Preparing articles on photocatalysis - beyond the illusions, misconceptions, and speculation

Chemistry Letters

Volumn 37, Issue 3, 2008, Pages 217-229

  Ohtani, Bunsho ^a  

^a HOKKAIDO UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 42049106417     PISSN: 03667022     EISSN: None     Source Type: Journal    
DOI: 10.1246/cl.2008.216     Document Type: Note

References (33)

1. A. Fujishima, K. Honda, Nature 1972, 238, 37. Although the order of author names in this paper is Fujishima and Honda, the order in the term "Honda-Fujishima Effect" is reversed. Many authors, including the present author, have mistakenly cited this paper as "K. Honda, A. Fujishima,...". It is important when making References and Notes to refer to papers correctly and checking a copy of the paper every time when citing is preferable, though some recent editing systems of scientific papers check the bibliographic data to give direct Internet links. The author hopes that this service does not accelerate the trend of not checking original copies of cited papers.
2. S. Kato, F. Masuo, Kogyo Kagaku Zasshi 1964, 67, 42. This paper reported photocatalytic oxidation of tetralin (1,2,3,4- tetrahydronaphthalene) by a titania suspension. Although, a paper was referred to as a preceding paper reporting titania photocatalysis (G. F. Huttig, Kolloid Z. 1943, 106, 166), the paper (Actually, the authors are G. F. Hüttig and W. Kunda) written in German does not seem to report titania photocatalysis.
3. I. S. McLintock, M. Ritchie, Trans. Faraday Soc. 1965, 61, 1007. In this paper, solid-gas phase photocatalytic oxidation of ethylene and propylene in the presence of adsorbed oxygen on titania is described. This seems to be the first paper on gas-phase titania photocatalysis written in English, though some studies had been reported on photoadsorption/photodesorption of molecules on a titania surface before this paper. Such gas-phase photocatalytic reaction by zinc oxide (ZnO) had been reported before this paper, e.g., Y. Fujita, Shokubai 1961, 3, 235.
4. http://rredc.nrel.gov/solar/spectra/aml.5/
5. -2. The difference is presumably attributable to the difference in instruments used for the measurements.
6. Although estimation of electronic structure of photocatalyst particles is very important, no reliable method for this estimation has been established. The following paper is cited as a reference of electronic structure of anatase (and rutile): L. Kavan, M. Grätzel, S. E. Gilbert, C. Klemenz, H. J. Scheel, J. Am. Chem. Soc. 1996, 118, 6716.
7. D. E. Scaife, Sol. Energy 1980, 25, 41. Although this paper clearly showed that the top of the valence band is constant for a large number of metal oxides, including mixed metal oxides (Only five out of more than fifty metal oxides have different valence-band positions.) and this paper is well known by researchers in this field of photocatalysis, there have been some published papers with figures showing different valence-band positions.
8. Y. Nosaka, A. Nosaka, Nyumon Hikarishokubai (Japanese), Tokyo Tosho, Tokyo, 2004, p. 59.
9. H. P. Klug, L. E. Alexander, X-ray Diffraction Procedures for Poly crystalline and Amorphous Materials, 2nd ed., Wiley, New York, 1974, p. 531. Although this book covers the theoretical background and experimental techniques of XRD measurements with detailed descriptions, the book seems not so popular in Japan, presumably because it has not been translated into Japanese.
10. Actually, peak intensity depending on the size of particles of silica has been reported: I. Nakai, F. Izumi, Funmatsu X-Sen Kaisetsu no Jissai (Japanese), Asakurashoten, Tokyo, 2002, p. 116.
11. B. Ohtani, Y. Ogawa, S. Nishimoto, J. Phys. Chem. B 1997, 101, 3746. Presumably, this is the only paper on the negligible photocatalytic activity of amorphous titania.
12. B. Ohtani, Y. Azuma, D. Li, T. Ihara, R. Abe, Trans. Mater. Res. Soc. Jpn. 2007, 32, 401.
13. T. Ohno, K. Sarukawa, M. Matsumura, J. Phys. Chem. B 2001, 105, 2417.
14. T. Ohno, K. Sarukawa, K. Tokieda, M. Matsumura, J. Catal. 2001, 203, 82.
15. R. Abe, D. Li, Y. Azuma, B. Ohtani, to be submitted. B. Ohtani, R. Abe, Y. Azuma, T. Ihara, 17th MRS-J Academic Symposium, Tokyo, Japan, December 10, 2006, Abstr. No. F-16. It should be noted that this ratio is valid only for the sample stored in a cabinet in the author's laboratory. There is no guarantee that all samples of P25 have the same crystalline content.
16. R. M. Spurr, H. Myers, Anal. Chem. 1957, 29, 760. This very old paper has been digitalized and uploaded on the web site of American Chemical Society. A check of the frequency of citation of this paper in "Web of Knowledge" showed that this paper has been cited more frequently in past few decades than in the period just after publication. It seems that authors of recent papers on titania photocatalysts have referred to this paper without reading the original copy.
17. While Rietveld method has recently been used for analysis of XRD patterns, the author thinks that this method can not also be used for determination of crystalline content of samples containing an amorphous (not giving XRD peaks) phase.
18. Sometimes this coefficient is called "shape factor," but the author does not know the reason for this.
19. The original paper on this plot is G. K. Williamson, W. H. Hall, Acta Metall. 1953, 1, 22. The author has not checked discussion, if any, on this plot following the original paper.
20. This stoichiometry has been clarified for the first time by the author's group and repotted as S. Nishimoto, B. Ohtani, H. Kajiwara, T. Kagiya, J. Chem. Soc., Faraday Trans, 1 1983, 79, 2685. Before submission to this journal, the author submitted a part of the experimental results to Chemistry Letters as the first paper in the author's career in the field of photocatalysis, but the paper was rejected presumably due to a reviewer's comment that the content had been reported in a Russian journal without showing bibliographic data (This could not be found.). To submit the results as a full paper, additional experiments were carried out to support the stoichiometry. For example, an oxygen-isotope experiment was carried out and showed the origin of molecular oxygen to be water. As a result, the paper could be published, and it has been cited more than 70 times, including recent citations. This is an example of rejection of a submitted paper not always being disadvantageous for the authors.
