U.S. patent application number 11/659540 was filed with the patent office on 2007-08-16 for ultrafine particle of rutile-type titanium oxide.
Invention is credited to Toyoharu Hayashi, Tomonori Iijima, Norio Nakayama.
Application Number | 20070190324 11/659540 |
Document ID | / |
Family ID | 35967348 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070190324 |
Kind Code |
A1 |
Hayashi; Toyoharu ; et
al. |
August 16, 2007 |
Ultrafine particle of rutile-type titanium oxide
Abstract
It is provided ultrafine particles of a rutile titanium oxide
obtained by maintaining the pH of an aqueous solution of a titanium
compound having a Ti concentration of from 0.07 to 5 mol/L in the
range of -1 to 3 in the presence of a chelating agent. Such
ultrafine particles of a rutile titanium oxide are useful for
photocatalysts, high refractive index materials, ultraviolet
absorbing materials and the like.
Inventors: |
Hayashi; Toyoharu;
(Yokohama-shi, JP) ; Nakayama; Norio;
(Ichihara-shi, JP) ; Iijima; Tomonori;
(Ichihara-shi, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
35967348 |
Appl. No.: |
11/659540 |
Filed: |
August 4, 2005 |
PCT Filed: |
August 4, 2005 |
PCT NO: |
PCT/JP05/14280 |
371 Date: |
February 6, 2007 |
Current U.S.
Class: |
428/402 ;
423/610 |
Current CPC
Class: |
B01J 35/004 20130101;
B01J 21/063 20130101; B82Y 5/00 20130101; A61K 8/29 20130101; C01G
23/047 20130101; C01P 2002/72 20130101; C09C 1/3669 20130101; Y10T
428/2982 20150115; C09C 1/3607 20130101; B01J 35/002 20130101; B01J
35/023 20130101; B01J 37/03 20130101; C01P 2002/82 20130101; A61K
2800/413 20130101; A61Q 17/04 20130101 |
Class at
Publication: |
428/402 ;
423/610 |
International
Class: |
B32B 15/02 20060101
B32B015/02; B32B 5/16 20060101 B32B005/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2004 |
JP |
2004-246745 |
Claims
1. Ultrafine particles of a rutile-type titanium oxide obtained by
maintaining the pH of an aqueous solution of a titanium compound
having a Ti concentration of 0.07 to 5 mol/L in the range of -1 to
3 in the presence of a chelating agent.
2. The ultrafine particles of a rutile-type titanium oxide
according to claim 1, wherein the chelating agent as set forth in
claim 1 is one or more selected from hydroxycarboxylic acids,
diketones, keto esters and dicarboxylic acids.
3. The ultrafine particles of a rutile-type titanium oxide
according to claim 2, wherein the hydroxycarboxylic acid is
glycolic acid, lactic acid, citric acid, tartaric acid or salts
thereof.
4. The ultrafine particles of a rutile-type titanium oxide
according to claim 2, wherein the diketone is acetylacetone or
salts thereof.
5. The ultrafine particles of a rutile-type titanium oxide
according to claim 1, wherein the chelating agent is added in a
mole ratio of the chelating agent to titanium of 0.0005 to
0.05.
6. A photocatalyst containing the ultrafine particles of a
rutile-type titanium oxide according to claim 1.
7. The photocatalyst according to claim 6, which is calcined at 100
to 800 degree centigrade.
8. A method for preparing ultrafine particles of a rutile-type
titanium oxide, comprising maintaining the pH of an aqueous
solution of a titanium compound having a Ti concentration of 0.07
to 5 mol/L in the range of -1 to 3 in the presence of a chelating
agent.
9. The method according to claim 8, wherein the chelating agent is
one or more selected from hydroxycarboxylic acids, diketones, keto
esters and dicarboxylic acids.
10. The method according to claim 9, wherein the hydroxycarboxylic
acid is glycolic acid, lactic acid, citric acid, tartaric acid or
salts thereof.
