A Water‐Stable Ionic MOF for the Selective Capture of Toxic Oxoanions of Se^VI and As^V and Crystallographic Insight into the Ion‐Exchange Mechanism

Abstract

Selectively capturing toxic oxoanions of selenium and arsenic is highly desired for the remediation of hazardous waste. Ionic metal-organic frameworks (iMOFs) especially cationic MOFs (iMOF-C) as ion-exchange materials, featuring aqueous phase stability, present a robust pathway for sequestration of the oxoanions owing to their ability to prevent leaching because of their ionic nature. On account of scarcity of water-stable cationic MOFs, the capture of oxoanions of selenium and arsenic has been a major challenge and has not been investigated using iMOFs. Herein, we demonstrate large scale synthesis of cationic MOF, viz. iMOF-1C that exhibits selective capture of oxoanions of Se VI (SeO 4 2À ) and As V (HAsO 4 2À ) in water with a maximum sorption capacity of 100 and 85 mg g À1 , respectively. This represents among the highest uptake capacities observed for selenate oxoanion in MOFs. Further, the ion-exchange mechanism was directly unveiled by single crystal analysis, which revealed variable modes of host-guest binding.

Nanomaterials for Water Treatment and Remediation

“…Accordingly, both cationic and anionic MOF adsorbents have been successfully applied for the removal of organic pollutants via ion-exchange interaction. Through ion exchange mechanisms, selective capturing of toxic oxoanions of arsenic As V (HAsO4 2− ) and selenium Se VI (SeO4 2− ) with maximum adsorption capacity of 85 and 100 mg g −1 have been achieved using cationic MOFs material (iMOF-C) (Sharma et al, 2020).…”

Metal–Organic Frameworks and Water: ‘From Old Enemies to Friends’?

“…This is the case for MAF-6, a hydrophobic zeolitic MOF built from Zn 2+ and 2-ethylimidazolate that can readily absorb large amounts of various organic molecules and separate them from water [44]. Selective capture of hazardous wastes such as toxic oxoanions (e.g., chromates, selenates, arsenates) has also been shown to be highly efficient using stable ionic MOFs (iMOFs) [45,46]. Their inherent charged nature affords the entrapment of charged species through an ion-exchange process.…”

Dye contaminated wastewater treatment through metal–organic framework (MOF) based materials

“…42,43 For selective adsorption of cationic/anionic dyes, ion exchange mechanisms have been followed. [44][45][46] Other intermolecular interactions between the active sites of host MOFs and guest dyes, such as hydrogen bonds, p-p stacking, Fig. 1 Percentage contribution of dye effluent in the environment by different industries.…”