A Thermally Regenerable Cationic MOF Adsorption Material for Sustainable and Selective Removal of Hexavalent Chromium from Water

Elimination of toxic Cr(VI) in industrial effluent is essential; numerous adsorbents have been developed for Cr(VI) adsorption, but a sustainable adsorbent with chemical-less and environmentally friendly regeneration methods that could greatly reduce chemical eluent usages, recycling costs, and secondary pollution is still lacking. Here, we report a copolymer network of diallyldimethylammonium chloride and N-isopropylacrylamide (pDDA-pNIPAm) functionalized metal–organic framework (MOF) materials as a thermally regenerable cationic ion adsorbent (pDDA-pNIAPm-MIL-53) for highly selective and sustainable Cr(VI) removal. At room temperature (ca. 25 °C), it quickly adsorbed Cr(VI) oxyanions from water with a maximum adsorption capacity of 45.5 mg g^–1, showing a remarkable Cr(VI) selectivity up to 130 in the presence of coexisting anions with ion molar ratio of 1:1. Importantly, pDDA-pNIAPm-MIL-53 with adsorbed ions could be efficiently regenerated in warm water (35–50 °C) with excellent reusability, so the low-grade waste heat from Cr(VI) pollutant industries can be used as an energy source. The high selectivity and thermal regeneration ability of this adsorbent ensure the efficient removal of Cr(VI) from water and the high purity of Cr(VI) from regeneration. This work provides scientific support for designing MOFs with selective adsorption behavior and thermally regenerable function for highly selective toxic ion removal and sustainable regeneration.