In-situ covalently bonded supramolecular-based protective layer for improving chlorine resistance of thin-film composite nanofiltration membranes

To improve the chlorine resistance of the polyamide-based NF membranes, ferric ion and tannic (Fe^III-TA) networks were grafted onto the polyamide membrane surface via an in-situ modification strategy. The separation performance tests by a cross-flow NF system showed that the grafted membrane (TFC-n) possesses an obviously improved rejection for the selected salts, dyes, and micropollutants with only ~10.0% decrease in water permeability. The chlorination experiments under various pH values demonstrated that the TFC-n membrane presents much superior chlorine resistance than that of the control membrane. Importantly, the grafting layer was also applied to a commercial NF 270 membrane, and the Fe^III-TA grafted NF 270 membrane exhibited much higher chlorine resistance than that of the bare NF 270 and polyvinyl alcohol (PVA) coated NF 270 membranes. The greatly enhanced chlorine resistance can be ascribed to the combined effects of enhanced size exclusion, additional protection, and sufficient radical scavenging originated from the grafted Fe^III-TA networks. The high-performance of the grafted membrane highlight the feasibility of Fe^III-TA networks as a promising material for the construction of chlorine resistant interfaces for environmental nanocomposites.