Ultrahigh permeable and selective nanofiltration membrane mediated by in-situ formed interlayer
Nanofiltration (NF) membranes with high permeability and selectivity are urgently needed to reduce energy consumption and improve separation efficiency in desalination and wastewater treatment. Herein, an ultrahigh permeable and selective NF membrane mediated by in-situ formed interlayer is designed and prepared through chitosan (CS) assisted interfacial polymerization of piperazine (PIP) in water with trimesoyl chloride (TMC) in n-hexane. CS exists in forms of free molecules and nanoparticles (CSPs) to in-situ form interlayer due to their slower diffusion rate compared with PIP during interfacial polymerization and to mediate the structure and performance of the NF membrane. Through controlling CS concentration and aging time of CSPs in the aqueous amine solution, the NF membrane surface morphology can be systematically tuned from nodular to vermicular and to convex structure; while the thickness of polyamide layer obtained can be all kept at about 20 nm. The resulting NF membrane shows an unprecedented separation performance with a pure water permeance up to 45.2 L·m-2·h-1·bar-1, equivalent to about 5-fold the controlled PIP/TMC NF membrane, while maintaining Na2SO4 rejection of 99.3%. The superior performance is attributed to a synergistic effect of reduced thickness of polyamide layer, increased special surface area with negative charges, and low-resistant water nanochannels in the interlayer. This work provides a cost-effective and simple route to fabricate ultrahigh permeable and selective NF membranes.