Nano-molar to milli-molar level Ag (I) determination using absorption of light by ZnS QDs without organic ligand

Despite of useful applications of Ag, it is hazardous to health and environment and hence early detection is required. Crystal defects influencing optical property is less likely utilized for Ag detection using prevalent UV-vis technique. Quantum dots (QDs) ZnS prepared by soft chemical route are exploited for the detection of Ag+ in aqueous solution for nM to mM concentrations. UV-vis and photoluminescence (PL) measurements reveal quantum confinement effect and presence of defects in ZnS nanoparticles (NPs). Controlled synthesis of ZnS NPs allows appearance of defects related peak at 400-550 nm in UV-vis spectra. A plausible mechanism is presented and elucidated by XRD and PL studies for chemical interaction between ZnS with Ag+. The interaction affects prominently the defects related absorption of ZnS NPs and allows single step Ag detection in aqueous medium. This absorption method is extended to other ions (Na+, K+, Mg+, Cat, Bat) including 'S' prone heavy and toxic ions like Pb, Hg, and Cd. Among them, Ag+ shows the best response with ZnS NPs. This demonstration using a portable and cost effective technique with no organic component opens up possibility for other inorganic materials.