JP4411385B2 - Method for producing brookite type titanium dioxide, monodispersed brookite type titanium dioxide aggregate, photocatalyst and photonic crystal - Google Patents

Description

The present invention relates to brookite-type titanium dioxide, and more specifically, a method for producing single-phase brookite-type titanium dioxide, secondary particles of monodisperse brookite-type titanium dioxide (hereinafter referred to as “aggregate”), and the use thereof And a photonic crystal using the photocatalyst.

Titanium dioxide has long been known as a white pigment for paints and cosmetics, for example. In recent years, titanium dioxide composed of nanocrystals has become a photocatalyst for removing pollutants from the atmosphere or water, photovoltaic cell materials for collecting solar energy, dielectric materials for next-generation ultrathin capacitors, It attracts attention as an optical element using a refractive index (2.4 to 2.9).

Titanium dioxide (TiO ₂ ) has three crystal structures: rutile (tetragonal), anatase (tetragonal) and brookite (orthorhombic). Among these crystal structures, brookite type titanium dioxide (hereinafter referred to as “B-TiO ₂ ”) is rutile type titanium dioxide (hereinafter referred to as R—TiO ₂ ) and anatase type titanium dioxide (hereinafter referred to as A -TiO ₂ hereinafter) has been suggested to have high photocatalytic properties compared to a promising photocatalyst candidates. Further, B-TiO ₂ has a higher refractive index than A-TiO ₂ and is expected to be optically applied like R-TiO ₂ .

There is a technique for producing B-TiO ₂ by hydrothermal treatment (for example, Patent Document 1). FIG. 6 is a diagram illustrating a process of manufacturing B-TiO _{2 according} to the conventional technique. Each process will be described.

Step S6100: Amorphous titanium dioxide is added to an aqueous sodium hydroxide solution. On this occasion,
The molar ratio of Na ₂ O / (Na ₂ O + TiO ₂ ) is adjusted to 0.15 to 0.45, and the TiO ₂ concentration is adjusted to 1 to 40 g / L.

Step S6200: The mixed liquid obtained in Step S6100 is hydrothermally treated at a temperature of 150 to 300 ° C. By hydrothermal treatment, layered sodium titanate is generated in the mixed solution, and then sodium is released to obtain B-TiO ₂ .

A technique for producing TiO ₂ composed of nanocrystals has also been studied. There exists a thing which manufactures brookite phase titanium dioxide in such a technique using titanium tetrachloride (for example, patent document 2).

JP 2000-095521 A JP 2004-131366 A

However, since the technique shown in Patent Document 1 uses sodium hydroxide as a starting material, the produced B-TiO ₂ contains a small amount of sodium as an impurity. Moreover, since hydrothermal treatment is used, a high temperature of 100 ° C. or higher is required. Similarly, Patent Document 2
According to the technique shown in (2), since it is necessary to add an alkaline aqueous solution, there is a possibility that impurities such as sodium and potassium may be contained. Furthermore, according to Patent Document 2, the concentration and p
Since it is necessary to adjust H in detail, it is difficult to easily produce B—TiO ₂ .

Accordingly, it is an object of the present invention to provide a method for easily (ie, under mild conditions) producing single phase brookite-type titanium dioxide secondary particles, or clusters.

A further object of the present invention is to provide a method for easily (ie under mild conditions) producing single phase and monodisperse brookite type titanium dioxide aggregates. In the present specification, “manufacturing single-phase brookite-type titanium dioxide” means R− as a by-product.
B- does not contain TiO ₂ and A-TiO ₂ and does not contain impurities such as sodium
Note that it means producing TiO ₂ . In addition, in this specification, it should be noted that “under mild conditions” means that the reaction conditions are a temperature of less than 100 ° C. and under atmospheric pressure.

The method for producing brookite-type titanium dioxide according to the present invention is a step of mixing titanium trichloride and urea, the concentration of titanium trichloride [Ti ³⁺ ] (mol / L) and the concentration of urea [urea]. (Mol / L) is the relational expression 10 <[urea] / [Ti ³⁺ ] <4
The mixed aqueous solution obtained in the step of satisfying 0 and the step of mixing is heated, and titanium hydroxide (
III), a step of washing the deposited titanium hydroxide (III) in an oxidizing atmosphere, and a step of drying the washed titanium hydroxide (III) in an oxidizing atmosphere. To achieve the above objectives.

