Loading density modulation of Zn0.5Cd0.5S nanoparticles on ZnS(en)0.5 nanosheets with effective hole transfer channels towards highly efficient hydrogen evolution

P-type semiconductor ZnS(en)0.5 (en = NH2CH2CH2NH2) hybridized with photocatalysts has been reported as an effective photocatalyst toward H2 production. However, photocatalytic efficiency is still limited by the low charge transfer and high charge recombination. In this work, ZnS(en)0.5 nanosheets with tunable loading densities of Zn0.5Cd0.5S nanoparticles were synthesized towards high photocatalytic H2 evolution. Sharp interfaces of hexagonal Zn0.5Cd0.5S nanoparticles with underneath orthorhombic ZnS(en)0.5 nanosheets, the strong electronic interaction with a large blue shift of S-Zn-N binding energy in the [S-Zn-(en)0.5] group have been found. From the multiple photoluminescence emissions of ZnS(en)0.5 and the Mott-Schottky curves of the composites, a type I band alignment with multiple midgaps is revealed for the Zn0.5Cd0.5S/ZnS(en)0.5 interface, where ZnS(en)0.5 provides an energy barrier for the photoexcited electrons of Zn0.5Cd0.5S and fast transfer channels for the holes from Zn0.5Cd0.5S to the redox via the midgaps. Together with the balance between light absorption and charge transfer property regulated by the loading density of Zn0.5Cd0.5S, an optimum H2 generation rate of 108.76 mmol/g/h and a solar to hydrogen efficiency of 2.15% have been realized. Such a study provides an effective strategy for enhancing the photocatalytic property of the "type I" heterostructures with fast transfer channels for photoexcited holes.