JP4933941B2 - Method for producing titanic acid nanosheet - Google Patents

Description

  The present invention relates to a method for producing titanate nanosheets, a method for controlling the particle diameter of titanate nanosheets, titanate nanosheets, and dispersions thereof.

Titanium oxide is widely used industrially as a raw material for ceramics and composite oxides, as a photocatalytic material, and the like. There are various forms of this titanium oxide, but the titanium oxide is not a conventional anatase-type or rutile-type titania, but a nanoscale-thick sheet containing titanic acid or a salt thereof, that is, Some form titanate nanosheets.
This titanic acid nanosheet is obtained by peeling a layered titanium compound to a layer that is a basic unit of a crystal structure by a soft chemical treatment, and the number thereof in the lateral direction with respect to the molecular level thickness (nm level). A dense and highly smooth film having a size 100 times larger can be formed. For this reason, application to various uses, such as barrier films, such as ultraviolet shielding, a corrosion-resistant film, a dielectric thin film, and a catalyst, is expected, for example.

As a method for producing a titanate nanosheet dispersion, a method for producing a titanate nanosheet dispersion called a lipid crosite 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 (non-patent literature) 1) has been reported.
Specifically, in this method, first, a mixed powder of Cs ₂ CO ₃ : TiO ₂ (molar ratio) = 1: 5.2 is calcined at 800 ° C. for 20 hours, and Cs, which is a lipid dodecite type layered titanic acid. By synthesizing _0.7 Ti _1.825 □ _0.175 O ₄ (□ is a vacancy) and stirring this powder in a 1 mol / L aqueous hydrochloric acid solution, all the Cs ions between the layers are all hydrogen ions while maintaining the layered structure. In place 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 above basic substance is intercalated between layers, and further delaminated to obtain a layered titanate nanosheet dispersion.
However, since this method is synthesized through a firing step, the thickness of the nanosheet is as thin as 1 nm or less, but there is a drawback that only a large one of several hundred nm can be obtained in the lateral direction. Although it is possible to make this nanosheet fine by pulverization or the like, it is very difficult to obtain a nanosheet of 100 nm or less, and it is difficult to blend it into an application that places importance on transparency, for example, an optical resin.

  On the other hand, a method of obtaining a titanic acid nanosheet aqueous dispersion by reacting water with a mixed liquid of amines and titanium alkoxide (see Non-Patent Document 2) is known. This aqueous dispersion is highly transparent, and it is considered that nanosheets having a particle size of about several nanometers are generated. However, since the particle diameter is too small, for example, when blended with an optical resin, there is a problem that the mechanical strength of the resin composition is lowered.

Takayoshi Sasaki, “New Nanomaterial: Oxide Nanosheet Colloid”, Color Material Association, 2003, Vol. 76, No. 10, p. 391-396 T. Ohya, A. Nakayama, Y. Shibata, T. Ban, Y. Ohya, Y. Takahashi, Journal of Sol-Gel Science and Technology, Vol. 26, p 799-802 (2003)

  The present invention relates to a method for producing titanic acid nanosheets having a highly versatile and moderately sized particle size and excellent transparency, a method for controlling the particle size of titanate nanosheets, titanate nanosheets, and dispersions thereof It is an issue to provide.

The present inventors have found that a titanate nanosheet having a controlled particle size and a dispersion thereof can be obtained by hydrothermal treatment of a dispersion of titanate nanosheets containing amines and the like.
That is, the present invention provides the following (1) to (4).
(1) A titanate nanosheet dispersion comprising a step of hydrothermally treating a titanate nanosheet dispersion stock solution obtained by hydrolysis reaction of titanium alkoxide and / or titanium salt in the presence of amines and / or phosphoniums Production method.
(2) A method for controlling the particle size of titanate nanosheets, wherein hydrolyzing a titanate nanosheet dispersion stock solution obtained by hydrolysis reaction of titanium alkoxide and / or titanium salt in the presence of amines and / or phosphoniums .
(3) A titanic acid nanosheet having a volume-based average particle diameter of 5 to 100 nm measured using a dynamic light scattering method in a dispersion having a TiO ₂ concentration of 1% by mass.
(4) A titanate nanosheet dispersion containing the titanate nanosheet of (3).