In the step of preparing the mixed aqueous solution, the concentration of titanium trichloride [Ti ³⁺ ] (mol / L
) And the urea concentration [urea] (mol / L), the relational expression 20 ≦ [urea] / [T
It is more preferable to satisfy i ³⁺ ] ≦ 35.

In the precipitation step, the mixed aqueous solution may be heated in an oxidizing atmosphere at a temperature in the range of 70 ° C to 100 ° C. In the washing step, the precipitated titanium hydroxide (III) may be washed with distilled water and further washed with absolute ethanol. In the drying step, the washed titanium hydroxide (III) may be heated at a temperature of 80 ° C. or more for 2 hours or more. The step of drying may further include a step of annealing the brookite-type titanium dioxide in an oxidizing atmosphere at a temperature of less than 600 ° C. for a period of 8 hours or less.

The monodisperse brookite-type titanium dioxide aggregates according to the present invention are composed of brookite-type titanium dioxide nanocrystals having a crystal grain size of 20 to 30 nm, thereby achieving the above object.
The particle diameter of the titanium dioxide aggregate is preferably in the range of 130 nm to 170 nm. The specific surface area of the titanium dioxide crumb ^is preferably in the range of 30m ² / g~50m 2 / g.

The photocatalyst using the brookite-type titanium dioxide aggregate according to the present invention comprises the brookite-type titanium dioxide nanocrystal having a crystal grain size of 20 to 30 nm, thereby achieving the above object.

The photonic crystal using brookite-type titanium dioxide aggregates according to the present invention comprises the brookite-type titanium dioxide aggregates comprising brookite-type titanium dioxide nanocrystals having a crystal grain size of 20 to 30 nm, thereby achieving the above object. .

The method for producing brookite-type titanium dioxide according to the present invention includes a step of mixing a predetermined amount of titanium trichloride and urea. The above-mentioned predetermined amount is the concentration of titanium trichloride [Ti ³⁺ ].
(Mol / L) and urea concentration [urea] (mol / L) are expressed by the relational expression 10 <[urea
] / [Ti ³⁺ ] <40. Thus, since titanium trichloride and urea are used as starting materials, impurities such as sodium are not contained in the produced brookite-type titanium dioxide.

Moreover, the manufacturing method according to the present invention heats the mixed aqueous solution obtained in the above-mentioned mixing step,
A step of precipitating titanium hydroxide (III), a step of washing the precipitated titanium hydroxide (III) in an oxidizing atmosphere, and a step of drying the washed titanium hydroxide (III) in an oxidizing atmosphere Including. In either process, because it is a mild condition, complicated temperature control, pressure control, etc. is not required, it is easy to produce the B-TiO _2.

Further, according to the production method of the present invention, single-phase B-TiO ₂ without containing R-TiO ₂ and / or A-RiO ₂ and without containing impurities such as sodium.
Can be easily manufactured.

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view showing a process for producing brookite type titanium dioxide (B-TiO ₂ ) according to the present invention. Each process will be described.

Step S110: Mixing titanium trichloride and urea. Here, the concentration of titanium trichloride [Ti
³⁺ ] (mol / L) and the urea concentration [urea] (mol / L), the relational expression 10 <[u
rea] / [Ti ³⁺ ] <40. When the above relational expression is not satisfied, R-TiO ₂ or A-TiO ₂ can be generated as a by-product. More preferably, the concentration of titanium trichloride [Ti ³⁺ ] (mol / L) and the concentration of urea [urea] (mol / L) satisfy the relational expression 20 ≦ [urea] / [Ti ³⁺ ] ≦ 35. Adjusted to

Step S120: The mixed aqueous solution obtained in Step S110 is heated to obtain titanium (III) hydroxide.
To precipitate. By controlling the shape and size (ie, particle size) of the titanium hydroxide (III) particles precipitated here, monodispersed B-TiO ₂ aggregates can be obtained. The shape and size of such titanium (III) hydroxide particles can be controlled by heating in an oxidizing atmosphere, for example, air, in a temperature range of 70 ° C. or higher and lower than 100 ° C. If it is less than 70 ° C., the progress of precipitation is slow, and if it is 100 ° C. or more, the reactants in the mixed aqueous solution may evaporate. It should be noted that single-phase B—TiO ₂ is produced even when such temperature and atmosphere control is not performed.

