Lignin-supported Co/O co-doped SnS with heterovalent Sn2+/Sn4+ state and sulfur vacancy for efficient reduction of multicomponent pollutants.

Herein, a lignin-supported Co/O co-doped SnS oxysulfide catalyst (L-SnCoOS) with mixed-valence Sn2+/Sn4+ species and abundant sulfur vacancies was prepared via a hydrolysis strategy. Lignin, a negatively charged natural aromatic polymer with abundant functional groups, can effectively enhance nanoparticle dispersion, suppress aggregation, and provide abundant adsorption sites for pollutant enrichment. The incorporation of Co and O into SnS modulates its electronic structure, leading to the formation of mixed-valence Sn2+/Sn4+ species and abundant sulfur vacancies. The Sn2+/Sn4+ redox pair facilitates rapid electron transfer via a hopping mechanism (Sn2+ ↔ Sn4+), while sulfur vacancies serve as active sites for proton adsorption, thereby promoting pollutant reduction and accelerating the catalytic process. Among the prepared catalysts, L-SnCoOS-3, featuring abundant sulfur vacancies and an optimized Sn4+/(Sn2++ Sn4+) ratio (32.97%), exhibited the best performance, achieving complete reduction of 100 mL solutions containing 20 ppm of Cr(VI), rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and 4-nitrophenol (4-NP) within 5, 4, 4, 4, and 6 min, respectively. In addition, L-SnCoOS-3 exhibited excellent stability and durability, preserving over 94% of its performance after 6 consecutive cycles. It also maintained high catalytic activity in mixed-pollutant systems over a wide pH range. These results demonstrate that L-SnCoOS-3 represents a promising and sustainable strategy for efficient treatment of actual wastewater.