  According to the present invention, a versatile and moderately sized particle diameter and a highly transparent titanate nanosheet production method, a particle diameter control method for titanate nanosheets, a particle diameter of 5 to 100 nm Titanate nanosheets and dispersions thereof can be provided.

<Titanate nanosheet>
The titanate nanosheet has an octahedral structure in which six oxygens are coordinated around titanium as a basic unit, and this unit has a molecular level thickness (for example, 0.3 to 0.8 nm) spread in a two-dimensional plane. A sheet structure (for example, 2 to 10 nm in length). This titanic acid nanosheet includes titanic acid nanosheets having a structure such as dititanic acid, trititanic acid, tetratitanic acid, pentatitanic acid, hexatitanic acid, and lipidocrocite type. It is considered that amines, phosphoniums and the like are included in the form.
It is inferred that titanate nanosheets are in a state where titanate nanosheets are dispersed separately one by one in the dispersion, and titanate nanosheet dispersion is a state in which titanate nanosheets are layered depending on the system. In addition, it is considered to include partially agglomerated materials.
Such titanate nanosheet, wavenumber Raman spectra having a respective peak in the region of 260~305cm ^-1, 440~490cm ^-1 and 650~1000cm ^-1. Incidentally, the conventional anatase titania which is a typical titanium oxide, wavenumber in Raman spectrum 140~160cm ^-1, 390~410cm ^-1, have a peak in the region of 510～520Cm ^-1 and 630～650Cm ^-1 Rutile-type titania has peaks in the Raman spectrum having wave numbers of 230 to 250 cm ⁻¹ , 440 to 460 cm ⁻¹ and 600 to 620 cm ⁻¹ .

A titanate nanosheet is a titanate nanosheet dispersion stock solution (hereinafter referred to as “titanate nanosheet dispersion stock solution” or simply “a titanate nanosheet dispersion stock solution” obtained by hydrolyzing a titanium alkoxide and / or a titanium salt in the presence of amines and / or phosphoniums. This is referred to as a “dispersion stock solution” and is easily obtained as a titanic acid nanosheet dispersion in which particles after hydrothermal treatment are controlled. As described in Background Art [0004], this titanate nanosheet dispersion stock solution generally has an average particle size of about 1 to 3 nm, and it is difficult to obtain a particle size larger than that.
The inventors of the present invention have found that a dispersion of titanate nanosheets having a larger particle size can be obtained by hydrothermally treating the titanate nanosheet dispersion stock solution without impairing transparency.
In the present specification, “excellent in transparency” means that the turbidity (according to JIS K-0101) of a dispersion having a TiO ₂ weight conversion concentration of 1% is 30% or less.

(Titanate nanosheet dispersion stock solution)
In this invention, before preparing the titanate nanosheet of this invention, the titanate nanosheet dispersion | distribution stock solution used as a raw material is prepared. The titanate nanosheet dispersion stock solution is composed of titanium alkoxide and / or titanium salt (hereinafter collectively referred to simply as “titanium source”), but primary amine, secondary amine, tertiary amine and Hydrolysis reaction in an aqueous solution in the presence of one or more amines selected from the group consisting of quaternary ammonium hydroxides and / or phosphoniums such as quaternary phosphonium hydroxides, more details Is presumed to be obtained by hydrolysis and condensation reaction.

(Titanium source)
In the present invention, the titanium source is preferably one that produces titanium hydroxide by a hydrolysis reaction, and titanium alkoxide and / or titanium salt is used. As the titanium alkoxide and / or titanium salt, those capable of producing titanium hydroxide by hydrolysis are preferable. Here, the titanium hydroxide includes those having a composition formula represented by Ti (OH) ₂ , Ti (OH) ₃ , Ti (OH) _4, or H ₄ TiO ₄ .
The titanium alkoxide is preferably a titanium alkoxide having an alkoxide having 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms. Specific examples include titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide and the like. . These can be used alone or in admixture of two or more.
Among these, titanium tetraalkoxide is particularly preferable, and titanium tetraisopropoxide is preferable from the viewpoint of general availability and handling.

