Polyamide nanofiltration membranes by vacuum-assisted interfacial polymerization: Broad universality of Substrate, wide window of monomer concentration and high reproducibility of performance

Vacuum assistance is used for filtering solid substances onto porous substrates to create composite membranes typically. However, the potential of this approach has rarely been assessed in facilitating the distribution of liquids within those porous substrates to fabricate composite membranes in typical interfacial polymerization. In this work, we demonstrate the advantages of vacuum-assisted interfacial polymerization (VAIP) in terms of substrate universality, monomer concentration range, and performance reproducibility in the fabrication of polyimide nanofiltration membranes. Aqueous solutions of PIP can be homogeneously distributed by vacuum filtration on diverse microfiltration substrates of polyether sulfone (PES), Nylon-66, polyvinylidene fluoride (PVDF), cellulose acetate (CA), and mixed cellulose esters (MCE), respectively. Interfacial polymerization is then performed on these substrates using different concentrations of piperazine (PIP, 0.0075-0.1000 wt%) and trimoyl chloride (TMC, 0.0112-0.1500 wt%). Remarkably, a uniform and ultra-thin polyamide layer with a thickness of 15 nm can be achieved at an exceptionally low PIP concentration of 0.0250 wt%, exhibits a rejection rate of over 98.8 % for Na2SO4 and a water permeance of 25.8 L.m(-2).h(-1).bar(-1). The membranes with a diameter of 30 cm demonstrate reproducibility in nanofiltration performance and satisfactory long-term stability. This method offers a simple yet effective strategy for regulating the liquid distribution and optimizing interfacial polymerization in fabricating polyamide composite membranes.