JP2007161532A - Method of manufacturing layered titanic acid nanosheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of simply manufacturing a layered titanic acid nanosheet superior in dispersibility to organic substances with a good efficiency, and the layered titanic acid nanosheet obtained by the method. <P>SOLUTION: In the method of manufacturing the layered titanic acid nanosheet which is a method (1) of hydrolyzing a titanium alkoxide and/or a titanium salt in the presence of a phosphine compound or a method (2) of bringing titanium hydroxide into contact with a phosphine compound, the titanium hydroxide is one obtainable by mixing an alcohol solution of the titanium alkoxide with water or obtainable by hydrolyzing a titanium salt; and the phosphine compound is a quaternary phosphonium hydroxide; and the layered titanic acid nanosheet (3) obtained by the manufacturing method; is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a layered titanate nanosheet. Specifically, the present invention relates to a method for easily and efficiently producing a layered titanate nanosheet excellent in dispersibility with respect to an organic material, and a layered titanate nanosheet useful for various applications obtained by the production method.

Titanium compounds are widely used industrially as raw materials for ceramics and composite oxides, photocatalytic materials, and the like. Although there are various forms of this titanium compound, the titanium-containing liquid has an advantage that a highly active one can be obtained when used as a catalyst because the titanium compound is generally finely dispersed.
Some titanium compounds form a nanoscale sheet.
Titanium compound nanosheets are obtained by peeling a layered titanium compound into a layer that is the basic unit of the crystal structure by soft chemical treatment, and several hundred times that in the lateral direction with respect to the molecular level thickness (nm level) Since it has the above size (μm level) and a high surface area, application to various uses is expected.

As a method for producing a titanium-containing aqueous solution, a method of reacting 5 to 50 times the amount of water with a mixed solution of amines and titanium alkoxide is known (see Patent Document 1).
However, since this method is a mixture of amines and water, it is difficult to apply long-chain amines that are poorly compatible with water, and layered titanic acid with excellent dispersibility in organic compounds. It was difficult to produce a nanosheet dispersion.

On the other hand, a method for producing a layered titanium oxide called a lipidocrosite type, in which a titanium-containing raw material is fired at a high temperature and a hydrochloric acid aqueous solution and a quaternary ammonium ion are further reacted, has been reported (see Non-Patent Document 1).
Specifically, in this method, first, a mixed powder of Cs ₂ CO ₃ : TiO ₂ (molar ratio) = 1: 5.2 is fired at 800 ° C. for 20 hours to obtain a lipidocrocite-type layered titanium oxide. By synthesizing Cs _0.7 Ti _1.825 □ _0.175 O ₄ (□ is a vacancy) and stirring this powder in an aqueous hydrochloric acid solution of about 1 mol / L, all the Cs ions between the layers are hydrogenated while maintaining the layered structure. It replaces with ions and is induced into a hydrogen-type substance having a composition of H _0.7 Ti _1.825 □ _0.175 O ₄ · H ₂ O. Next, a solution containing tetrabutylammonium hydroxide, which is a basic substance, is allowed to act on this, and the basic substance is intercalated between layers to obtain a colloidal solution.
However, this method requires firing the raw material containing titanium at a high temperature, and the subsequent operation is complicated.
From such a viewpoint, a method for easily and efficiently producing a layered titanate nanosheet, particularly a layered titanate nanosheet excellent in dispersibility with respect to an organic substance, has been demanded.

Japanese Patent No. 3502904 Takayoshi Sasaki, “New Nanomaterial: Oxide Nanosheet Colloid”, Color Material Association, 2003, Vol. 76, No. 10, p. 391-396

  An object of the present invention is to provide a method for easily and efficiently producing a layered titanate nanosheet excellent in dispersibility with respect to an organic substance, and a layered titanate nanosheet obtained by the production method.

