pH-RESPONSIVE WOOD SLICES FOR THE CONTINUOUS SEPARATION OF LIGHT OIL/WATER/HEAVY OIL TRIPHASE MIXTURES

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.