EICCS 2009
Dependence of Photocatalytic Activities on the Crystal Structure of
Titanium(IV) Oxide Particles for Environmental Applications
Bunsho Ohtani,1,2 Orlando-Omar Prieto-Mahaney,2 Fumiaki Amano1,2 and Ryu Abe1,2
1
Catalysis Research Center and 2Graduate School of Environmental Science, Hokkaido University
Anatase and rutile are predominant polymorphs of titanium(IV) (titania) and titania
photocatalysts, widely used in environmental applications, are composed of each of them or their
mixture. Their photocatalytic activity is often discussed in relation with these polymorphs, e.g.,
anatase is better than rutile. However, it is rather difficult in strict scientific sense to prove these
hypotheses, because a pair of powder samples of completely same physical properties except for
crystal structure can not be prepared and compared with each other. This study aims at clarifying the
above-mentioned hypothesis through statistical analyses of physical properties and photocatalytic
activity of 35 commercial titania samples.
Five test photocatalytic reactions were as follows: a) Oxygen (O2) liberation from a deaerated
silver sulfate aq., b) Dehydrogenation of methanol in a deaerated water, c) Oxidative decomposition
of acetic acid in an aerated aqueous solution, d) Oxidative decomposition of acetaldehyde in air, and
e) Synthesis of pipecolinic acid (PCA) from L-lysine (Lys) in a deaerated aqueous solution. The
standardized reaction rates were compared with each structural property, specific surface area (BET),
density of lattice defects (DEF), primary particle size (PPS), secondary particle size (SPS), and
existence of anatase (ANA) and rutile (RUT) phases. The data were analyzed statistically by solving
a following matrix equation, [rate]351 = [property]356  [coefficient]61, for each reaction.1)
Table 1 shows the results of analyses. As a
Table 1
Squared multiple correlation
general trend, reactions a) and e) gave
coefficient (R2) and partial regression
coefficients (k).
relatively larger R2s, i.e., higher reproducibility
coefficient
a)
b)
c)
d)
e)
of the results, while those for the others were
2
R
0.86 0.52 0.58 0.60 0.85
also fairly high. Another significant feature is
k
–0.01
0.43 –0.09 0.13 0.19
BET
that coefficient of kANA has large positive value
kDEF
–0.15 -0.25 0.19 0.43 0.32
in all the cases except for reaction a). This is
kPPS
0.12 -0.20 –0.18 –0.20 –0.52
the first example supporting a general
kSPS
0.57 0.08 –0.20 –0.04 –0.07
understanding that anatase is more active than
kRUT
0.14 0.28 0.11 –0.06 0.02
rutile. On the other hand, kRUT was relatively
kANA
0.04 0.40 0.57 0.55 0.63
small suggesting that rutile is rather inert
compared with anatase. For reaction a), kANA was small but positive, while kRUT was not so large,
suggesting that rutile is not indispensable for higher activity. It seems that large secondary particles
(large positive kSPS) composed of large primary particles of less crystalline defects (negative kDEF) are
preferable as reported so far. A significant point is that the reported higher activity of rutile powders
for reaction a) is mainly attributable to their secondary particle size, but not to rutile crystal.
1) Prieto-Mahaney, O. O.; Murakami, N.; Abe, R.; Ohtani, B. Chem. Lett, 2009, 37, in press.
2) Murakami, N.; Prieto-Mahaney, O. O.; Abe, R.; Torimoto, T.; Ohtani, B. J. Phys. Chem. C 2007, 111,
11927-11935.
1
EICCS 2009
Name: Bunsho OHTANI
Position and Affiliation: Professor of Catalysis Research Center, Hokkaido
University
Postal Address: North 21, West 10, Kita-ku, Sapporo 001-0021, Japan
Phone/Facsimile: +81-11-706-9132/+81-11-706-9133
Email: ohtani@cat.hokudai.ac.jp
Web Page URL: http://www.hucc.hokudai.ac.jp/~k15391/
Research Interest and Keywords: Photocatalysis, Development of Anisotropic Particles,
Mechanism of Photocatalytic Reaction, Correlation between Activity and Properties of
Photocatalysts, Design of Active and Selective Photocatalysts, Development of Novel Methods
of Photocatalyst Preparation
Recent Publications:
1) Amano, F.; Yamakata, A.; Nogami, K.; Osawa, M.; Ohtani, B. "Visible Light Responsive Pristine
Metal Oxide Photocatalyst: Enhancement of Activity by Crystallization under Hydrothermal
Treatment", J. Am. Chem. Soc. 2008, 130, 17650-17651.
2) Murakami, N.; Abe, R.; Ohtani, B. "In-situ observation of photocatalytic reaction by
photoacoustic spectroscopy: Detection of heat of exothermic photocatalytic reaction", Chem.
Phys. Lett. 2008, 416, 316-320.
3) Ohtani, B.; Nohara, Y.; Abe, R. "Participation of Molecular Oxygen in Photocatalytic Oxidative
Decomposition of Organic Compounds by Metal Oxide Particulate Suspensions and Thin Film
Electrodes", Electrochemistry 2008, 76, 147-149.
4) Ohtani, B. "Preparing Articles on Photocatalysis―Beyond The Illusions, Misconceptions and
Speculation", Chem. Lett. 2008, 37, 216-229.
5) Yan, X.; Abe, R.; Ohno, T.; Toyofuku, M.; Ohtani, B. "Action spectrum analyses of
photoinduced superhydrophilicity of titania thin films on glass plates", Thin Solid Films 2008,
516, 5872-5876.
Biographical Sketch:
A research work on photocatalysis by Professor Ohtani started in 1981 when he was a Ph. D.
course student in Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University
under the supervision of Professor Tsutomu Kagiya. Since then he has been studying photocatalysis
and relating topics for more than 25 years. After getting Ph. D. degree in Kyoto University in 1985,
he became an assistance professor in the university. In 1996, he was promoted to an associate
professor in Division of Chemistry, Graduate School of Science, Hokkaido University. After
collaboration work with Professor Kohei Uosaki for about 2 and half years including a period of
studying in Kansas University for approximately 3 months, he got a full professor position in
Catalysis Research Center, Hokkaido University in 1998. For education of graduate students,
Professor Ohtani's laboratory belongs to Graduate School of Environmental Science since 1999.
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