The present inventors have found that a desired layered titanate nanosheet can be easily and efficiently produced by using a phosphine compound.
That is, the present invention provides the following (1) to (4).
(1) A method for producing a layered titanate nanosheet in which a titanium alkoxide and / or a titanium salt is hydrolyzed in the presence of a phosphine compound.
(2) A method for producing a layered nanosheet in which titanium hydroxide and a phosphine compound are brought into contact, wherein the titanium hydroxide is obtained by mixing an alcohol solution of titanium alkoxide and water, and the phosphine compound is a fourth. A method for producing a layered titanate nanosheet, which is a grade phosphonium hydroxide.
(3) A method for producing a layered nanosheet in which titanium hydroxide and a phosphine compound are contacted, wherein the titanium hydroxide is obtained by hydrolysis of a titanium salt, and the phosphine compound is quaternary phosphonium water. The manufacturing method of the layered titanate nanosheet which is an oxide.
(4) A layered titanate nanosheet obtained by the production method of any one of (1) to (3) above.

  ADVANTAGE OF THE INVENTION According to this invention, the layered titanate nanosheet useful for various uses obtained by the method of manufacturing the layered titanate nanosheet excellent in the dispersibility with respect to an organic substance simply and efficiently can be provided. .

In the method of the present invention, (i) a method of hydrolyzing titanium alkoxide and / or a titanium salt in the presence of a phosphine compound, (ii) (a) water obtained by mixing an alcohol solution of titanium alkoxide and water. A layered titanate nanosheet is produced by a method in which titanium oxide or (b) titanium hydroxide obtained by hydrolysis of a titanium salt and a phosphine compound are mixed and brought into contact with each other.
Here, the layered titanate nanosheet has an octahedral structure in which six oxygens are coordinated around titanium as a basic unit, and this unit is arranged in a plane. In the present invention, the layered titanate nanosheet specifically includes a titanate nanosheet having a structure such as 3 titanic acid, 4 titanic acid, 5 titanic acid, 6 titanic acid, or a lipid docrosite type.

(Titanium source)
In the method of the present invention, as a titanium source, (i) titanium alkoxide and / or titanium salt, (ii) (a) titanium hydroxide obtained by mixing an alcohol solution of titanium alkoxide and water, or (b) titanium Titanium hydroxide obtained by salt hydrolysis is used.

(Titanium alkoxide)
As titanium alkoxide, what has a C1-C8, Preferably C2-C6 alkoxy group is preferable. Specific examples include titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, and the like. From the viewpoint of general availability and handleability, titanium tetraisopropoxide is particularly preferable.
The titanium alkoxides can be used alone or in admixture of two or more.

(Titanium salt)
Examples of the titanium salt include titanium chloride such as titanium tetrachloride, titanium trichloride, and titanium dichloride, titanium sulfate, titanyl sulfate, and titanyl nitrate. One or more selected from titanium tetrachloride, titanium sulfate, and titanyl sulfate, which are generally easily available and widely used as titanium raw materials, are more preferable.
The above titanium salts can be used alone or in admixture of two or more.

(Titanium hydroxide)
In the present invention, titanium hydroxide used as a titanium source can be obtained by hydrolysis of titanium alkoxide or a titanium salt. Here, titanium hydroxide includes those having a composition formula of Ti (OH) ₂ , Ti (OH) ₃ , Ti (OH) _4, or H ₄ TiO ₄ .
(a) Production of titanium hydroxide by hydrolysis of titanium alkoxide can be performed by mixing the alcohol solution of the above titanium alkoxide and water and heating if necessary. Examples of the alcohol used for preparing the alcohol solution of titanium alkoxide include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and isopentyl alcohol.
The amount of water added in the hydrolysis is not particularly limited as long as it is more than the amount necessary for obtaining titanium hydroxide, but it is preferably 5 to 50 times, more preferably 10 to 15 times the mass of titanium alkoxide. preferable. The temperature and time for hydrolysis can be appropriately selected according to the titanium alkoxide used.

