β-Cyclodextrin capped ZnS nanoparticles for CER-assisted colorimetric and spectrophotometric detection of Pb(2)⁺, Cu(2)⁺, and Hg(2)⁺ in an aqueous solution

Herein, simple, low-cost, and room-temperature synthesis of beta-cyclodextrin (β-CD) stabilized zinc sulfide nanoparticle (ZnS NP) through the chemical precipitation method has been reported for cation exchange reaction (CER) based colorimetric sensing of Pb(2+), Cu(2+), and Hg(2+). Formation of β-CD stabilized ZnS NPs (ZnS@β-CD) was verified by physicochemical characterization techniques such as XRD, XPS, FE-SEM, and TEM. ZnS@β-CD NPs showed color change selectively for the metal ions Pb(2)⁺, Cu(2)⁺, and Hg(2)⁺ among the various metal ions including Sn(2)⁺, Cr³⁺, Mn(2)⁺, Fe³⁺, Co(2)⁺, Ni(2)⁺, and Cd(2)⁺. The solubility product of reactants and the transformed products are the reason for selective CER of ZnS@β-CD NPs towards Pb(2)⁺, Cu(2)⁺, and Hg(2)⁺ ions. ZnS@β-CD NPs dispersion revealed rapid color change from white to orange, black, and bright yellow on the addition of higher concentrations of Pb(2)⁺, Cu(2)⁺, and Hg(2)⁺ 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 Zn(1−x),Pb(x)S, Zn(1−x)Cu(x)S and Zn(1−x)Hg(x)S 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@β-CD NPs act as an efficient CER-based sensor for distinguishing and determining Pb(2)⁺, Cu(2)⁺, and Hg(2)⁺ at different level concentrations in the aqueous solution.