In-situ fabricated covalent organic frameworks-polyamide hybrid membrane for highly efficient molecular separation

Covalent organic frameworks (COFs) membranes fabricated via interfacial polymerization typically present high permeance but relatively low selectivity for small molecules. To address this issue, COFs-polyamide hybrid membranes were in-situ fabricated onto polyacrylonitrile (PAN) substrate via interfacial polymerization for highly efficient molecular separation. Specifically, P-phenylenediamine (Pa) or benzidine (BD) as the aqueous monomer was reacted with a mixture of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) and trimesoyl chloride (TMC) to generate COFs-polyamide hybrid structure, comprising the imide-linked COFs and the amide-linked polyamide. Since the TMC could react with the residual unreacted amine groups after COFs formation, the COFs-polyamide hybrid structure exhibited few defects and excellent stability. The as-prepared TpPaTMC/PAN or TpBDTMC/PAN hybrid membranes presented excellent performance for dye rejection and dye desalination with pure water permeances of 84∼95 L·m-2·h-1·bar-1, congo red rejection of ∼99%, acid red 66 rejection of 85%∼92%, and Na2SO4/CR separation factor of 65∼86. Moreover, the separation performance of COFs-polyamide hybrid membranes could be easily tunable by adjusting the TMC contents in the organic phase during the membrane fabrication, and the optimized membranes could be applied for dye rejection or dye desalination. The COFs-polyamide hybrid membranes also showed excellent anti-fouling performance and chemical stability. Therefore, the convenient and efficient in-situ fabrication of high-performance COFs-polyamide hybrid membrane would provide novel insight into the structure, property and application prospects of COFs membrane.