Nano carbon sphere modified CoAl2O4–CdS Z-scheme heterojunctions: broad-spectrum absorption enhanced photocatalytic hydrogen evolution

The rapid recombination of carriers and the low efficiency of solar energy utilization remain major challenges in the field of hydrogen evolution. This study utilised coal tar pitch as a carbon source to synthesise nanocarbon spheres (CS), which were then employed to modify CoAl2O4 nanoblossoms (CAO) and hexagonal CdS, thereby constructing a highly active composite photocatalyst. Activity testing indicates that under visible light irradiation, the photocatalytic hydrogen evolution rate of the 20% CAO–CdS–CS composite material reached a maximum of 43.1 mmol g−1 h−1 within 5 h. Furthermore, its apparent quantum yield (AQY) at 475 nm was 2.5%. The successful construction of this composite material not only significantly enhanced hydrogen evolution performance but also effectively broadened the catalyst's photoresponsive range into the near-infrared region. Characterization and band structure analysis reveal that CAO–CdS forms a Z-scheme heterojunction. CS, acting as a co-catalyst, not only provides abundant hydrogen evolution active sites for the reaction system but also accelerates charge transfer, playing a pivotal role in the photocatalytic process. This study provides valuable insights into the application of coal-based nanocarbon materials in the field of photocatalytic hydrogen evolution.