Covalent Organic Framework Nanosheets as Reactive Fillers to Fabricate Free-Standing Polyamide Membranes for Efficient Desalination

Mixed matrix membranes (MMMs) have been increasingly utilized in membrane processes. Covalent organic frameworks (COFs) hold great promise as emergent nanofillers to fabricate high-performance MMMs; however, only few studies about COF materials in MMMs have been reported where COFs are all used as nonreactive fillers. Herein, we propose using -NH2-functionalized COF nanosheets as reactive fillers (rCON) to fabricate MMMs. rCON altered the morphology and chemistry of MMMs by controlling the diffusion rate of piperazine through hydrogen bonding prior to the interfacial polymerization process and inducing the creation of ridges in the MMMs with subsequent increase in surface area (∼24%). rCON was chemically cross-linked to the trimesoyl chloride through amide bonding, subsequently elevating the hydrophilicity (∼35%) and fouling resistance of MMMs. The presence of -NH2 groups elevated the rCON-PA compatibility, ensuring the high rCON loading of 5 wt % in the MMMs without sacrificing salt rejection. Accordingly, the PA-rCON MMMs exhibited a flux of 46.5 L m-2 h-1 bar-1, which is 6.8 times higher than that of the pristine PA membrane, with a high rejection rate of 93.5% for Na2SO4.