A durable thin-film nanofibrous composite nanofiltration membrane prepared by interfacial polymerization on a double-layer nanofibrous scaffold

A novel kind of thin-film nanofibrous composite (TFNC) nanofiltration membrane consisting of a polypiperazine amide (PPA) barrier layer, an ultrathin electrospun poly(acrylonitrile-co-acrylic acid) (PAN-AA) transitional mid-layer and an electrospun polyacrylonitrile (PAN) nanofibrous supporting layer, was successfully fabricated by interfacial polymerization with piperazine (PIP) and trimesoyl chloride (TMC) onto the PAN-AA/PAN double-layer substrate. The PAN-AA nanofibrous mid-layer played two important roles between the PPA barrier layer and the PAN nanofibrous supporting layer. It could be swollen in the alkaline aqueous monomer (PIP) solution to form an intermediate hydrogel film, which acted as the transitional mid-layer to cover the majority of the large surface pores of the electrospun PAN nanofibrous substrate. On the other hand, the hydrophilic PAN-AA hydrogel film could capture and reserve abundant PIP monomer to facilitate interfacial polymerization with TMC to form an endurable ultrathin PPA barrier layer, resulting in an integrated composite membrane confirmed by the mechanical properties. The resultant TFNC membranes demonstrated a high rejection rate (98.2%) and high permeate flux (64.4 L m⁻² h⁻¹) for MgSO₄ aqueous solution (2.0 g L⁻¹), and also exhibited excellent structural stability due to the strong interactions between the barrier layer and the nanofibrous support that were enhanced by the transitional PAN-AA mid-layer.