagonal ZnS exhibits relatively reduced absorption energy of CO2 reduction intermediates and increased absorption energy of H* as cubic ZnS, which result in better selectivity toward CO2 reduction reactions. This study offers deep insights into the synthesis and electronic structure of hexagonal ZnS for CO2 reduction reactions, which inspire the design of highly active photocatalysts for artificial photosynthesis.