Covalent organic framework assisted interlocked graphene oxide based thin-film composite membrane for effective water remediation

Abstract

2D materials like graphene oxide (GO) based free-standing membranes, although have shown excellent salt rejection at short time scales, suffer from structural stability and swelling on prolonged use. Hence, in this study, a unique approach of crosslinking GO sheets with a dense ‘covalent organic framework’ (to yield GO@COF) was designed to selectively reject ions and dyes. The swelling of the GO@COF membrane was also restricted due to the crosslinking of GO nanosheets. The GO@COF membrane was supported on a porous crystalline support (here polyvinylidene difluoride, PVDF) designed by etching out the amorphous phase (here polymethyl methacrylate, PMMA) from a demixed crystalline/amorphous pair. This arrangement showed good water flux, fouling resistance, and >90% dye rejection. In order to enhance the rejection further and to improve the chlorine tolerance of the membrane, a COF embedded polyamide (PA) thin film composite membrane was designed in situ on this highly stable, non-swellable GO@COF membrane. This modified membrane showed excellent salt (>94% and >98% for monovalent and divalent ions, respectively) and dye (>99.90% for both cationic and anionic dyes) rejection and in addition, demonstrated excellent resistance to fouling (>93%). Moreover, this sandwich structure revealed outstanding chlorine tolerance performance, thereby addressing most major challenges faced by either 2D material based or thin film composite membranes.