Fabrication of mesoporous titania thin film on p-type semiconductor substrate
toward efficient wastewater purification*N. Suzuki1), A. Okazaki2), C. Terashima1), K. Nakata1)3), K. Katsumata1) and A. Fujisima1)

1)

Photocatalysis International Research Center, Tokyo University of Science, Noda, Chiba, Japan,
ORC Manufacturing Co., Ltd., 3) Graduate School of Science and Technology, Tokyo University of Science*suzuki.norihiro@rs.tus.ac.jp
Keywords: surfactant-assisted sol-gel method, porous thin film, titania, photocatalyst, p-n heterojunction
2)

Mesoporous material, which has pores with 2 – 50 nm in diameter, has unique properties such as uniform poresize, large pore volume, high surface area, and so on. Owing to these, mesoporous materials have a potential to showsuperior efficiency on surface related phenomena like catalytic reaction.
Titania (TiO2) is a well-known metal oxide n-type semiconductor. Though its band gap differs depending on thecrystal phase, it is about 3.2 eV (387 nm) in anatase phase. When UV light with wavelength shorter than 387 nm isirradiated, electrons in the valence band are excited to the conduction band, creating holes and electrons in thevalence band and the conduction band, respectively. Because the photo-generated holes show strong oxidation
ability, they can decompose organic pollutants. Thus, titania works as photocatalyst under UV light. Besides its highphotocatalytic efficiency, titania has high stability and good biocompatibility. Furthermore, because titanium is anabundant metal, the production cost of titania is very low. Therefore, titania is one of the most widely-usedphotocatalyst.
To achieve an effective oxidation by photocatalysts, as many as photo-generated holes should react with organicpollutant. However, in the single titania, recombination of photo-carriers often occurs. This carrier recombination
decreases the number of holes react with organic pollutants, leading the lowering photocatalytic properties. To
suppress the carrier recombination, p-n heterojunction has been used. At hetero-interface, an energy gradient iscreated to match the energy level of both bulk, and this gradient is useful to promote photo-generated charge
separation. Thus, we fabricated mesoporous titania thin film on the p-type semiconductor substrate, aiming toenhancing the photocatalytic activity.
Mesoporous titania thin film was fabricated bysurfactant-assisted sol-gel method as described in theprevious papers1). The precursor solution containing
amphipathic surfactant micelles and titania sol werespin-coated on the boron-doped Si or diamond substrate(p-type semiconductor). During the evaporation ofFig. 1. Fabrication process of mesoporous ceramics bysolvent, surfactant micelles self-assembles and they act
surfactant-assisted sol-gel method.
as organic template. After removal of the template bycalcination, mesoporous titania thin film is obtained.
Schematic image is shown in Fig. 1.
The morphology of synthesized film was examinedwith SEM image. As shown in Fig. 2, very well ordered
porous structure was obtained. Mesopores with around
20 nm in diameter was hexagonally packed. The
structural change depending on the substrate did notobserved.
Fig. 2. Top-view SEM image of mesoporous titania thin film
In the presentation, we would like to show thefabricated on boron-doped (a) silicon and (b) diamond substrate
photocatalytic activity of prepared films and theirpotential for wastewater purification.
References
1) X. Jiang, N. Suzuki et al., Eur. J. Inorg. Chem., 2013, 3286-3291 (2013); N. Suzuki et al., Chem. Lett., 44,656-658 (2015).