Leaf-inspired hybrid membrane assembled by covalent organic framework and cellulose nanocrystals for efficient desalination

Covalent organic framework (COF) membranes hold great promise in molecular separations. However, COF membranes fabricated from COF nanosheets only often suffer from boundary defects with undesirable separation performance due to the small lateral size and weak interlayer interaction of COF nanosheets. Inspired by the 2D lamellar structure of leaf where 1D veins distributed in the leaflets render them integrity and robustness, vein-mimic 1D sulfonated cellulose nanocrystals (S-CNC) were assembled with the leaflet-mimic COF nanosheets to fabricate S-CNC-COF hybrid membranes. The hydrogen bonding between crystalline COF nanosheets and hydrophilic S-CNC could effectively eliminate boundary defects. More importantly, S-CNC with high rigidity could ensure the oriented assembly of COF nanosheets during the membrane formation process. With ordered structure, high hydrophilicity, and reduced mass transport resistance, the optimal S-CNC-COF membrane exhibits an excellent water flux of 314.93 kg m−2 h−1 and rejection of NaCl (99.99%). This leaf-inspired strategy sets up a platform for designing advanced hybrid COF membranes for molecular separations.