Heavy metal removal from wastewater by SnS thin films deposited by the modified SILAR technique at ambient temperature

This study investigates the effectiveness of tin monosulfide (SnS) thin films in removing heavy metals from wastewater. The SnS thin films were deposited at room temperature using a modified version of the successive ionic layer adsorption and reaction (SILAR) method. The deposited samples were confirmed to be SnS through XRD, XPS, and EDAX analysis. The XRD analysis revealed that the SnS thin films are polycrystalline with an orthorhombic crystal structure. Variations in the number of SILAR cycles resulted in changes in film thickness, crystallinity, crystallite size, and morphology. The SnS thin films were utilized to remove heavy metals from wastewater. UV–visible spectroscopic examination and ICP-OES analysis demonstrated that SnS thin films effectively removed chromium (Cr(VI)) from contaminated water. Under irradiation from a xenon lamp, the SnS thin films eliminated nearly 99 % of Cr(VI) from a 100 ml solution (initial concentration - 25 mg/l, pH - 2.5) within 80 min. Additionally, the SnS thin films removed 97 % of Cr(VI) under ambient light conditions and 94 % in dark conditions. The removal of Cr(VI) by the SnS thin films was identified as an adsorption-reduction process, with XPS analysis of the spent sample confirming the formation of Cr(III). The SnS thin films exhibited high efficiency, easy recovery, and reusability for Cr(VI) removal. The study also investigated the impact of several factors on chromium removal efficiency, including initial pollutant concentration, solution pH and salinity, and speed of magnetic stirring. Furthermore, the selectivity of SnS thin films was demonstrated through their efficiency in removing cadmium and lead. The thin films removed 72 % of cadmium in dark conditions and 82 % under illumination within 40 min. The lead removal rates were 78 % in dark conditions and 99.8 % in illuminated conditions within 40 min. This study highlights the advantages of using thin films for water remediation compared to nanoparticles.