Mineralization-inspired preparation of composite membranes with polyethyleneimine-nanoparticle hybrid active layer for solvent resistant nanofiltration

Inspired by mineralization, a series of composite membranes with polymer-nanoparticle hybrid active layer were prepared via a generic and facile approach in this study for solvent resistant nanofiltration. Polyethyleneimine (PEI) was employed as polymer matrix, the -NH2/-NH- groups of which catalyzed the inorganic precursor (tetraethoxysilane/tetra-n-butyl titanate) to synthesize inorganic nanoparticles (silica/titania) with tunable structure. Then, the active layers were covalently cross-linked for further enhancing the thermal and structural stabilities of the composite membranes. The composition and microstructure of the composite membranes were investigated through Fourier transform infrared spectroscopy, scanning electron microscope, thermogravimetric analysis, and contact angle measurement. The nanofiltration performances in terms of solvent uptake, area swelling, flux, and rejection of the composite membranes were measured using n-heptane, toluene, butanone, ethyl acetate, and isopropanol as solvents, as well as polyethylene glycol as solute. The results suggested that the presence of nanoparticles in active layer endowed the composite membrane with excellent solvent resistance in the above solvents (area swelling below 6%). Meanwhile, the nanoparticles dramatically elevated the rejection of the composite membrane while remaining the sufficient solvent flux and promising long-term operation stability. Moreover, the influence of the type of nanoparticle on the membrane performances was evaluated in detail.