Sequential two-step hydrothermal growth of MoS₂/CdS core-shell heterojunctions for efficient visible light-driven photocatalytic H₂ evolution

The visible-light driven, Pt-free photocatalytic H₂ evolution (PHE) is promising for clean and sustainable H₂ production. The construction of the heterojunction structure with intimate contact and good light adsorption ability is important for realizing the high effective PHE. Here, the core-shell structured MoS₂/CdS hybrids were constructed through “sequential two-step hydrothermal growth” route for Pt-free PHE. In the synthesis, the hierarchical flower-like MoS₂ was firstly obtained through the reaction of ammonium molybdate and excessive thiourea. Subsequently, without need of centrifugation, the cadmium acetate (Cd source) was added into the cooled MoS₂ solution directly followed by a secondary hydrothermal reaction. In the process, the Cd²⁺ could react with partially S²⁻ in MoS₂ (substituted reaction) and with the excessive S²⁻ ions in solution to generate CdS, resulting in the formation of CdS shell contacted with MoS₂ core. The micro-structure of the composites (such as the thickness and morphology of CdS shell) could be tuned by changing the amount of Mo source and Cd source. In the composites, the CdS on the outside is convenient to absorb the solar light. The intimate contact of CdS and MoS₂ is beneficial to charge transfer. As a result, the MoS₂/CdS catalyst showed high catalytic activity for PHE under visible light irradiation (λ > 420 nm). The H₂ evolution rate could reach to 775 μmol h⁻¹ (20 mg catalyst), which is much higher than pure CdS (12 μmol h⁻¹) and Pt-CdS (64 μmol h⁻¹). The good activity should be related with CdS outside shell beneficial for light adsorption and intimate contact of CdS and MoS₂ for easy charge transfer. A series of experiments demonstrate that the formation of the heterojunction can effectively enhance the charge transfer ability and retard the recombination of electron-hole pairs, thus improving PHE activity and alleviating the photocorrosion of CdS component.