A multifunctional coating with switchable wettability for efficient oil-water and emulsions separation

Superwettable materials with switchable wettability have been attracting tremendous attention in the field of oil-water separation. In this work, a multifunctional coating with switchable wettability was designed for efficient oil-water and emulsions separation. Fe3O4 was combined with TiO2 nanoparticles and hydrophobically modified by low surface energy stearic acid (SA) to form the Fe3O4/TiO2@SA coating with uniform micro-nanostructures. The introduction or removal of amino group via ammonia treatment or heating treatment endowed the coating with reversible conversion between hydrophilicity and hydrophobicity. By switching hydrophilicity and hydrophobicity, the coating could separate oil/water/oil ternary mixtures in sequence with high separation efficiency of more than 99.9 %. More importantly, it displayed excellent separation efficiency with oil rejection above 99.5 % for oil-in-water (O/W) emulsions and water rejection above 98.7 % for water-in-oil (W/O) emulsions. Moreover, this coating showed reliable reusability and mechanical stability after 10 cycles of O/W and W/O emulsions separation and 20 cycles of sandpaper abrasion. Fe3O4 and TiO2 imparted magnetic and photocatalytic properties to the coating, allowing it to be used for magnetic navigation of oil absorption and photocatalytic degradation of organic dyes. The unique features of multifunctional coating with switchable wettability provide the blueprint for treating oily wastewater and marine oil spills.