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

The development of efficient photocatalysts for sustainable hydrogen production via water splitting is vital for advancing renewable energy technologies. In this study, we present the synthesis and characterization of a novel visible-light-active photocatalyst comprising hedgehog-shaped zinc oxide (ZnO) nanostructures coupled with graphene quantum dots (GQDs). Optical properties assessed by UV-visible and photoluminescence (PL) spectroscopy revealed that the ZnO/GQDs heterostructure possessed a reduced band gap (2.86 eV) compared with pristine ZnO (3.10 eV), resulting in improved light absorption and charge separation. Electrochemical analyses indicated a significantly higher photocurrent response and lower charge transfer resistance for the ZnO/GQDs heterostructure compared with the pristine ZnO nanostructure. Photocatalytic tests demonstrated that the ZnO/GQDs heterostructure achieved over 3-fold higher hydrogen (H₂) production rates, with an apparent quantum yield (AQY) of 1.51% at 440 nm, and maintained stable activity over prolonged reaction periods. These results highlight the enhanced photocatalytic efficiency and stability of the ZnO/GQDs heterostructure, underscoring its potential as a high-performance photocatalyst for sustainable hydrogen generation. The synergistic effects between ZnO nanostructures and GQDs offer valuable insights into the design of advanced photocatalytic materials for renewable energy applications.