Polyamide-Supported Covalent Organic Framework Nanomembranes for Molecular Size-Dependent Selective Separation

Membrane-based separation has been demonstrated as an ecofriendly technology in the field of energy and the environment. However, simultaneously enhancing the permeability and selectivity of membranes remains a great challenge due to the lack of a tunable and ordered pore structure. Herein, a facile approach for the interfacial synthesis of polyamide (PA)-supported covalent organic framework (COF) nanomembranes was introduced for the first time, in which interfacial crystallization of COF was formed in a two-phase interface using 1,3,5-triformylphloroglucinol (Tp) and 2,5-diethoxy-terephthalohydrazide (Dth) as building units. The thickness of COF layers covered on a PA substrate ranged from 90 to 550 nm. The as-prepared COF nanomembranes (defined as Tp-Dth/PA) possessed many superior properties, including high porosity, tunable and ordered micropores, and good chemical/mechanical stability. Arising from the synergetic effect of the hydrophilic PA support and highly ordered porous structure of COF layers, the obtained Tp-Dth/PA nanomembranes exhibited outstanding performances in terms of permeability and rejection efficiency, in which the water permeance was up to 31.7 L m^–2 h^–1 bar^–1 and the retention rates for congo red (CR) and alcian blue 8GX (AB) were higher than 99.5 and 99.8%, respectively. Moreover, molecular separation of AB from a mixed aqueous solution was achieved with the Tp-Dth/PA nanomembranes based upon the principle of the size-exclusion effect. In addition, the Tp-Dth/PA nanomembranes could be successfully applied to the selective separation of dyes from industrial wastewater, demonstrating their great potential in water treatment.