Multi-Scale Structural Regulation of PVA/SiO ₂ Hybrid Nanofiber Aerogels for Dual-Mode Separation of Water/Oil Mixtures

In addressing the enhancement needs for hydrophilic aerogels utilized in oil–water separation, with a particular focus on mechanical properties, filtration flux, and oil repellency, this study investigates the fabrication and performance modification of poly(vinyl alcohol)/silica (PVA/SiO 2 ) hybrid nanofiber aerogels. A synergistic mechanism is established between molecular transport channels and size-sieving effects through systematic multiscale structural regulation. This results in aerogels featuring uniform fine-diameter fiber units, internally oriented large-pore channels, and micronano-tiered rough surfaces, achieving an optimized balance between selectivity and permeability while ensuring structural stability. Furthermore, based on the thickness-dependent filtration performance of the aerogel, an innovative dual-mode oil–water separation mechanism is demonstrated: thin-layer aerogels (0.5 mm) utilize gravity to achieve high-flux filtration of oil–water mixtures (pure water filtration flux >6500 L·m –2 ·h –1 ); while thick-layer aerogels (>2 mm) are driven by capillary-dominated reverse transport, efficiently adsorbing water from high-density oil phases (adsorption capacity >30.6 g·g –1 ). In contrast to the preceding studies, this research uses industrial engine oil for experimental purposes. The findings indicate that controllable switching between oil and water separation modes can be achieved through the simple adjustment of aerogel thickness. This finding broadens the application scope of the material and provides an efficient and reliable strategy for treating variable oil–water mixtures in industrial spill scenarios.