Interfacial polymerized and pore-variable covalent organic framework composite membrane for dye separation

Covalent organic frameworks (COFs) with crystalline imide structure achieved remarkable application in the field of water treatment membrane. In this work, 1,3,5-triformylphloroglucinol (Tp) and benzidine (Bd) or melamine (Me) monomers as the assemble units were firstly in-situ interfacial polymerized upon polysulfone (PSf) porous substrate to form COFs composite membrane with a thin and stable COFs selective layer. Furthermore, adding melamine monomer during interfacial polymerization between Tp and Bd monomers could further introduce a triazine ring type-keto-enol tautomeric type into COFs selective layer, and adjust the molecular network structure and crystallinity of the COFs layer with variable pore aperture. The results indicated that the as-prepared TpBd/PSf and TpBdMe/PSf membranes could be efficiently applied for dye separation process with congo red rejection above 99.0%. Compared with TpBd/PSf membrane, water permeability of TpBdMe/PSf membrane increased from 33.6 L·m−2·h−1·bar−1 to 62.2 L·m−2·h−1·bar−1. Moreover, both TpBd/PSf and TpBdMe/PSf membranes exhibited excellent anti-fouling property, chemical and thermal stability. This work develops a facile method to prepare the imine-linked COFs membrane with variable pore aperture by changing reaction parameters and selecting appropriate amine monomers.