11. The method according to claim 9, wherein the diketone is
acetylacetone or salts thereof.
12. The method according to claim 8, comprising adding the
chelating agent in a mole ratio of the chelating agent to titanium
of 0.0005 to 0.05.
13. An aggregate comprising ultrafine particles of a rutile-type
titanium oxide obtained by maintaining the pH of an aqueous
solution of a titanium compound having a Ti concentration of 0.07
to 5 mol/L in the range of -1 to 3 in the presence of a chelating
agent.
14. The aggregate comprising ultrafine particles of a rutile-type
titanium oxide according to claim 13, wherein the chelating agent
is one or more selected from hydroxycarboxylic acids, diketones,
keto esters and dicarboxylic acids.
15. The aggregate comprising ultrafine particles of a rutile-type
titanium oxide according to claim 14, wherein the hydroxycarboxylic
acid is glycolic acid, lactic acid, citric acid, tartaric acid or
salts thereof.
16. The aggregate comprising ultrafine particles of a rutile-type
titanium oxide according to claim 14, wherein the diketone is
acetylacetone or salts thereof.
17. The aggregate comprising ultrafine particles of a rutile-type
titanium oxide according to claim 13, wherein the chelating agent
is added in a mole ratio of the chelating agent to titanium of
0.0005 to 0.05.
18. A photocatalyst containing the aggregate according to claim
13.
19. The photocatalyst according to claim 18, which is calcined at
100 to 800 degree centigrade.
20. A method for preparing an aggregate comprising ultrafine
particles of a rutile-type titanium oxide, comprising maintaining
the pH of an aqueous solution of a titanium compound having a Ti
concentration of 0.07 to 5 mol/L in the range of -1 to 3 in the
presence of a chelating agent.
21. The method for preparing an aggregate comprising ultrafine
particles of a rutile-type titanium oxide according to claim 20,
wherein the chelating agent is one or more selected from
hydroxycarboxylic acids, diketones, keto esters and dicarboxylic
acids.
22. The method for preparing an aggregate comprising ultrafine
particles of a rutile-type titanium oxide according to claim 21,
wherein the hydroxycarboxylic acid is glycolic acid, lactic acid,
citric acid, tartaric acid or salts thereof.
23. The method according to claim 21, wherein the diketone is
acetylacetone or salts thereof.
24. The method according to claim 20, comprising adding the
chelating agent in a mole ratio of the chelating agent to titanium
of 0.0005 to 0.05.
25. A photocatalyst according to claim 6, which is for decomposing
an organic compound.
26. A method for decomposing an organic compound using the
photocatalyst according to claim 6.
27. The photocatalyst according to claim 25, wherein the organic
compound is aldehyde, toluene or an organic dye.
28. The decomposing method according to claim 26, wherein the
organic compound is aldehyde, toluene or an organic dye.
Description
TECHNICAL FIELD
[0001] The present invention relates to ultrafine particles of a
rutile-type titanium oxide which are useful for photocatalysts,
high refractive index materials, ultraviolet absorbing materials
and the like.
BACKGROUND ART
[0002] Titanium oxide has been known as a typical photo-oxidation
catalyst, and hitherto applied to an antibacterial agent, an
antifogging agent that utilizes their super hydrophilicity, or the
like. There have been known three types of crystal structures for
titanium oxide; anatase, rutile and brookite. Of these types,
anatase is considered to have the highest photocatalytic activity.
In recent years, however, it has been known that the photocatalytic
activity is further enhanced by bringing a rutile-type component
partially into contact with an anatase-type component and mixing
them. For that reason, there has been proposed that ultrafine
particles of a rutile-type titanium oxide are mixed with an
anatase-type titanium oxide. It has also been expected that high
activity is exhibited by using ultrafine particles of a rutile-type
titanium oxide alone. However, since in the conventional vapor
phase method, a rutile-type titanium oxide is treated at a high
temperature, its particle diameter becomes large due to sintering.
