Modulating hydrophobicity of composite polyamide membranes to enhance the organic solvent nanofiltration

Abstract

A kind of thin film composite polyamide nanofiltration (NF) membrane was synthesized via the interfacial polymerization between a new diamine monomer of 4,4′-diaminodiphenylmethane and trimesoyl chloride on the surface of cross-linked polyetherimide, and evaluated in some organic solvents including ACN, MeOH, EtOH, THF, etc. The optimal organic solvent NF membrane was selected to prepare respectively the hydrophilic membrane (Phi-NF) via grafting of Tris and the hydrophobic membrane (Pho-NF) via grafting of 2,2,2-trifluoroethylamine, combining with the characterization of ATR-FTIR, XPS, SEM, 13C NMR, AFM, etc. The permeance values of Phi-NF and Pho-NF membranes change greatly with organic solvents. Pho-NF-2 possesses the highest permeance of 66.4 L m−2 h−1 MPa−1 in THF with the erythrosin B (EB) rejection of 99.5%. Through analyzing the physiochemical properties of the organic solvents and calculating the surface energy, the correlations are deduced for the synthesized membranes, illustrating that the permeances of organic solvents are roughly proportional to the specific solvent properties for Phi-NF-2 and Pho-NF-2. The results suggest one promising method to enhance the separation performance of organic solvent NF membranes.