Loose nanofiltration membranes functionalized with in situ-synthesized metal organic framework for water treatment

In this study, modified loose nanofiltration membranes were prepared by in-situ decoration with Zeolitic Imidazolate Framework-7 (ZIF-7) on the surface of porous polyethersulfone substrates functionalized with co-deposited sulfobetaine methacrylate (SBMA) zwitterion (ZW) and polydopamine (PDA). With the aid of ZW/PDA active layer co-deposition under mild conditions, ZIF-7 metal organic framework (MOF) nanocrystals were successfully formed and anchored onto the membrane surface via both non-covalent and covalent bonds to simultaneously achieve the desired selectivity and productivity of the loose nanofiltration membranes. The characterization results confirmed the successful deposition of the ZW/PDA active layer and the consequent decoration with ZIF-7 nanocrystals. The average water contact angle decreased notably from 81.4 to 51.43 degrees upon the formation of ZIF-7. This membrane showed high rejection (~99.9%) of methyl blue and Congo red dyes and high water flux with dye solutions (around 40 L m-2h-1) at a very low applied pressure of 1.5 bar. Moreover, the filtration experiments revealed that functionalized membranes exhibited a significant reduction in fouling and biofouling propensity. Notably, the MOF-SBMA/PDA membrane displayed favorable antifouling behavior associated with a significant ability to recover flux upon simple physical cleaning. The combination of these two properties is possibly the most promising feature of the membrane proposed in this study.