Polyamide infiltration phenomenon on microfiltration support reduced by covalent organic frameworks net for faster desalination

Abstract

Covalent organic frameworks (COFs) are a new periodic porous crystalline material, that has nano pore sizes. Herein, a novel COFs MPDTp was introduced into nylon microfiltration substrate to reduce polyamide (PA) infiltration condition for highly permselective nanofiltration (NF). The resultant PA-COF/nylon membrane was achieved after twice interfacial polymerization (IP) processes. The first was the introduction of COFs, and the second was the preparation of PA selected layer. The optimal membrane showed outstanding pure water permeance (PWP) of 27.3 L m−2 h−1 bar−1, which was about three times larger than the PA/nylon membrane, and rejection of 98.4 % for Na2SO4. The excellent performance was benefit from the existence of COFs, on the one hand, the COFs on the surface and inside could be seem as a net which prevented PA infiltration and blockage. On the other hand, a thinner PA separation layer was generated due to the slower piperazine (PIP) diffusion rate, which was also certified by molecular dynamics (MD) simulation. Therefore, this work not only demonstrates the high application value for desalination of the PA-COF/nylon membrane, but also provides a new strategy to adjust the relationship between the microporous substrate and the PA layer.