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 Zn_1−x,Pb_xS, Zn_1−xCu_xS and Zn_1−xHg_xS 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, Cu_xS 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.

室温下的纳米级阳离子交换反应（CER）可作为多功能工具，替代繁琐的传统方法进行比色检测水样中的重金属离子。在本文中，我们报告了选择性和灵敏的CER在比色法检测的含水淀粉加帽的ZnS纳米颗粒（NPs）中用于检测和评估水中的Pb 2 ⁺，Cu ²⁺和Hg ²⁺及其相应的转化产物。其他重金属离子，例如Sn 2 ⁺，Cr ³⁺，Mn 2 ⁺，Fe ³⁺，Co 2 ⁺，Ni ²⁺和Cd ²⁺不参与CER。传感器显示时间相关的多个信号，即成分，带隙和颜色，以识别相应的金属。将部分转化产物的Zn _{1- X，}铅_X S，锌_{1- X}的Cu _X S和锌_{1- X}汞柱_X小号是瞬间识别由于橙色，淡棕色和在各自的金属离子，并从存在淡黄色着色其光谱数据。完全转化的产物PbS，Cu _xS和HgS可以分别用不同的颜色识别，例如棕色，浅棕色和亮黄色。由于具有良好的室温纳米尺度CER，所提出的基于ZnS NPs的方法在不使用任何仪器的情况下，可以监测各种真实水样中Pb 2 ⁺，Cu ²⁺和Hg ^2+的定性和定量示踪。