Instantaneous Colorimetric Visual Detection of Toxic Lead (II) ions

Lead (II) ion (Pb$^{\mathrm{2+}})$ is one of the poisonous heavy metal ions which is detrimental to the human body and the surrounding environment. In this work, a simple and faster colorimetric sensor has been reported to detect the trace amount of toxic Pb$^{\mathrm{2+}}$ ions. Here, we have utilized Methylammonium Iodide (MAI), dissolved in dimethylformamide solvent, as a sensing material to visually detect toxic Pb$^{\mathrm{2+}}$ ions instantaneously. When the Pb$^{\mathrm{2+}}$ ions even at a low level are added to a colorless MAI solution, immediately it forms MAPbI$_{\mathrm{3}}$ perovskite precursor solution which has exceptional light absorption property. This light absorption property critically depends on the concentration of added Pb$^{\mathrm{2+}}$ followed by perovskite precursor formation. Because this phenomenon affects the bandgap of the formed MAPbI$_{\mathrm{3}}$ solution. Interestingly, MAI solution with Pb$^{\mathrm{2+}}$ ions exhibits a transparent yellow color. However, the color saturation varies from strong to light appearance according to the concentration of added Pb$^{\mathrm{2+}}$ ions. MAI solution generates this unique color characteristic selectively only with Pb$^{\mathrm{2+}}$ ions in the ambient environment. Depending on this distinguishable color saturation variation, it is possible to detect the presence and level of Pb$^{\mathrm{2+}}$ ions in a liquid sample within a few seconds through the naked eye. Our successful lowest detection level for Pb$^{\mathrm{2+}}$ was 10 micromolar.