Highly selective and sensitive detection of Cu2+ ions using TGA capped Ce(III)-doped ZnS nanoparticles as fluorescent probe

Abstract

Abstract The synthesis of water dispersible thioglycolic acid (TGA)-capped Ce3+-doped ZnS nanoparticles (coded as ZnS:Ce@TGA) was carried out using environment friendly co-precipitation approach with water as solvent. The as-synthesized nanoparticles were characterized by the different analytical techniques such as powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, and fluorescence spectroscopy. These nanoparticles are highly stable due to the coating of robust TGA capping agent. TGA capped Ce3+-doped ZnS nanoparticles showed significant fluorescence enhancement upon continuous addition of urea. This enhancement in fluorescence intensity was observed due to formation of new layer of urea over TGA which led to the decreases in surface defects. Further, urea treated TGA capped Ce3+-doped ZnS nanoparticles served as active sensor for the for the selective detection of Cu2+ ions as the urea layer in ZnS:Ce@TGA-urea provide active sites for the binding of Cu2+ ions. This selective binding quenched the fluorescence intensity of ZnS:Ce@TGA-urea possibly due to non-radiative recombination as Cu2+ act as electron trapping center. ZnS:Ce@TGA material could be used as an ultrafast primary sensor for detection of urea and the resultant ZnS:Ce@TGA-urea complex can then be used as a secondary sensor for determination of Cu2+ ions. The LOD for detection of urea and Cu2+ ions were found to be 2.3 mM and 26.6 μM, respectively. Factors affecting the Cu2+ ions detection were investigated and the optimum conditions were also determined. Under the optimum conditions, the relative fluorescence intensity of urea-TGA-capped@Ce3+-doped ZnS nanoparticles was linearly proportional to Cu2+ over a concentration range from 0 to 80 µM with a correlation coefficient of 0.989. The proposed method was also employed to detect trace Cu2+ in water with satisfactory results.