Integrating cationic metal-organic frameworks with ultrafiltration membrane for selective removal of perchlorate from Water.

• A novel designed PVA/Cu-iMOFs/PVDF UF membrane is prepared successfully. • Cu-iMOFs particles immobilized on PVDF membrane surface is reinforced by amido bonds. • Membrane exhibits outstanding selectivity and reusability toward ClO 4 − trapping. • Membrane shows excellent permeability and stability in cross-flow filtration. • The mechanism is specific exchange between R-SO 3 group and tetrahedral oxo-anion. We design a novel cationic metal-organic framework hybrid ultrafiltration polyvinylidene fluoride membrane (PVA/Cu-iMOFs/PVDF-0.05) and report its unique capture of aqueous perchlorate (ClO 4 −) at ppm-level. This membrane outperformed traditional adsorption materials and exhibited a specific affinity toward ClO 4 − in the presence of various competing anions at greater levels (up to a concentration ratio of 20). In the batch experiment, the ClO 4 − removal ratio reached 99.6% over a wide pH range (3˜10). Membrane filtration by using a 12.56 cm2 PVA/Cu-iMOFs/PVDF-0.05 membrane could effectively treat 4.71 L of ClO 4 −-contaminated water before breakthrough occurred, while maintaining a satisfactory permeability (˜627.32 L/(m2 h bar)) and antifouling property. The exhausted membrane could easily be regenerated in aminoethanesulfonic acid solution for repeated use with a negligible decrease in capacity. Moreover, the membrane showed excellent long-term stability in a cross-flow filtration process due to the amido bond between the Cu-iMOFs and membrane surface as well as the "protection" of polyvinyl alcohol. Selective and reversible ion-exchange between the sulfonic acid (R-SO 3) ligands of Cu-iMOFs and tetrahedral oxo-anionic species was verified to be the pathway for ClO 4 − trapping. Thus, other problematic elements that also occur in tetrahedral form in water can be removed by this method. [ABSTRACT FROM AUTHOR]