JPH0688786B2 - Titanic acid having orthorhombic layered structure and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a layered titanic acid having a novel composition and a method for producing the layered titanic acid. Has an adsorbent, an ion exchange material, a catalyst,
It is expected to be used as a separating material and for the disposal of radioactive liquid waste.

[0002]

BACKGROUND OF THE INVENTION Grey et al. Have reported the synthesis of orthorhombic cesium titanate having Cs ions coordinated between layers (IE Gray,
IC Madsen and JA Watts, J Solid Solid
Chem. 66, 7 (1987)). However, there is no report up to now regarding layered titanic acid containing hydrogen ions (or hydronium ions) and water molecules between layers.

The present invention converts the above-mentioned orthorhombic cesium titanate in which Cs ions are coordinated so that hydrogen ions (or hydronium ions) are not contained between layers. ), A layered titanic acid having a novel composition containing water molecules, and a method for producing the same.

[0004]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to solve the above problems, and as a result, discovered a novel compound.

That is, the compound according to the present invention has a composition formula

Embedded image A compound having an orthorhombic layered structure represented by H _x Ti _{2-x / 4} O ₄ .nH ₂ O (where x is 0.60 to 0.75 and n is 0 to 2) is there.

[0006] Further, the manufacturing method is cesium oxide (C
s ₂ O) or a compound that decomposes to cesium oxide by heating and titanium dioxide (TiO ₂ ) or a compound that produces titanium dioxide by heating are mixed at a molar ratio of 1/4 to 1/7. Cesium titanate obtained by firing at a temperature of 700 ° C or higher (

Embedded image By contacting Cs _x Ti _{2−x / 4} O ₄ ) with an aqueous acid solution, all Cs ions between layers are eluted.

Embedded image An orthorhombic layered titanic acid having a composition represented by H _x Ti _{2-x / 4} O ₄ .nH ₂ O is obtained.

The present invention is described in detail below.

[0008]

[Action]

The compounds of the present invention have the compositional formula

Embedded image A compound having an orthorhombic layered structure represented by H _x Ti _{2-x / 4} O ₄ .nH ₂ O (where x is 0.60 to 0.75 and n is 0 to 2). Yes,

Embedded image is a new layered material containing hydrogen ions between the host layer having a composition of _{Ti 2-x / 4 O 4} . The hydrogen ions in this material are active,
Other cations and organic molecules can be reversibly incorporated between layers.

This compound has a layered structure as shown in FIG. That is, it is a crystal belonging to an orthorhombic crystal in which TiO ₆ octahedra are linked by edge sharing to form a two-dimensional sheet, and hydrogen ions (hydronium ions as a form of existence) and water molecules are included therebetween. The crystallographic composition of this two-dimensional sheet is TiO _2, which is electrically neutral in nature,

[Chemicals 9] 7-9% of the octahedral seats of Ti ⁴⁺ are vacant, and the composition is

Embedded image Ti _{2−x / 4} O ₄ ^x− (where x is 0.60 to 0.75) and is negatively charged. Hydrogen ions between layers compensate for this.

As described above, Gray et al. Reported a compound in which Cs ions were charge-compensated, but this time, a substance containing hydrogen ions between the layers was obtained, which resulted in remarkable intercalation. Of the adsorbent, ion exchange material, catalyst,
It is considered to be useful as a separating material, a treatment and disposal material for radioactive waste liquid, etc.

The space group of this novel material is Immm. Also, the crystallographic data

^{Embedded image Although} it depends on the amount of vacant Ti ^4+, a typical composition, that is, a composition formula

Embedded image Powder X-ray diffraction data for H _x Ti _{2-x / 4} O ₄ · nH ₂ O when x = 0.70 and n = 1.0

[Table 1] Shown in. The lattice constants are a = 3.783 (1) Å, b = 18.
750 (9) Å, c = 2.977 (2) Å, V = 211.
2 (1) Å ³ , 2 molecules are included in the unit cell, and the calculated density is 2.675.

