Functionalized carbon fiber felts with selective superwettability and fire retardancy: Designed for efficient oil/water separation

•Functionalized carbon fiber felts after UV-O3 treatment and diazonium modification with selective superwettability can effectively separate the oil (different density)/water mixture.•Functionalized carbon fiber felts have flame retardancy, recycling performance and wide environmental applicability. Advanced materials with special wettability have attracted wide attention for their potential application in environmental remediation, catalysis or superfluid now. This contribution reports a straightforward and low-cost high-performance methodology for the preparation of carbon fiber felt with selective superwettability and fire resistance. The functionalized carbon fiber felt (UV-CFF) is prepared by a simple UV-O3 treatment process for the enhancement of its superamphiphilicity in air and superoleophobicity underwater, the underwater contact angles of the organics is over 155°. Subsequently, surface functionalization of UV-CFF with 4-trifluoromethyldiazobenzene hydrochloride is carried out. Its surface could be effectively modified with aryl and carbon–fluorine groups through diazonium chemistry to obtain a superhydrophobic carbon fiber felt (f-CFF) with water contact angle of 152.5 ± 0.8°. Both of the UV-CFF and f-CFF samples exhibits effective oil/water separation behavior. Benefiting from the selective superwettability, the two samples provide the potential to selectively eliminate underwater oily phases and emulsions under different hydraulic pressures. For UV-CFF, its rejection of oil reaches 100%, and the rejection of water for f-CFF reaches 98.21 ± 0.7%. The adsorption capacities of different types of organic solvents for f-CFF is 4–14 g g−1, and its demulsification capacity can reach to 99.9%. Due to its corrosion resistance, facile fabrication technique, cycle stability and flame retardancy, the carbon felts hold great promise for potential applications in environmental remediation of water.