Preparation of composite anion-exchange membrane with acid-blocking performance for brine reclamation by bipolar membrane electrodialysis

It has been realized the proton leakage behavior of anion-exchange membrane (AEM) seriously influences the practical applications of bipolar membrane electrodialysis (BMED), for example, the reclamation of brine. In this work, a concept of composite AEM, coating a thin acid-blocking layer bearing weak base functional groups onto a strong base AEM substrate, is put forward to alleviate the membrane conductivity deterioration due to the endowment of acid-blocking property. Above all, Poly(vinylidene fluoride)-graft-Poly[2-(N,N-dimethylamino) ethyl methacrylate] (PVDF-g-PDMAEMA which embraces significant hydrophilic differences between the side and main chains is synthesized by atom transfer radical polymerization (ATRP) and used for preparing the acid-blocking layer by solvent evaporation. Subsequently, series of experiments for measuring the water uptake, the acid adsorption, the current-voltage curve and transport number are performed to optimize the ion-exchange capacity of as-synthesized membrane material. Furthermore, as-prepared acid-blocking layer is coated onto the a strong base AEM substrate fabricated from the blend of PVDF and cross-linking PDMAEMA to prepare the supposed composite AEM. SEM observation clearly demonstrates the bilayer structure and good adhesion therein. AFM phase image confirms the formation of microphase separation morphology in which the hydrophilic channel used for ion transport looks uniform, continuous and well-connected. The ED-based acid concentration and BMED-based brine reclamation experiments show as-prepared composite AEM has an excellent acid-blocking performance and acceptable membrane resistance in comparison with the conventional AEM and even the commercial acid-blocking AEM. This indicates that the proposed AEM-preparing strategy may contribute to beating the trade-off effect between acid-blocking performance and membrane conductivity.