A New Molecular Probe for Colorimetric and Fluorometric Detection and Removal of Hg²⁺ and its Application as Agarose...

A new molecule incorporating two units of 7-nitro-benzoxadiazole (NBD), bridged by m-xylylenediamine, was synthesized and characterized on the basis of analytical and spectroscopic techniques. The metal ion sensing property of this molecule was studied spectroscopically with a large number of metal ions. This study revealed that it can perform as a dual-channel probe for colorimetric as well as fluorometric detection of Hg²⁺. In presence of Hg²⁺, a substantial change in UV-Vis spectrum with the appearance of a new band at 545 nm and a distinct colour change from yellow to red was observed. In the fluorescence spectrum, the intensity of the emission band was substantially quenched only upon addition of Hg²⁺. No significant interference from any other metal ion used in this study was noted, the limit of detection (LOD) for Hg²⁺ was found to be 60 and 10 nM for colorimetric and fluorometric detection method, respectively. This new chemosensor was used for removal of Hg²⁺ from aqueous solution with 92% efficiency. For on-site monitoring and field application, this molecule was immobilized into the agarose based hydrogel film, which was used successfully for detection of Hg²⁺ in water. The study on reversible behaviour of this chemosensor revealed that it can be recycled in solution as well as in solid phase by treatment with Na₂S.