This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Lithium, magnesium, potassium and many other ions usually occur together in natural and industrial solutions. Separating them from one another is a challenge, for example, in the extraction and processing of raw materials.
Researchers at the Max Planck Institute of Colloids and Interfaces and the University of Alberta in Canada have developed a membrane whose ability to separate ions can be controlled with light and an electric field. Under the conditions studied, the membrane transported lithium ions more than 200 times as readily as magnesium ions. For potassium ions, the ratio was over 500.
The results have been published in Angewandte Chemie. Membranes contain tiny channels through which certain ions can pass more easily than others. However, in complex systems such as brines, ion separation is more challenging.
Ions are surrounded by water molecules that form a hydration shell, whose size and strength vary between ions. These differences strongly influence how easily individual ions can pass through narrow nanoscale channels. Monovalent ions such as lithium (Li⁺) and potassium (K⁺) carry a single positive charge, while magnesium (Mg²⁺) carries two positive charges.
Because of differences in their hydration and interactions with the charged nanochannels, the ions move at different speeds. The researchers are exploiting this difference to separate monovalent and divalent ions from one another. The researchers developed a hierarchically structured membrane with three components.
Anodic aluminum oxide with aligned nanochannels serves as the substrate. On top of this is a thin layer of carbon nitride, which is the photoactive component. The third layer consists of a poly(ionic liquid), which is applied to the carbon nitride layer and forms the membrane's positively charged surface.
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