Preparation and enhanced photocatalytic hydrogen-evolution activity of ZnGa2O4/N-rGO heterostructures

Abstract

Semiconductor–graphene composites have been widely reported as photocatalysts for hydrogen generation. The structure of the semiconductor, intimate interfacial contact between the components, and high electrical conductivity of the catalyst support can affect the performance of semiconductor–graphene composite photocatalysts. We successfully synthesized size-controlled ZnGa₂O₄ nanospheres by adjusting the amount of surfactant trisodium citrate, and assembled size-controlled ZnGa₂O₄ nanospheres on the two-dimensional platform of an N-doped reduced graphene oxide (N-rGO) sheet through the conventional and efficient hydrothermal method, during which the intimate interfacial contact between ZnGa₂O₄ nanospheres and the N-rGO sheet are achieved. The obtained photocatalysts were characterized by X-ray powder diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet visible diffuse reflectance spectroscopy. The photocatalytic activity of the prepared samples for H₂ evolution was tested using sodium sulfite as the sacrificial agent. The effects of the crystallinity, morphology, and specific surface area of the ZnGa₂O₄ samples on the rate of photocatalytic hydrogen production were studied. Considering the above three factors, the rate of H₂ production was highest when the diameter of the ZnGa₂O₄ spheres reached 230 nm. The rate of H₂ evolution of the ZnGa₂O₄/rGO and ZnGa₂O₄/N-rGO composites dramatically improved when compared with that of pure ZnGa₂O₄. ZnGa₂O₄/N-rGO had higher photocatalytic activity than ZnGa₂O₄/rGO because the nitrogen atoms in N-rGO could anchor the metal nanoparticles to form an intimate interfacial contact between N-rGO and ZnGa₂O₄, and N-rGO had higher electrical conductivity than rGO, resulting in more effective charge separation and transfer in the ZnGa₂O₄/N-rGO composites. This study offers a promising method to design more efficient graphene-based nanocomposite photocatalysts for enhancing photocatalytic activity.