Covalent linkages are the key component of covalent organic frameworks (COFs). The development of stable and functional linkages is essential to expand the COFs family and broaden their application prospects. In this work, we report the synthesis of crystalline and chemical stable 4-carboxyl-quinoline linked COFs (QL-COFs) via Doebner reactions in both one-pot (OP) and post-synthetic modification (PSM) methods. Both methods can be universally applied to most of the reported imine COFs family via bottom-up construction or linkage conversion. Owing to the contractive pore size, more hydrophilic structure and better chemical stability than the conventional imine COFs endowed by 4-carboxyl-quinoline linkage, QL-COFs are supposed to possess a wider application range. We further demonstrate the nanofiltration membrane (NFM) based on QL-COF exhibited a desirable separation capacity with high rejection for small dye molecules (> 90%), high water permeance (850 L m⁻² h⁻¹ MPa⁻¹) and tolerance of extreme conditions (1 M HCl/NaOH), which were benefitted from the enhanced properties of QL-COFs. Additionally, efficient ion sieving properties were also achieved by QL-COF membrane. We anticipate that this work opens up a way for the construction of robust and functional COFs materials for practical applications.

A novel terpolymer (abbreviated as THV), which is a copolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, that possesses advantages of excellent hydrophobicity, mechanical properties, and chemical resistance is an ideal material for membrane distillation. In this study, THV hydrophobic membranes were fabricated by the electrospinning method. Morphology and properties (pore size distribution, liquid entry pressure, porosity, and contact angle) of the THV electrospun membranes with various fabrication conditions (solvent composition, THV concentration, and applied voltage) were systematically studied. Under the optimized condition, the membrane exhibited a good structure, wetting resistance, and surface hydrophobicity. The mean pore size, liquid entry pressure of water (LEP_w), and contact angle were 0.79 μm, 118.0 kPa, and 130.7°, respectively. Owing to the advantages of the raw material and fabrication method, the membrane showed excellent mechanical properties and desalination performance. The tensile strength was 5.41 MPa, and the elongation at break was 247.9%, which were 2.47 and 5.61 times higher than those of the poly(vinylidene fluoride) (PVDF) membrane, respectively. Additionally, the membrane distillation flux was 4.42 kg m⁻² h⁻¹, which was 1.93 times higher than that of the PVDF counterpart obtained under the same test condition via sweeping gas membrane distillation, and the salt rejection rate was higher than 99.8%.