Step S130: Titanium (III) hydroxide precipitated in Step S120 is washed with water in an oxidizing atmosphere, for example, air. Preferably, the water can be distilled water. Step S130
Then, titanium (III) hydroxide may be washed with absolute ethanol.

Step S140: Titanium hydroxide (III) washed in step S130 is dried in an oxidizing atmosphere. The drying can be preferably performed at a temperature of 80 ° C. or more for 2 hours or more. The upper limit of the drying temperature is not particularly limited, but any temperature that does not cause phase transition can be applied as long as it is 80 ° C. or higher. However, assuming that a general heating device (heater) is used, a temperature of 80 ° C. or higher and 200 ° C. or lower is applicable. Moreover, although the upper limit of drying time is not specifically limited, 2 hours or more and 30 hours or less are enough. As a result, it does not contain impurities such as sodium and R-
A single-phase brookite-type titanium dioxide containing no TiO ₂ and / or A-TiO ₂ is obtained.

The reason why single-phase B-TiO ₂ is produced by the above steps S110 to S140 will be described using chemical formulas. Formula (1) is realized by heating the mixed aqueous solution prepared in step S110 in step S120.

Ti ³⁺ + OH ⁻ (obtained by hydrolysis of urea) → Ti (OH) ₃ (1)
The titanium hydroxide (III) obtained in step S120 is used in steps S130 and S140.
And the following formulas (2) and (3) are satisfied.

Ti (OH) ₃ + H ₂ O + O ₂ → Ti (OH) ₄ (2)
Ti (OH) ₄ → TiO ₂ · 2H ₂ O → TiO ₂ (3)
It should be noted that the occurrence of the above expressions (2) and (3) may occur simultaneously in step S130 and step S140, and thus cannot be clearly distinguished. Thus, by using titanium trichloride and urea that do not contain impurities such as sodium as starting materials, B-TiO ₂ can be easily produced under mild conditions without using hydrothermal treatment.

Next, in step S120, reaction conditions are set as appropriate (in an oxidizing atmosphere, at 70 ° C. or higher and 10
The control of the shape and size of titanium hydroxide (III) particles, that is, the control of the shape and size of B-TiO ₂ particles finally produced will be described. It is known that monodisperse particles are obtained mainly by clearly separating the nucleation step and the growth step.

It turns out that when a titanium (IV) salt having the same valence as B-TiO ₂ is used as a starting material, the nucleation step and the growth step cannot be clearly separated because hydrolysis occurs very rapidly. ing. However, the process of the present invention does not produce B—TiO ₂ directly from a titanium (IV) salt, but rather via titanium (III) hydroxide. Therefore, in order to control the shape and size of the finally obtained B-TiO ₂ particles,
It is necessary to control the shape and size of the titanium (III) hydroxide particles.

In this way, the titanium hydroxide (III) passes through the ionic radius of Ti ³⁺ (0.067
(nm) is larger than the ionic radius of Ti ⁴⁺ (0.0605 nm). Since the ionic radii are different, the number of OH ⁻ ions coordinated to Ti ³⁺ ions is Ti
More than the number of OH ⁻ ions coordinated to ⁴⁺ ions. That is, the limit concentration of OH ⁻ ions coordinated to Ti ³⁺ is higher than the limit concentration of OH ⁻ ions coordinated to Ti ⁴⁺ .

Therefore, when Ti ⁴⁺ is used, a nucleation step is easily generated by a small amount of OH ⁻ ions, so that it is difficult to separate the nucleation step and the growth step by controlling the amount of OH ⁻ ions. On the other hand, when Ti ³⁺ is used, the amount of OH ⁻ ions necessary for nucleation is larger than in the case of Ti ⁴⁺ . This means that the control range of the amount of OH ⁻ ions necessary for nucleation is wide, and it becomes easy to clearly separate the nucleation step and the growth step.

In the present invention, OH ⁻ ions are generated by hydrolysis of urea. The amount of OH ⁻ ions gradually increases comparatively under the hydrolysis conditions of urea according to the present invention (temperature in an oxidizing atmosphere and not lower than 70 ° C. and lower than 100 ° C.). This can also contribute to the separation of the nucleation step and the growth step. In this way, monodispersed Ti (OH) ₃ aggregates are obtained.

