Interfacial polymerization of a covalent organic framework layer on titanium dioxide@graphene oxide/polyacrylonitrile mixed-matrix membranes for high-performance dye separation

Interfacial polymerization of imine-linked covalent organic frameworks (COFs) on support membranes is one of the most promising routes for realizing COF composite membranes for industrial applications. In the present work, first, the influences of the pore structure, microtopography, and chemical structure of TiO2@graphene oxide (GO)/polyacrylonitrile (PAN) support membranes on the structure and performance of 1,3,5-triformylphloroglucinol (Tp)–p-Phenylenediamine (Pa) COF composite membranes were studied. The results showed that the hydrophilic and smooth top surface, homogenous pore distribution, and large pore size of TiO2@GO/PAN support membranes enabled them to be easily infiltrated by aqueous-phase solutions. These features promoted the homogenous diffusion of an aqueous solution from the bottom surface to the top surface of the TiO2@GO/PAN membranes, which generated a stable interface between the organic and aqueous phases. A thin, crystalline TpPa layer with a mean pore size of 1.78 nm on the top surface of TiO2@GO/PAN endowed the COF composite membranes with excellent filtration performance, including a pure-water permeance of 89.08 L m−2 h−1 bar−1 (testing pressure = 1.0 bar) and the Congo red dye rejection rate of 94.83%. Membranes that displayed steady filtration properties for a 300-h filtration test will be given greater attention, as they will be suitable for industrial applications.