Anisotropic waste PVC/Cotton stalk cellulose composite sponges with under-oil superhydrophobicity for efficient oil-water separation

• One-step impregnation method was used to prepare anisotropic composite sponges. • Sponges from waste cotton stalks and discarded PVC plastics. • Sponges exhibited good underoil super-hydrophobicity. • Sponges showed excellent removal effects on w/o emulsions (over 99.8%). • PVC and TPP increased sponge’s roughness, mechanical strength and flame retardancy. Addressing the dual challenges of oily wastewater pollution and plastic/agricultural waste accumulation, we present a sustainable cellulose/polyvinyl chloride-triphenyl phosphate (cellulose/PVC-TPP, CPxTy) composite sponge fabricated from discarded cotton stalk, waste polyvinyl chloride (PVC) and triphenyl phosphate (TPP) for efficient water-in-oil (w/o) emulsion separation. The composite sponge is synthesized via a simple, low-cost impregnation-coating technique that creates a super-wettable PVC-TPP coating on the cotton stalk-derived cellulose sponge. The obtained composite sponge possesses a micro-wrinkled structured surface with intriguing superlipophilicity and underoil superhydrophobicity, which is due to the synergistic effect of the surface wrinkle-like roughness and lipophilic groups (chlorine (−Cl) and phenyl (−Ph) groups). The anisotropic porous structure and the dense rough coating on the surface result in the composite sponge exhibiting excellent w/o emulsion separation efficiency. The high separation efficiency of > 99.8 % with filtrate water content < 40 ppm is obtained solely under the driving of gravity. Notably, the PVC-TPP coating enhances the mechanical properties of the sponge, enabling the sponge to withstand longitudinal compression up to 873 kPa while maintaining structural integrity under 20 % strain deformation, which was at least 8 times higher than that of other cellulose-based aerogels. Moreover, with the advantage of excellent environmental resistance, self-extinguishing flame retardancy (ignition cessation within 18 s) and reusability, the composite sponge can retain > 99 % separation efficiency after five reuse cycles. The synergistic reuse of agricultural and plastic waste into high-performance materials provides a scalable, eco-friendly strategy for tackling complex oil–water separation tasks, advancing both environmental remediation and circular economy goals.