Zeolite membranes for ion separations from aqueous solutions

• We review recent studies on zeolite membranes as a new type of ion separator.
• Zeolite membranes are capable of purifying water from salt solutions by RO.
• Zeolite membranes are highly proton-selective ion conductors in aqueous solutions.
• Permselectivity of water and proton over metal ions by size exclusion effect.
• Ion separation efficiency depends on zeolite pore size and surface chemistry.

Zeolite membranes have been recently demonstrated as a new type of ion separator for brine desalination and proton conduction in redox flow batteries. Although it is still in early stage of research and development, experimental and theoretical works have shown that ion separation by zeolite membranes relies primarily on the size exclusion (steric) effect enabled by the zeolite's uniform subnanometer pore sizes. Research has also revealed that the zeolite surface properties, for example, hydrophilicity, framework charges, and extraframework charge compensators, and operating conditions, for example, temperature, pressure and solution concentration, could play significant roles in determining the ion separation efficiency.

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