(b) The production of titanium hydroxide by hydrolysis of the titanium salt can be performed by mixing the above titanium salt and water, or by heating after mixing with water.
An alkali may coexist in the hydrolysis. Examples of the alkali that can coexist include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth hydroxides such as calcium hydroxide and magnesium hydroxide. Ammonia and amines can also be used as alkali. Among these, alkali metal hydroxides, ammonia, and amines are more preferable from the viewpoint of easy availability and handling.
The amount of alkali added is preferably such that the pH of the aqueous titanium salt solution is 2 or more, more preferably 4 or more.

The titanium salt may be dissolved in a solvent highly compatible with the titanium salt and / or water. Examples of such a solvent include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and isopentyl alcohol.
The amount of water added in the hydrolysis may be more than the amount necessary for obtaining titanium hydroxide, but is preferably 5 to 50 times, more preferably 10 to 15 times the mass of the titanium salt.
The temperature and time of hydrolysis can be appropriately selected according to the titanium salt used. In addition to titanium, other elements such as vanadium, niobium, tantalum, zirconium, aluminum, iron, cobalt, nickel, manganese, and the like can coexist and be combined.
The obtained titanium hydroxide can be used as a powder while being dispersed in a solution or by removing the solvent.

(Phosphine compound)
Examples of the phosphine compound used in the present invention include trialkyl phosphines, triphenyl phosphines, and quaternary phosphonium hydroxides.
As trialkylphosphines, those having an alkyl group having 1 to 10 carbon atoms and / or a cycloalkyl group having 5 or 6 carbon atoms are preferable. Specific examples include trimethylphosphine, triethylphosphine, tri-n-propylphosphine, triisopropylphosphine, tri-n-butylphosphine, trihexylphosphine, trioctylphosphine, and tricyclohexylphosphine.
Examples of the triphenylphosphine include triphenylphosphine, tolylphosphine, tribenzylphosphine, and tris (2,6-dimethoxyphenyl) phosphine.
As the quaternary phosphonium hydroxide, a compound represented by the following formula (1) is preferable.

In formula (1), R ¹ , R ² , R ³ and R ⁴ are each independently a linear or branched alkyl group having 1 to 10 carbon atoms, which may have a substituent. , A hydroxyalkyl group or an alkoxyalkyl group, or an aryl group or hydroxyaryl group having 6 to 18 carbon atoms.
R ^{1 to} R ⁴ of the alkyl group and the hydroxyalkyl group are each independently preferably a linear or chain having 1 to 8 carbon atoms, particularly preferably having 1 to 6 carbon atoms.
R ^{1 to} R ⁴ of the aryl group or hydroxyaryl group are each independently preferably one having 6 to 12 carbon atoms.
Examples of the substituent include an alkyl group having 1 to 6 carbon atoms, an alkoxy group, an amino group, and a nitro group.

Preferred examples of the quaternary phosphonium hydroxide include tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutylphosphonium hydroxide, tetrapentylphosphonium hydroxide, and tetrahexylphosphonium hydroxide. Tetraalkylphosphonium hydroxide having 1 to 8 carbon atoms; tetraphenylphosphonium hydroxide; ethyltriphenylphosphonium hydroxide, butyltriphenylphosphonium hydroxide, pentyltriphenylphosphonium hydroxide, 2-dimethylaminoethyltriphenyl Triphenylphosphonium, such as phosphonium hydroxide and methoxymethyltriphenylphosphonium hydroxide Muhidorokishido and the like.
Among these, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, and tetrabutylphosphonium hydroxide are particularly preferable.
The phosphine compound preferably has a pH of 9 or more in an aqueous solution having a concentration of 9 mmol / L from the viewpoint of nanosheet generation.

