Wettability control of a solid surface by utilizing photocatalysis

Abstract

This paper describes a strategic approach utilizing a photocatalyst to obtain a solid surface with a high level of sustainable wettability (hydrophilicity or hydrophobicity). We clarified that the substances adsorbed on the surface could be successfully removed by photocatalytic oxidation resulting in sustainable high hydrophilic and high hydrophobic states. In addition to the conventional redox reaction, photoinduced wettability conversion plays an inevitable role in obtaining a superhydrophilic state. Both of the aforementioned photoinduced properties can be applied to sustain a high level of hydrophilicity. A superhydrophobic surface can be designed based on the Cassie theory. However, a combination with the usual TiO2 photocatalyst leads to a decrease in hydrophobicity because the photocatalyst becomes hydrophilic itself as a result of the photoinduced hydrophilic reaction. Utilizing the newly developed hydroxyapatite doped with Ti(IV) ions (TiHAP) photocatalyst, which has a considerably reduced hydrophilic effect, a superhydrophobic surface can be sustained after exposing it to outdoor conditions for a long period. As for sustaining the hydrophobic state, the introduction of a material design based on dynamic wettability leads to the possibility of novel functional materials with a high dynamic hydrophobicity. Our study shows that a high level of wettability (hydrophilic or hydrophobic) of a solid surface as that sustained by biologic action is possible by utilizing photocatalysis.

Effect of surface fluorination on the photocatalytic and photo-induced hydrophilic properties of porous TiO2 films

“…Recently, it has been reported that photo-induced hydrophilicity is not only because of photo-oxidation of hydrophobic contaminant layers but also because of structural changes of the TiO 2 surface [45]. However, the F-TiO 2 film in this work was surface fluorinated, which means the surface hydrophobic species of Ti-F cannot be practically removed under UV irradiation.…”

Superhydrophobic Photocatalytic Surfaces through Direct Incorporation of Titania Nanoparticles into a Polymer Matrix by Aerosol Assisted Chemical Vapor Deposition

“…These include the reduction of bacterial adhesion11 and the superior cleaning action of the lotus effect (versus water sheeting),12 in addition to providing other superhydrophobic properties such as water proofing and anti‐misting 6. There are limited examples of superhydrophobic photocatalysts in the literature,13–19 however, without exception, these materials either lose their superhydrophobicity upon irradiation with light or do not show photocatalytic breakdown of material. Here we report the formation of a new class of material that is simultaneously both superhydrophobic and photocatalytic.…”

Completely <001> oriented anatase TiO2nanoarrays: topotactic growth and orientation-related efficient photocatalysis

“…Wettability is highly dependent on the surface morphology 37 and surface energy. 61 Only when the surface energy of solid is greater than the solid-liquid interfacial energy can the saturating process occur spontaneously. 62 A film with a hydrophilic surface has a high surface energy, which is thermodynamically unstable.…”