Thus, there has been a drawback such that the photocatalytic
activity is consequently reduced due to the decrease in the surface
area.
[0003] On the other hand, there has been reported a method for
synthesizing a rutile-type titanium oxide using the low temperature
wet process by H. D. Nam et al. (Non-patent Document 1). However,
in this method, there is also the problem of decrease in the
photocatalytic activity because there is formed an aggregate having
a particle diameter of 200 to 400 nm in which a long-fibrous
rutile-type titanium oxide is gathered. In order to overcome these
drawbacks, it is also provided highly dispersive rutile ultrafine
particles useful for high refractive index materials or ultraviolet
absorbing materials requiring transparency.
[0004] Non-patent Document 1: Jpn. J. Appl. Phys., Vol. 37, p. 4603
(1998)
DISCLOSURE OF THE INVENTION
[0005] An object of the present invention is to provide ultrafine
particles of a rutile-type titanium oxide which are used for
photocatalysts, high refractive index materials, ultraviolet
absorbing materials and the like.
[0006] In order to solve the above problems, the present inventors
have conducted an extensive investigation, and as a result, have
found that the increase in a crystal grain diameter is suppressed
and the aggregation of a crystal is also suppressed in the event
that a chelating agent is used in the preparation of a rutile-type
titanium oxide. Thus, the present invention has been completed.
[0007] That is, the present invention relates to ultrafine
particles of a rutile-type titanium oxide obtained by maintaining
the pH of an aqueous solution of a titanium compound having a Ti
concentration of 0.07 to 5 mol/L in the range of -1 to 3 in the
presence of a chelating agent.
EFFECT OF THE INVENTION
[0008] According to the present invention, it can be provided novel
ultrafine particles of a rutile-type titanium oxide and a
photocatalyst containing the ultrafine particles of a rutile-type
titanium oxide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a diagram illustrating an X-ray diffraction
spectrum of the air-dried powder obtained in Example 1.
[0010] FIG. 2 is a diagram illustrating an infrared absorption
spectrum of the air-dried powder obtained in Example 1.
[0011] FIG. 3 is a diagram illustrating the results from the test
on the photocatalytic activity of the air-dried powder of the
rutile-type titanium oxide obtained in Example 1, the powder of the
rutile-type titanium oxide subjected to calcination at 400 degree
centigrade and the powder of the anatase-type titanium oxide
obtained in Comparative Example 2.
[0012] FIG. 4 is a diagram illustrating the results from the test
on decomposition of acetoaldehyde in Example 5.
[0013] FIG. 5 is a diagram illustrating the results from the test
on decomposition of toluene in Example 6.
BEST MODE FOR CARRYING OUT THE INVENTION
[0014] Ultrafine particles of a rutile-type titanium oxide of the
present invention are obtained by maintaining the pH of an aqueous
solution of a titanium compound having a Ti content concentration
of 0.07 to 5 mol/L in the range of -1 to 3 in the presence of a
chelating agent.
[0015] The chelating agent to be used for the preparation of
ultrafine particles of a rutile-type titanium oxide of the present
invention is not particularly limited as far as it has at least two
functional groups capable of coordinating to titanium cations.
[0016] Examples of the compound having at least two functional
groups capable of coordinating to titanium cations include
hydroxycarboxylic acids, diketones, ketocarboxylic acids, keto
esters and dicarboxylic acids.
[0017] For preparing of ultrafine particles of a rutile-type
titanium oxide of the present invention, one or more agents
selected from hydroxycarboxylic acids, diketones, ketoesters and
dicarboxylic acids may be used.
[0018] Examples of the hydroxycarboxylic acids include glycolic
acid, lactic acid, citric acid, tartaric acid, salicylic acid, and
salts thereof such as sodium citrate and the like. Examples of the
diketones include acetylacetone, propionylacetone and salts thereof
such as aluminum acetylacetonate and the like.
