Design, synthesis and characterization of chemosensors for determination of heavy metal ions

Abstract

Heavy metals such as Hg2+, Cd2+, Pb2+, As3+/As5+ are highly toxic because of clinical and environmental reasons. Here we have been designed and synthesized five new series of chemosensors for the colorimetric detection of heavy metal ions (Cu2+, Hg2+, Cd2+, Pb2+, As3+/As5+) and utilized for versatile applications of environmental concern. All the chemosensors have been characterized using different standard spectroscopic techniques like FT-IR, 1H-NMR, 13C-NMR and LC-Mass (ESI-MS). The selected chemosensors have been considered for three-dimensional structural elucidation using Single Crystal X-Ray diffraction (SCXRD) studies. The qualitative and quantitative, binding properties and detection limits for the developed chemosensors have been carried out using UV–Vis spectroscopic studies. The binding mechanism has been proposed based on UV–Vis titration and the same has been confirmed by FT-IR, 1H-NMR, LC-Mass and DFT studies. Among the synthesized chemosensors, the S4R1 showed a lower detection limit of 2, 11, 2, 7 ppb for Cu2+, Hg2+, Cd2+, Pb2+ ions, respectively. The S5R1 showed 8 ppb detection limit for As3+ ions, which is much lower than the WHO, US–EPA stated limit of 10 ppb. From the experimental and theoretical DFT results, it has been concluded that the simple organic molecules could act as very good colorimetric chemosensors for heavy metal ions such as Cu2+, Hg2+, Cd2+, Pb2+ and arsenate/arsenite ions. The S2R1 S3R3 and S3R4 showed brilliant analytical and environmental significant applications for the quantitative analysis of Cu2+, Cd2+, Hg2+ ion present in river, tap, and drinking water samples. The analytical method results of S3R3 and S3R4 for the determination of Cu2+ and Cd2+ indicates acceptable precision, linearity and accuracy of the developed method. Further, a good agreement found between proposed and wellestablished methods (AAS). The chemosensors S4R1–S4R3 and S5R1–S5R3 displayed colorimetric responses towards detection of heavy metal ions. S4R3 and S5R1 showed good naked eye response for the As3+/ As5+ ions. The S4R3 showed detection limit of 213 ppb for As3+ and the S5R1 displayed detection limit of 8 ppb/13 ppb for As3+/ As5+ ions. Further, successfully demonstrated the test strips applications.