Covalent organic framework membrane on electrospun polyvinylidene fluoride substrate with a hydrophilic intermediate layer.

Generally, electrospun membranes have high mechanical strength, high porosity and low permeation resistance. Although covalent organic frameworks (COFs) have attracted great interest as advanced membrane materials, few works disclosed that the COFs composite membranes were synthesized on electrospun substrates. In this work, the electrospun polyvinylidene fluoride (PVDF) membranes were used as substrates for the preparation of COF composite membranes with graphene oxide and oxidized carbon nanotubes (GO-OCNTs) as an intermediate layer. The COF/GO-OCNTs/PVDF composite membranes were prepared by suction filtering the GO-OCNTs intermediate layer on the electrospun substrate, and then interfacial polymerization of COF layer. After adding the intermediate layer, the water permeance and dye retention rate of the composite COF membrane are both improved. By exploring the reaction parameters in the interfacial polymerization process, the optimized membrane shows that the rejection rate of Coomassle brilliant blue G250 (BBG-250) is about 97.1%, and the water permeability achieves 96.7 L m-2 h-1 bar-1. In addition, the COF/GO-OCNTs/PVDF composite membrane exhibits excellent chemical and mechanical stability. The long-term filtration experiment of the composite membrane shows good water permeation stability. This work provides a method to prepare dense and defect-free COF films on electrospun substrates.