This compound is synthesized by the following procedure. First, the molar ratio of cesium oxide (Cs ₂ O) or a compound that is decomposed to cesium oxide by heating and titanium dioxide (TiO ₂ ) or a compound that produces titanium dioxide by heating is 1/4 to 1/7. Mix in proportions and this is 700 ° C
By firing at the above temperature, orthorhombic cesium titanate (

Embedded image Cs _x Ti _{2−x / 4} O ₄ ) is obtained.

Next, by immersing this substance (cesium titanate) in an aqueous acid solution, all the Cs ions are replaced with hydrogen ions, and the composition formula of the desired compound is obtained.

Embedded image An orthorhombic layered titanic acid having a composition represented by H _x Ti _{2-x / 4} O ₄ .nH ₂ O is obtained. The conditions for completely extracting Cs ions depend on many parameters such as acid concentration, solid-liquid ratio, reaction temperature, contact time, etc., but typically, cesium titanate (

Embedded image For 1 gram of Cs _x Ti _{2-x / 4} O ₄ ) powder, 1N hydrochloric acid aqueous solution 100
This is achieved by reacting cm ³ for 3 days at room temperature.

Here, x in the composition formula can be controlled by changing the mixing ratio of titanium dioxide (TiO ₂ ) as a starting material and cesium oxide (Cs ₂ O). When air-dried at room temperature after Cs extraction, n takes a value of around 1, but various hydration states can be obtained depending on the drying conditions.

The orthorhombic layered titanic acid (

Embedded image H _x Ti _{2-x / 4} O ₄ .nH ₂ O) has a remarkable ability to take in cations and organic molecules existing in a liquid phase or a gas phase between layers. For example, in the case of K and Cs ions dissolved in an aqueous solution, about 1 milliequivalent per 1 gram of solid phase is taken up in the weakly acidic region where the pH of the liquid phase is around 2. The amount taken up increases as the pH value rises, reaching 3 meq / g in the alkaline region above pH 12. At this time, the interlayer distance changes depending on the amount of incorporation.

Next, examples of the present invention will be described.

[0018]

Example 1 Cesium carbonate (Cs ₂ CO ₃ ) and titanium dioxide (TiO ₂ ) were mixed at various molar ratios in the range of 1/4 to 1/7 and thoroughly ground. After transferring this to a platinum crucible and heating in an electric furnace at 800 ° C for 30 minutes,
It was taken out, ground again, and baked at 800 ° C. for 40 hours.
At that time, in order to promote the reaction and make it uniform, it was taken out of the electric furnace once after 20 hours and ground. The product was identified by powder X-ray diffractometry to find that the starting mixture molar ratio was 1
In the range of /5.7 to 1 / 5.3, orthorhombic cesium titanate (

It was found that Cs _x Ti _{2-x / 4} O ₄ ) was obtained as a single phase. On the other hand, in the region of 1 / 5.3 or less, in addition to the above compounds, monoclinic cesium pentatitanate (Cs ₂ Ti ₅ O ₁₁ ) is produced as a by-product.
Furthermore, in the range of 1 / 5.7 or more, titanium dioxide (TiO ₂ )
Remained unreacted.

Next, with respect to 100 cm ^{3 of} 1 N hydrochloric acid solution, the orthorhombic cesium titanate (

Embedded image Powder of Cs _x Ti _{2-x / 4} O ₄ ) was brought into contact with the mixture at a ratio of 1 g, and reacted at room temperature with occasional stirring. The operation of replacing with a new hydrochloric acid solution every day was repeated 3 times, and then the solid phase was filtered, washed with water and air-dried.

