Z-scheme CdS/Co9S8-RGO for photocatalytic hydrogen production

Abstract

Z-scheme photocatalytic systems, consisting of semiconductor/semiconductor heterostructures, mimic the natural photosynthesis and enhance the photocatalytic activity dramatically. Herein, we have for the first time synthesized unique all-solid-state Z-scheme ternary heterostructures by growing CdS nano-hemispheres radially assembled with nanorods as the core and CoS hexagonal nanoflakes as the shell on graphene sheets (CdS/Co₉S₈-RGO) through a facile one-pot hydrothermal method and subsequent annealing treatment. Furthermore, the growth mechanism is explored and analyzed by monitoring the intermediates in terms of structure and composition. The heterostructures form three paths available for charge carrier transfer and separation, wherein a redox-mediator-free Z-scheme constitutes CdS and Co₉S₈ and upgrades to an all-solid-state Z-scheme system by combination with RGO. Moreover, due to the excellent photon capture capability and electric conductivity, RGO also made great contribution to the effective separation and transfer of photogenerated carriers. Benefiting from efficient charge transfer and separation, CdS/Co₉S₈-RGO exhibits a H₂ evolution rate up to 4.82 mmol h⁻¹ g⁻¹ and remarkable activity stability even after 20 h of photocatalytic reaction. We believe that the design philosophy via the plain synthesis merges multiple structural interfaces and transfer paths in a system reported here, shedding an insight into the design of other photocatalysts.