Mechanism of Photoinduced Superhydrophilicity on the TiO₂ Photocatalyst Surface

Abstract

The physicochemical properties of the H(2)O molecules adsorbed on TiO(2) surfaces during UV light irradiation were fully investigated by near-infrared (NIR) absorption spectroscopy. It was found that the H(2)O molecules adsorbed on the TiO(2) surfaces desorb during UV light irradiation by the heating effect of the light source. Since the amount of the H(2)O adsorbed on the TiO(2) surfaces decreased, the distribution of the hydrogen bonds within the H(2)O molecules decreased, resulting in a decrease in the surface tension of the H(2)O clusters. The decrease in the surface tension of H(2)O under UV light irradiation was found to be one of the most important driving forces in which the H(2)O clusters on the TiO(2) surface spread out thermodynamically, forming H(2)O thin layers. The partial elimination of the hydrocarbons from the TiO(2) surface by the photocatalytic complete oxidation was seen to be the other important factor, providing free spaces on the surface where the H(2)O clusters could spill over and spread out to form the thin H(2)O layers. Moreover, the temperature changes of the TiO(2) powder samples during UV light irradiation were found to show a good correspondence with the changes in the contact angle of the H(2)O droplets on the TiO(2) thin film surfaces. Especially the time scale for the hydrophilic conversion on the TiO(2) surfaces under UV light irradiation was in good agreement with the decrease in the amount of H(2)O molecules adsorbed on the TiO(2) surfaces but not the amount of the hydrocarbons eliminated by the photocatalytic oxidation reactions, showing that the adsorption and desorption of H(2)O molecules are generally quite sensitive to the temperature changes of solid surfaces.

Effect of ultraviolet photofunctionalisation on the cell attractiveness of zirconia implant materials

“…In addition, UV-treated surfaces yielded nearly 100 % bone-to-titanium implant contact, as opposed to less than 55 % for the untreated titanium surfaces (Aita et al, 2009b;Iwasa et al, 2010). This phenomenon has been attributed to the alteration of the physicochemical properties of the surface upon UV treatment, characterised by the removal of surface carbons, conversion of the surface status from hydrophobic to superhydrophilic and possible conversion of the surface charge (Aita et al, 2009b;Iwasa et al, 2010;Takeuchi et al, 2005b). Such findings were not only limited to titanium surfaces, but also for other implantable materials (Att et al, 2009a;Att et al, 2009c).…”

Superwetting of TiO 2 by light-induced water-layer growth via delocalized surface electrons

“…The phenomenon has been attributed to production of surface radical groups (1,(3)(4)(5) or photo-oxidation of hydrophobic surface contaminants (6)(7)(8), but its origin remains controversial (9,10) in part because conventional contact-angle analysis alone cannot fully account for the complex surface wettability (11). To address the fundamental mechanism responsible for superwetting, one has to go beyond the contact-angle measurement that reflects the specific surface properties and to probe the temporal growth dynamics of the water layer itself adsorbed on TiO 2 under wide-spectrum illumination of visible and near-infrared (NIR) in addition to UV light.…”

In situ Measurements of the Desorption of Water from a TiO2 Surface under Dry Air by Collecting the Photoemission Yield with an Open Counter

“…The relationship between the surface electronic structure measured using the conventional PYSA and the photocatalytic activity have been reported by Yamagishi et al, 7 Song et al, 8 Miyamura et al, 9 and Fukumoto et al 10 On the other hand, the high wettability of the TiO2 surface has been extensively studied, [11][12][13][14][15][16][17] and has attracted considerable attention. Therefore, a newly designed PYSA was applied in order to evaluate the change in the TiO2 surface depending upon the humidity.…”