Side grafting tertiary amine in polyaryl ether sulfone membranes for reversible-multiple separations

Abstract

In this study, a new category of copolymer was designed by side grafting of tertiary amines (TA) on polyaryl ether sulfone. The synthesized copolymers PES/ATA displayed superior thermal properties with a glass transition temperature of 200–225 °C. These copolymers with favorable film-forming properties were used to fabricate ultrafiltration membranes via a phase inversion approach. Surprisingly, it was found that the filtration performance of these resultant membranes could be reversibly tuned between a facile acid oxidation (CH3COOH:H2SO4:H2O2 = 40:1:1) and alkali solution (solution of 20 wt% NaOH, immersed for 4–8 h) treatment. While the water flux of dye solution had a twofold reduction, the oxidized membranes showed distinctly enhancement of methylene blue rejection from 35% to 91.5% after oxidation treatment. Subsequently, alkali treatment of the oxidized membranes allowed their water flux to recover up to 89% as that of pristine membranes, and the methylene blue rejection can recover to almost the same as that of pristine membranes. This phenomenon was closely related to the introduced reactive TA units: the TA group in the polymeric membrane was converted into stimulus-responsive amine oxide (AO) unit, then its charge can be reversibly changed between the acid oxidation and alkali treatment, and that can be used to tune the electrostatic repulsion and further tuned the membrane pore size. In addition, compared with the polyarylene sulfone membrane, the mechanical properties of these membrane had almost no deterioration after several treatment cycle. This study supplies a novel and facile routine to fabricate functional membranes with reversible-tunable filtration properties.