Synergy of Sulfur Vacancies and SnS₂/SnO₂ Heterojunction for Highly Efficient Photocatalysis

In this study, SnS₂ and SnS₂/SnO₂ composites rich in sulfur vacancies were successfully synthesized via a low-temperature solid-state reaction using Sn₂₁Cl₁₆(OH)₁₄O₆ and thiourea as precursors. Systematic characterization reveals that the thiourea content decisively influences the product’s phase composition: a lower thiourea content results in the formation of minor SnO₂ impurity phases and peak broadening in XRD patterns, whereas an appropriate increase in thiourea effectively suppresses SnO₂ formation, yielding pure SnS₂. The presence of abundant sulfur vacancies is confirmed by both XPS and Raman spectroscopy. The optimal sample exhibits a mesoporous structure with a high specific surface area (55.30 m²/g). Optical and photoelectrochemical analyses indicate that the sulfur vacancies effectively narrow the band gap and significantly enhance the separation efficiency of photogenerated charge carriers as well as interfacial electron transfer. In the photocatalytic degradation of methyl orange, all samples demonstrate good performance under both UV and visible light. Trapping experiments identify superoxide radicals as the dominant active species under both UV and visible light, with hydroxyl radicals also playing a critical role under UV irradiation. The enhanced photocatalytic performance is attributed to the synergistic effect between sulfur vacancies and the SnS₂/SnO₂ heterojunction.