Selective Sensing and Removal of Mercury Ions by Encapsulating Dansyl Appended Calix[4]Conjugate in a Zeolitic Imidazolate Framework as an Organic-Inorganic Hybrid Nanomaterial

A lower rim dansyl appended calix[4]arene, DanC4A has been synthesized and characterized. DanC4A is a promising sensor for selective detection of toxic metal ions, Hg2+, among the twelve separate metal ions studied. The fluorescence titration of DanC4A with Hg2+ shows approximately 80% quenching. Competitive metal ion studies suggest the selective binding of Hg2+ to DanC4A. The biocompatibility of DanC4A has been confirmed by an MTT assay performed using HeLa cells. Confocal microscopy and fluorescence microscopy studies suggest that DanC4A exhibits strong green fluorescence in HeLa cells, and the same is quenched as the concentration of Hg2+ increases in the cells. Apart from sensing, the main concern is the removal of Hg2+ from water and this is not possible with the direct use of DanC4A due to its solubility. Therefore, DanC4A has been embedded into a zeolitic imidazolate framework (ZIF8) to result in an inorganic-organic hybrid nanomaterial, DanC4A_ZIF8_MOFs, by an in situ reaction. Approximately 95% of the Hg2+ ions were removed from water by using the hybrid material, viz., DanC4A_ZIF8_MOFs. Thus, DanC4A is not only a superior sensor for Hg2+ in solution and in mammalian cells but can be converted into an organic-inorganic hybrid material, DanC4A_ZIF8_MOFs, for efficient removal of Hg2+ from water.