Cellulose acetate-based composite fibrous membrane with asymmetric wettability for directional water transport and high-flux oil–water separation

The investigation of dual-layer fibrous membranes with asymmetric wettability is gaining growing interest. Here, we conceive a novel composite fibrous membrane base on cellulose acetate (CA), characterized by a hydrophobic-on-hydrophilic configuration, using a designed co-electrospinning system. A thin layer of hydrophobic thermoplastic polyurethane (TPU) side is overlaid onto a hydrophilic CA/TPU membrane to achieve directional water transport and oil–water separation. The core–shell CA/TPU bicomponent fibers exhibit a much higher tensile stress (3.6 MPa) and tensile strain (72.15%), when compared with CA fibrous membrane. The TPU membrane displays beads-on-string morphology, which promote the directional water transport capacity, and the possible mechanism is discussed. The measurements show that our composite membrane can effectively separate various oil–water mixtures, solely driven by gravity. Interestingly, the membrane shows high oil–water separation flux (up to 109,918 Lm⁻² h⁻¹). This study expands the range of potential applications for CA fibrous membranes.