Preparation of PVDF mixed matrix membrane based on hydrophilic imine type covalent organic framework(COF) for dye and salt separation

Due to its high porosity, excellent chemical stability, and low density, covalent organic frameworks have been widely researched in membrane separation technology. This study prepared COF-LZU1 PVP/PVDF membranes with different loadings of covalent organic framework (0-0.8 wt% COF-LZU1) synthesized by the room temperature method incorporated into a polyvinylpyrrolidone (PVP) /polyvinylidene fluoride (PVDF) matrix. The addition of hydrophilic COFs improved the hydrophilicity of the membrane, reducing the water contact angle on the membrane surface from 79 degrees (PVDF membrane) to 58 degrees (optimized membrane, M0.4). The water permeance of membranes was improved by 2.3 times by incorporating 0.4 wt% COF-LZU1 nanoparticles. Moreover, the rejection ratio for eriochrome black T (CBT), acid red (AR), congo red (CR), and methylene blue (MB) are all higher than 94.5%. Furthermore, it exhibits excellent permeance of 19.37 L.m(-2).h(-1).bar(-1) in the mixed solution of CR and NaCl, with respective rejection of 96.3% and 1.6%. The BSA filtration test demonstrated that after three cycles, the FRR of COF-LZU1 PVP/PVDF membrane reached 91.52%. Generally speaking, incorporating COF-LZU1 into PVDF polymer matrix can lead to the preparation of membranes with excellent anti-fouling properties for dye separation and dye/salt separation purposes.