Based on the obtained monodispersed Ti (OH) ₃ aggregate, the above-described step S130 and step S14 are performed.
By 0, monodisperse B—TiO ₂ aggregates are obtained. Monodispersed B—TiO ₂ aggregates consist of nanocrystalline B—TiO ₂ . The range of the average crystal grain size of such nanocrystalline B—TiO ₂ is 20
~ 30 nm. It should be noted that steps S130 and S140 oxidize Ti ³⁺ to Ti ⁴⁺ , so that changes such as the volume of Ti (OH) ₃ occur, but monodispersed aggregates can be maintained. In this specification, “monodisperse” means B-TiO to be obtained.
It means that the average particle size of the _two aggregates is in the range of 130 nm to 170 nm.

Returning again to FIG. Step S150: B-TiO ₂ obtained in Step S140 is annealed in an oxidizing atmosphere, for example, air. By this annealing, the crystallinity of monodispersed B—TiO ₂ can be improved. Specifically, the nanocrystal T constituting monodispersed B-TiO ₂ aggregates
The crystal grain size of iO ₂ can be increased. Such annealing conditions are performed in an oxidizing atmosphere at a temperature of less than 600 ° C. for 8 hours or less. Although there is no lower limit of annealing temperature,
If the temperature is higher than the temperature used for drying in step S140, the effect of annealing can be obtained. When the annealing time exceeds 8 hours, R-TiO ₂ may be precipitated. There is no problem if the annealing time is 8 hours or less, but preferably, if the drying time is longer than the drying time in step S140, the effect of annealing can be obtained.

  Next, examples will be described, but the present invention is not limited to these examples.

0.015 mol / L titanium trichloride (TiCl ₃ ) and 0.5 mol / L urea were mixed to prepare a 2000 mL mixed aqueous solution. Here, the concentration of TiCl ₃ [Ti ³⁺ ] (m
ol / L) and urea [urea] (mol / L): [urea] / [Ti ³⁺ ]
= 34. The prepared mixed aqueous solution was purple. The prepared mixed aqueous solution was heated on a hot plate provided with a temperature controller at 70 ± 1 ° C. for 40 minutes. Thereafter, the hot plate was maintained at 70 ± 1 ° C. for 2 hours to deposit titanium (III) hydroxide. The mixed aqueous solution was purple even after precipitation at a temperature of 70 ± 1 ° C.

The deposited titanium hydroxide (III) was subjected to adsorption filtering using a 0.2 μm membrane. The recovered titanium (III) hydroxide particles were purple. The recovered titanium (III) hydroxide particles were washed four times with distilled water. The titanium (III) hydroxide particles were then washed with absolute ethanol. Thereafter, the washed titanium (III) hydroxide particles were dried in the atmosphere at 100 ° C. for 24 hours using a hot plate. The powder obtained after drying was yellowish white, which was a typical TiO ₂ color.

Phillips PW1800X-Ray Diffractometer (Phillips Resa
The final product powder was identified using X-ray diffractometry by rch Laboratories, Netherlands and Raman spectroscopy by NR-1800 instrument (JASCO, Tokyo, Japan). The operating conditions of the X-ray diffractometer were a scanning speed of 40 kV / 50 mA and 0.5 ° 2θ / min using Cu-Kα rays. For Raman spectroscopy, an Ar ⁺ laser (wavelength 514.5 nm) was used with a light source output of 20 mW and a resolution of 1 cm ⁻¹ .

The specific surface area of the final powder is determined by the BET single point method (Model4201, Beta Scie
ntific Corp. Albertson, U.S.A. S. A) and measured via nitrogen chemisorption at 77K. Field Emission Scanning Electron Microscope (S-5000, Hit
(Achi, Tokyo, Japan) and JOEL FEM-3000 transmission electron microscope were used to observe the final powder. The acceleration voltages were 10 kV and 300 kV, respectively. The above results are shown in Table 1 and FIGS.

0.03 mol / L titanium trichloride (TiCl ₃ ) and 0.6 mol / L urea were mixed to prepare a 2000 mL mixed aqueous solution. Here, the concentration of TiCl ₃ [Ti ³⁺ ] (mo
l / L) and urea [urea] (mol / L): [urea] / [Ti ³⁺ ] =
It was 20. Since it is the same as Example 1 except the density | concentrations of mixed aqueous solution differing, description is abbreviate | omitted. The results are shown in Table 1 and will be described later.

