Exploring H-bonding interaction to enhance proton permeability of an acid-selective membrane

Abstract Acid recovery from industrial aqueous streams is an essential process, which commonly requires a cost-effective, energy-efficient, and straightforward approach, such as membrane technology. However, the limited acid/salt separation performance of the membrane materials makes the use of membrane technology very challenging. In this study, we fabricated acid-selective membranes by grafting urea groups and quaternary ammoniums (QA) containing side chains on the hydrophobic poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) backbones. As confirmed by Nano-scale microscopy and Small-angle X-ray scattering techniques, the intramolecular H-bonding interactions between urea units facilitate self-assembly of the side chains and the formation of continuous acid transport channels. The produced QA clusters also enabled fast anion transportation but reject cations transport, while the H-bonding networks provide a proton conduction pathway to endow high acid/salt selectivity. The resultant acid selective membranes showed a higher H+ dialysis coefficient (0.081 m h−1) and better selectivities for the separation of HCl from FeCl2 aqueous solution (31.1) than the recently reported commercial membranes. Moreover, ten consecutive cycles of acid recovery tests demonstrated excellent operational stability of the representative membrane.