Surface chemical analysis of photocatalytic wettability conversion of TiO2 nanoparticle coating

Surface chemical analysis of photocatalytic wettability conversion of the TiO2 nanoparticle coating is performed by the water contact angle measurement and X-ray photoelectron spectroscopy (XPS). It is observed that the UVA irradiation and heat treatment strongly affect on the water contact angle. Initially superhydrophobic TiO2 nanoparticle coated paperboard surfaces can undergo several transition loops between hydrophobic and hydrophilic states: the surface hydrophilicity can be induced by ultraviolet A (UVA) radiation whereas high temperature oven treatment results in superhydrophobic surface. The XPS spectra shows that UVA irradiation induces photocatalytic oxidation of the TiO2 nanocoated surface whereas the oven treatment decreases the amount of oxygen related to the hydroxyl groups. The wettability changes are related to the degree of hydroxyl groups or aliphatic chains present on the TiO2 surface.