Non-polyamide nanofiltration (NPA-NF) membrane: A non-mainstream but indispensable member of the "membrane family"

The unique sieving capability of nanofiltration (NF) technology has built up its important role in water or organic solvent purification. Polyamide (PA) thin film composite (TFC) NF membranes (PA-TFC-NF) have dominated research and applications involving NF technology because of the facile, mature manufacturing method and acceptable permeability/selectivity. However, non-polyamide NF membranes (NPA-NF) without a conventional polyamide selective layer also experienced great progress during the past decade in terms of anti-fouling ability, chlorine resistance, durability, chemical stability, and/or extreme pH resistance. In this review, NPA-NF membranes are classified into six categories: 1) NPA-NF membranes based on the substitution of a monomer in interfacial polymerization, 2) NPA-NF membranes fabricated with phase inversion, 3) Graphene based NPA-NF membranes, 4) Metal organic framework (MOF) based NPA-NF membranes, 5) Covalent organic framework (COF) based NPA-NF membranes and 6) Ceramic NPA-NF membranes. On the basis of this classification, the fabrication mechanism, material performance and advantages/disadvantages of each kind of NPA-NF membrane are systematically expounded. Finally, current challenges and future prospects are provided. Lessons gained from this review may clarify the exact role of NPA-NF membrane in "Membrane family" and promote its sustainable development.