Ultraviolet-water-induced angstrom-sized channels in membrane for precise ion sieving

Membranes with angstrom-sized channels can enable precise ion separation. While progress has been achieved in polymer membranes, which are the dominant commercial membranes, significant technical challenges of creating angstrom-sized channels remain in these membranes. Here, we report an ultraviolet-water (UV-W) strategy to create angstrom-sized channels (2.9-7.8 Å) with tunable size and charges in ion-tracked polymer membranes, where 'UV-W' refers to water illuminated by ultraviolet light, which is able to generate highly oxidative hydroxyl radicals. These generated hydroxyl radicals can scissor polymer chains within the ion tracks. Thus, we first create water passages within the polymer, then with the aid of hydroxyl radicals we subsequently form transport channels. The resultant membrane exhibits outstanding separation performance with a Li⁺ permeation rate of 0.3 mol m^-2 h^-1 and Li⁺/Mg²⁺ selectivity of 1024, which surpassed the performance of the existing polymer membranes. This easy approach provides an avenue for developing angstrom-sized channels in diverse polymers, offering broad application potential in clean energy fields.