(Comparative Example 1)
0.015 mol / L titanium trichloride (TiCl ₃ ) and 0.15 mol / L urea were mixed to prepare a 2000 mL mixed aqueous solution. Here, the concentration of TiCl ₃ [Ti ³⁺ ] (
mol / L) and urea [urea] (mol / L): [urea] / [Ti ³⁺
] = 10. Since it is the same as Example 1 except the density | concentrations of mixed aqueous solution differing, description is abbreviate | omitted. The results are shown in Table 1 and will be described later.

(Comparative Example 2)
0.0125 mol / L titanium trichloride (TiCl ₃ ) and 0.5 mol / L urea were mixed to prepare a 2000 mL mixed aqueous solution. Here, the concentration of TiCl ₃ [Ti ³⁺ ] (
mol / L) and urea [urea] (mol / L): [urea] / [Ti ³⁺
] = 40. Since it is the same as Example 1 except the density | concentrations of mixed aqueous solution differing, description is abbreviate | omitted. The results are shown in Table 1 and will be described later.

The final product powder obtained in Example 1 was annealed in air at 500 ° C. for 2 hours. The catalytic properties of the annealed powder were evaluated. Using a 200 W Hg-Xe lamp (wavelength λmax = 365 nm) with a light source output of 20 mW / cm ^2, the catalytic properties were evaluated by measuring the amount of acetaldehyde decomposed under UV irradiation. The results are shown in Table 1 and FIGS. 1 to 5 and will be described later.

(Comparative Example 3)
The final product powder obtained in Example 1 was annealed in air at 600 ° C. for 2 hours. Since other than that is the same as Example 1, description is abbreviate | omitted. The results are shown in Table 1 and FIGS.

図２は、本発明による単分散ブルッカイト型二酸化チタン団粒のＸ線回折パターンを示
す図である。図２（ａ）は、実施例１で得られた粉末のＸ線回折パターンである。粉末の
Ｘ線回折パターン（回折ピークおよびピーク強度）は、Ｂ−ＴｉＯ_２（ＪＣＰＤＳ：２９
−１３６０）に良好な一致を示した。なお、Ｒ−ＴｉＯ_２および／またはＡ−ＴｉＯ_２に
該当する回折ピークは検出されなかった。これにより、実施例１で得られた粉末が単相Ｂ
−ＴｉＯ_２粉末であることが確認された。

FIG. 2 is a diagram showing an X-ray diffraction pattern of monodisperse brookite type titanium dioxide aggregates according to the present invention. 2A is an X-ray diffraction pattern of the powder obtained in Example 1. FIG. The X-ray diffraction pattern (diffraction peak and peak intensity) of the powder is B-TiO ₂ (JCPDS: 29
-1360) showed good agreement. The diffraction peaks corresponding to the R-TiO ₂ and / or A-TiO ₂ was not detected. As a result, the powder obtained in Example 1 became single phase B.
-TiO it was confirmed that the ₂ powders.

As a result of calculating the lattice constant of the powder using the Rietveld method, a = 0.544421 ± 0.0
0083 nm, b = 0.01679 ± 0.00184 nm and c = 0.51319 ± 0
. 00007 nm. These values are reported values (JCPDS: 29-13).
60, a = 0.54558 nm, b = 0.91849 nm and c = 0.51429 nm
). From this, it can be said that the powder obtained in Example 1 obtained single-phase B—TiO ₂ free from lattice distortion due to oxygen deficiency or the like.

FIG. 2B shows the powder obtained in Example 3 (that is, B-TiO ₂ obtained in Example 1).
Is an X-ray diffraction pattern of powder annealed at 500 ° C. for 2 hours in the atmosphere. The X-ray diffraction pattern in FIG. 2B is the same as the X-ray diffraction pattern in FIG.

FIG. 2C shows the powder obtained in Comparative Example 3 (that is, B-TiO ₂ obtained in Example 1).
Is an X-ray diffraction pattern of a powder annealed at 600 ° C. for 2 hours in the atmosphere. In addition to the diffraction pattern showing B-TiO ₂ , the X-ray diffraction pattern shown in FIG.
₂ (for example, (110), (101), (200), (111), (
210), (211) and (220)). 2 (b) and 2 (c), it was found that B-TiO ₂ undergoes a phase transition to R-TiO ₂ at a temperature of 600 ° C. or higher. Therefore, it can be seen that the as-made B-TiO ₂ is preferably annealed at less than 600 ° C.

