Functionalization of polyacrylonitrile with tetrazole groups for ultrafiltration membranes

Abstract

A series of tetrazole-functionalized polyacrylonitrile (TZ-PAN) copolymers were synthesized via a post-modification cycloaddition reaction of nitriles with azide for ultrafiltration (UF) membrane application. The as-obtained TZ-PAN copolymers were further modified by N-arylation with methyl iodide to get methylated tetrazole polyacrylonitrile (MTZ-PAN). The chemical structures of TZ-PAN and MTZ-PAN copolymers were confirmed by ¹H NMR spectra. The degree of functionalization (DF) of PAN copolymers ranged from 5% to 16%. Subsequently, the ultrafiltration membranes based on the TZ-PAN and MTZ-PAN copolymers were prepared by a non-solvent phase inversion method. The morphological structure, hydrophilicity and mechanical properties of the UF membranes were thoroughly investigated. The TZ-PAN membranes showed a lower water contact angle than that of the PAN UF membrane (about 63°) due to the high hydrophilicity of the tetrazole groups. Thus, a high water flux was observed for TZ-PAN membranes. Moreover, the hydrophilicity of PAN copolymers with tetrazole copolymers could be tuned by N-arylation of the tetrazole groups. The highest water flux of 715.41 L per (m² h bar) was achieved for the TZ-PAN-16 UF membrane. The investigation of water recovery ratio indicated the TZ-PAN-16 showed excellent anti-fouling properties. Although the hydrophilicity of MTZ-PAN decreased after N-arylation, the water flux was still as high as 242.1 L per (m² h bar) with a BSA rejection of 80.1%. These results indicated that tetrazole modification of PAN is an effective approach to tune PAN UF membrane properties.