Examples of the titanium salt include titanium chloride such as titanium tetrachloride, titanium trichloride, and titanium dichloride, titanium sulfate, titanyl sulfate, and titanyl nitrate. These can be used alone or in admixture of two or more. Among these, titanium tetrachloride, titanium sulfate, and titanyl sulfate are more preferable from the viewpoint of general availability and handleability.
The titanium salt produces titanium hydroxide by mixing with water or by heating after mixing with water, and in that case, an alkali may be further allowed to coexist. Examples of the alkali that coexists when producing titanium hydroxide include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkaline earth hydroxides such as calcium hydroxide and magnesium hydroxide. Furthermore, ammonia and the above amines can also be used as an 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 source may be dissolved in water and / or a solvent highly compatible with the titanium source. Examples of such a solvent include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and isopentyl alcohol.
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.

(Amines)
As the amines, one or more selected from the group consisting of primary amines, secondary amines, tertiary amines, and quaternary ammonium hydroxides are used, preferably alkyl having 1 or more carbon atoms. Amines having a group or an alkenyl group are preferred.
Specifically, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, tripropylamine, tetrapropylammonium hydroxide, butylamine, dibutylamine, tributylamine, tetrabutylammonium hydroxide, pentylamine, dipentylamine, tripentyl Preferred are amine, hexylamine, dihexylamine, trihexylamine, dimethylhexylamine, dimethylbenzylamine, dimethyloctylamine and the like. In addition, substituted amines such as monoethanolamine, diethanolamine, and triethanolamine can also be used. These can be used alone or in admixture of two or more.
Among these, from the viewpoint of easy distillation of amines, the boiling point at normal pressure is preferably 200 ° C. or less, more preferably 150 ° C. or less, and still more preferably 100 ° C. or less. Further, secondary alkylamines and tertiary alkylamines are preferable, secondary alkylamines and tertiary alkylamines having an alkyl group having 1 to 6 carbon atoms, particularly 2 to 4 carbon atoms are more preferable, diethylamine, Triethylamine and di-n-propylamine are particularly preferred.
The amine is preferably an amine having a pH of 9 or more in an aqueous solution having an amine concentration of 9 mmol / L from the viewpoint of production of titanate nanosheets.

(Phosphoniums)
As the phosphoniums, quaternary phosphonium hydroxides are preferable, and the quaternary phosphonium hydroxides are compounds in which the hydrogen of 4 atoms bonded to the phosphorus atom of the inorganic phosphonium compound is substituted with an alkyl group, a phenyl group or the like. .
The quaternary phosphonium hydroxide includes an alkyl group having 2 to 8 carbon atoms such as tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutylphosphonium hydroxide, tetrapentylphosphonium hydroxide, and tetrahexylphosphonium hydroxide. Tetraalkylphosphonium hydroxide, tetraphenylphosphonium hydroxide, ethyltriphenylphosphonium hydroxide, butyltriphenylphosphonium hydroxide, pentyltriphenylphosphonium hydroxide, 2-dimethylaminoethyltriphenylphosphonium hydroxide, methoxymethyltriphenylphosphonium And triphenylphosphonium hydroxide such as hydroxide.
Among these, one or more selected from tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutylphosphonium hydroxide, and tetrapentylphosphonium hydroxide are preferable.
The phosphonium is preferably a quaternary phosphonium hydroxide having a pH of 9 or more in an aqueous solution having a quaternary phosphonium hydroxide concentration of 9 mmol / L from the viewpoint of producing titanate nanosheets.

(Production of titanate nanosheet dispersion stock solution)
The titanic acid nanosheet dispersion stock solution can be obtained by hydrolyzing a titanium source in the presence of the amines and / or phosphoniums (hereinafter sometimes collectively referred to as “amines and the like”).
The amount of water added in the hydrolysis may be more than the amount necessary for obtaining titanium hydroxide. Usually, the mass of 3-50 times is preferable with respect to the mass of a titanium source, and the mass of 5-15 times is more preferable. The temperature and time of the hydrolysis and condensation reaction can be appropriately selected according to the titanium alkoxide and / or titanium salt used.
Although the manufacturing method of titanic acid nanosheet dispersion | distribution stock solution containing amines etc. is not specifically limited, According to the 1st method and the 2nd method shown below, it can manufacture efficiently.

