Pregelation of sulfonated polysulfone and water for tailoring the morphology and properties of polyethersulfone ultrafiltration membranes for dye/salt selective separation

Sulfonated polysulfone (SPSf) and water as additives were employed to tailor the morphology and performance of polyethersulfone (PES) ultrafiltration (UF) membrane using non-solvent induced phase separation (NIPS) for the purposes of dye and salt selective separation. Results showed that the viscosity of PES/SPSf/DMAc casting solution (polymer concentration 28 wt%) sharply increased from 1900 to 2650 mPa s with the addition of H2O (7 wt%) owning to the formation of pregelation. It was also revealed that PES polymer chains solidified and shrank faster than SPSf polymer chains during NIPS process, leading to –SO3- groups of SPSf to cover the surface of PES/SPSf polymer matrix. The resultant PES/SPSf UF membrane possessed superior pure water permeance (110.4 L/m2 h bar) compared with the pristine PES membrane (0.13 L/m2 h bar). The improvement in water permeance was ascribed to the synergy of SPSf and water, which enhanced the surface pore size, top surface porosity and hydrophilicity of PES membrane. Meanwhile, molecular dynamic (MD) simulations revealed that H2O can weaken the interaction between PES and SPSf chains and slow down the mutual diffusion in favour of the movement and ordered arrangement of chains. Additionally, the rejection of Evans blue (EB), Coomassie brilliant blue (BBR), Congo red (CR) and Acid fuchsin (AF) dye solution (0.1 g/L) by PES/SPSf membrane were 99.0%, 99.9%, 99.2% and 90.1%, respectively, whereas Na2SO4 rejection was less than 5%. In sum, this work supplies a simple avenue to tailor PES membrane with enhanced permeance as well as separation performance of dye/salt mixture.