Intelligent Devices Harnessing Underwater Superoleophobic and Underoil Superhydrophobic Quartz Sands for the Separation of Diverse Stratified and Emulsified Water–Oil Mixtures

To achieve the green, sustainable, and controllable recovery of oil–water resources and to address the limited functionality of single superwet materials in oil–water separation, this study reports a multifunctional oil–water separation strategy by compositing the underwater superoleophobic and underoil superhydrophobic materials (HS). The underwater superoleophobic quartz sands with an oil contact angle of 152.68° were prepared by adjusting the particle size. This material demonstrated a water flux of 4688 L m–2 h–1 and a low-density oil and water mixture separation efficiency of 98.6%, which remained above 97.9% over 50 cycles. It was effective in separating oil-in-water emulsions with a separation efficiency of >99%. For HS, quartz sands were modified with dodecyltrimethoxysilane. The optimized HS-4 exhibited superhydrophobic properties with a water contact angle of 157.06°. It achieved an oil flux of 5775 L m–2 h–1 and a water and dichloromethane mixture separation efficiency of 98.4%. Additionally, they exhibited significant potential in the separation of water-in-oil emulsions. Furthermore, by placing the underwater superoleophobic and underoil superhydrophobic units at the bottom of the filter, we achieved cyclic separation of high-density oil and water mixtures, low-density oil and water mixtures, water-in-oil emulsions, and oil-in-water emulsions. The separation efficiency consistently exceeded 96.5% over 10 cycles. In addition, the oil–water separation mechanism of underwater oleophobic and underoil hydrophobic materials was demonstrated by the relative concentration distribution of water and oil with molecular dynamics simulations. This intelligent oil–water separation method marks a significant advancement in the sustainable separation of diverse oil–water mixtures.