Polyphenol-assisted in-situ assembly for antifouling thin-film composite nanofiltration membranes

Construction of a selective layer with high hydrophilicity is a promising way to prepare thin-film composite (TFC) nanofiltration (NF) membranes with high separation and antifouling performances. Nowadays, a common strategy is to incorporate hydrophilic additives through interfacial polymerization process, which is effective but complex. In this study, a facial polyphenol-assisted in-situ assembly approach during non-solvent induced phase separation (NIPS) was developed to prepare antifouling TFC NF membranes. Polyvinylpyrrolidone (PVP), a common pore-forming agent in the polyethersulfone (PES) casting solution, was in-situ assembled with tannic acid (TA) in the coagulation solution through hydrogen bonding interactions during solvent exchange in NIPS. A hydrophilic TA-PVP complex was generated as the selective layer on the membrane surface. The chemical compositions and hydrophilicity of the membrane surface can be tuned by varying the TA content in the coagulation solution. The optimized TA-PVP/PES TFC membrane exhibited a high pure water flux of 152.9 ± 3.2 L m⁻² h⁻¹ and satisfying rejections to small organic molecules (methyl orange of 73.6%, organic GII of 90.0%, congo red, methyl blue and alcian blue of nearly 100%). Moreover, the TA-PVP/PES TFC membrane showed superior antifouling performance against bovine serum albumin (BSA) during ternary-cycle filtration test, as well as satisfying long-term operational pH stability and chlorine-resistant property.