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 (V S ) and the self-assembly of a p–n homojunction through prolonged aqueous washing of SnS 2 nanosheets. The experimental studies have validated increased hydrophilicity, layer thinning, V S generation, and extended photocarrier lifetime in washed SnS 2 nanosheets. Density functional theory has revealed the changes in the local electronic structure of SnS 2 in the presence of structural defects. An electrochemical impedance spectroscopy study has shown that V S actuates the self-assembly of a pseudo-p-type SnS layer over n-type SnS 2 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 SnS 2 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, V S 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 SnS 2 promotes the formation of V S and the self-assembly of a p – n homojunction in SnS 2 nanosheets with improved visible light photocatalytic performances.