Again, referring to Table 1, the preferred molar ratio of the starting materials will be described. From Examples 1 and 2 and Comparative Examples 1 and 2, the molar ratio of the starting material titanium trichloride (TiCl ₃ ) to urea is 10 <
It can be seen that [urea] / [Ti ³⁺ ] <40. Beyond this range, it was confirmed by X-ray diffraction that R-TiO ₂ or A-TiO ₂ was produced as a by-product. Preferably, the molar ratio of titanium trichloride (TiCl ₃ ) to urea is 20 ≦ [urea] / [T
i ³⁺ ] ≦ 35.

Next, the average nanocrystal grain size of the produced B—TiO ₂ will be described. The average nanocrystal grain size was determined by performing wide-angle X-ray diffraction on the unit cell (121) diffraction peak, and Scherrer
rrer). B-TiO ₂ obtained in Example 1 and Example 2 was both 25 nm. On the other hand, B-TiO ₂ obtained in Example 3 was 30 nm. As a result, it was found that the particle size of the B—TiO ₂ nanocrystals did not depend on the molar ratio of the starting materials, but depended on the annealing temperature. By annealing, the B—TiO ₂ nanocrystals were grown. This suggests that the crystal grain size of the B—TiO ₂ nanocrystals can be controlled by optimizing the annealing conditions.

FIG. 3 is a diagram showing a Raman spectrum of monodisperse brookite type titanium dioxide aggregates according to the present invention. FIG. 3A is a Raman spectrum of the powder obtained in Example 1. BT
Peaks at 128, 153, 247, 322 and 636 cm ⁻¹ indicating iO ₂ were observed. The diffraction peaks corresponding to the R-TiO ₂ and / or A-TiO ₂ was not detected. This confirmed that the powder obtained in Example 1 was a single-phase B-TiO ₂ powder.

FIG. 3 (b) shows the powder obtained in Example 3 (that is, B-TiO ₂ obtained in Example 1).
Is a Raman spectrum of a powder annealed at 500 ° C. for 2 hours in the atmosphere. The Raman spectrum in FIG. 3B is the same as the Raman spectrum in FIG.

FIG. 3 (c) shows the powder obtained in Comparative Example 3 (that is, B-TiO ₂ obtained in Example 1).
Is a Raman spectrum of powder annealed at 600 ° C. for 2 hours in the atmosphere. In the Raman spectrum shown in FIG. 3 (c), peaks indicating R—TiO ₂ (for example, 143, 235, 449, and 610 cm ⁻¹ ) existed in addition to the peak indicating B—TiO ₂ . FIG.
From b) and FIG. 3 (c), it was found that B-TiO ₂ undergoes a phase transition to R-TiO ₂ at a temperature of 600 ° C. or higher. Therefore, it can be seen that the as-made B-TiO ₂ is preferably annealed at less than 600 ° C. The above results completely matched the X-ray diffraction results shown in FIG.

FIG. 3 (d) is a Raman spectrum of the powder obtained by annealing the powder obtained in Example 1 at 700 ° C. for 2 hours in the atmosphere. By annealing at 700 ° C., B—TiO ₂ is completely R—Ti.
The transition to O ₂ was confirmed.

FIG. 4 is an SEM photograph and TE of monodisperse brookite type titanium dioxide aggregates according to the present invention.
It is a figure which shows M photograph. 4A is an SEM photograph of the powder obtained in Example 1. FIG. It was confirmed that the particles of the obtained powder were substantially spherical and uniform in size and shape. In the present specification, “substantially spherical” means that it is not completely spherical but does not affect the application example using the B—TiO ₂ powder of the present invention. Note what you say.

FIG. 4B is a TEM photograph of the powder obtained in Example 1. The spherical powder obtained in Example 1 was confirmed to be aggregates composed of thin plate-like B—TiO ₂ nanocrystals.