[First method]
The first method is a method of mixing an aqueous solution such as amines with a titanium source.
The aqueous solution of amines and the like may contain an organic solvent in order to facilitate dissolution of amines and the like. As such an organic solvent, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and isopentyl alcohol are preferable.
When mixing the aqueous solution containing amines and the titanium source, the mixing ratio of the titanium source and the amines is preferably such that the molar ratio of amines / Ti / Ti is 0.2 to 5, More preferably, it is ~ 3. By increasing the ratio of amines and the like to the titanium source when producing titanic acid nanosheets, a transparent dispersion stock solution can be obtained even for a lower polarity organic solvent. Here, the amines / Ti molar ratio means the molar ratio of amines or titanium quaternary phosphonium hydroxide molecules per titanium atom in the titanate nanosheet dispersion stock solution, respectively.
The titanium concentration in the mixed solution of the aqueous solution containing amines and the titanium source is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass in terms of titanium oxide (TiO ₂ ). 05-5 mass% is still more preferable.

When the aqueous solution containing amines and the titanium source are mixed, the titanium compound may become cloudy, but a colorless transparent to light yellow liquid can be obtained by continuously stirring.
The temperature at which the titanium source is mixed is not particularly limited. Although nanosheets of titanic acid containing amines and the like are produced at 2 to 200 ° C, 10 to 150 ° C is more preferable and 20 to 100 ° C is more preferable from the viewpoint of the stability of the long-chain amine. The reaction time is preferably 0.1 to 20 hours, and more preferably 1 to 10 hours.

[Second method]
The second method is a method of preparing a titanium-containing aqueous solution by mixing amines and a titanium source in advance and then mixing water. The amines and the like may contain the same organic solvent as in the first method.
When water is added to the mixture of amines and the titanium source, the amount of water may be an amount necessary for titanium to decompose. The amount of water to be added is preferably 5 to 50 times, more preferably 10 to 15 times the mass of the mixture of amines and the titanium source. Although the temperature which adds water is not specifically limited, 2-200 degreeC is preferable and 20-100 degreeC is more preferable. Moreover, 0.01-5 hours are preferable and the dripping time of water is more preferable 0.02-2 hours. Furthermore, it is preferable to perform aging for 0.1 to 20 hours after the addition of water.
The titanium concentration in the titanate nanosheet dispersion stock solution containing amines and the like is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, in terms of titanium oxide (TiO ₂ ), and 0.05 to 5 mass% is still more preferable.

(Confirmation of titanate nanosheet in titanate nanosheet dispersion stock solution)
The production of titanate nanosheets can be confirmed by Raman spectroscopy, ultraviolet absorption spectrum, transmission electron microscope (TEM) observation, and the like.
It is presumed that a titanate sheet containing amines and the like is formed in the dispersion stock solution of titanate nanosheets. This uses an argon ion laser (wavelength 488 nm) as a light source, and in the measurement of a transmission Raman spectrum under the conditions of a laser output of 100 to 600 mW and an integration time of 30 to 300 seconds, the wave number is 260 to 305 cm ⁻¹ , 440 to 490 cm ^{−. This is because} peaks were respectively obtained in the regions of ¹ and 650 to 1000 cm ⁻¹ and the structures of the titanium atom and the titanate sheet were derived.
In addition, as for the ultraviolet absorption spectrum of the titanate nanosheet containing amines, the rising wavelength (absorption edge) of the absorption spectrum is found at 300 to 340 nm. On the other hand, the rising wavelength (absorption edge) of the absorption spectrum is observed at a wavelength of 360 to 380 nm for anatase type titania and at a wavelength of 400 to 420 nm for rutile type titania.
The layered structure can be confirmed by drying the titanate nanosheet dispersion stock solution and performing X-ray diffraction. It has been confirmed that the layer spacing increases as the cation size of the amines increases, and it is considered that the amines are present between the layers. From this, it is estimated that the titanic acid nanosheet containing amines or the like improves the dispersibility in an organic solvent.

