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

TL;DR

This paper presents a simple, cost-effective UV-Vis absorption method using ZnS quantum dots for detecting silver ions at nanomolar to millimolar levels without organic ligands, leveraging defect-related optical properties.

Contribution

It introduces a novel inorganic nanoparticle-based detection technique for Ag ions that does not require organic ligands or complex procedures.

Findings

ZnS quantum dots exhibit defect-related absorption peaks useful for Ag detection.

The method detects Ag ions effectively in aqueous solutions from nM to mM concentrations.

Ag ions produce the strongest response among tested ions, including toxic heavy metals.

Abstract

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 ions 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 ion. The interaction affects prominently and defects related absorption of ZnS NPs and allows single step Ag ion detection in aqueous medium. This absorption method is extended to other ions (Na, K, Mg, Ca, Ba ions) including S prone heavy and toxic ions like Pb, Hg and Cd. Among them, Ag ion 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.