21. T. Torimoto, Y. Aburakawa, Y. Kawahara, S. Ikeda, B. Ohtani, Chem. Phys. Lett. 2004, 392, 220. This paper showed that the rate of photocatalytic reactions in the presence of molecular oxygen, i.e., photocatalytic oxidative decomposition, may strongly depend on the intensity of light irradiation, while the rate of reactions in the absence of oxygen seems to be almost independent of the light intensity.
22. Strictly speaking, when apparent quantum efficiency is discussed, the light intensity should be adjusted to be the same in number of photons, not in energy.
23. In the Japanese Industrial Standards (JIS B7113, discontinued), limiting transmission wavelength is defined as the center of wavelengths giving 72% and 5% transmission. For example, the limiting transmission wavelength for an Asahi Technoglass L-42 cut-off filter is 420 nm based on the standard, and this filter transmits ca. 60% at 420 nm The figure "42" shows only that 420 nm is the limiting transmission wavelength defined in JIS, and practically >390nm irradiation is made using this filter. Statements such as "visible-light irradiation at >420nm was performed using an optical sharp cut filter" seem misleading when L-42 has been used.
24. X. Yan, T. Ohno, K. Nishijima, R. Abe, B. Ohtani, Chem. Phys. Lett. 2006, 429, 606. Citation of this paper is not ex-pected at all (and actually so), since authors using methylene blue (MB) as a model compound for photocatalytic reaction never want to refer to this and, on the other hand, those who do not use MB need not to refer to this. However, the author's friend, an associate editor for a scientific journal, told the author that this paper has often been referred to in referee reports for papers reporting photocatalytic systems including MB or other dyes. Watanabe et al. have reported a similar action spectrum analysis of photoinduced degradation of Rhodamine B with a cadmium sulfide suspension and pointed out a similar dye-sensitization mechanism: T. Watanabe, T. Takizawa, K. Honda, J. Phys. Chem. 1977, 81, 1845. Photocatalytic reaction of MB in aerated titania suspensions was reported in 1937 by a Japanese photochemist: M. Horio, Nihon Gakujutsu Kyokai Hokoku 1937, 12, 204. As far as the author knows, this is the first report on titania photocatalysis.
25. Sometimes the term "active site" is used for a photocatalytic reaction system with dispersed chemical species, e.g., metal complexes or atomically adsorbed species, on support materials. Even in this case, a photocatalytic reaction occurs only when the species absorb light, and species not irradiated therefore cannot be active sites.
26. Photoexcited electrons and positive holes must react with the substrate independently. However, to simplify the discussion, it is presumed here that an electron-hole pair reacts with the substrate.
27. r is presented: S. Murakami, H. Kominami, Y. Kera, S. Ikeda, H. Noguchi, K. Uosaki, B. Ohtani, Res. Chem. Intermed. 2007, 33, 285.
28. The author thinks that the use of "rate-determining step" for photoreactions is misleading, since a photoreaction in principle proceeds via species in their excited state and they undergo both chemical reaction and deactivation (deexcitation). The assumption for rate-determining step is that the reaction proceeds sequentially, not in parallel, such as photoreactions.
29. The author could not find the original description of why this linear adsorption isotherm is called "Henry-type." One possible reason is the resemblance of linear relation with that of dissolution of gas in liquid.
30. Honestly speaking, the author does not like to describe such criticisms in this article, since some of them have been employed when referee reports were prepared for papers in this field of photocatalysis and thereby authors submitting such papers may recognize that the papers had been rejected by the author's criticism when reading this article. However, the author would like to say that those criticisms may be acceptable for researchers in this field and hence reviewers other than the present author may state them in their reviewers' reports.
31. In this sense, conversely, statistical analyses of the reaction rate with measured properties of photocatalysts may be helpful for estimation of the significance of property on the reaction rate. O. O. Prieto-Mahaney, R. Abe, F. Amano, B. Ohtani, to be submitted.
32. Since the discovery of this phenomenon in 1997 (R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 1997, 388, 431), it has been believed that this is induced by band-gap excitation of photocatalytic coatings. However, the corresponding action spectra were reported for the first time in 2007 by the author's group (X. Yan, R. Abe, T. Ohno, M. Toyofuku, B. Ohtani, Thin Solid Films 2007, in press. DOI: 10.1016/j.tsf.2007.10.033).
33. Another frequently asked question is the comparison of photocatalytic activity of brookite. The author used to answer as "Brookite is similar to anatase.", but this tended to be misunderstood as brookite shows better activity than that of rutile as has been observed for anatase. Therefore, it is necessary to state that such comparison does not make sense before answering so. The fact that brookite crystallites were prepared as a mixture with other polymorphs, anatase and/or rutile makes it difficult to discuss their photocatalytic activities, but, even if pure brookite crystallites are obtained, such discussion on the structure is complicated as described in Structure - photocatalytic activity correlation. 34 American Chemical Society, The ACS Style Guide - Effective Communication of Scientific Information, 3rd ed., ed. by A. M. Coghill, L. R. Garson, Oxford University Press, Oxford, 2006, 23. This book is recommended by the author to graduate students and postdoctoral fellows, who will write scientific papers in English, and a copy of the book is given to them as a remembrance when they leave the author's laboratory.