Negatively charged polyamide thin film composite membrane with ultra-smooth selective layer and excellent organic solvent resistance for nanofiltration application

This work reports a novel negatively charged thin film composite-polyamide (TFC-PA) membrane with ultra-smooth selective layer prepared via interfacial polymerization for nanofiltration (NF) and organic solvent nanofiltration applications. Alkali-modified polyacrylonitrile (PAN) ultrafiltration (UF) was used as substrate. Poly(ethyleneimine) (PEI) and trimesoyl chloride were used as functional monomers of aqueous and organic solution, respectively. The effect of supporting salt concentration in the aqueous PEI solution on the improvement of the PEI assembly regularity was investigated. Under optimal conditions, the average surface roughness (Sa) of the prepared TFC-PA membrane surface was 5.4 nm. It achieved a salt rejection of 97.6% and a flux of 38.2 L m–2 h–1 for 2,000 mg L–1 Na2SO4 aqueous solution at 1.0 MPa and 20°C. Furthermore, it maintained nearly constant rejection and flux after being immersed in methanol, n-hexane, acetone and ethyl acetate, respectively, for 60 d, indicating the excellent resistance to these solvents.