Self-Assembled p–n Homojunction in SnS₂ Nanosheets for Enhanced Visible Light-Driven Photocatalysis

Defect engineering and hetero-interfacial bending are standard approaches for enhancing carrier separation and increasing visible light absorption in a semiconductor photocatalyst. Here, we demonstrate the evolution of sulfur vacancies (VS) and the self-assembly of a p–n homojunction through prolonged aqueous washing of SnS2 nanosheets. The experimental studies have validated increased hydrophilicity, layer thinning, VS generation, and extended photocarrier lifetime in washed SnS2 nanosheets. Density functional theory has revealed the changes in the local electronic structure of SnS2 in the presence of structural defects. An electrochemical impedance spectroscopy study has shown that VS actuates the self-assembly of a pseudo-p-type SnS layer over n-type SnS2 to generate the p–n homojunction. The p-type carrier densities are increased twice as the number of washings is increased from 3 to 10 times. The photocatalytic efficacy of the SnS2 homojunction is evaluated in the study of the degradation of several water contaminants under white light and monochromatic excitations. The proposed mechanism shows that the built-in electric field at the p–n junction promotes the separation of the photogenerated electrons and holes. Meanwhile, VS traps the electrons and transfers them to the catalytically reactive centers to participate in photocatalysis. Our findings demonstrate that a simple approach that involves prolonged aqueous washing of as-produced SnS2 promotes the formation of VS and the self-assembly of a p–n homojunction in SnS2 nanosheets with improved visible light photocatalytic performances.