Regular study of lanthanide oxides for boosting photocatalytic hydrogen production on ZnIn2S4 photocatalysts

Lanthanide oxides have potential advantages for photocatalytic hydrogen production. To systematically investigate the photocatalytic performance of lanthanide oxides on metal sulfides, a series of LnxOy/ZnIn2S4 (LnxOy/ZIS) were synthesized by hydrothermal method. Comprehensive characterization demonstrated that LnxOy synergistically improved the performance of ZnIn2S4 by extending light absorption, reducing contact interface resistance and enhancing carrier separation. The photocatalytic hydrogen evolution (PHE) rates of the LnxOy/ZIS photocatalysts were improved, which were 1.6 to 4.2 times higher than those of pure ZnIn2S4 (198.0 μmol g-1 h-1). The PHE rates of LnxOy/ZIS decreased with increasing lanthanide atomic number, and when the lanthanides contained variable valence ions, the PHE rates of LnxOy/ZIS were superior to those of neighbouring lanthanides. The heterojunction formed by LnxOy and ZnIn2S4 effectively promoted carrier separation. Lanthanide ions with unoccupied 4 f orbital were more likely to accept electrons and served as a hydrogen adsorption site for further hydrogen reduction. Multivalent ions could also promote the migration of electrons and generate oxygen vacancies to inhibit the recombination of carriers. In conclusion, for ZnIn2S4, lanthanide oxides are promising candidates to improve the performance of PHE. This study provides guidance on the selection of appropriate lanthanide oxides for the construction of efficient sulphur-based heterojunction photocatalysts.