(Production method)
In the production method of the present invention, (i) a method in which titanium alkoxide and / or titanium salt is hydrolyzed in the presence of a phosphine compound, (ii) (a) an alcohol solution of titanium alkoxide and water are mixed. A layered titanate nanosheet is produced by a method in which titanium hydroxide or (b) titanium hydroxide obtained by hydrolysis of a titanium salt and a phosphine compound are mixed and brought into contact with each other.
When mixing the titanium alkoxide and / or titanium salt and the phosphine compound, the upper limit of the molar ratio of the Ti / phosphine compound is preferably 5 or less, more preferably 3.0 or less, from the viewpoint of reaction efficiency. Preferably it is 2.5 or less, Especially preferably, it is 1.5 or less, The lower limit becomes like this. Preferably it is 0.1 or more, More preferably, it is 0.2 or more.
In the case of the method (i), it is preferable to prepare an alcohol solution of titanium alkoxide in the presence of water. Alcohols that can be used are as described above.
The titanium concentration in the mixed solution is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and still more preferably 0.05 to 5% by mass in terms of titanium oxide (TiO ₂ ).

In the case of the method (ii), the obtained titanium hydroxide and the phosphine compound are mixed, and in that case, it is preferable to coexist water. The amount of water to be coexisted may be at least the total number of moles of titanium hydroxide and phosphine compound.
In addition, it is preferable to add a highly compatible solvent to the phosphine compound because the solubility of the phosphine compound having an alkyl group having a large number of carbon atoms can be improved. Examples of such solvents include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol and isopentyl alcohol, oxygen-containing organic solvents such as acetone and tetrahydrofuran, and nitrogen-containing organic solvents such as acetonitrile. Among these, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and isopentyl alcohol are preferable.

When the phosphine compound-containing aqueous solution and the titanium source are mixed, the titanium compound may become cloudy, but a colorless and transparent liquid can be obtained by continuously stirring.
Although the temperature at the time of mixing a titanium source is not specifically limited, The nanosheet of an organic cation containing layered titanic acid produces | generates preferably at 2-200 degreeC. From the viewpoint of the stability of the long-chain phosphine compound, 10 to 150 ° C is more preferable, and 20 to 100 ° C is still more preferable. The reaction time is preferably 0.1 to 20 hours, and more preferably 1 to 10 hours.
Moreover, in order to develop a layer structure, after mixing a phosphine compound and a titanium source, you may perform hydrothermal synthesis further at 50-200 degreeC.
In this way, a transparent dispersion containing the organic cation-containing layered titanate nanosheet can be obtained. Moreover, an organic cation containing layered titanate polyanion nanosheet is manufactured by removing water or a solvent from the dispersion by drying.

An organic solvent dispersion of an organic cation-containing layered titanate nanosheet dispersed in an organic solvent different from the organic solvent used in the production is manufactured by mixing the organic cation-containing layered titanate nanosheet with the organic solvent again. You can also
Examples of the organic solvent used at this time include water, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and butyl alcohol, oxygen-containing organic solvents such as acetone, tetrahydrofuran, and propylene carbonate, and nitrogen-containing organic solvents such as acetonitrile. Can be mentioned.
The titanium concentration in the dispersion is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and still more preferably 0.05 to 5% by mass in terms of titanium oxide (TiO ₂ ).

Formation of titanate nanosheets having a layer structure can be confirmed by X-ray diffraction, transmission electron microscope (TEM) observation, or the like.
In the present invention, it has been confirmed by X-ray diffraction that the layer spacing increases as the cation size increases, and it is considered that the organic cation is present between the layers. It is presumed that the property is improved.

