In this research, Zinc sulfide quantum dots a pure and doped with different transition metal ions were synthesized in a aqueous medium, in the presence of various capping agent such as 2-mercaptoethanol, L-cysteine and thiourea, at room temperature, without using organic solvents. The effect of the presence of transition metal ions such as Fe3+, Mn2+, Ni2+ and Co2+ as dopant with various mol fraction, as well as effect of capping agent type on the colour optical and structural properties of the QDs were studied. The particle size of the prepared QDs was investigated by transmission electron microscopy (TEM). According to TEM results, the average size of the prepared QDs was calculated to be in the range of 0.5-3.0 nm. There distinguish X-ray diffraction (XRD) peak in the place of (1 1 1), (2 2 0) and (1 1 3) indicate the cubic crystals of pure and doped zinc sulfide nanoparticles. In addition, confirm the study of optical properties of the pure and doped zinc sulfide quantum dots have also been performed by using UV-Vis spectrophotometry, show a broad absorption spectrum in the wavelength range of 270-310 nm.
In addition, three pollutant dyes were chosen ad model molecule of investigated the photocatalytic activies of the QDs prepared in the presence of 2-mercaptoethanol, thiourea and L-cysteine capping agent. Comparative photodecolorization of thymol blue (as an anionic dye), methyl violet and crystal violet (as cationic dyes) was studied under UV irradiation light, in the presence of QDs. The influence of the operational parameters including the amount and type of nanophotocatalytic, exposure time, pH of samples and electrolyte concentration on the decolorization efficiency of organic dye was investigated and optimized. Repeated use of the nanoparticles shows that the prepared QDs can be used at least four times for the photodecolorization of dyes. Also, kinetic of the reaction and the possible mechanism were studied.