An effective and sustainable dye removal via sunlight-based photocatalysis and adsorption using eco-friendly and low-cost ZnS nanoparticles: Experiments, modelling, and mechanism

Abstract

Abstract Novel sulfur zinc nanoparticles functionalized with thioglycolic acid were synthetized via hydrothermal route and tested in a solar radiation-based dye photodegradation process. These nanoparticles were characterized, and the findings revealed that thioglycolic acid was a strong capping ligand for the generation of sulfur zinc nanoparticles with a specific surface area of 36.82 m2/g and 7.15 nm average nanocrystal size. The cubic and wurtzite phases of these nanoparticles were confirmed via X-ray diffraction. The quantum confinement effect caused a larger energy band gap and a blue shift in the absorbance band of these nanoparticles in contrast to the bulk sulfur zinc. The improved adsorption effectiveness of these nanoparticles was proved to remove methylene blue from aqueous solutions. They can remove 30.92 mg/g of tested dye molecule. To understand the synergy between adsorption and photocatalysis, these nanoparticles were used to analyze the dye adsorption prior to the photodegradation via the experimental measurement of isotherms and kinetics. The rationalization of the dye adsorption on these nanoparticles was performed with calculated statistical physics parameters including the estimation of dye – nanoparticles adsorption energy. Dye molecules and nanoparticles surface exhibited physical interactions with adsorption energies of 25.92–23.31 kJ/mol. The sunlight-based photocatalytic activity of these nanoparticles demonstrated 91.1% dye degradation efficiency in 180 min. Overall, the photocatalytic efficiency remained almost unchanged after five consecutive degradation cycles with a methylene blue degradation of 88 ± 3%. These results indicate that these sustainable nanoparticles can be applied in the cleaning of industrial and urban fluids polluted by hazardous organic compounds like dye molecules.