Hierarchically engineered flexible COF/CNT-MOF composite membrane with interpenetrated pores for water purification

Covalent organic frameworks (COFs) have shown great potential in separation applications owning to their tunable framework and rich chemical properties. However, preparing flexible COF membrane with precise separation performance is challenging. Herein, inspired by the “brick–mortar” structure, we designed a flexible COF composite membrane with the synergy of carbon nanotube (CNT) and metal–organic framework (MOF) through a multi-interface regulation strategy. Specifically, CNT (sand) was inserted in COF interlayers (brick) for improved flexibility. To achieve better molecular-sieving effect of the membrane, MOF (cement) was confined grown in the pores of COF/CNT composite. The formed heterogeneous structure endows the COF composite membrane with interpenetrated molecular sieving pores. As a result, the obtained COF composite membrane exhibits good flexibility. Meanwhile, the COF composite membrane shows high permeability and rejection ratios for dyes because of the precise sieving pores. This facile strategy presents an attractive insight into the development of other advanced membranes for broad application prospects.