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

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 H-2 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 H-2 production was highest when the diameter of the ZnGa2O4 spheres reached 230 nm. The rate of H-2 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.