Graphene-based ternary composite photocatalysts with genuine heterostructure constituents have attracted extensive attention in photocatalytic hydrogen evolution. Here we report a new graphene-based ternary composite consisting of CdS nanorods grown on hierarchical layered WS₂/graphene hybrid (WG) as a high-performance photocatalyst for hydrogen evolution under visible light irradiation. The optimal content of layered WG as a co-catalyst in the ternary CdS/WS₂/graphene composites was found to be 4.2 wt %, giving a visible light photocatalytic H₂-production rate of 1842 μmol h⁻¹ g⁻¹ with an apparent quantum efficiency of 21.2 % at 420 nm. This high photocatalytic H₂-production activity is due to the deposition of CdS nanorods on layered WS₂/graphene sheets, which can efficiently suppress charge recombination, improve interfacial charge transfer, and provide reduction active sites. The proposed mechanism for the enhanced photocatalytic activity of CdS nanorods modified with hierarchical layered WG was further confirmed by transient photocurrent response. This work shows that a noble-metal-free hierarchical layered WS₂/graphene nanosheets hybrid can be used as an effective co-catalyst for photocatalytic water splitting.

The incorporation of cocatalysts into semiconductors is proved to be an effective approach to improving the efficiency of the photocatalytic H₂ production. Noble metals such as Pt have been widely used as cocatalysts and can significantly improve the performance of photocatalytic H₂ production. However, owing to the high cost and low abundance, the use of Pt in practical applications is restricted. Herein, we report two well-known 2 D layered materials, MoS₂ and graphene, as highly active cocatalysts for H₂ production in CdS-based photocatalytic systems. The CdS–MoS₂ and CdS-MoS₂–graphene nanocomposites were prepared by using a facile two-step solvothermal method, and the morphologies of CdS and MoS₂ can be well controlled. The as-prepared binary CdS–MoS₂ nanocomposite exhibits the enhanced visible-light photocatalytic activity for H₂ production in lactic acid aqueous solution compared with a CdS–graphene nanocomposite and a conventional platinized CdS photocatalyst. Moreover, the ternary CdS–MoS₂–graphene nanocomposite achieves the highest visible-light photocatalytic H₂ production activity of 621.3 μmol h⁻¹ and the apparent quantum efficiency of 54.4 % at λ=420 nm. The enhanced photocatalytic activity of the CdS–MoS₂–graphene nanocomposite can be primarily attributed to the positive synergistic effect between graphene sheets and thin MoS₂ nanoplates. The graphene sheets can accelerate the efficient electron transfer from CdS nanorods to the active edge sites of MoS₂ nanoplates, and the nanosized MoS₂ can facilitate the photogenerated electrons participating in the photocatalytic H₂ production. The mechanisms for improving the photocatalytic performance of the MoS₂- and/or graphene-modified CdS nanocomposites were proposed by using the electrochemical analysis and photoluminescence measurement.

Cadmium sulfide and oxide hexagonal nanoplates were prepared by a facile ion-exchange strategy and crystal transformation process by using morphology-analogous cadmium oxyhydroxide as a precursor. The precursors of uniform Cd(OH)₂ hexagonal nanoplates was first synthesized by a simple ethylenediaminetetraacetic acid disodium salt assisted hydrothermal method. Then, through ion-exchange reactions of the as-prepared Cd(OH)₂ precursors with S²⁻ anions, cubic-phase CdS was formed immediately on the surface of Cd(OH)₂ nanoplates. The above intermediates could be further completely converted into CdS and CdO nanoplates without morphology changes through thermal treatment at 280 °C for 4 h under a sulfur atmosphere and under air, respectively. The photocatalytic activity of all samples was evaluated by the photocatalytic decolorization of an aqueous solution of methylene blue and photocatalytic hydrogen production under visible-light irradiation. The results show that the CdS hexagonal nanoplates exhibit high visible-light photocatalytic degradation properties and photocatalytic hydrogen production activity. The enhanced visible-light photocatalytic activity can be related to several factors, including a suitable band gap, phase structure, and morphology of the hexagonal nanoplates.