Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination

Aqueous two-phase system features with ultralow interfacial tension and thick interfacial region, affording unique confined space for membrane assembly. Here, for the first time, an aqueous two-phase interfacial assembly method is proposed to fabricate covalent organic framework (COF) membranes. The aqueous solution containing polyethylene glycol and dextran undergoes segregated phase separation into two water-rich phases. By respectively distributing aldehyde and amine monomers into two aqueous phases, a series of COF membranes are fabricated at water-water interface. The resultant membranes exhibit high NaCl rejection of 93.0-93.6% and water permeance reaching 1.7-3.7 L m^-2 h^-1 bar^-1, superior to most water desalination membranes. Interestingly, the interfacial tension is found to have pronounced effect on membrane structures. The appropriate interfacial tension range (0.1-1.0 mN m^-1) leads to the tight and intact COF membranes. Furthermore, the method is extended to the fabrication of other COF and metal-organic polymer membranes. This work is the first exploitation of fabricating membranes in all-aqueous system, confering a green and generic method for advanced membrane manufacturing.