Efficient cation separation based on humidity control and adsorption

Precise ion sieving techniques are of great importance in various fields including the energy and environment. However, existing extraction methods, often associated with environmental risks, are lack of selectivity, time-consuming, and high cost. Here, we report a high-capacity sorbent made of polyacrylonitrile-chitosan composite spheres, capable of selectively adsorbing alkali or alkaline earth metal salts through controlled humidity levels, leveraging their distinct deliquescent humidity ranges. For lithium extraction specifically, this method demonstrates an extremely high adsorption capacity of 133.60 mg g^-1, far above all existing adsorbents and sieves. Moreover, a rapid adsorption rate of 83.64 mg g^-1 h^-1 is achieved, with a high selectivity and a recovery rate. Crucially, this approach is heralded for its environmental friendliness, cost-efficiency, and low energy consumption.