•The membranes show a much higher critical tensile stress and tensile strain.•The membranes are superhydrophobic and superoleophilic.•The membranes can effectively separate oil/water mixtures with high flux.In recent years, efficient, cost effective oil-water separation technologies are highly desired due to frequent oil spill accidents. To design fibrous membranes for efficient oil-water separation, ‘flexible’ polyamide acid (PAA), being polyamide acid with ether linkages in the backbone, and ‘heavily’ fluorinated polybenzoxazine (F-PB) were synthesized. Cellulose acetate (CA) and PAA were co-axially electrospun; the PAA core was then imidizated at high temperature to obtain core/shell structured CA/polyimide (PI) electrospun fibrous membranes; subsequently the surface of the fibers was modified with F-PB, in the presence or in absence of silica nanoparticles (SNPs). The mechanical strength, surface wettability, chemical and thermal stability, and oil-water separation potential of thus obtained PI/CA fibrous membranes were evaluated. The membranes show a much higher critical tensile stress (130 MPa) and critical tensile strain (52%), when compared with CA fibrous membranes. Due to the use of the ‘heavily’ fluorinated polybenzoxazine, the membranes are superhydrophobic with a water contact angle of 162° and an oil contact angle which approaches 0°. Interestingly, the newly designed PI/CA/F-PB-1/SNP-4 membranes can effectively separate various oil-water mixtures, solely driven by gravity, with a high flux (3106.2 ± 100 L m−2 h−1) and a high separation efficiency (>99%) and thus possess great potential for oil–water separation.

The increasing worldwide oil pollution intensifies the needs for new techniques of separation of oil from oily water. Separation by the use of electrospun fibers with selective oil/water absorption is a relatively new but highly promising technique. Owing to their highly specific surface areas, interconnected nanoscale pore structures and the potential to incorporate active chemistry on a nanoscale surface, electrospun fibers have become a promising versatile platform for the separation of oil/water mixtures and emulsions. In this review, after a short introduction to the imperative for oil/water separation and electrospinning technique, we will focus on superhydrophobic/superoleophilic electrospun fibers for oil/water separation, including the preparation of electrospun fibers with superhydrophobic/superoleophilic surfaces, and superhydrophobic/superoleophilic fibrous membranes for oil absorption and oil filtration. Further, superoleophobic/superhydrophilic electrospun fibers and their application for oil–water separation will be discussed as well. Finally, conclusions about this review will be presented while addressing remaining problems and future challenges.

In recent years, both the increasing frequency of oil spill accidents and the urgency to deal seriously with industrial oil-polluted water, encouraged material scientists to design highly efficient, cost effective oil–water separation technologies. We report on electrospun nanofibrous membranes which are composed of core–sheath structured cellulose-acetate (CA)–polyimide (PI) nanofibers. On the surface of the CA–PI fibers a fluorinated polybenzoxazine (F-PBZ) functional layer, in which silica nanoparticles (SNPs) were incorporated, has been applied. Compared with F-PBZ/SNP modified CA fibers reported before for the separation of oil from water, the PI-core of the core–shell F-PBZ/SNP/CA–PI fibers makes the membranes much stronger, being a significant asset in their use. Nanofibrous membranes with a tensile strength higher than 200 MPa, a high water contact angle of 160° and an extremely low oil contact angle of 0° were obtained. F-PBZ/SNP/CA–PI membranes seemed very suitable for gravity-driven oil–water separation as fast and efficient separation (>99%) of oil from water was achieved for various oil–water mixtures. The designed core–sheath structured electrospun nanofibrous membranes may become interesting materials for the treatment of industrial oil-polluted water.