Hollow ZnCdS dodecahedral cages for highly efficient visible-light-driven hydrogen generation

Abstract

Hydrogen production through water splitting under visible-light irradiation is considered as an ideal process to convert solar energy into chemical energy. In this work, we report the rational design of a new kind of visible-light photocatalyst, hollow ZnCdS rhombic dodecahedral cages, fabricated via simple sulfurization and cation-exchange using zeolitic-imidazolate-framework-8 (ZIF-8) as the single precursor. The hollow cages and mesoporous structures can endow Zn_1−xCd_xS solid solutions with significantly improved visible-light utilization and charge carrier separation and transfer. In addition, the BET surface areas of hollow ZnCdS cages were also significantly enhanced with the introduction of Cd as compared to those of ZnS cages, benefitting the provision of abundant exposed active sites and decrease of the charge transport distance. Moreover, suitable band matching and strong electron coupling in these solid solutions could be simultaneously achieved via ion-exchange, featuring the balance between the light absorption ability and the potential of the conduction band of the Zn_1−xCd_xS photocatalysts. Consequently, the hollow Zn_0.6Cd_0.4S cage material exhibited the highest hydrogen production rate of 5.68 mmol h⁻¹ g⁻¹ under cocatalyst-free and visible-light irradiation (λ > 420 nm) conditions. Furthermore, these hollow ZnCdS cages showed excellent long-term stability, maintaining high photocatalytic activity for hydrogen evolution over a number of cycles. We believe that this facile strategy for developing highly efficient ZnCdS photocatalysts from MOFs could be extended to the synthesis of other metal hollow cages for a variety of advanced applications.