Electrospun transition layer that enhances the structure and performance of thin-film nanofibrous composite membranes

Electrospun nanofibers with completely interconnected pore structures are increasingly considered as substrates for fabricating thin-film nanofibrous composite (TFNC) nanofiltration (NF) membranes. The poor adhesion between the large-pore substrate and dense selective layer has been considered as the bottleneck for wide application. This work presents the role of a transition layer on membrane structure as well as performance enhancement. Specifically, both polyethyleneimine (PEI)/polyacrylonitrile (PAN) transition layer and PAN substrate layer are formed by electrospinning. Interfacial polymerization (IP) is subsequently performed with trimesoyl chloride and piperazine. The introduction of the PEI modified transition layer improves the hydrophilicity, provides additional reaction sites for IP, and avoids the polymerization in the pores of nanofibers. The resultant composite NF membranes exhibit a compact and defect-free selective layer. Such an optimal structure leads to an excellent separation performance of 95.6% for orange ΙΙ dye (MW = 350.32 g/mol) rejection and 38.5 L m⁻²h⁻¹ bar^-1 for the pure water permeability. It exhibits stable long-term performance during low pressure (0.2 MPa) nanofiltration, which will afford significant directions for the actual application of the TFNC membranes in water purification and other fields.