In the following Examples and Comparative Examples, “%” is “% by mass” unless otherwise specified.
Example 1
Titanium tetraisopropoxide (0.34 g, 1.18 mmol) was dissolved in 10 mL of isopropyl alcohol to obtain a titanium source. 0.94 g (1.36 mmol) of 40% tetrabutylphosphonium hydroxide aqueous solution was added to 150 g of distilled water, and the titanium source was gradually added dropwise with stirring at room temperature. The solution became cloudy immediately after the addition, but became a colorless and transparent solution when stirring was continued. The concentration in terms of TiO _{2 at} this time was 0.06%, and the molar ratio of Ti / tetrabutylphosphonium hydroxide was 0.87.
Several drops of the obtained colorless and transparent solution were dropped on a glass plate, and X-ray diffraction analysis was performed using the dried film. As a result, the X-ray diffraction pattern shown in FIG. 1 was obtained. In this X-ray pattern, a main peak (first peak) is observed in the vicinity of 18.28 (4.83 ° at an angle 2θ) in terms of d value, and then the second peak is d = 9.35 (9.45 °). In the vicinity, a third peak was observed near d = 6.24 (14.19 °). Since the d value of the second peak and the third peak is about 1/2 and 1/3 with respect to the first peak, the generated titanic acid has a layer structure in which an organic cation is sandwiched between layers. Was confirmed. The clear colorless solution results of Raman spectroscopy, the layered titanate (lepidocrocite type layered titanium oxide) to the specific 278cm ^-1, 442cm ^-1, the peak is obtained around 702cm ^-1.
The colorless and transparent solution was dried at 60 ° C. using a vacuum dryer to obtain a white powder. To 0.1 g of this powder, 9.9 g of each solvent of water, methyl alcohol, ethyl alcohol, isopropyl alcohol, propylene carbonate, acetonitrile, acetone, and tetrahydrofuran was added and stirred. As a result of visual observation of the state after stirring, it was confirmed that all the solutions were transparent solutions and a dispersion solution in which titanic acid nanosheets were sufficiently dispersed was obtained.

Example 2
A titanium source in which 33.54 g (118 mmol) of titanium tetraisopropoxide was dissolved in 10 mL of isopropyl alcohol was obtained.
40.78 g (59 mmol) of 40% tetrabutylphosphonium hydroxide aqueous solution was dissolved in distilled water to make 150 g. While the aqueous solution was stirred at room temperature, the titanium source was gradually added dropwise. The solution became cloudy immediately after the addition, but became a colorless and transparent solution when stirring was continued. The concentration in terms of TiO _{2 at} this time was about 5%, and the molar ratio of Ti / tetrabutylphosphonium hydroxide was 2.0.
Using the resulting colorless and transparent solution, it was dried and subjected to X-ray diffraction analysis in the same manner as in Example 1. As a result, the same X-ray diffraction pattern as in FIG. 1 showing the layer structure was obtained, and it was confirmed that the generated titanic acid had a layer structure in which an organic cation was sandwiched between layers. As a result of Raman spectroscopic analysis of this solution, a peak similar to layered titanic acid (repidocrocite-type layered titanium oxide) was obtained.
Dispersibility with water, methyl alcohol, ethyl alcohol, isopropyl alcohol, propylene carbonate, acetonitrile, acetone, and tetrahydrofuran solvents using white powder obtained by drying the colorless and transparent solution in the same manner as in Example 1. As a result, it was confirmed that all the solutions were transparent solutions, and the titanate nanosheets were sufficiently dispersed in each solvent.

Example 3
Suspension containing titanium hydroxide produced by adding a titanium source in which 0.34 g (1.18 mmol) of titanium tetraisopropoxide is dissolved in 10 mL of isopropyl alcohol to 150 g of stirring distilled water and hydrolyzing it. Got.
While stirring the suspension containing titanium hydroxide, 0.94 g (1.36 mmol) of 40% tetrabutylphosphonium hydroxide solution was added. When stirring was continued, a colorless transparent solution was obtained. The concentration in terms of TiO _{2 at} this time was 0.06%, and the molar ratio of Ti / tetrabutylphosphonium hydroxide was 0.87.
Using the resulting colorless and transparent solution, it was dried and subjected to X-ray diffraction analysis in the same manner as in Example 1. As a result, the same X-ray diffraction pattern as in FIG. 1 showing the layer structure was obtained, and it was confirmed that the generated titanic acid had a layer structure in which an organic cation was sandwiched between layers. As a result of Raman spectroscopic analysis of this solution, a peak similar to layered titanic acid (repidocrocite-type layered titanium oxide) was obtained.
Dispersibility with water, methyl alcohol, ethyl alcohol, isopropyl alcohol, propylene carbonate, acetonitrile, acetone, and tetrahydrofuran solvents using white powder obtained by drying the colorless and transparent solution in the same manner as in Example 1. As a result, it was confirmed that all the solutions were transparent solutions, and the titanate nanosheets were sufficiently dispersed in each solvent.

