Improving permeability, hydrophilicity and antifouling characteristic of PES hollow fiber UF membrane using carboxylic PES: A promising substrate to fabricate NF layer

In this work, carboxylic polyethersulfone (CPES) was synthesized through acetylation and oxidation of polyethersulfone (PES). The success rate of the reaction and the formation of CPES were analyzed by fouriertransform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Negatively charged CPES/PES blend hollow fiber ultrafiltration (UF) membranes were fabricated via the wet-spinning method. Surface and structural properties of the membranes were characterized by scanning electron microscopy (SEM), water contact angle (WCA), and atomic force microscopy (AFM). significant improvement of the membranes' hydrophilicity due to the presence of the CPES was approved through the decrease of WCA from 76 degrees (neat PES) to 42 degrees. The permeability was increased up to about three times of the neat PES membrane, while the rejection was not affected that much and just decreased from 94% to 86%. Membrane's antifouling properties were significantly improved according to the flux recovery ratio (FRR) of more than 90%. The best-suited hollow fiber membrane was used as a substrate for hyperbranched polyethyleneimine (HPEI) thin-film layer assembly to achieve nanofiltration (NF) membrane. It was shown that the presence of the CPES improved the layer assembly of the HPEI and thus the MgCl2 rejection in NF membranes. In this case, the salt rejection increased up to 95% for the best-suited membrane from 81% for the membrane with a neat PES substrate.