An intelligent and robust coating with switchable wettability for on-demand oil–water separation

Intelligent materials demonstrate promising applications in switchable oil/water separations. A stearic acid (SA) hydrophobically modified SiO₂ coating (SA/SiO₂) with switchable wettability was developed by simply spraying. The SA/SiO₂ coating with micro-nanostructure showed excellent superhydrophobicity with water contact angle (WCA) and oil contact angle (OCA) of 158.7° and 0°, respectively. When the SA/SiO₂ coating was contacted with ammonia, it showed excellent superhydrophilicity, with WCA and underwater oil contact angle of 0° and 155.4°, respectively. After heating treatment, the SA/SiO₂ coating returned to superhydrophobicity. Through wettability switching, the prepared SA/SiO₂ coating could be applied for on-demand separation of oil/water/oil ternary mixtures as well as various water-in-oil emulsions and oil-in-water emulsions, and the separation efficiency of oil-in-water emulsion could reach up to 99.97%, accompanied by a high flux at the same time. More importantly, the SA/SiO₂ coating exhibited significant robustness and excellent reusability, which maintained a superior separation efficiency of over 99.80% after 10 cycles emulsion separation, suggesting its promising potential for oily wastewater treatment. The simple and environmentally friendly coating preparation method as well as easy implementation of response conditions and short switching time provide a reference for the preparation of intelligent response oil/water separation materials.