(Hydrothermal treatment of titanate nanosheet dispersion stock solution)
In the method of the present invention, the average particle diameter of titanate nanosheets can be grown by hydrothermally treating the titanate nanosheet dispersion stock solution. Hydrothermal treatment means aging by applying temperature and pressure to a dispersion stock solution or a dispersion stock solution to which seed crystals described later are added. When the particles in the dispersion stock solution are aged by applying both temperature and pressure, it is considered that particle dissolution / precipitation reaction occurs and the particle diameter increases.
The temperature of the hydrothermal treatment is preferably 75 to 200 ° C, more preferably 95 to 150 ° C, and still more preferably 100 to 130 ° C. If the temperature is too high, the titanate nanosheets containing amines and the like undergo crystal transition to anatase-type titanium oxide, and if the temperature is too low, control for increasing the particle size cannot be performed efficiently.
The pressure of the hydrothermal treatment varies depending on the solvent to be used, but is 0.8 MPa or more, preferably 1 MPa or more, and the upper limit is preferably about 1.5 MPa or less.
Although the treatment time varies depending on the solvent, pressure, and temperature, it is approximately 0.5 hours or more, preferably 1 hour or more. The particle size grows as the treatment time becomes longer, but when it takes too much time, it transitions to the anatase type. Therefore, the upper limit of the processing time is 24 hours or less, preferably 12 hours or less.

The pH of the solution at the time of hydrothermal treatment is preferably about 10 to 13, which is the pH range when synthesizing titanate nanosheets. If the pH is less than 10, the crystals are easily transferred to anatase during hydrothermal treatment, and if the pH exceeds 13, it is difficult to control the particle size.
Stirring during the hydrothermal treatment may be unstirred as long as there is no sedimentation of particles, but it is preferable to stir in consideration of thermal conductivity. There is no particular upper or lower limit for the stirring speed, but it is sufficient that the hydrothermal treatment apparatus is not burdened.
In addition, as a factor affecting the particle size, there is a titanic acid concentration in the dispersion, and the titanic acid concentration in the titanic acid nanosheet dispersion is preferably 0.1 to 15% by mass, more preferably 0 in terms of TiO _2. 5 to 10% by mass, most preferably 1 to 6% by mass.

(Manufacturing method of titanate nanosheet dispersion using seed crystal titanate nanosheet)
In order to further increase the average particle size of the titanate nanosheet of the present invention, a method of adding a seed crystal titanate nanosheet to the titanate nanosheet-dispersed stock solution and hydrothermally treating is preferable.
That is, according to the present invention, the titanium source nanosheet dispersion stock solution obtained by condensation reaction of a titanium source in the presence of amines and / or phosphoniums has a step of adding a seed crystal titanate nanosheet and hydrothermally treating it. A method for producing a titanate nanosheet dispersion is provided.
As the titanate nanosheet dispersion stock solution to which the seed crystal titanate nanosheet is added, a dispersion stock solution prepared separately from the titanate nanosheet dispersion stock solution that performs hydrothermal treatment for adjusting the seed crystal may be used.

(Preparation of seed crystal titanate nanosheet)
The seed crystal is for increasing the particle size of the titanate nanosheet or for growing the titanate nanosheet. In particular, when preparing a titanate nanosheet having a volume-based average particle diameter of 5 nm or more, it is preferable to use a seed crystal.
As seed crystal titanate nanosheets, (i) one obtained by hydrothermally treating a titanate nanosheet dispersion stock solution once to improve crystallinity, or (ii) a lipidocrosite type obtained by firing a titanium-containing raw material at a high temperature A layered titanic acid nanosheet that has been exfoliated in a sheet form with a hydrochloric acid aqueous solution and a solution containing amines and / or phosphoniums can be used as a dispersion. In the case of (ii), it is preferable to use a seed crystal from which excess titanic acid has been removed by centrifugation.
As a method for producing the seed crystal titanate nanosheet, (i) a method of hydrothermally treating the titanate nanosheet dispersion stock solution is preferable. In addition, it is possible to grow titanate nanosheets by hydrothermally treating the titanate nanosheet dispersion stock solution. However, if the titanate nanosheet dispersion is too large, the titanate nanosheet dispersion stock solution is easily transferred to the anatase type. In order to suppress this, it is preferable to use a method of blending the seed crystal titanate nanosheet into the titanate nanosheet dispersion stock solution.

