Enhanced photocatalytic degradation of rhodamine (RhB) and erichrome black (EBT) by nanoparticles of SnS and SnS2 prepared by the sol–gel method

The increasing presence of dyes in water bodies poses a significant ecological risk, highlighting the need to develop efficient photocatalytic materials for their removal. In this study, tin sulfide-based nanoparticles (SnS and SnS₂) were synthesized using a conventional sol–gel method, with ethylene glycol as the solvent and two different sulfur sources: thiourea (SC(NH₂)₂) and sodium sulfide (Na₂S). We investigate the role of these precursors in determining structural, surface morphology, and optical characteristics of the obtained compounds. X-ray diffraction analysis showed that using SC(NH₂)₂ led to the formation of pure SnS₂, while Na₂S favored the formation of SnS, with crystallite sizes ranging from 16 to 19 nm. Scanning electron microscopy revealed that SnS₂ formed spherical nanoparticles, whereas SnS exhibited a more layered morphology. UV–Visible absorption spectroscopy indicated direct optical band gap energies of 1.64 eV for SnS and 1.9 eV for SnS₂, values within the optimal range for visible light-driven photocatalysis. The performance of the synthesized tin sulfides in photocatalysis was assessed by monitoring the breakdown of rhodamine B (RhB) and eriochrome black T (EBT) under both UV light and natural sunlight, SnS₂ exhibited an 81% degradation efficiency for RhB, with a corresponding rate constant of 0.014 min⁻¹, and an 85% efficiency for EBT, with k = 0.017 min⁻¹. In comparison, SnS showed slightly lower efficiency for RhB (74%) but higher efficiency for EBT (90%), with rate constants of 0.017 min⁻¹ and 0.020 min⁻¹, respectively. Both materials demonstrated enhanced photocatalytic activity under sunlight. SnS₂ achieved 90% degradation of RhB (k = 0.019 min⁻¹) and 91% of EBT (k = 0.020 min⁻¹), while SnS reached 81% degradation of RhB (k = 0.013 min⁻¹) and 93% of EBT (k = 0.021 min⁻¹). These results indicate that SnS₂ exhibits more consistent performance under both light sources, particularly for RhB, whereas SnS demonstrates higher degradation efficiency for EBT under solar radiation.