Engineering Superhydrophilic and Fouling‐Free COF Armor for Ultrafast Oil–Water Separation

Polymeric nanofibrous membranes are promising candidates for highly efficient oily wastewater separation, however, they suffer from irreversible membrane fouling. Herein, hydrophilic β-ketoenamine-linked covalent organic frameworks (COFs)-modified polyacrylonitrile (PAN) nanofibrous membranes (PNMs-COF) are developed, and the microstructures and hydrophilicities of the membranes are finely tailored. The hydrophilic rigid COF armor can induce the formation of hydrogen bonds with water, increase the polar component of the apparent surface tension, enhancing the driving force toward water and increasing the repulsion against oil droplets. Moreover, the inherent rigidity of the COFs further prevents deformation of the flexible fiber chains under gravity, precluding irreversible contamination due to embedded oil droplets. The multiple-mechanism-driven membrane exhibits superior oil rejection (99.3%), anti-fouling ability (nearly zero irreversible fouling), and ultra-high permeance (3.4 × 10⁴ L∙m^-2∙h^-1∙bar^-1), enabling a sound step toward oil-wastewater remediation.