Rough and porous silica-modified fiber membranes decorated with oleic acid for ultra-high flux and pH-responsive oil/water separation

[Display omitted] •The pH-responsive membranes were prepared by electrospinning and immersion.•The composite membrane had rough structures, large pore sizes, and high porosities.•The membrane had both pH responsiveness and ultra-high permeation flux.•The membrane provided on-demand separation for oil-water mixtures and emulsions. The design of fiber membranes with both ultra-high flux and pH-responsive oil/water separation is challenging but of great significance to environmental protection and human health. In this work, the pH-responsive fiber membranes were prepared by immersing the silica-modified polyacrylonitrile fiber substrates into oleic acid solution. The obtained membranes exhibited highly rough surface structures (Ra = 14.26 µm), large pore sizes (5.35 µm), high porosities (86.04%), and pH-responsive functional groups, respectively. The pH-responsive fiber membranes also had superhydrophobic surfaces and excellent selective separation for oil/water mixtures, for example, a trichloromethane permeation flux of 87,829 L m-2h-1 for immiscible oil/water separation, and a water permeation flux of 69,802 L m-2h-1 after turning the pH of water from 7 to 13. The above data were much higher than those of stimulus-responsive fiber membranes used for oil/water separation. In addition, the pH-responsive fiber membranes were also used for separating water-in-oil emulsions and oil-in-water emulsions, and achieved the highest separation flux of 15,120 L m-2h-1. This work provides a simple strategy for the preparation of a stimulus responsiveness and high-performance material that can be used in the direction of treating practical oily wastewater.