Fabrication of COF-LZU1/PVDF composite loose nanofiltration membranes through oligomer-triggered interfacial polymerization (OT-IP) for highly efficient dye/salt separation

Covalent organic frameworks (COFs) have advantages such as easy functionalization, abundant regular pores, low density, and are widely used in the preparation of membrane materials. In this study, the well-grown COF-LZU1 (LZU for Lanzhou University)/polyvinylidene fluoride (PVDF) loose nanofiltration (NF) composite membranes were prepared through oligomer-triggered interfacial polymerization (OT-IP) at room temperature. Due to its pore size of 1.72 nm, the prepared COF-LZU1/PVDF membrane not only exhibited an ultra-high rejection for dyes (99.4 % for Methyl blue, 99.7 % for Congo red, and 99.1 % for Eriochrome black T). In addition, the filtration experiment of the mixed CR/NaCl solution showed a dye/salt selectivity factor of 328.7, as well as a permeance of 77.0 L·m⁻²·h⁻¹·bar⁻¹ and a high pure water permeability of 112.3 L·m⁻²·h⁻¹·bar⁻¹. A continuous filtration experiment showed that the COF-LZU1/PVDF membrane exhibited excellent operational stability. The findings suggest that COF-LZU1/PVDF membrane show promise for use in separating dyes and salts.