Improved visible-light photocatalytic H2 generation over CdS nanosheets decorated by NiS2 and metallic carbon black as dual earth-abundant cocatalysts

CdS nanosheets (NSs) photocatalysts modified with dual earth-abundant co-catalysts of metallic carbon black (CB) and NiS2 were synthesized by a two-step solvothermal/impregnation method. All the experiment results demonstrated that the co-loading of CB and NiS2 could significantly enhance the photocatalytic H-2-evolution activity of CdS NSs. The photocatalytic performance of the as-prepared CdS/CB/NiS2 samples was tested under visible light (lambda >= 420 nm) by using an aqueous solution containing 0.25 mol L-1 Na2S-Na2SO3 as the sacrifice agent. The CdS-0.5%CB-1.0%NiS2 composite photocatalysts exhibited the highest H-2-evolution rate of 166.7 mu mol h(-1), which was approximately 5.16 and 1.87 times higher than those of pure CdS NSs and CdS-1.0%NiS2, respectively. The possible mechanism for the enhanced H-2-evolution activity of CdS/CB/NiS2 composite photocatalysts was proposed. The results showed that the enhanced photocatalytic H-2-evolution activities could be ascribed to the co-loading of metallic CB and NiS2 as co-catalysts onto the surface of CdS NSs. The excellent synergetic effect between the CB and NiS2 could obviously improve visible light absorption, promote separation of photogenerated electron-hole pairs and boost the H-2-evolution kinetics, thus leading to an enhanced activity for H-2 evolution. More interestingly, the metallic CB could not only act as a cocatalyst for H-2 evolution, but also serve as a conductive electron bridge to promote the charge migration. This work not only demonstrates that loading CB as a co-catalyst is a promising strategy to further boost the photocatalytic activity of CdS/NiS2 composites, but also offers a new mechanistic insight into the construction of highly efficient and stable CdS NSs-based hybrid photocatalysts with dual earth-abundant co-catalysts for photocatalytic applications. (C) 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.