Wettable and Flexible Silica Nanofiber/Bead-Based Membranes for Separation of Oily Wastewater

Surfactant-stabilized oil-in-water emulsions (SSEs) are parts of oily wastewater that are incredibly difficult to separate, especially for SSEs under complex conditions. Constructing ceramic fiber membranes with good flexibility, high flux, low energy consumption, and good antifouling performance is an effective method and highly desired for SSE separation; however, it has proven to be extremely challenging. Herein, we report a strategy for the synthesis of flexible silica nanofiber/nanobead (SNB) membranes by combining electrospinning and electrospraying techniques. The nanofiber-supported bead-on-string structure endows membranes with superhydrophilicity and underwater superoleophobicity (oil contact angle of 162°), small sliding angles (2.5°), and a small oil adhesion force (0.4 mN). Benefiting from the superwettability and hierarchical pore structure, the SNB membranes exhibited good separation performance toward SSEs with high efficiency (>98.8%) and permeate flux (∼2237 L m–2 h–1) under low pressure (<10 kPa). Significantly, the plausible mechanism for emulsion separation was analyzed and verified by the pathway of surfactants. Additionally, SNB membranes exhibited intriguing separation performance toward SSEs under different conditions such as acidic, alkaline, and high temperatures (∼80 °C). Furthermore, the resultant membranes possessed robust mechanical properties, excellent antifouling performance, and good reusability. The synthesis of SNB membranes provides a facile method for fabricating ceramic microfiltration membranes for industrial and domestic wastewater separation.