Hybrid surface modification of an anion exchange membrane for selective separation of monovalent anions in the electrodialysis process

Electrodialysis is an electrochemical separation process which is used for the removal of ionic species from aqueous solutions. In this study selectivity of an anion exchange membrane was tuned towards formate (CHOO - ) anions compared to oxalates (C 2 O 4 2- ) based on the characteristics of formate anions which show lower hydration energy. In order to enhance the removal efficiency of monovalent anions in electrodialysis, a hybrid surface modification on a heterogeneous anion exchange membrane was carried out. Surface modification consisted of three steps: plasma treatment (activation of the membrane surface), functionalization (acidification) and coupling with Polyethylenimine and Glutaraldehyde. Treatment of the membrane was verified using FTIR, Scanning Electron Microscopy, and Atomic Force Microscopy. The electrochemical properties of the membrane were measured before and after the modification. The results showed that due to the presence of the amide groups on the surface of the membrane upon modification, the water content of the membrane decreased by 8% while no other significant changes were observed in the membrane properties. Finally, the membrane selectivity towards CHOO - / C 2 O 4 2- in electrodialysis process increased from 0.88 to 4.29 upon surface modification. • Hybrid surface modification of a heterogenous anion exchange membrane through three steps. • Hybrid modification include: plasma treatment, functionalization, and coupling with Polyethylenimine and Glutaraldehyde. • Enhancing the selectivity toward monovalent anions (formate) against multivalent anions (oxalate) in the Electrodialysis. • Increasing the membrane selectivity towards anions with less hydration energy by changing the surface hydrophilicity.