PH-responsive polyaryl sulfide sulfone amide membrane containing tertiary amine unit: Oxidation and reversible acid-base treatment

Abstract

Developing functional membranes with switchable pores for the separation of contaminants with different sizes has been challenging due to the lack of novel materials with adaptable and adjustable structures. Polymers containing the tertiary amine (TA) unit can be transformed via oxidation into amine oxide (AO) structure that can modulate the membrane pore size. In this study, new monomers containing pH-responsive TA units and diacyl chloride containing reducible thioether (-S-) groups were used to yield pore-size-adjustable membrane resin polyarylene sulfide sulfone amide/amide tertiary amine (PASSA/ATA) at room temperature. By varying the polymerization ratio of the reaction solution, membranes could be prepared directly through non-solvent induce phase separation (NIPS) method without extra treatment. By oxidizing the TA units to AO through acid condition (H2O2/H2SO4/CH3COOH), the PASSA/ATA membrane can be switched from ultrafiltration to loose-nanofiltration with the rejection of RO16 and rhodamine B increased from 18.4% to 34.3 % (pristine membrane) to 91.7 % and 98.5 %. The permeance and rejection rate of the oxidized membrane were found to recover to the initial state after alkali-treatment. The mechanism of the switchable pore size was elucidated by dissipative particle dynamics (DPD) simulations. Interestingly, the oxidized PASSA/ATA membrane showed good organic solvent resistance and in nanofiltration performance, as it was capable of retaining about 95 % of Congo red in N,N-dimethylformamide (DMF) with permeance of about 10 L m−2 h−1 bar−1. This work presents a facile and low-carbon approach to develop novel membranes with multiple filtration capabilities, potentially applicable in various separation processes.