Glycerol is a byproduct of biodiesel manufacturing. The room temperature photocatalytic hydrogen generation from glycerol by the ZnO-ZnS/graphene photocatalyst was investigated. The in-situ C K-edge near edge X-ray absorption fine structure (NEXAFS) spectra were measured with/without light illumination to study the electronic properties of photocatalysts at atomic and molecular level. A mechanism of water splitting and glycerol oxidation/reforming reactions over the photocatalyst under light irradiation is proposed. Effects of graphene content in photocatalysts and glycerol concentration in solution on the photocatalytic activity were examined. The results of enhanced photocurrents, fluorescence quenching, NEXAFS spectra, and decreased arc radius of electrochemical impedance spectra of ZnO-ZnS/graphene photocatalysts revealed the fast transfer of photoexcited electrons from ZnO-ZnS nanoparticles to graphene. There was an optimal graphene content and a glycerol concentration for the maximum photocatalytic H-2 production rate (1070 lmol h(-1) g(-1)). Incorporation of graphene can enhance the separation of photogenerated charge through the ZnO-ZnS/graphene interfaces and improve the photocatalytic H2 production rate of the photocatalysts. The composite photocatalysts exhibited improved performance because of efficient charge separation and enhanced light absorption. (C) 2018 Elsevier B.V. All rights reserved.