(Hydrothermal treatment conditions for preparation of seed crystal titanate nanosheet)
When hydrothermally treated seed crystal titanate nanosheets are used, the titanate nanosheet dispersion stock solution for seed crystals has an amines / Ti molar ratio of preferably 0.2 to 5, more preferably 0.3 to 3. belongs to. The TiO ₂ concentration in the dispersion stock solution is preferably 0.1 to 15% by mass, more preferably 0.5 to 10%, and most preferably 1 to 6%. Accordingly, the TiO ₂ concentration in the seed crystal titanate nanosheet dispersion is also a similar value.
The temperature of the hydrothermal treatment for adjusting the seed crystal is preferably 75 to 200 ° C, more preferably 100 to 150 ° C. If the temperature is too high, the crystals are transferred to anatase, and if the temperature is too low, no improvement in crystallinity is observed.
The hydrothermal treatment time is preferably 0.5 to 24 hours, more preferably 1 to 12 hours. In order to increase the particle size, the treatment may be performed for a long time when the hydrothermal treatment temperature is low and for a short time when the hydrothermal treatment temperature is high, but the above time is preferable in view of efficient production. As other hydrothermal treatment conditions, the hydrothermal treatment conditions described above can be used.

(Mixing of seed crystal titanate nanosheet and titanate nanosheet dispersion and hydrothermal treatment)
The TiO ₂ concentration of the titanate nanosheet dispersion stock solution to which the seed crystal is added and the molar ratio of amines / Ti / Ti are as described above.
The added amount of the seed crystal is such that the ratio of the seed crystal in the total amount of the titanate nanosheet and the seed crystal contained in the titanate nanosheet dispersion stock solution is preferably 1 to 90% by mass, more preferably 10% in terms of TiO ₂ concentration. It mixes so that it may become -80 mass%, More preferably, it is 20-75 mass%. In order to increase the volume-based average particle diameter of titanate nanosheets, it is usually sufficient to increase the ratio of titanate nanosheets from the seed crystal. In terms of suppression, the upper limit value or less is preferable. The seed crystal titanate nanosheet is preferably mixed with the titanate nanosheet dispersion stock solution as a dispersion.

In addition, the conditions of the hydrothermal treatment after adding the seed crystal titanate nanosheet to the titanate nanosheet dispersion undiluted solution can be performed under the same conditions as those shown when the seed crystal is not used.
The conditions for using the seed crystal titanate nanosheet dispersion are summarized as follows.
That in terms of TiO ₂ concentration of 0.1 to 15 wt% of the titanate nanosheet stock dispersion is TiO ₂ concentration in terms of seed crystals titanate nanosheet dispersion is 0.1 to 15 wt%, titanium seed crystals titanate nanosheet It is added in a range of 1 to 90% by mass in terms of TiO _{2 with} respect to the acid nanosheet dispersion stock solution, pH 10 to 13 (25 ° C.), temperature 75 to 200 ° C., pressure 0.8 to 1.5 MPa, treatment time 0. Hydrothermal treatment is performed for 5 to 24 hours.

<Method for controlling particle diameter of titanate nanosheet>
The average particle diameter of the titanate nanosheet can be controlled by performing a hydrothermal treatment. In addition, according to the method of adding seed crystal titanate nanosheet dispersion liquid to the titanate nanosheet dispersion stock solution and hydrothermal treatment, it becomes possible to control the average particle diameter of titanate nanosheets in a wide range, and the maximum average particle diameter The particle diameter of the titanate nanosheet can be controlled with a size up to 100 nm.
Specific control conditions include the following conditions.
TiO ₂ concentration in terms of titanium acid nanosheet stock dispersion is 0.1 to 15 wt%, the seed crystal TiO ₂ concentration in terms of titanium acid nanosheet dispersion is 0.1 to 15 wt%, seed crystals titanate nanosheet titanate It is added in a range of 1 to 90% by mass in terms of TiO _{2 with} respect to the nanosheet dispersion stock solution, pH 10 to 13 (25 ° C.), temperature 75 to 200 ° C., pressure 0.8 to 1.5 MPa, treatment time 0.5 It is characterized by hydrothermal treatment under conditions of up to 24 hours.

