Carboxyl-functionalized covalent organic framework as a two-dimensional nanofiller for mixed-matrix ultrafiltration membranes

Abstract

A new carboxyl-functionalized covalent organic framework (referred to as COF hereafter, unless otherwise noted) contains aromatic backbones and carboxyl-functionalized nanopores has been synthesized and used as a two-dimensional (2D) nanofiller in polyacrylonitrile (PAN) polymer matrix of ultrafiltration (UF) membranes. A series of mixed-matrix UF membranes with various concentrations COF ranging from 0 to 0.8 wt% have been investigated using non-solvent induced phase separation (NIPS) method. The effect of COF concentration has been evaluated on the membrane morphology, intrinsic and mechanical properties, separation performance, and fouling propensity. Increasing COF concentration from 0 to 0.8 wt% could significantly enhance the rejection rate from 3.5 to 81.9 wt% for bovine serum albumin (BSA) and 65.0–99.4 wt% for γ-globulin. Moreover, membrane hydrophilicity greatly increased, with the decrease of water contact angle from 64.4° to 45.3°. Overall, compared to the pristine PAN membrane, the mixed-matrix PAN membrane with 0.8 wt% COF demonstrated high water flux of 940 L m−2 h−1 bar−1, better protein retention rate, thermal stability, mechanical properties, and fouling resistance.