Photocatalytic decomposition of methylene blue (BM) solution by Cu-doped ZnS nanoparticles in the presence of UV light has been studied. The effect of the molar ratio of Cu ions affecting the rate of degradation reaction has been investigated. Photocatalytic reactivity of ZnS:Cu nanoparticles could be tailored by the proper amount of Cu ions. The maximum decolorizing efficiency (85%) of 5 ppm MB was obtained by 30 mgL−1 nanoparticles containing 2 wt% Cu, which was ascribed to the most effective surface area of these particles. However, at more than 2 wt% Cu doping concentration, nanoparticles aggregated due to their high surface energy, and the decomposition efficiency was decreased.
