Constructing visible-light-driven heterojunctions NiS/ZnO photocatalyst for H2 evolution by glycerol photoreforming

Abstract

The incorporation of NiS as a cocatalysts can effectively boost the separation of photocharge carriers in NiS/ZnO photocatalyst for promoting the H₂ evolution yield. Herein, mesoporous ZnO nanoparticles (NPs), with an average particle size of ∼ 10 nm, were hydrothermally synthesized in the presence of tetrapropylammonium hydroxide (TPAOH). NiS NPs (10 nm) as a cocatalyst are uniformly distributed on the mesoporous ZnO NPs. The photocatalytic activity of xNiS/ZnO (x = 3, 6, 9, and 12 wt%), as a photocatalyst, are evaluated for H₂ evolution through photoreforming of glycerol under visible light illumination of λ ≥ 420 nm. A small amount of the platinum (0.5 %, w/w) was photodeposited onto NiS/ZnO nanocomposites under illumination during the photocatalytic process. The 9 % NiS/ZnO photocatalyst showed the maximum H₂ evolution rate of ∼3078.3μmol g⁻¹h⁻¹, which was improved by 108 folds over sole ZnO NPs (28.42μmol g⁻¹h⁻¹). The NiS/ZnO nanocomposites offered sufficient stable H₂ evolution rate for five cycles within 45 h. The enhancement of the photocatalytic activity of NiS/ZnO nanocomposites was verified by photoluminescence, which was confirmed by the photocurrent-time results. The enhanced H₂ evolution from glycerol photoreforming over NiS/ZnO nanocomposites was ascribed to their high surface area, high crystallinity and narrowed bandgap energy, formation of Schottky barriers, high light harvesting, and the accelerated separation of the photocharge carriers. This work highlights the novel design of low-cost photocatalysts for realizing considerable H₂ evolution yield under visible illumination.