[0019] Examples of the keto esters include ethyl acetoacetate,
ethyl malonate and the like.
[0020] Examples of the dicarboxylic acids include malonic acid,
succinic acid and the like.
[0021] The amount of the chelating agent to the titanium compound
to be used is selected such that a mole ratio of the chelating
agent to the Ti content in the titanium compound is in the range of
0.0005 to 0.05. It is desired that the chelating agent is used
within this range because it is difficult for ultrafine particles
of a rutile-type titanium oxide to aggregate and form a huge
aggregate within above range.
[0022] The titanium compound to be used in the present invention is
not limited as far as it forms titanium oxide by a chemical
reaction. Preferable examples thereof include titanium compounds
selected from titanium tetrachloride, titanium oxychloride,
titanium sulfate, titanium nitrate, titanium alkoxide, hydrous
titanium oxide (including those obtained by subjecting a titanium
compound to hydrolysis in advance under alkaline conditions as
well) and the like.
[0023] The concentration of the titanium compound in the aqueous
solution to be used in the present invention is 0.07 to 5 mol/L and
preferably from 0.1 to 1 mol/L, which is presented as a
concentration of the Ti content of the titanium compound (hereafter
simply referred to as "Ti concentration").
[0024] When the Ti concentration is lower than 0.07 mol/L, an
anatase-type titanium oxide is formed. On the other hand, when the
Ti content concentration is higher than 5 mol/L, the formation of
titanium oxide is prevented because the water concentration is
lowered.
[0025] The pH of the aforementioned aqueous solution containing the
titanium compound is varies depending on the type of the chelating
agent and the titanium compound to be used. For that reason, the pH
of the aqueous solution containing the titanium compound is
adjusted by using hydrochloric acid, nitric acid or the like, as
needed.
[0026] The pH of the aqueous solution containing the titanium
compound is adjusted in the range of -1 to 3. However, when the pH
is greater than 3 for the reaction, it is not preferable because
the formation of a titanium oxide crystal is prevented.
[0027] The aqueous solution containing the above chelating agent
and the titanium compound after the pH is adjusted is usually
maintained at a temperature selected from the temperature of -10 to
100 degree centigrade. The temperature in the range of 20 to 60
degree centigrade is preferably recommended. The temperature of the
aqueous solution is usually maintained within the above temperature
range for 0.5 to 10 hours.
[0028] As described above, ultrafine particles of a rutile-type
titanium oxide are precipitated in the aqueous solution by
maintaining the pH of the aqueous solution of a titanium compound
having a Ti concentration of 0.07 to 5 mol/L in the range of -1 to
3 in the presence of a chelating agent. Incidentally, the aqueous
solution contains a small amount of aggregate in which ultrafine
particles of a rutile-type titanium oxide aggregate.
[0029] Ultrafine particles precipitated in the aqueous solution are
those of a rutile-type titanium oxide. Such a fact can be confirmed
by the X-ray diffraction measurement. Furthermore, an average
particle diameter of the ultrafine particles of a rutile-type
titanium oxide can be obtained from the Debye-Sherrer equation as
well.
[0030] The ultrafine particle of a rutile-type titanium oxide
precipitated in the above aqueous solution has an average particle
diameter of 2 to 10 nm in short axis thereof and 15 to 30 nm in
long axis thereof. The aggregate in which ultrafine particles of a
rutile-type titanium oxide aggregate to one another has an average
particle diameter of 10 to 100 nm.
[0031] Ultrafine particles of a rutile-type titanium oxide and an
aggregate formed by aggregation of ultrafine particles of a
rutile-type titanium oxide are separated by a method such as
filtration or the like from the aqueous solution containing them,
and as needed, are washed by a method such as dispersion into a
solvent such as water and/or alcohol, ultrafiltration,
reprecipitation or the like.