Example 4
1.18 mmol (0.22 g) of titanium tetrachloride was dissolved in 150 g of distilled water while cooling with ice, and after dissolution, it was allowed to stand until it reached room temperature. Thereafter, 5% aqueous ammonia was added until the pH became 7, to obtain titanium hydroxide.
After the titanium hydroxide was filtered off and washed, 150 g of distilled water was added again, and 2.79 g (1.36 mmol) of 8% tetraethylphosphonium hydroxide solution was added with stirring. When stirring was continued, a colorless transparent solution was obtained. The concentration in terms of TiO _{2 at} this time was 0.06%, and the molar ratio of Ti / tetraethylphosphonium hydroxide was 0.87.
Using the resulting colorless and transparent solution, it was dried and subjected to X-ray diffraction analysis in the same manner as in Example 1. As a result, the same X-ray diffraction pattern as in FIG. 1 showing the layer structure was obtained, and it was confirmed that the generated titanic acid had a layer structure in which an organic cation was sandwiched between layers. As a result of Raman spectroscopic analysis of this solution, a peak similar to layered titanic acid (repidocrocite-type layered titanium oxide) was obtained.
Dispersibility with water, methyl alcohol, ethyl alcohol, isopropyl alcohol, acetonitrile, acetone, tetrahydrofuran, and propylene carbonate solvents using white powder obtained by drying the colorless and transparent solution in the same manner as in Example 1. As a result, it was confirmed that all the solutions were transparent solutions and a dispersion solution in which titanic acid nanosheets were sufficiently dispersed was obtained.

  According to the method of the present invention, a layered titanate nanosheet excellent in dispersibility with respect to an organic substance can be easily and efficiently produced. The obtained layered titanate nanosheet can be expected to be used as a highly active catalyst.

2 is an X-ray diffraction pattern showing a layer structure of layered titanic acid obtained in Example 1. FIG.

Claims (9)

  A method for producing a layered titanate nanosheet in which a titanium alkoxide and / or a titanium salt is hydrolyzed in the presence of a phosphine compound.   The method for producing a layered titanate nanosheet according to claim 1, wherein the titanium alkoxide is titanium tetraisopropoxide.   The method for producing a layered titanate nanosheet according to claim 1 or 2, wherein the titanium salt is at least one selected from titanium tetrachloride, titanium sulfate, and titanyl sulfate.   The method for producing a layered titanate nanosheet according to any one of claims 1 to 3, wherein the phosphine compound is a quaternary phosphonium hydroxide.   A method for producing a layered nanosheet in which titanium hydroxide and a phosphine compound are brought into contact, wherein the titanium hydroxide is obtained by mixing an alcohol solution of titanium alkoxide and water, and the phosphine compound is quaternary phosphonium water. The manufacturing method of the layered titanate nanosheet which is an oxide.   The method for producing a layered titanate nanosheet according to claim 5, wherein the titanium alkoxide is titanium tetraisopropoxide.   A method for producing a layered nanosheet in which titanium hydroxide and a phosphine compound are brought into contact, wherein the titanium hydroxide is obtained by hydrolysis of a titanium salt, and the phosphine compound is a quaternary phosphonium hydroxide. A method for producing a layered titanate nanosheet.   The method for producing a layered titanate nanosheet according to claim 7, wherein the titanium salt is at least one selected from titanium tetrachloride, titanium sulfate, and titanyl sulfate.   A layered titanate nanosheet obtained by the production method according to claim 1.

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