FIG. 4 (c) shows the powder obtained in Example 3 (that is, B-TiO ₂ obtained in Example 1).
Is a TEM photograph of a powder annealed for 2 hours at 500 ° C. in the atmosphere. As in FIG. 4B, no significant change was observed in the particle size of the aggregate, but grain growth was observed in the B—TiO ₂ nanocrystals constituting the aggregate.

The average particle diameter of B-TiO ₂ aggregates according to the present invention was determined from the TEM photographs shown in FIGS. 4 (b) and 4 (c). The average particle diameter was determined by measuring the diameter of 200 aggregates arbitrarily selected. As a result, as shown in Table 1, it was found that the average particle diameter of the B—TiO ₂ aggregates was not dependent on the molar ratio of the starting materials and the annealing temperature.

From the above results, as-made of B-TiO ₂ nanocrystals and annealed B
-TiO ₂ crumb are the non-cohesive, it was found that can be dispersed in readily water or ethanol using ultrasound. That is, the B-TiO ₂ aggregate according to the present invention can form a stable sol without adding any surfactant or the like. Such a feature is advantageous when, for example, colloidal crystals and photonic crystals are produced.

Again referring to Table 1, the specific surface area will be described. The specific surface area of the obtained monodisperse brookite-type titanium dioxide aggregates was in the range of 30 to 50 m ² / g. From the results of Example 1 and Example 3, it was found that the specific surface area tends to decrease by annealing. This is because B-TiO ₂ nanocrystals constituting aggregates grow by annealing, but the particle size of the aggregates themselves does not change, so the defects existing in the aggregates disappear and the specific surface area decreases. It is. By appropriately setting the annealing conditions, monodispersed titanium dioxide aggregates having a desired specific surface area can be obtained. FIG. 5 is a graph showing the catalytic properties of monodisperse brookite type titanium dioxide aggregates according to the present invention.

The catalytic properties of monodisperse B-TiO ₂ Dan grains obtained by the process according to the invention was investigated by measuring the yield (%) CO ₂ produced by the decomposition of acetaldehyde. The black circle is the result of the powder obtained by annealing the powder obtained in Example 1 at 250 ° C. for 2 hours in the atmosphere, and the white circle is the result of the powder obtained in Example 3. As shown in FIG. 5, all showed good catalytic properties.

Incidentally, catalytic properties of annealed B-TiO ₂ Dan grains 500 ° C. is, 250 ° C. to greater than catalytic properties of the annealed B-TiO ₂ Dan grains is annealed B-TiO ₂ at 500 ° C.
The crystal grain size of the B-TiO ₂ nanocrystals constituting the aggregate is B-Ti annealed at 250 ° C.
This is because it is larger than the crystal grain size of the B—TiO ₂ nanocrystals constituting the O ₂ aggregate (that is, the crystallinity is high). This suggests that higher catalytic properties can be expected by further improving the crystallinity of the B—TiO ₂ nanocrystals.

In addition, the particle size of the monodispersed B-TiO ₂ aggregate according to the present invention is larger than the particle size of a currently commercially available photocatalyst (eg, Degussa P-25). This means that when the monodispersed B-TiO ₂ aggregate according to the present invention is used in an aqueous solution containing an organic solvent or the like as a photocatalyst,
Separation of water and monodispersed B—TiO ₂ aggregates is easy. Thereby, since a filter diameter larger than the filter diameter conventionally required for separating the photocatalyst is allowed, not only the filter selection range can be expanded, but also the separation efficiency of the photocatalyst can be improved. From the above results, it was found that monodispersed B—TiO ₂ aggregates obtained by the method according to the present invention can be used as a photocatalyst.

A regular dielectric material with a spatial grating having the wavelength of light forms a photonic band gap. Such a material having a photonic band gap is a so-called photonic material that exhibits complete reflection with respect to an electromagnetic wave in a specific direction having a wavelength similar to that of the periodic structure of the crystal. In the visible and infrared regions, macroporous materials have been studied as photonic materials. However, in order to exhibit strong photonic properties, the photonic material needs to be composed of a material having a refractive index at least twice that of air.

As such a photonic material, monodispersed B—TiO ₂ aggregates and their nanocrystals according to the present invention are effective. In order to obtain a high-quality photonic crystal, it is necessary to use nanocrystals having a uniform particle size. In order to obtain good photonic characteristics, the refractive index of the photonic material should be higher. Currently, for example, a photonic crystal using silica and a photonic crystal using A-TiO ₂ are known. Monodispersed B-TiO according to the present invention
_{The two} aggregates and the nanocrystals have a higher refractive index than silica and A-TiO ₂ and can be easily manufactured as photonic crystals because they are nanocrystals having a uniform particle size.

