Reversible control of underwater oil wettability of a titanium dioxide surface through ultraviolet and ultrasonic irradiation

Ultraviolet (UV)-irradiated titanium dioxide (TiO₂) photocatalyst surfaces exhibit excellent oil repellency and therefore an oil droplet cannot adhere to its surface in water even when tightly pressed to it. Ultrasonic irradiation treatment in water greatly decreases the degree of underwater oleophobicity, allowing the oil droplet to adhere to the surface in water. We demonstrate that UV and ultrasonic irradiation treatment can be used to reversibly change the underwater oil repellency of TiO₂ surfaces.