Multifunctional amines enable the formation of polyamide nanofilm composite ultrafiltration and nanofiltration membranes with modulated charge and performance†
Conventional thin film composite (TFC) nanofiltration (NF) membranes are positively or negatively charged with an active layer thickness of several nanometers depending on the preparation conditions. Low molecular weight cutoff (MWCO) ultrafiltration (UF) membranes obtained by the phase inversion process show low permeate flux due to the formation of a several micrometre thick skin layer. We have developed an extremely simple route to produce novel TFC NF (MCO∼180 Da) and UF (MWCO∼1 and 10 kDa) types of membranes with an active layer thickness in the range of 12–36 nm via supported interfacial polymerization using polyethyleneimine (PEI) as a monomer. The membrane charge, solute rejection, active layer thickness, and MWCO have been modulated by simple adjustment of diffusion of PEI towards the interfacial zone. TFC UF type of membranes were formed at PEI concentrations in the range of 0.01–0.03% w/v while NF membranes were formed at PEI concentrations in the range of 0.05–0.3% w/v. Our TFC NF membranes exhibited a permeate water flux of 19–24 L m−2 h−1 bar−1 which is about 4–5 times higher than those of PEI-based membranes and 1.3–4 times higher than those of a few commercial NF membranes of similar MWCOs. The TFC UF membranes showed a permeate flux of ca. 48–69 L m−2 h−1 bar−1, about 2–5 times higher than those of some UF membranes reported here. The process is scalable, and the membranes are useful for the separation of charge and neutral solutes with high efficiency.