Multifunctional carboxylated polyimide fiber membrane for gravity-driven efficient simultaneous separation of oil-in-water emulsions and methylene blue dye

The development of multifunctional nanofiber membranes with high separation efficiency for the simultaneous removal of oil–water emulsions and organic dyes is essential due to the complexity of hazardous components in real wastewater. Herein, a polyimide (PI) fiber membrane prepared by electrospinning was carboxylated and used to simultaneously separate oil-in-water emulsions and methylene blue (MB) dye for the first time. A superhydrophilic/underwater oleophobic electrostatically spun carboxylated polyimide (Cx-PI) fibrous membrane was successfully prepared through electrostatic spinning, thermal imidization, and alkaline hydrolysis to construct carboxyl and imide groups on the polyimide fibrous membrane. The resulting membranes exhibited excellent performance in gravity-driven separation for the effective removal of oil, oil-in-water emulsions, and MB dye. The separation efficiency was ≥ 99.4 % for oil-in-water emulsions stabilized with various surfactants with a flux of up to 1128.5 L m −2  h −1 . In addition, the oil and dye in the emulsion could be simultaneously separated with an emulsion separation efficiency of ≥ 99.2 %, a flux of about 910.6 L m −2  h −1 , and an MB dye removal rate of 98.6 %, even when the MB dye concentration was as high as 100 mg/L. The Cx-PI nanofiber membrane also demonstrated excellent stain resistance, salt resistance, high-temperature resistance, and mechanical durability. The above results indicated that the Cx-PI membranes were suitable for the separation of oil-in-water emulsions containing MB dyes under complex conditions. This study provides a promising application in solving the global water pollution caused by oily organic solvents and water-soluble dyes.