β-Cyclodextrin capped ZnS nanoparticles for CER-assisted colorimetric and spectrophotometric detection of Pb2⁺, Cu2⁺, and Hg2⁺ in an aqueous solution
Vyshnavi T. Veetil, Anakha D. Rajeeve, Saran G.P, K.S. Manish Kumar, Margandan Bhagiyalakshmi, Mari Vinoba, R. Yamuna
Abstract
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.