Solar hydrogen generation through overall water splitting on gallium-zinc oxynitride visible-light activated photocatalyst

In this study, novel approaches for the development of solar-responsive photocatalysts for water splitting are investigated, with a focus on the gallium-zinc oxynitride solid solution (GaN:ZnO). A facile synthesis technique was developed for the fabrication of nanoporous GaN:ZnO photocatalyst. The synthesis time was reduced substantially to 12 min (from original 10+ h) as the result of effective solid–solid and gas–solid reactant interactions at the nanoscale. The synthesized photocatalyst samples were characterized for their optical, structural, and photochemical properties. Despite the short synthesis time, the prepared nanoporous GaN:ZnO photocatalyst maintained the overall visible-light water splitting activities at reasonable rates, reaching to the maximum apparent quantum efficiency of 2.71% at 420–440 nm. Decoration of the photocatalyst surface with the optimal amount of various hydrogen and oxygen evolution co-catalyst materials through photo-deposition and impregnation was investigated. Our experimental and characterization data suggest a mechanism for minimizing the effect of the undesired charge recombination and reverse reaction through the utilization of structural nanopores as the active water splitting regions. To reduce the recombination of photo-excited charges, the hybridization of GaN:ZnO photocatalyst on highly conductive graphene support was studied. Effective electrochemical interaction between composite components was confirmed through material characterization, photo-induced conversion of graphene oxide to reduced graphene oxide (rGO), and visual observation of co-catalyst nanoparticles on the surface of the conductive nanosheets. The GaN:ZnO-rGO composite photocatalyst exhibited ~70% improvement in photocatalytic hydrogen evolution. Finally, a number of approaches for the synthesis of one-dimensional (1-D) GaN:ZnO photocatalysts were studied. A novel direct fabrication route for 1-D GaN:ZnO through gold-catalyzed atmospheric pressure chemical vapour deposition was proposed. The material characterization data indicated that the proposed method is capable of preparing 1-D GaN:ZnO nanostructures with a wide range of morphologies, including nanofibers and nanowires, via vapour–liquid–solid epitaxy. In addition, via the proposed method, the dimensions of the obtained nanomaterials can be tailored. The synthesized GaN:ZnO nanowires demonstrated promising sacrificial hydrogen evolution compared to the powder and nanofiber photocatalysts. The work presented in this research provides an in-depth understanding of the nanoscale fabrication and optimization of GaN:ZnO photocatalysts for visible-light hydrogen generation.Chemical and Biological Engineering, Department ofGraduat