Increasing the TiO ₂ equivalent concentration of the titanate nanosheet dispersion stock solution or the seed crystal titanate nanosheet dispersion shows that the particle size growth tends to increase remarkably, and if the concentration is lowered, the particle size tends not to cause significant particle growth. Show. Further, when the TiO ₂ equivalent concentration of the seed crystal titanate nanosheet dispersion is increased, the particles are more likely to grow. In addition, in the mixing ratio of the seed crystal titanate nanosheet and the titanate nanosheet dispersion stock solution, the particle diameter can be effectively increased by increasing the seed crystal addition ratio.
Moreover, the particle diameter of the titanate nanosheet can be controlled by adjusting pH, temperature, pressure, and treatment time as the hydrothermal treatment conditions. That is, when the pH is lowered, the particle diameter tends to increase, and when the hydrothermal time is lengthened, the particle diameter tends to increase remarkably. When the pressure is increased, the particle diameter tends to increase, and the treatment temperature is increased. Then, the particle diameter tends to become remarkably large. If the crystal growth is advanced too much, it is dislocated to anatase, so each parameter for controlling the particle size is adjusted by appropriately adjusting.

According to the production method of the present invention, it is possible to control the average particle size by hydrothermal treatment, and it is possible to obtain titanate nanosheets of 5 nm or more, which is clearly superior to the titanate nanosheets in the conventional dispersion stock solution. Become. In addition, if a seed crystal titanate nanosheet is added, a product having a maximum average particle size of about 100 nm can be prepared.
That is, the present invention provides a new titanate nanosheet having a volume-based average particle diameter of 5 to 100 nm, preferably 10 to 90 nm, measured using a dynamic light scattering method in a dispersion having a TiO ₂ concentration of 1% by mass. To provide.
The volume-based average particle diameter can be measured by the method described in the examples.

<Titanate nanosheet dispersion>
Obtaining the titanate nanosheet of the present invention as a dispersion is preferable from the viewpoint of application development. The main component of the dispersion medium of the dispersion is preferably water or a water-soluble organic solvent from the viewpoint of versatility of the dispersion, storage stability, and cost. Examples of the water-soluble organic solvent include alcohols having 1 to 8 carbon atoms such as methanol, ethanol, isopropanol, n-butanol, and tertiary butanol, and 3 to 3 carbon atoms such as acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. 10 polar organic solvents such as ketones. In these, a C1-C6 alcohol is more preferable and methanol is especially preferable. These organic solvents can be used individually or in mixture of 2 or more types.
In order to maintain the transparency of the titanate nanosheet dispersion, the concentration of titanate nanosheet is 0.1 to 15% by mass, particularly 0.5 to 5% by mass in terms of TiO _2. It is preferable. The other conditions of the amines concentration, the amines / TiO ₂ dispersion, etc. are the same as the conditions shown in the above production method.

In the following examples and comparative examples, confirmation of the titanate nanosheet structure by Raman spectroscopy and measurement of the volume-based average particle diameter were performed by the following methods.
<Confirmation of titanate sheet structure by Raman spectroscopy>
The Raman spectrum of the solution was measured at room temperature using a Raman spectrometer (Nanofinder 30 manufactured by Tokyo Instrument Co., Ltd.) using an argon ion laser (wavelength 633 nm) as a light source, a grating of 600 grp / mm, and an integration time of 400 seconds. And measured by the transmission method.
<Measurement of volume-based average particle size>
A dispersion with a TiO ₂ concentration of 1% by mass (as it is when the concentration during hydrothermal treatment is less than 1% by mass) was prepared, and a nanotrack particle size distribution measuring device (UPA-EX150, dynamic light scattering) manufactured by Nikkiso Co., Ltd. Method), the refractive index of niobium oxide is 2.33, the refractive index of water is 1.333, the refractive index of ethanol is 1.361, and the particle size distribution is measured by capturing data 60 times. The volume-based average particle diameter was determined.

