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

Abstract 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.