Improved antifouling of anion-exchange membrane by polydopamine coating in electrodialysis process

The fouling, in particular the organic fouling of anion exchange membranes (AEMs), is a serious problem in electrodialysis (ED). In this paper, we attempted to improve the antifouling potential of AEM by surface modification with polydopamine (PDA). The antifouling potential was evaluated by the transition time, i.e. the time elapsed before fouling took place, using sodium dodecyl benzene sulfonate (SDBS) as a model foulant. The negative surface charge density, hydrophilicity and roughness of the membrane surface were increased with increasing dopamine concentration in the modification solution. The increases in negative surface charge density and hydrophilicity increased the antifouling potential, while the increase in surface roughness decreased the antifouling potential. Consequently, the optimum modification condition was the immersion into a 0.1 kg/m3 dopamine aqueous solution at pH 8.8 for 24 h. Under this condition, the antifouling potential of AEM was sufficiently improved. It was shown by theoretical analysis of the fouling data that the surface modification with PDA prevented the adsorption of SDBS micelles and improved the antifouling potential. Furthermore, it was experimentally confirmed that the modified membrane was highly stable. © 2013 Elsevier B.V. All rights reserved.

Surface modification with PDA was attempted to improve the antifouling potential of anion exchange membrane in the ED process. PDA has a strong adhesive force with many materials and it was expected to improve the negative surface charge and hydrophilicity of membrane. The membrane surface was modified by immersing the membrane in the dopamine solution at pH 8.8. The antifouling potential of anion exchange membrane was evaluated with transition time, i.e. the time elapsed before fouling took place. The hydrophilicity of modified membrane surface increased with immersion time and became almost constant after 24 hour immersion. The negative surface charge density and the hydrophilicity increased with increasing of dopamine concentration in the modification solution. On the other hand, the surface roughness increased with dopamine concentration. The increase in negative surface charge density and hydrophilicity indicates the increase of antifouling potential, while the increase in surface roughness indicates the decrease of antifouling potential. Improvement of the overall antifouling potential was determined by the competition between improved antifouling potential through increased negative charge density and hydrophilicity of membrane surface and decreased antifouling potential through increased membrane surface roughness on the other. Consequently, the optimal dopamine concentration and optimum immersion time were 0.1 kg/m3 dopamine aqueous solution at pH 8.8 and 24 h, respectively. Under these conditions, the antifouling potential of anion exchange membrane was sufficiently improved. In addition, the fouling data were analyzed theoretically with the model previously proposed. It was concluded that the adsorption of SDBS micelles was prevented by the surface modification with PDA through increased negative surface charge density and hydrophilicity.