[0032] The thus recovered ultrafine particles of a rutile-type
titanium oxide (including an aggregate formed by aggregation of
ultrafine particles of a rutile-type titanium oxide) are dried or
calcined at 100 to 800 degree centigrade, whereby the ultrafine
particles may be obtained as the powder, but the ultrafine
particles may also be obtained as a sol, as desired.
[0033] Since the thus obtained ultrafine particles of a rutile-type
titanium oxide act as a catalyst in a photodecomposition reaction
or the like, they are useful as a photocatalyst containing the
ultrafine particles. Examples of the photodecomposition reaction
include a reaction for decomposing an organic compound such as an
organic dye, formalin or aromatic hydrocarbon, and the like.
EXAMPLES
[0034] The present invention is now more specifically illustrated
below with reference to Examples. However, the present invention is
not restricted to these Examples.
[0035] Incidentally, the activity of a photocatalyst is evaluated
in accordance with the following method.
[0036] To a 1 cm cuvette cell, 6 mg of titanium oxide TiO.sub.2 (in
case of a sol, a sol containing TiO.sub.2 in the same amount) was
charged. To this cuvette cell, 2.times.10.sup.-5 mol/L of an
aqueous methylene blue solution was added and the resulting mixture
was stirred with a magnetic stirrer. The cuvette cell was
irradiated at the side thereof with light from a high pressure
xenon lamp through a water filter having a length of 5 cm. The
amount of light in the front surface of the cell was measured and
adjusted to 120 mW/cm.sup.2. The sample solution was taken out at
intervals of every 10 minutes and centrifuged to measure a UV-VIS
absorption spectrum of the filtrate, and evaluate the
photocatalytic activity from the change in absorbance of methylene
blue.
Example 1
[0037] To a 100 mL eggplant flask, 0.001 mole ratio to 25 mmol of
Ti that is 0.025 mmol of glycolic acid and 50 mL of ion exchange
water were added. Subsequently, to the flask, 5 mL of a
TiOCl.sub.2.HCl solution (Ti content: 25 mmol, a product of Fluka)
was added to prepare a 0.45 M TiOCl.sub.2 solution. This solution
was allowed to react at 50 degree centigrade for 1 hour. The
obtained precipitate was redispersed in ion exchange water for
carrying out the electron microscope observation. As a result, a
mixture containing ultrafine particles having an average particle
diameter of 25 nm in long axis and 10 nm in short axis, and a small
amount of aggregate of ultrafine particles having an average
particle diameter of 50 nm was obtained. The obtained precipitate
was washed with acetonitrile and air-dried to give powder. The
X-ray diffraction spectrum of the air-dried powder was measured. As
a result, the powder was identified as a rutile-type titanium
oxide.
[0038] The X-ray diffraction spectrum and infrared absorption
spectrum of the air-dried powder are shown in FIGS. 1 and 2,
respectively. Furthermore, the calculated values in the long axis
and short axis of ultrafine particles evaluated from the
Debye-Sherrer equation correspond to the results from the electron
microscope observation.
[0039] The air-dried powder and the powder obtained by putting the
air-dried powder in a crucible and calcining at 400 degree
centigrade for 2 hours were each tested for the photocatalytic
activity and as a result, it was found that they had high activity.
The results were shown in FIG. 3.
Example 2
[0040] The same operations as in Example 1 were carried out except
that lactic acid was used instead of glycolic acid. As a result, a
mixture of ultrafine particles having an average particle diameter
of 20 nm in long axis and 8 nm in short axis, and a small amount of
aggregate of ultrafine particles having an average particle
diameter of 30 nm was obtained.
Example 3
[0041] The same operations as in Example 1 were carried out except
that acetylacetone was used instead of glycolic acid. As a result,
a mixture containing ultrafine particles having an average particle
diameter of 20 nm in long axis and 7 nm in short axis, and a small
amount of aggregate of ultrafine particles having an average
particle diameter of 25 nm was obtained.
