Light oil/water/heavy oil triphase mixtures are common in industrial wastewater, while nearly all separation materials with superwettability can only separate biphase mixtures of light oil/water or/and heavy oil/water. Here, a balsa wood slice with superhydrophilic/superoleophilic property in air was fabricated by a blade-cutting and ethanol-treating process. Therefore, the slice could be dually prewetted with both water and oil and thus showed underwater superoleophobic and underoil superhydrophobic properties without any further chemical modification. Such a slice showed underoil superhydrophobicity in nonbasic environment while transition into underoil superhydrophilicity under basic condition. Combining with the porous structure possessed by wood designed to transport liquids, this superwettability of the treated wood slice could be leveraged in the continuous separation of light oil/water/heavy oil triphase mixtures only driven by gravity with a high permeation flux and separation efficiency. After each separation, the slice was easily recovered by washing with acidic solution, and it could be recycled up to 15 times without any loss of pH responsibility. During repeated cycling separation, the slice exhibited excellent separation stability.

Controllable geometry silicon surfaces with superhydrophobicity are difficult to be fabricated without photolithography techniques. Superhydrophobic silicon surfaces with water contact angle larger than 150º and sliding angle less than 10º have been successfully fabricated by electrochemical etching strategy. Squarelike hole arrays with controllable geometries, especially ole width and depth were formed on silicon. Compared with the chemical composition, the obvious change of the hole size and surface roughness with etching time was actually the intrinsic factors for wetting regulation. The superhydrophobic silicon exhibited good stability even after storage in air and oil for 2 months. Moreover, the relatively stable superhydrophobic silicon exhibited good self-cleaning and water-proofing properties in air and oil.

Cork is a renewable, biocompatible, environmentally friendly and abundant biological material with microscale cellular structure. Fabrication of filtration membranes for the separation of oil and water by utilizing such natural materials to replace nonnatural membranes is a green method. A cork membrane with a water contact angle greater than 150° and an oil contact angle close to 0° was fabricated by chemically modifying cork membranes with 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane. The special wettability was achieved owing to the cellular structure and the surface composition of the cork membrane. Just like nonnatural filtration membranes, natural cork membranes exhibited excellent permeability for oils. After at least 40 cycles of oil-removal processes, the separation efficiency of the membrane was still above 99.1%. Under harsh conditions such as strong acid/alkali, high humidity, and high temperature environments, the wettability and separation efficiency exhibited excellent stability and durability. This method offers an opportunity to the practical applications of the superhydrophobic cork membrane.