Liquid-solid interfacial polymerization of thin-film composite nanofiltration membrane

Interfacial polymerization prepared polyamide (PA) nanofiltration membranes are widely used for desalination and wastewater recovery due to their lower operating pressure compared to reverse osmosis desalination and ease of scalability. The diffusion behavior of amine (PIP) and acyl chloride (TMC) monomers make a significant impact on PA structure and performance. In this paper, through freezing the aqueous amine reactive solution which turned the liquid–liquid reaction process into liquid–solid and regulated the amine monomer diffusion behavior, an ultra-thin, defect-free PA layer was achieved. The effect of PIP solution temperature in the range of −15 to 25 °C on membrane morphology, chemical composition and surface properties was investigated. The results indicated that PIP diffusion rate had a positive effect on the crosslinking degree of formed PA layer. However, frozen amine solution effectively inhibited the diffusion rate of PIP and hydrolysis of TMC which simultaneously improve the permeability and selectivity. The fabricated membrane by liquid–solid reaction process showed hydrophilic, dense and ultrathin PA layer with a high pure water permeance (23.7 L·m−2·h−1·bar−1) and good retention of salt (95.4 % for Na2SO4). Also, the good selectivity to divalent cation and anion, and excellent stability of the membrane prefigured its potential in application of various water treatment fields.