Facile fabrication of sulfonated polyphenylenesulfone (sPPSU) membranes with high separation performance for organic solvent nanofiltration

By means of (1) electrostatic interactions between polyethyleneimine (PEI) and sulfonated polyphenylenesulfone (sPPSU) as well as (2) subsequent glutaraldehyde (GA) cross-linking modification, two types of OSN membranes with high solvent permeances and good solute rejections have been fabricated. The PEI-coated sPPSU membrane fabricated under the optimized dip-coating condition has a molecular weight cut-off (MWCO) of about 500 Da in ethanol, while the GA-cross-linked membrane has a MWCO of 300 Da. The former has a rejection of 99.8% to Rose Bengal and a permeance of > 40 Lm⁻² h⁻¹ bar⁻¹ in the methanol system because methanol has a small kinetic diameter and a low viscosity. The permeance drops to about 10 Lm⁻² h⁻¹ bar⁻¹ and the rejection dips slightly to 99.1% in the ethanol system because ethanol has a large kinetic diameter and a high viscosity. The latter possesses an ethanol permeance of 1.4 Lm⁻² h⁻¹ bar⁻¹ and shows stable OSN performance in 14-day tests to Methylene Blue in methanol, ethanol and isopropanol (IPA) systems. The GA-cross-linked membrane and the commercially available DuraMem 300 membranes have a similar MWCO, but the GA-cross-linked membrane has a 3.5-time higher ethanol permeance than DuraMem 300. This study may provide useful insights to design sPPSU membranes with high separation performance for OSN applications.