Metal-free phosphorus-doped ZnIn₂S₄ nanosheets for enhanced photocatalytic CO₂ reduction

ZnIn₂S₄ (ZIS) has shown great potential in photocatalytic solar-energy conversion. However, it is still suffering from severe charge recombination and poor surface area. Nonmetal heteroatom doping is considered as an effective strategy for improving its photocatalytic performance. Herein, phosphorus-doped ZIS (P-ZIS) nanosheets were prepared by a simple hydrothermal treatment of ZIS using NaH₂PO₄ as a precursor. The effect of P doping on the crystal structure, band structure, and the photocatalytic CO₂ reduction activity of ZIS under visible light were investigated. It was found that P doping in the lattice of ZIS plays a key role in tuning its electronic properties. The ratio of ZIS to NaH₂PO₄ influences the photocatalytic performance of P-ZIS, and the optimum ratio is 1:15. Optimized P-ZIS exhibits a remarkable visible-light photocatalytic CO production rate of 18.8 μmol/30 min, 2.5-folds higher than that of the pure ZIS. The ultrathin nanosheets feature and an upward shift of CB edge result in the enhancement of CO₂ photoreduction efficiency of P-ZIS. This work demonstrates a simple route for P doping in ZIS and provides guidance for the controllable design and synthesis of high-efficient photocatalysts by nonmetal heteroatom doping.