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 SeVI (SeO42−) and AsV (HAsO42−) in water with a maximum sorption capacity of 100 and 85 mg g−1, 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.

Recognition and Sequestration of Toxic Inorganic Water Pollutants with Hydrolytically Stable Metal‐Organic Frameworks

“…It is a well known fact that although essential for living beings (400 μg per day), selenium can be lethal when present in surplus amount while arsenic is identified as “class A” human carcinogen (safety limit <10 ppb in drinking water). After careful analysis of the fundamental factors governing the ion‐exchange procedure e. g., shape & size of the target anions, charge similarity and stability we zeroed our interest to a Ni‐based 3D cationic MOF previously reported by us [92] . The chosen MOF, {[Ni 2 (L) 3 (SO 4 )(H 2 O) 3 ] ⋅ (SO 4 ) ⋅ xG} n ( iMOF‐1C, where L=tris(4‐(1H‐imidazol‐1‐yl)phenyl)amine, G=guest solvent molecules and C=Cationic), with its excellent hydrolytic stability and ease of bulk scale synthesis served as an efficient scavenger toward SeO 4 2− and HAsO 4 2− in water medium (Figure 10).…”

Precise fabrication of porous polymer frameworks using rigid polyisocyanides as building blocks: from structural regulation to efficient iodine capture

“…The iodine adsorption capacity of C-poly-1 5 in particular was extremely high at 574 wt%, which is a higher value than those reported for most materials for which iodine adsorption has been investigated. 10,[53][54][55] Probably, the small pore size of C-poly-1 5 and the abundant phenyl rings and nitrogen atoms in the said helical polymer synergistically promoted iodine adsorption. For comparison, the iodine adsorption was also performed using uncrosslinked 4-poly-1 5 and linear analogue poly-1 5 .…”

“…[1][2][3][4][5][6][7][8][9] Porous polymers were commonly fabricated by using rigid small molecules as building blocks. [10][11][12] Thanks to the structural diversity of organic frameworks and connecting methods, a variety of porous polymers have been readily developed. [13][14][15][16] However, due to the limited dimensions of the available building blocks, the pores present in the reported porous polymers are intrinsically quite small, usually less than 10 nm in size.…”

Anion binding in metal-organic frameworks

“…In a more recent study, the same MOF was shown to adsorb SeO4 2 − and HAsO4 2 − from water. [43] The MOF structure after exchange with these anions were characterized by X-ray crystallography. The HAsO4 2ions in the MOF were found to shift to the center of the cavity compared with SO4 2due to their larger sizes (Fig.…”