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

Abstract Membrane with angstrom-sized channels can enable precise ion separation. While progress has been achieved in polymer membranes, which serve as 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 that water illuminated by ultraviolet light can generate highly oxidative hydroxyl radicals. These generated hydroxyl radicals can scissor polymer chains within the ion tracks. Thus, we create water passages within the polymer firstly, then with the aid of hydroxyl radicals to subsequently form transport channels. The resultant membrane exhibits outstanding separation performance with 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 facile approach provides an avenue for developing angstrom-sized channels in diverse polymers, offering broad application potential in clean energy fields.