A critical review on polyamide and polyesteramide nanofiltration membranes: Emerging monomeric structures and interfacial polymerization strategies

Thin film composite (TFC) nanofiltration (NF) membranes —constructed via interfacial polymerization (IP) of piperazine (PIP) and trimeric chloride (TMC)— have demonstrated versatile usage in water treatment and critical resources extraction. Flexible regulation of membrane pore apertures in the range of 0.5–2 nm further enables their increasing role as a potential driver in circularity; this puts forward higher requirements for precise separation. Nonetheless, rapid and irreversible IP reaction between highly reactive monomers forms a thick and high-crosslinked PA layer, leading to a permeability-selectivity trade-off limit. Fouling propensity and weak chlorine resistance of PA membranes further impede industrial usage in liquid separations. On this basis, the design of new monomeric structures with different reactive groups and geometries is highly efficacious to develop high-permeable NF membranes with improved water-solute and/or solute-solute selectivity. This review introduces different categories of new monomers and highlights their impact on the physicochemical structures and filtration performance of TFC membranes. An additional focused description is given to newly developed IP strategies assisted by molecular-level design, with an emphasis on recent breakthroughs on ultrahigh permselective TFC membranes. Finally, current challenges and prospects on newly monomer-based TFC membranes are given to provide useful guidance for design and development of fit-for-purpose NF membranes.