Selective and sensitive cation exchange reactions in the aqueous starch capped ZnS nanoparticles with tunable composition, band gap and color for the detection and estimation of Pb2+, Cu2+ and Hg2+

Abstract

Room temperature nanoscale cation exchange reactions (CER), acts as a versatile tool and alternative to the tedious traditional approaches for colorimetric detection of heavy metal ions in water samples. Herein, we report selective and sensitive CER in aqueous starch capped ZnS nanoparticle (NPs) as colorimetric sensor for detection and estimation of Pb2+, Cu2+ and Hg2+ and their corresponding transformed products in water samples. Other heavy metal ions such as Sn2+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+ and Cd2+ do not involve in CER. The sensor shows time dependent multiple signals, namely, composition, band gap and colour to identify corresponding metals. The partially transformed products Zn1−x,PbxS, Zn1−xCuxS and Zn1−xHgxS were instantaneously identifiable due to orange, pale brown and pale yellow coloration in presence of respective metal ions and from their spectroscopic data. The completely transformed products PbS, CuxS and HgS were again identifiable with different colour such as brown, pale brown and bright yellow coloration, respectively. Due to favorable room temperature nanoscale CER, the proposed ZnS NPs based method has potential applications in monitoring qualitative and quantitative tracing of Pb2+, Cu2+ and Hg2+ in various real water samples without using any instruments.