Superwettable Carbon Fiber Membranes Functionalized with Cu-TiO2: High-Performance Oil–Water Separation and Sustainable Reusability

Oily wastewater poses severe ecological and health threats, but conventional separation technologies have limitations like low efficiency or high energy consumption. Herein, two superwettable carbon fiber (CF)-based membranes were fabricated for efficient oil–water separation. Using CF (low cost, excellent mechanical stability) as the substrate, Cu-TiO2@CF (superhydrophilic/underwater superoleophobic, renewable) was prepared via a deep ultraviolet (DUV)-assisted sol–gel method, and OTMS/Cu-TiO2@CF (superhydrophobic/superoleophilic) was obtained by modifying Cu-TiO2@CF with octadecyltrimethoxysilane (OTMS) via hydrothermal synthesis. Characterization showed Cu-TiO2 coatings uniformly covered CF, with strong substrate bonding. Both membranes exhibited outstanding performance: Cu-TiO2@CF achieved water fluxes of up to 79,839.6 L·m−2·h−1 and >97.3% separation efficiency for four oil–water mixtures; OTMS/Cu-TiO2@CF had a maximum oil flux of 86,593.4 L·m−2·h−1 and >98.1% efficiency. Cu-TiO2@CF regenerated via 10 min UV irradiation (restoring underwater oil contact angle to 153°), while OTMS/Cu-TiO2@CF achieved recovery through the process of UV irradiation followed by OTMS re-modification. Both membranes maintained stable performance over 100 cycles, demonstrating considerable potential for engineering applications.