Sustainable Synthesis of Chitosan-SnO2 Nanocomposite for Enhanced Visible-Light Photocatalytic Degradation of Crystal Violet Dye

Abstract

A chitosan–tin oxide (CS–SnO₂) nanocomposite was prepared by a co-precipitation-based approach and investigated for the visible-light-assisted removal of Crystal Violet (CV) dye from aqueous solution. The incorporation of chitosan was intended to provide additional adsorption sites and improve the dispersion of SnO₂ nanoparticles. The prepared nanocomposite was characterized using FT-IR, XRD, FE-SEM, EDS, TGA, and UV-Vis spectroscopy. XRD analysis indicated the formation of crystalline SnO₂ with an estimated crystallite size of 4.34 nm, while FE-SEM analysis showed an average particle size of 69.4 ± 13.6 nm. The optical band gap was estimated to be 3.40 eV for the CS–SnO₂ nanocomposite compared with 3.65 eV for SnO₂. The removal of CV was investigated as a function of catalyst dosage, initial dye concentration, temperature, pH, and irradiation time. A considerable contribution from adsorption was observed during the initial dark-equilibrium period. Under the investigated conditions, the highest CV removal efficiency of 97.5% was obtained at an initial dye concentration of 5 mg/L, catalyst dosage of 60 mg, pH 12, and 180 min of visible-light irradiation. The photocatalytic process followed an apparent pseudo-first-order kinetic model, with a rate constant of 0.0033 min⁻¹ at 5 mg/L CV. The catalyst also exhibited measurable reusability over four successive cycles, although a decrease in removal efficiency was observed during repeated use. The results demonstrate the potential of the CS–SnO₂ nanocomposite for combined adsorption and visible-light-assisted dye removal.