A luminescent cationic MOF for bimodal recognition of chromium and arsenic based oxo-anions in water

• Published in: Dalton transactions : an international journal of inorganic chemistry 2021-07, Vol.5 (29), p.1133-1141
• Main Authors: Dutta, Subhajit, Let, Sumanta, Shirolkar, Mandar M, Desai, Aamod V, Samanta, Partha, Fajal, Sahel, More, Yogeshwar D, Ghosh, Sujit K
• Format: Article
• Language: English
• Subjects: Anions; Aqueous solutions; Arsenic; Cations; Chromium; Crystallography; Fluorescence; Heavy metals; Mathematical analysis; Metal-organic frameworks; Selectivity; Water pollution; Zinc
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d1dt01097b

Water pollution from heavy metals and their toxic oxo-anionic derivatives such as CrO 4 2− , Cr 2 O 7 2− , HAsO 4 2− , and HAsO 3 2− has become one of the most critical environmental issues. To address this, herein, we report a new hydrolytically stable luminescent Zn( ii ) based cationic metal organic framework (MOF), iMOF-4C, which further successfully exhibited a rare dual "turn off/on" fluorescence response toward Cr( vi ), As( v ) and As( iii ) based oxo-anions respectively in water medium. In addition, iMOF-4C was found to maintain its superior selectivity in the presence of other concurrent anions ( e.g. SO 4 2− , Cl − , Br − , ClO 4 − , NO 3 − , SCN − and CO 3 2− ). More importantly, iMOF-4C exhibited an excellent selective and sensitive luminescence "turn-off" response towards CrO 4 2− and Cr 2 O 7 2− anions in water medium with the quenching constant ( K sv ) values as high as 1.31 × 10 5 M −1 (CrO 4 2− ) and 4.85 × 10 5 M −1 (Cr 2 O 7 2− ), which are found to be the highest among the values reported in the regime of MOFs. Interestingly, iMOF-4C showed fluorescence "turn-on" response toward HAsO 4 2− and HAsO 3 2− with an enhancement coefficient ( K ec ) of 1.98 × 10 4 M −1 and 3.56 × 10 3 M −1 respectively. The high sensitivity and low detection limits make iMOF-4C more feasible for real-time sensing of such toxic oxo-anions in an aqueous medium. Furthermore, the probable sensing mechanism has been investigated by DFT calculation studies and discussed in detail. Selective bimodal "turn off/on" response in a water stable cationic MOF toward toxic water pollutants (CrO 4 2− , Cr 2 O 7 2− , HAsO 4 2− , and HAsO 3 2− ).