Enhancement of compatibility between covalent organic framework and polyamide membrane via an interfacial bridging method: Toward highly efficient water purification

A key challenge in polyamide (PA) based nanocomposite membranes is to achieve non-accumulation filler and defect-free features, based on proper compatibility and great dispersion between the particles in the matrix. To address this issue, herein, an interfacial bridging strategy was introduced to fabricate the nanocomposite membrane. A covalent organic framework (COF), TAPB-BPTA (TAPB = 1,3,5-tris(4-aminophenyl)benzene and BPTA = 1,4-benzenedicarboxaldehyde), containing alkynyl was synthesized by a microwave-assisted solvothermal route and preliminarily grafted with the cysteine (CYS) bridge via a click reaction. Furthermore, the short chain of amine moieties in TAPB-BPTA not only makes more amine groups and carboxy groups in the COF pore wall, thereby elevating its hydrophilicity and improving its dispersion in the polyethyleneimine coating solution, but also presumably brings further free motion for amine groups to react with acyl functions in trimesoyl chloride (TMC). The COF was copolymerized using TMC to finally obtain the crosslinked top skin layer without the defect formation between filler and polymer during the interfacial reaction. The pure water permeance of the optimized nanocomposite membrane is higher than that of the pristine PA membrane. Accordingly, the optimized membrane exhibited good permeability and competitive selectivity for dyes and antibiotics. Meanwhile, it had a highly rejection of 92% for methylene blue after multi-cycle separation test, showing excellent industrial wastewater treating capability.