Constructing asymmetric mixed matrix membrane with high permeance and antifouling performance by magnetic control of COF-coated Fe3O4 particles

Background

Nanofiltration membranes are widely used for treating dye wastewater, while two major challenges hinder their application: the trade-off between permeance and selectivity, and membrane fouling.

Methods

Covalent organic frameworks (COFs) can help membranes overcome the trade-off effect, and the combination of positively and negatively charged groups exhibit excellent antifouling properties. In this study, COF-coated Fe₃O₄ particles are synthesized and functionalized with sulfonic acid groups, through magnetically induced surface segregation, a membrane with asymmetric structure is formed. The effects of modified particles on the membrane's structure are systematically investigated. Most importantly, the water permeance, dye rejection, and antifouling properties of as-prepared mixed matrix membranes are thoroughly evaluated.

Significant Findings

The magnetic-assisted method enriches more COFs containing both positively and negatively charged groups on the membrane surface, as a result, the prepared membranes exhibit outstanding performance in water permeance, dye removal and antifouling ability. For example, the P/Z-COF-5 membrane shows enhanced permeance from 65.2 L m⁻² h⁻¹ bar⁻¹ (polyethersulfone, PES) to 165.6 L m⁻² h⁻¹ bar⁻¹, exhibits high rejection of 99.8 % for Eriochrome black T and 96.7 % for Congo red. In addition, the flux recovery ratio of P/Z-COF-5 membrane is 98.2 %, much higher than that of pristine PES (72.9 %).