Example 4
[0042] The same operations as in Example 1 were carried out except
that succinic acid was used instead of glycolic acid. As a result,
a mixture containing ultrafine particles having an average particle
diameter of 25 nm in long axis and 12 nm in short axis, and a small
amount of aggregate of ultrafine particles having an average
particle diameter of 40 nm was obtained.
Example 5
[0043] Preparation of a Sample Plate A for the Test on
Decomposition of Acetoaldehyde
[0044] To 100 mL polyethylene vessel, 5.0 g of the photocatalyst of
ultrafine particles of a rutile-type titanium oxide obtained by
calcining at 400 degree centigrade for 2 hours in Example 1 was
charged, and 50.0 g of a glass bead having a diameter of 1 mm, 44.0
g of ethanol, 0.5 g of 1 N hydrochloric acid and 0.5 g of a
nonionic surfactant (TritonX-100, registered trademark owned by
Union Carbide) were additionally added and sealed. The sealed
vessel was placed in a stainless ball mill pot having inner volume
of 300 mL and fixed by filling the empty space of the pot with
cloth such that the vessel was set in the middle of the ball mill
pot. The ball mill pot was tightly sealed, and then it was set on
the ball mill rotator and subjected to dispersion treatment at 60
rpm for 18 hours. After the treatment, the vessel was taken out,
and the content was filtered through a nylon mesh sheet for
removing the glass bead to obtain an ethanol dispersion of a
photocatalyst of ultrafine particles of a rutile-type titanium
oxide. Then, a slide glass (2.6 cm.times.7.6 cm, thickness: 1 mm)
which was weighed in advance was immersed in and pulled up from the
dispersion 42 times at intervals of every 90 seconds with a speed
of 0.4 cm/s. Thus, the photocatalyst of ultrafine particles of a
rutile-type titanium oxide was deposited on a surface of the slide
glass. The photocatalyst deposited on the surface other than a
surface of a 2.6 cm width was all wiped off. The resulting plate
was calcined at 400 degree centigrade for 3 hours in an air
atmosphere by using an electric furnace to prepare a
photocatalyst-deposited sample plate A. The weights before and
after deposition of the photocatalyst were measured and the
thickness of the deposited layer of the photocatalyst of ultrafine
particles of a rutile-type titanium oxide was measured, whereby it
was found that, in the sample plate, the weight of the deposited
photocatalyst of ultrafine particles of a rutile-type titanium
oxide was 6.6 mg, the deposited area thereof was 12.2 cm.sup.2, and
the deposited quantity per area was 5.4 g/cm.sup.2.
[0045] Test on Decomposition of Acetoaldehyde
[0046] The photocatalyst-deposited sample plate A was irradiated
with ultraviolet light of 5.4 mW/cm.sup.2 for 3 hours in an air
atmosphere. A 27 W black-blue light (Sankyo, FPL27BLB) was used as
a light source. UVA-365 (a product of Custom) was used for the
measurement of UV intensity.
[0047] The photocatalyst-deposited sample plate A irradiated with
UV light was attached to the center inside a 1 L Tedlar (registered
trademark owned by DuPont) bag equipped with one each of a silicon
packing-attached connector and a mini-cock using a double-sided
adhesive tape of 5 mm square. At this time, one side of the bag was
cut once, and after attaching the sample plate A, the cut part was
tightly sealed by using a heat sealer. Subsequently, air inside the
bag was pumped out through the mini-cock using a vacuum pump and
the cock was closed, and the sample plate was allowed to stand in
the dark overnight at a state that it was vacuum-packed.