According to the production method of the present invention, single-phase B-TiO ₂ is easily produced without containing R-TiO ₂ and / or A-RiO ₂ and without containing impurities such as sodium. be able to. The monodispersed B—TiO ₂ aggregates according to the present invention thus obtained can be applied as a photocatalyst and a photonic crystal.

It shows a process for producing brookite-type titanium dioxide according to the present invention (B-TiO _2). (A), (b), (c) is a figure which respectively shows the X-ray-diffraction pattern of the monodisperse brookite type titanium dioxide aggregate obtained by Example 1, Example 3, and Comparative Example 3 of this invention. (A), (b), (c), (d) are obtained by monodisperse brookite type titanium dioxide aggregates obtained in Example 1, Example 3 and Comparative Example 3 of the present invention and Example 1, respectively. The figure which shows the Raman spectrum of the powder which annealed the obtained powder at 700 degreeC. (A) is a drawing-substitute SEM photograph of monodisperse brookite-type titanium dioxide aggregates obtained in Example 1 of the present invention, and (b) and (c) are single units obtained in Example 1 and Example 3, respectively. The figure which shows the drawing substitute TEM photograph of a dispersion | distribution brookite type titanium dioxide aggregate. The figure which shows the catalyst characteristic of the monodisperse brookite type | mold titanium dioxide aggregate obtained by Example 1 (black circle) and Example 3 (white circle) of this invention. It shows a process for producing a B-TiO ₂ according to the prior art.

Claims (11)

A method for producing brookite-type titanium dioxide,
A step of mixing titanium trichloride and urea, the concentration of titanium trichloride [Ti ³⁺ ]
(Mol / L) and the urea concentration [urea] (mol / L) are represented by the relational expression 10 <[ur
ea] / [Ti ³⁺ ] <40,
Heating the mixed aqueous solution obtained in the mixing step to precipitate titanium (III) hydroxide;
Washing the precipitated titanium hydroxide (III) with water in an oxidizing atmosphere;
Drying the washed titanium (III) hydroxide in an oxidizing atmosphere. In the step of preparing the mixed aqueous solution, the concentration of titanium trichloride [Ti ³⁺ ] (mol / L
) And the urea concentration [urea] (mol / L), the relational expression 20 ≦ [urea] / [T
The method according to claim 1, wherein the titanium trichloride and the urea are mixed so as to satisfy i ³⁺ ] ≦ 35. The method of claim 1, wherein the step of precipitating heats the mixed aqueous solution at a temperature in the range of 70 ° C. to 100 ° C. in an oxidizing atmosphere. 2. The method according to claim 1, wherein the water is distilled water, and further comprising a step of washing the deposited titanium hydroxide (III) with absolute ethanol after the washing step. 2. The method according to claim 1, wherein in the drying step, the washed titanium hydroxide (III) is heated at a temperature of 80 ° C. or more for 2 hours or more. After the drying step, the brookite-type titanium dioxide is removed in an oxidizing atmosphere.
The method of claim 1, further comprising annealing at a temperature below 0 ° C. for a period of 8 hours or less. Monodispersed brookite-type titanium dioxide aggregates composed of brookite-type titanium dioxide nanocrystals having a crystal grain size of 20 to 30 nm. The monodisperse brookite-type titanium dioxide aggregate according to claim 7, wherein the titanium dioxide aggregate has a particle size in a range of 130 nm to 170 nm. The specific surface area of the titanium dioxide crumb ^is in the range of 30m ² / g~50m 2 / g, according to claim 7 monodispersed brookite type titanium dioxide crumb according. A photocatalyst using brookite-type titanium dioxide aggregates, wherein the brookite-type titanium dioxide aggregates are composed of brookite-type titanium dioxide nanocrystals having a crystal grain size of 20 to 30 nm. A photonic crystal using brookite-type titanium dioxide aggregates, wherein the brookite-type titanium dioxide aggregates are composed of brookite-type titanium dioxide nanocrystals having a crystal grain size of 20 to 30 nm.

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