Although photocatalytic activity of TiO 2 is mainly discussed in terms of the band gap energy, the importance of surface oxygen for the decomposition of chemicals on the photocatalyst is emphasized in several reports. The availability and stability conditions of the surface oxygen atoms on TiO 2 crystals depend on the surface orientation of the crystals. In this study, rutile TiO 2 single crystals with different orientations are used and we evaluate the progress of photocatalytic decomposition reactions by the weight loss of the salad oil and linoleic acid due to formation of gaseous species. If the surface of rutile TiO 2 single crystals is not reconstructed and surface oxygen is involved, the orientation of the surface affects the photocatalytic activity of TiO 2 ; the photocatalytic activity increases in the order of (114) < (100) < (101) < (001).©2013 The Ceramic Society of Japan. All rights reserved.Key-words : Photocatalyst, Surface orientation, Rutile TiO 2 , Single crystal [Received August 15, 2012; Accepted October 15, 2012] When titanium dioxide (TiO 2 ) crystal is exposed to UV light, it exhibits photocatalytic activity 1) and hydrophilic behavior 2) at the crystal surface. The photocatalytic activity of TiO 2 is mainly discussed in terms of the band gap energy, 3),4) because a light with a certain energy is required to promote electrons from the valence band to the conduction band. The electronhole pairs created are used to reduce and oxidize chemicals that are near the photocatalyst.There are, however, other factors that are also important for the photocatalytic activity of TiO 2 . The importance of surface oxygen for the decomposition of chemicals on the photocatalyst is emphasized in some reports. 5),6) Wilson and Idriss 5),6) have shown that the oxygen of TiO 2 is involved in the decomposition reaction of acetic acid at the surface. An electron at the surface reacts with an oxygen molecule in the gas phase to produce O 2 minus radical (O 2 ¹ •) which then reacts with chemicals on the surface to form other intermediates. The final reaction products are CH 4 /C 2 H 6 and CO 2 . The main reactions are as follows:CH 3 COOH ðAds:Þ ! CO 2 ðgÞ þ CH 4 ðgÞ ð 1Þ 2CH 3 COOH ðAds:Reaction (2) suggests that surface oxygen atoms (O s ) on TiO 2 crystals play an important role in the decomposition (or oxidation) of acetic acid. Although surface atoms or ions, which are energetically unstable, are surrounded by fewer atoms or ions compared to bulk atoms or ions, the availability and stability conditions of the surface oxygen atoms on TiO 2 crystals depend on the surface orientation of the crystals. Lowekamp et al. 8) have reported the orientation dependence of photocatalytic reactions on TiO 2 film surfaces and the anisotropic photocatalytic reaction on polycrystalline TiO 2 . 9) In the two papers, they studied the following reaction:Their findings showed that TiO 2 grains with the (100) and (110) rutile TiO 2 surfaces have lower photoreduction rates than those with the (101), (111) and (001) surfaces, and ...
The effect of the surface conditions of (001) and (100) rutile TiO2 surfaces on the photocatalytic decomposition of linoleic acid was investigated. The rate of decomposition was observed by measuring the weight of the remaining linoleic acid. The as-received (polished) (001) surface showed a higher photocatalytic activity than the (100) surface, but the activity was greatly reduced when the surface was treated by HF solution and heated to 400°C. Condition of the surface strongly affects the photocatalytic activity. The heated (001) surface partially regained its activity after multiple parallel grooves were introduced along the [110] direction. However, the surface did not regain its activity if these grooves were instead introduced along the [1-10] or [100] directions.
The photocatalytic activity of a hydrogen fluoride (HF)-treated rutile TiO 2 (001) surface for the decomposition reaction of linoleic acid was lower than that of an asreceived (polished) rutile TiO 2 (001) surface. The surfaces of as-received TiO 2 (001) and HF-treated TiO 2 (001) were investigated using low-energy electron diffraction (LEED) and surface X-ray diffraction (SXRD) to elucidate differences in their photocatalytic activities. The as-received (polished) surface did not yield good LEED patterns, which implied that the surface was not well-ordered and was thus not examined using SXRD. In contrast, the HF-treated surface produced good LEED patterns with a 1×1 structure and was thus studied using SXRD. The analysis of crystal truncation rods indicated that all atoms in the four layers of the surface moved toward the bulk and that the HF-treated surface was (101)-faceted with terraces. On average, the facet was found to be four layers deep. The difference in the condition of the surface influences the photocatalytic activity of the surface.
Photocatalytic decomposition reaction of linoleic acid and oleic acid on rutile TiO 2 single crystals were studied by measuring the weight of acid. UV light with maximum intensity at the wavelength of 366 nm was used as light source. Single crystals were oriented at (100), (114), (101) and (001) surfaces. For both acids, decomposition at (001) surface was the fastest and the decomposition at (114) surface was the slowest. The difference might be related to unstableness of (001) surface. The decomposition of linoleic acid was faster than that of oleic acid. This difference in reaction rate is related to the number of unsaturated bond in the acid molecule.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.