[0048] Then, a wet mixed gas obtained by passing a mixed gas of 20%
of oxygen and 80% of nitrogen through ion exchange water at 15
degree centigrade was mixed with a mixed gas of 1% acetoaldehyde
and nitrogen to prepare a gas having an acetoaldehyde concentration
of 96 ppm. 600 mL of the gas was collected and introduced into the
bag with the photocatalyst-deposited sample plate A attached
thereinside. Then, the bag was allowed to stand in the dark for 20
hours. Subsequently, the acetoaldehyde concentration and carbon
dioxide concentration of the gas inside the bag were measured. A
gas chromatograph (a product of Shimazu, GC-10A) equipped with a
methanizer was used for the measurement of concentration. After the
analysis, the bag with the photocatalyst-deposited sample plate A
attached thereinside was placed such that the deposited surface of
the photocatalyst-deposited sample plate A was at a distance of 4
cm from a white fluorescent lamp (a product of Matsushita Electric
Works, Ltd., 10W, FL10N), and irradiated with the light
perpendicularly. So, the gas inside the bag was analyzed at
intervals of every 2 hours in the course of irradiation by a
fluorescent lamp. At this time, the UV intensity measured at the
same place as the deposited surface using a sheet of film as a
filter that is the same as the bag was 11 .mu.W/cm.sup.2. Herein,
UVA-365 (a product of Custom) was used for the measurement of UV
intensity. The transition of carbon dioxide concentration was shown
in FIG. 4. By irradiating with light from a fluorescent lamp, it
was confirmed that acetoaldehyde was decomposed, and accordingly
carbon dioxide was formed.
Example 6
[0049] Preparation of a Plate Sample B for the Test on
Decomposition of Toluene
[0050] A photocatalyst-deposited sample plate B was prepared in the
same manner as in Example 5 except that the treatment cycle of
immersion and pulling-up was 40 times. In the sample plate, the
weight of the deposited photocatalyst of ultrafine particles of a
rutile-type titanium oxide was 5.8 mg, the deposited area thereof
was 12.3 cm.sup.2, and the deposited quantity per area was 4.7
g/cm.sup.2.
[0051] Test on Decomposition of Toluene
[0052] The same operations as in Example 5 were carried out except
that the photocatalyst-deposited sample plate B was used instead of
the photocatalyst-deposited sample plate A, toluene was used
instead of acetoaldehyde, and a mixed gas containing toluene having
a toluene concentration of 31 ppm was used instead of a mixed gas
containing acetoaldehyde having a acetoaldehyde concentration of 96
ppm. Decomposition reaction of toluene was carried out by
irradiating light from a fluorescent lamp. The transition of carbon
dioxide concentration was shown in FIG. 5. By irradiating with
light of a fluorescent lamp, it was confirmed that toluene was
decomposed, and accordingly carbon dioxide was formed.
Comparative Example 1
[0053] The same operations as in Example 1 were carried out except
that glycolic acid was not added. As a result, an aggregate of
ultrafine particles of a rutile-type titanium oxide could be
prepared. The obtained ultrafine particles had difficulties in
redispersing in an aqueous solution after being precipitated and
filtered. An average particle diameter of ultrafine particles
obtained from the Debye-Scherrer equation of X-ray diffraction was
the same as that in Example 1, while an average particle diameter
of the aggregate of ultrafine particles was large, that was 270
nm.
Comparative Example 2
[0054] An anatase-type titanium oxide was prepared in the following
manner.
[0055] To 250 mL of ion exchange water, 2.5 mL of a TiOCl.sub.2.HCl
solution (a product of Fluka) was added to give a 0.05 M
TiOCl.sub.2 solution. This solution was heated at 60 degree
centigrade for 5 hours to give a sol. By adding acetonitrile to
this sol, the precipitate was obtained and dried to obtain powder.
From a result of X-ray diffraction, the obtained powder was found
to be an anatase-type crystal. The spherical ultrafine particle had
an average particle diameter of 5 nm according to the electron
microscope observation and aggregation was hardly found.
[0056] The obtained powder was tested for its photocatalytic
activity and the results thereof were shown in FIG. 3.
* * * * *