Fabrication of hierarchical ZnO/CdS heterostructured nanocomposites for enhanced hydrogen evolution from solar water splitting

ZnO/CdS heterostructured nanocomposites were fabricated with enhanced light harvesting capability and photostability using sequential sonochemical and hydrothermal methods from ZnO rods and particles. Interestingly, in the composite made up of CdS sensitized ZnO rods, both ZnO and CdS exist in the hexagonal wurtzite form with different morphologies. On the other hand, in the composite made up of CdS sensitized ZnO particles, ZnO exists in the hexagonal wurtzite form, whereas CdS in the cubic form but with a similar morphology. The synthesized photocatalysts under simulated solar irradiation exhibited hydrogen evolution rates of 870 and 1007 μmol h−1 g−1 for the ZnO rod/CdS and ZnO nanoparticle/CdS composites, respectively, compared to the native ZnO (40 μmol h−1 g−1 for rods and 154 μmol h−1 g−1 for particles) and CdS (208 μmol h−1 g−1) structures. The apparent quantum yield of CdS was only 1.2%, whereas the composites exhibited much higher quantum yields of 4.9% and 5.7%. Our results confirmed that the morphology of the host matrix ZnO played a crucial role in forming ZnO/CdS heterostructures with improved interface for the direct Z-scheme mechanism with enhanced hydrogen evolution efficiency.