Superhydrophilicity and underwater superoleophobicity TiO2/Al2O3 composite membrane with ultra low oil adhesion for highly efficient oil-in-water emulsions separation

Abstract To improve the separation efficiency and decrease fouling of the membranes used in oil-in-water emulsions separation, a superhydrophilic and underwater superoleophobic TiO2/Al2O3 composite membrane with ultra low oil adhesion was designed. TiO2 nanorod arrays were prepared on Al2O3 porous ceramic membrane surface by simple magnetron sputtering and hydrothermal oxidation. The microstructure and surface photosensitivity of TiO2 nanorod array-coated ceramic membrane can effectively increase the efficiency of oil-water separation and reduce the degree of surface fouling. The layer of TiO2 nanorod arrays not only reduced the pore size of traditional ceramic membrane (enhanced sieving effect of porous structures) but also endowed its superhydrophilicity (enhanced flux) and underwater superoleophobicity (enhanced oil/water selectivity and antifouling). Based on the superhydrophilicity (water contact angle (WCA) of 0°) and underwater superoleophobicity (oil contact angle (OCA) higher than 150°) of ceramic membrane, oil droplets were blocked by the membrane (oil-water separation efficiency 99.1% under gravity) and water will pass (flux is maintained at 41.8 L/(m2 h) under gravity). It also has excellent anti-fouling ability due to the ultra-low oil adhesion force (0.084 mN) of the TiO2 nanorod array-coating after UV irradiation. These features, combined with energy-saving, low-cost and easy-to-scale manufacturing schemes will be of great versatility and practicality in environmental rehabilitation and wastewater purification.