Controllable Synthesis of Polyamide-Supported Covalent Organic Framework Membrane for Efficient Desalination

Desalination is an effective strategy to tackle global freshwater shortages. Membrane separation, as an emerging desalination technique, possesses broad application prospects. Herein, a series of ABC-stacking COF-HT-x (x = 1, 2, 3, 4) membranes with different thicknesses were controllably synthesized on a polyamide substrate via a solvothermal method. Benefiting from interlayer staggered stacking, the membrane possessed ultra-micropores (0.53 nm), which were among the smallest pores reported for COF membranes and matched well with the dimensions of hydrated salt ions. Meanwhile, the fabricated membranes had a relatively large specific surface area, negative surface charge, and excellent structural stability. Owing to these merits, the synthesized membrane was utilized for desalination. The optimal COF-HT-3 membrane achieved high desalination efficiencies of 98.9, 99.3, 94.6, 99.4, 98.6, and 99.8% for Na2SO4, MgSO4, NaCl, MgCl2, CaCl2, and FeCl3, respectively. Besides, the COF-HT-3 membrane also showed an outstanding desalination effect to high-salinity solutions and real seawater. It could also maintain a good desalination effect over a wide pH range. A series of experiments and characterizations disclosed that size sieving and the Donnan effect jointly dominated the desalination mechanism of the membrane. This work offers a facile strategy for designing high-performance COF desalination membranes and guides the development of advanced water purification materials.