Hedgehog Zinc Oxide–Graphene Quantum Dot Heterostructures\nas Photocatalysts for Visible-Light-Driven Water Splitting

The development of\nefficient photocatalysts for sustainable hydrogen\nproduction via water splitting is vital for advancing renewable energy\ntechnologies. In this study, we present the synthesis and characterization\nof a novel visible-light-active photocatalyst comprising hedgehog-shaped\nzinc oxide (ZnO) nanostructures coupled with graphene quantum dots\n(GQDs). Optical properties assessed by UV–visible and photoluminescence\n(PL) spectroscopy revealed that the ZnO/GQDs heterostructure possessed\na reduced band gap (2.86 eV) compared with pristine ZnO (3.10 eV),\nresulting in improved light absorption and charge separation. Electrochemical\nanalyses indicated a significantly higher photocurrent response and\nlower charge transfer resistance for the ZnO/GQDs heterostructure\ncompared with the pristine ZnO nanostructure. Photocatalytic tests\ndemonstrated that the ZnO/GQDs heterostructure achieved over 3-fold\nhigher hydrogen (H<sub>2</sub>) production rates, with an apparent\nquantum yield (AQY) of 1.51% at 440 nm, and maintained stable activity\nover prolonged reaction periods. These results highlight the enhanced\nphotocatalytic efficiency and stability of the ZnO/GQDs heterostructure,\nunderscoring its potential as a high-performance photocatalyst for\nsustainable hydrogen generation. The synergistic effects between ZnO\nnanostructures and GQDs offer valuable insights into the design of\nadvanced photocatalytic materials for renewable energy applications.