LAUSR

Membrane-based ion separation is environmental friendly, energy efficient and easy to be integrated, which has been widely used in water desalination and purification systems. The existing separation technologies are yet difficult to achieve real time, in situ and reversible control of the separation process. Here, we design and fabricate a Prussian blue (PB) coordination polymer based membrane with uniform and electrochemically size-tunable subnanopores. The ion separation can be significantly and reversibly modulated through the electrochemical conversion between PB and Prussian white (PW). The permeation rates of small hydrated metal ions (Cs+ and K+) obviously increase upon switching from PB to PW, while the permeation rates of large hydrated metal ions (Li+, Na+, Mg2+ and La3+) remain constant. The membrane selectivity of small hydrated ions to large hydrated ions can be increased by more than two times during the electrochemical switch, which could be assigned to the slightly larger crystal size (e.g., pore window size) of PW than PB. The present approach provides a new strategy for constructing tunable seawater desalination and ion extraction systems.