In this research, green and aqueous based synthesis routes were performed for chemical preparation of pure and transition metal ions doped ZnS quantum dots at room temperature. Doping of ZnS QDs by three transition metal ions (Mn2+, Co2+, Ni2+ ions) as dopants have been investigated by various techniques. In the optical absorption studies, a broad absorption band in the wavelength range of 280-300 nm clearly reveals quantum size effect in ZnS QDs. The crystal structure and the approximate size of QDs were measured by XRD pattern. The average particle size of QDs was found to be around 1-3 nm. In addition, the photocatalytic activities of the prepared ZnS QDs as their abilities to remove methyl violet (MV) cationic dye, as a model molecule, were studied. Effect of the experimental parameters, such as the type of dopant and the amount of QDs, pH of the initial dye solution, irradiation time, ionic strength of reaction media, and initial dye concentration on the decolorization efficiency (DE) of QDs as green nano-semiconductors were studied. The results demonstrated that doped QDS (for 5% of dopants) effectively bleached out MV, showing positive photocatalytic enhancement over pure ZnS nanoparticles. (c) 2015 Elsevier B.V. All rights reserved.