Influences of synthetic conditions on the photocatalytic performance of ZnS/graphene composites

A simple solid-state chemical method was used for fabricating ZnS/graphene composites. The prepared samples were measured by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption, X-ray photoemission spectroscopy (XPS), ultraviolet-visible (UV-vis) absorption spectra, XPS-valance band spectroscopy, transient photocurrent response (PC), and photoluminescence (PL) spectra. The study shows that ZnS nanoparticles were well distributed on the graphene nanosheet in the composites, and the specific surface area enlarged when introducing graphene. The performances of the synthesized ZnS/graphene composites were assessed by the photocatalytic degradating methyl orange (MO). We found that the composites displayed excellent photocatalytic activity, and achieved 93% degradation within 120 min of UV irradiation. The impacts of graphene, NaBH4, and metallic salt and sulfide species on MO degradation were also investigated. Mechanism exploration found the excellent photocatalytic activity was attributed to high large specific surface area, strong oxidizability of active species, and the slow recombination of photoinduced carriers with the introduction of graphene. The band gap energy for the composites was 2.46 eV, suggesting the higher light absorption capacity. Transient photocurrent responses and photoluminescence spectra revealed a more efficient separation of the photoinduced charges for the composites. XPS-valance band spectroscopy and trapping experiments both verified that center dot O-2(-) played significant role in the degradation process. (C) 2018 Elsevier B.V. All rights reserved.