The powder X-ray diffraction pattern of the product (see Table 1) was indexable on the body-centered orthorhombic lattice. Motherhood (

It was confirmed from the comparison with the crystallographic data of Cs _x Ti _{2-x / 4} O ₄ ) that the layered structure shown in FIG. 1 was retained. When heated, this material dehydrates in the range of 40-500 ° C with a total weight loss of 15-1.
Reached 6%. After that, when it is heated to 1000 ° C., it changes into a single phase of rutile (TiO ₂ ).
It was found that s ions did not remain.

From the above, the composition formula

It was concluded that orthorhombic layered titanic acid, which is a new compound represented by H _x Ti _{2-x / 4} O ₄ .nH ₂ O, was obtained. In this case, since a single phase is obtained when the mixing molar ratio (Cs ₂ O / TiO ₂ ) of the starting materials is in the range of 1 / 5.3 to 1 / 5.7, x in the composition formula is 0.67. ~
0.73, and the value of n was found to be about 1 from the loss on dehydration. However, various hydration states were obtained by changing the drying conditions.

[0022]

[Example 2] The orthorhombic layered titanic acid synthesized by the procedure shown in Example 1 (

Embedded image A titration experiment was carried out with K and Cs ions for the purpose of obtaining knowledge about the acid / basicity and intercalation property of H _x Ti _{2-x / 4} O ₄ .nH ₂ O). That is, 20 g ³ of an aqueous solution of K or Cs adjusted to a solid phase of 0.2 g and an ionic strength of 0.1 was placed in an Erlenmeyer flask
The reaction was carried out for 7 days in a constant temperature bath maintained at 25 ° C. that time,
The basicity of the aqueous solution was controlled by changing the mixing ratio of chloride and hydroxide as solutes. After the contact, the residual amount of cations in the supernatant was measured by an atomic absorption method and the pH value was measured by a digital pH meter to obtain a titration curve (FIG. 2). As a result, the K and Cs ions showed similar tendencies, and the exchange capacity was around 1 milliequivalent per gram in the weakly acidic region of pH 2. This value increased with increasing basicity of the liquid phase and reached about 3 meq / g at pH 12 and above. The change in the solid phase at that time was traced by the powder X-ray diffraction method, and the interlayer distance was 9.4Å to 9.1Å for K ions.
In addition, it was found that Cs ions continuously contracted to 8.9Å.

[0023]

As described in detail above, according to the present invention,
A layered titanic acid containing hydrogen ions (or hydronium ions) and water molecules can be provided between the layers. Since this new compound has a remarkable ability to take in cations and organic molecules from the liquid phase or gas phase between layers, it is possible to treat adsorbents, ion exchange materials, catalysts, separation materials and radioactive waste liquids. Expected to be used as a disposal material.

[Brief description of drawings]

FIG. 1 shows orthorhombic layered titanic acid (

Is a projection view of the crystal structure of H _x Ti _{2-x / 4} O ₄ .nH ₂ O) on the (100) plane, and the portion surrounded by the dotted line corresponds to a unit cell.

FIG. 2 is a pH titration curve, and the vertical axis represents p of the liquid phase after equilibration.
H and the horizontal axis indicate the amount of incorporated cations (milliequivalent / g).

Claims (2)

[Claims] 1. An orthorhombic crystal represented by the composition formula: H _x Ti _{2-x / 4} O ₄ .nH ₂ O (where x is 0.60 to 0.75 and n is 0 to 2). A compound having a layered structure of. 2. A molar ratio of cesium oxide (Cs ₂ O) or a compound which is decomposed to cesium oxide by heating and titanium dioxide (TiO ₂ ) or a compound which produces titanium dioxide by heating in a molar ratio of 1/4 to 1/7. Of cesium titanate (Cs _x Ti _{2 -x / 4} O ₄ ) obtained by mixing the mixture in a proportion of 100 ° C. and calcining the mixture at a temperature of 700 ° C. or higher A method which comprises eluting all Cs ions to obtain orthorhombic layered titanic acid having a composition represented by H _x Ti _{2-x / 4} O ₄ .nH ₂ O.