Sub-nanoporous polyimide membrane with selective and fast K+ transport

Biological ion channels have excellent monovalent ion separation performance, and it is of great significance to develop artificial membrane materials with monovalent ion selectivity based on their mechanism. The latent-track method is a new technology to prepare sub-nanometer channels on polymer membranes by swift heavy ion irradiation. This method has been widely applied in the study of mono/divalent ion separation membranes, but its application in monovalent ion separation membranes still needs to be explored. In this work, polyimide (PI) film was irradiated by swift heavy ion, then water rinsed, and the sub-nanoporous PI membrane with effective channel size in the range of 0.30 and 0.66 nm was fabricated, then its electrical and transport properties were studied. Due to the smaller hydrated diameter and lower hydration energy of K+, the membrane exhibited good selectivity for K+. The selectivity ratio of K+/Li+ is 3.4–3.9, and the maximum K+ flux can reach 0.44 mol m−2 h−1 at 55℃. The sub-nanoporous PI membranes are expected to be applied in salt lake lithium extraction, fine processing of potassium and lithium, and other relevant scenarios. [Display omitted] •A sub-nanoporous PI membrane with more concentrated effective size between 0.30 and 0.66 nm was prepared by ion irradiation and water rinse.•The sub-nanoporous PI membrane exhibited an actual K+/Li+ selectivity ratio of 3.4–3.9, and the maximum K+ flux can reach 0.44 mol m−2 h−1 at 55℃.