In this work, a Mn-based metal−organic framework (MOF) {[H-Phen] 2 [Mn 3 (FDA) 4 (H 2 O) 2 ]•2H 2 O} n (SM-1) has been synthesized solvothermaly using 2,5-furandicarboxylic acid (2,5-FDA) as a linker and 4,7-phenanthroline (4,7-Phen) as a coligand. SM-1 was characterized using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and crystallographic studies. Single-crystal X-ray data reveal that the SM-1 framework is constituted by trinuclear Mn secondary building units (SBUs) as a dianion ([Mn 3 (COO) 6 ] 2− ), 2,5-FDA, and free 4,7-phenanthrolinium cation [H-Phen] + rings containing uncoordinated amino and imino moieties, which provide extra stability to the framework and feasible recognition sites to interact with analytes. Overall, the MOF is anionic in nature, which is counterbalanced by two protonated phenanthrolinium cations, thus giving rise to +2 oxidation states for all three Mn ions. Topological analysis shows that SM-1 has a {4 4 .6 2 } point symbol having a 4-c uninodal net with sql topology. SM-1 is an excellent fluorescent sensor for d 10 heavy metal ions in an aqueous environment. SM-1 developed as a highly sensitive sensor exhibits a fluorescence "turn-on" response for Ag + and Cd 2+ ions and a fluorescence "turn-off" response in the case of Hg 2+ ion with much lower limit of detection (LOD) values. Moreover, SM-1 application is not limited to only sensing, but it can also serve as an adsorbent to capture hazardous substances. Owing to the presence of π-electron-rich moieties and uncoordinated nitrogen atoms in the SM-1 framework, it is also explored for efficient iodine uptake. SM-1 captures iodine reversibly in cyclohexane solution with high adsorption capacity within 36 h. Further, a plausible mechanism of sensing and iodine adsorption was also discussed briefly. As far as we know, this is the first example of a Mn-based anionic MOF functioning as a fluorescent chemosensor to simultaneously detect d 10 heavy metal ions in water and as an adsorbent to trap iodine. Thus, metal− organic chemistry has been employed to develop multifunctional MOF material for the sensing of hazardous metal ions and as an adsorbent for the removal of toxic iodine.
From the perspective of environment, civilian safety and human health it is utmost important to selectively and sensitively detect hazardous substances in the running water. In the last few decades, metal organic frameworks (MOFs) have been utilized for the detection of lethal substances in the aqueous phase using fluorescence method. Herein, a highly fluorescent MOF, Zn-MOF-1, namely, {[Zn2(pydc)2(DMF)]·2DMF}n, based on the ligand pyridine-2,5-dicarboxylic acid (H2pydc), was synthesized by employing solvothermal conditions. The Zn-MOF-1 was thoroughly characterized by crystallographic, PXRD, elemental, FTIR, and TG analysis. Single crystal data elucidated the exact structure of Zn-MOF-1. Due to its better emission spectra, the fluorescence sensing behavior of Zn-MOF-1 was checked in the aqueous medium. It was found that Zn-MOF-1 could detect Cr3+ with high sensitivity and selectivity and serve as an excellent fluorescent probe for TNP among other interfering nitroaromatic compounds in aqueous media. Furthermore, a plausible sensing mechanism has been demonstrated employing UV-Visible, fluorescence, and theoretical data. The observed Ksv values for TNP and Cr3+ are 2.1×108 M-1 and 1.46×107 M-1, respectively. Selective fluorescence quenching with high Ksv values and low detection limits validates the superior sensing performance shown by Zn-MOF-1 toward TNP and Cr3+. Thus, the fine-tuning of MOF for the detection of hazardous substances in wastewater is a challenging task and needs to address in future endeavors.
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