Photocatalytic degradation of anionic Congo red dyes in wastewater using visible light-driven Fe-doped SnS2 nanoparticles synthesized under alkaline conditions

This study focuses on synthesizing and characterizing Fe-doped tin disulfide nanoparticles (NPs) via a hydrothermal method under alkaline conditions, followed by oven drying. The Fe-ion doping level ranged from 0 to 10 at% in the initial solution. Stannic chloride pentahydrate (SnCl 4 ·5 H 2 O), thioacetamide (C 2 H 5 NS), and ferric chloride (FeCl 3 ) served as chemical precursors for tin (Sn), sulfur (S), and iron (Fe), respectively. X-ray diffraction (XRD) confirmed the hexagonal crystal structure of undoped SnS 2 . Fe doping into SnS 2 alters the crystal matrix, resulting in the formation of secondary phases, specifically Sn 2 S 3 and Fe 2 SnS 4 , alongside the original hexagonal structure. Fourier-transform infrared (FT-IR) spectroscopy elucidated the functional groups associated with the Sn-S bond in the nanoparticles. Energy-dispersive X-ray spectroscopy (EDX) analysis revealed the elemental composition of Fe, Sn, and S with a high concentration of oxygen (O) in nanoparticles, suggesting an oxidized tin-iron sulfide structure. Field-emission scanning electron microscopy (FESEM) observations indicated a decrease in grain size with increasing Fe doping concentration. TEM images revealed the crystal planes of the hexagonal SnS 2 phase. Optical analysis confirmed an increased absorption coefficient and a reduced band gap from 2.7 eV to 2.1 eV upon incorporating Fe ions into the SnS 2 lattice. The 6 at% Fe-doped SnS 2 nanoparticles have demonstrated a maximum efficiency of 98% photocatalytic activity for the decolorization of Congo red after 120 min under visible light irradiation. The results indicate that alkaline treatment during synthesis is associated with distinct changes in Fe-doped SnS 2 growth, including altered morphology and the introduction of oxygen-rich defects that correlate with enhanced catalytic activity for wastewater treatment applications.