ß-Cyclodextrin capped ZnS nanoparticles for CER-assisted colorimetric and spectrophotometric detection of Pb2⁺, Cu2⁺, and Hg2⁺ in an aqueous solution.

Herein, simple, low-cost, and room-temperature synthesis of beta-cyclodextrin (ß-CD) stabilized zinc sulfide nanoparticle (ZnS NP) through the chemical precipitation method has been reported for cation exchange reaction (CER) based colorimetric sensing of Pb2+, Cu2+, and Hg2+. Formation of ß-CD stabilized ZnS NPs (ZnS@ß-CD) was verified by physicochemical characterization techniques such as XRD, XPS, FE-SEM, and TEM. ZnS@ß-CD NPs showed color change selectively for the metal ions Pb2⁺, Cu2⁺, and Hg2⁺ among the various metal ions including Sn2⁺, Cr³âº, Mn2⁺, Fe³âº, Co2⁺, Ni2⁺, and Cd2⁺. The solubility product of reactants and the transformed products are the reason for selective CER of ZnS@ß-CD NPs towards Pb2⁺, Cu2⁺, and Hg2⁺ ions. ZnS@ß-CD NPs dispersion revealed rapid color change from white to orange, black, and bright yellow on the addition of higher concentrations of Pb2⁺, Cu2⁺, and Hg2⁺ respectively. This color change is due to the formation of complete CER-transformed nanostructures such as PbS, CuS, and HgS in higher concentrations (10⁻1- 10⁻³ M) of corresponding metal ions. The partial CER altered products Zn1-x,PbxS, Zn1-xCuxS and Zn1-xHgxS were detected due to the appearance of pale color in the lower metal ions concentrations of 10⁻4 - 10⁻6 M. This CER assisted transformation was also monitored through spectrophotometric methods. Moreover, infrared spectroscopic analysis was used to testify the structure of CER transformed product. The synthesized ZnS@ß-CD NPs act as an efficient CER-based sensor for distinguishing and determining Pb2⁺, Cu2⁺, and Hg2⁺ at different level concentrations in the aqueous solution.