Ultrafast turn-on/turn-off fluorescent detection of hazardous metals and highly efficient iodine capture using Zn(II) coordination polymers

In this work, Zn-based coordination polymers (CPs) [Zn(dpe)Cl₂]_n (HT-5) and [Zn(tmdp)Cl₂]_n (HT-6) have been synthesized solvothermally using 1,2-di(4-pyridyl)ethylene (dpe), and 4,4′- trimethylenedipyridyl (tmdp) as linkers. HT-5 and HT-6 were characterized using elemental analysis, FTIR, PXRD, SEM, EDS, and crystallographic studies. The HT-5 and HT-6 adsorbents have been employed for removing toxic iodine from a hexane solution with a capacity of 182 mg g⁻¹, while 129 mg g⁻¹ in the vapor phase for HT-5 within 48 h. The presence of π-electron-rich moieties in the HT-5 and HT-6 frameworks was responsible for effective iodine adsorption. Furthermore, HT-5 and HT-6 are not only utilized to capture iodine, they may be used as sensitive sensors that emit fluorescence. The fluorescence “turn-off” response for Mn⁷⁺ and Cr⁶⁺ ions and a fluorescence “turn-on” response in the case of Hg²⁺ ions are observed for the CPs. Under optimal conditions, the limit of detection (LOD) of HT-5 is 1.4 µM, 1.1 µM, and 1.3 nM for Mn⁷⁺, Cr⁶⁺, and Hg²⁺, respectively. As a result, the developed Zn based CPs can serve as an efficient material for iodine capture as well as fluorescent sensor for detection of hazardous metal ions.