Electrospun superwetting membranes with vertically aligned COF nanorods for high-efficiency oil–water emulsion separation

The design of wettable membranes with tailored micro- and nanostructures for the efficient separation of oily wastewater remains a challenge. Herein, a cellulose acetate nanofiber/covalent organic framework (ETCNF/COF) composite membrane was fabricated, featuring vertically aligned COF nanorods, achieved via an electrospinning-assisted, amino-mediated in situ confined growth method. Utilizing this vertically arranged COF micro/nano rough structure, the superhydrophobic ETCNF/COF-ODM membrane and superhydrophilic ETCNF/COF-CHA membrane was constructed using thiol-ene click chemical grafting of octadecylthiol (ODM) and cysteamine hydrochloride (CHA) methods, respectively. As a result, the ETCNF/COF-ODM membrane exhibited excellent superhydrophobicity (contact angle > 150°) and self-cleaning properties, enabling the efficient separation of water-in-oil emulsions with a separation efficiency exceeding 99%. In contrast, the ETCNF/COF-CHA membrane exhibited outstanding superhydrophilicity (contact angle approaching 0°) and underwater superoleophobicity (underwater oil contact angle > 150°), achieving high-efficiency separation of oil-in-water emulsions with a separation efficiency above 99%. The superior superwetting performance of both membranes is attributed to the synergistic construction of hierarchical porous superwetting interfaces by the COF and the electrospun substrates. In conclusion, the in situ domain-limited growth of vertically aligned COF nanorods for superwetting membranes by electrostatically spun membranes provides an effective strategy for advancing the development of oil-water separation technology.