Selective Polymeric Membranes for Ion Specific Separation

Providing sustainable supply of clean water and energy is critical for the survival and development of human kind. Membrane-based technologies are widely applied for water purification (e.g., electrodialysis (ED) and membrane capacitive deionization (MCDI)), energy generation (e.g., reverse electrodialysis (RED)) and storage (e.g., redox flow battery (RFB)). To achieve maximum water and energy generation efficiency, those technologies all rely on ion exchange membranes (IEMs) to selectively transport certain ions of interest. Moreover, those technologies expose IEMs to a wide variety of ions, which are typically different from the commonly studied sodium and chloride. Fundamental knowledge of interactions between polymeric IEMs and diverse ions to guide membrane permselectivity optimization remains insufficient. Therefore, this work is aimed at closing the knowledge gap by understanding how the experimental, ion and polymer chemistry specific factors affect the ion-membrane interaction as well as membrane separation performance.

The influence of experimental factors on membrane apparent permselectivity measurement inaccuracy was examined, and experimental factors were demonstrated to introduce no-larger-than 2% uncertainty to permselectivity. Ion specific factors such as bare and hydrated ion radii, ion geometry and complexation-forming nature were demonstrated to affect membrane permselectivity via thermodynamic sorption and kinetic diffusion effects. The membrane fixed charge group chemistry was demonstrated to introduce up to 6% permselectivity enhancement. Results from this research addressed knowledge gaps from the experimental, ion and polymer chemistry specific perspectives and can be applied to guide the design, engineering and optimization of ion specific selective membranes, which will facilitate the sustainable supply of clean water and energy.