A Wide-Spectrum\nOil/Water Separation Scenario Enhanced\nby a Chitosan-Based Superwetting Membrane with a Tunable Microstructure\nand Powerful Photocatalytic Self-Cleaning Capability

Oil\nspills and industrial oily wastewater pose serious threats\nto the environment. A series of modified membranes with special wettability\nhave been widely used for separating oil/water mixtures and emulsions.\nHowever, these membranes still face challenges such as the detachment\nof the modified coatings and membrane fouling. Here, a freestanding\nbiobased superwetting nanofibrous membrane for oil/water mixture separation\nwas electrospun with chitosan (CS) and poly(vinyl alcohol) (PVA) as\nprecursors, followed by chemical cross-linking and in situ growth\nof β-FeOOH nanoparticles on the surface. Moreover, by precisely\ncontrolling both the cross-linking time between CS and PVA and the\ngrowth time of β-FeOOH nanoparticles, the nanosize apertures\nand rough structures on the membrane surface can be regulated toward\na wide range of oil/water separation scenarios. As a result, FeOOH@CS/PVA-4–12\ndemonstrated superwettability, with a water contact angle of 9.5 ±\n3.5° in air and an underwater–oil contact angle above\n140°, achieving a separation efficiency of 98.5% and a water\npermeation flux of 2350 L·m<sup>–2</sup>·h<sup>–1</sup> for <i>n</i>-heptane/water mixtures. The membrane FeOOH@CS/PVA-24–24\nexhibited exceptional oil-in-water emulsion separation performance\nwith a separation efficiency of up to 99.9% for water/<i>n</i>-heptane emulsions. Additionally, the membrane exhibited remarkable\nantifouling properties, attributed to its superwetting surface and\nthe photocatalytic ability of β-FeOOH nanoparticles. After five\nphotocatalytic self-cleaning cycles, the water permeation flux and\nseparation efficiency remained almost unchanged, demonstrating its\ngreat potential for practical application.