Sol–Gel SiO₂ on electrospun polyacrylonitrile nanofiber for efficient oil-in-water emulsion separation

A membrane for efficient oil-in-water emulsion separation requires a surface with hydrophilic/underwater oleophobic properties. In this study, a simple and facile sol–gel strategy was proposed for preparing oil-in-water emulsion separation membrane with hydrophilic/underwater oleophobic surface by growing amorphous SiO₂ sheets on an electrospun polyacrylonitrile nanofiber membrane (PAN NFM). The composite membranes (PAN@SiO₂ NFMs) showed excellent properties in mechanical strength, hierarchical microporous structure, hydrophilicity and underwater oleophobicity, as well as remarkable performance in water flux, separation efficiency and cyclic stability. Under a low pressure of 1 kPa driven by the self-weight of emulsion, the PAN@SiO₂ NFM demonstrated a large flux of 3994.3 ± 356.0 L m⁻² h⁻¹ and a high separation efficiency of 99.50%. In ten successive cycle tests, fluxes of the PAN@SiO₂ NFM remained above 3000 L m⁻² h⁻¹, while the residual TOC in filtrate was stable at around 30 mg L⁻¹, indicating the PAN@SiO₂ NFM has excellent cyclic stability. It is also demonstrated that the PAN@SiO₂ NFM is suitable for the separation of various kinds of emulsions, such as toluene, n-heptane, paraffin liquid, n-hexane and xylene. Hence, the prepared PAN@SiO₂ NFM is a promising hydrophilic/underwater oleophobic membrane for efficient emulsion separation.