Example 1
(Production of titanate nanosheet dispersion stock solution)
An amine aqueous solution in which 0.05 mol (3.657 g) of diethylamine was dissolved in 160 g of distilled water was stirred, and 0.1 mol of titanium tetraisopropoxide [Ti (OiPr) ₄ ] was added to 10 mL of 2-propanol (28. The liquid in which 422 g) was dissolved was added dropwise as a titanium source. The solution became cloudy with the dropwise addition, but by continuing the stirring, a transparent solution containing titanate nanosheets, that is, a titanate nanosheet dispersion stock solution (TiO ₂ equivalent concentration: 4%) was obtained.
The titanium compound produced in this transparent solution has a lipidocrosite type titanate nanosheet structure as a result of measurement by the Raman spectroscopy, and the volume-based average particle size of the obtained titanate nanosheet is 1.5 nm. Met.
(Manufacture of seed crystal titanate nanosheet)
80 g of this titanate nanosheet dispersion stock solution was charged into a 100 mL autoclave (Teflon (DuPont, registered trademark) lining) and hydrothermally treated at 110 ° C. for 6 hours with stirring at 100 rpm. The resulting solution was a clear solution (TiO ₂ concentration: 4%).
As a result of measuring this dispersion solution by the Raman spectroscopy, it had a lipidocrocite-type titanate nanosheet structure, and the volume-based average particle diameter was 1.7 nm. This was used as a seed crystal.
(Hydrothermal treatment)
24 g of the obtained dispersion liquid (TiO ₂ concentration: 4%) containing seed crystal titanate nanosheets having a particle diameter of 1.7 nm was added to the transparent solution containing the titanate nanosheets obtained above (dispersion stock solution, TiO ₂ concentration: 4). %) 56 g was added and charged in an autoclave (amount of seed crystal added: 30% by mass in terms of TiO ₂ concentration). Thereafter, hydrothermal treatment was performed for 6 hours at 110 ° C. with stirring at 100 rpm. The resulting dispersion was a clear solution.
As a result of measuring this dispersion solution by the Raman spectroscopy, it had a lipidocrocite-type titanate nanosheet structure, and the volume-based average particle diameter was 17.1 nm.

Example 2
In Example 1, the same operation as in Example 1 was performed except that the seed crystal addition amount was 50% by mass in terms of TiO ₂ . As a result, the obtained titanate nanosheet had a lipidocrocite-type titanate nanosheet structure, and the volume-based average particle diameter was 40.0 nm.
Example 3
In Example 1, the same operation as in Example 1 was performed, except that the seed crystal addition amount was 75% by mass in terms of TiO ₂ . As a result, the obtained titanate nanosheet had a lipidocrocite-type titanate nanosheet structure, and the volume-based average particle diameter was 65.4 nm.
Example 4
In Example 1, the same operation as in Example 1 was performed except that the seed crystal addition amount was 20% by mass in terms of TiO ₂ . As a result, the obtained titanate nanosheet had a lipidocrocite-type titanate nanosheet structure, and the volume-based average particle diameter was 5.5 nm.

Example 5
An amine aqueous solution in which 0.05 mol (3.657 g) of diethylamine was dissolved in 160 g of distilled water was stirred, and 0.1 mol of titanium tetraisopropoxide [Ti (OiPr) ₄ ] was added to 10 mL of 2-propanol (28. The liquid in which 422 g) was dissolved was added dropwise as a titanium source. The solution became cloudy with the dropwise addition, but by continuing stirring, a transparent solution containing titanate nanosheets, that is, a titanate nanosheet dispersion stock solution was obtained (TiO ₂ equivalent concentration: 4%).
80 g of this transparent solution was charged into a 100 mL autoclave (Teflon (registered trademark) lining) and hydrothermally treated at 100 ° C. for 12 hours with stirring at 100 rpm. The resulting solution was a clear solution.
As a result of measuring this dispersion by the Raman spectroscopy, it had a lipidocrocite-type titanic acid nanosheet structure, and the volume-based average particle diameter was 6.0 nm.

  Since the titanic acid nanosheet of the present invention is controlled to a highly versatile particle size with an appropriate size, a coating agent for a functional film (a barrier film such as an ultraviolet shielding, a corrosion-resistant film, etc.), a dielectric thin film material In addition to catalysts and the like, it can also be used as an additive such as a resin (for example, a polyester resin) in which mixing of amines is not allowed.

Claims (6)

  A step of adding a seed crystal titanate nanosheet to a titanate nanosheet dispersion undiluted solution obtained by hydrolysis reaction of a titanium alkoxide and / or a titanium salt in the presence of amines and / or phosphoniums, and hydrothermally treating the solution. A method for producing a titanic acid nanosheet dispersion. A seed crystal titanate nanosheet is a dispersion obtained by hydrothermally treating a titanate nanosheet dispersion stock solution at 75 to 200 ° C. for 0.5 to 24 hours, or a lipidocrosite type layered titanate nanosheet obtained by a firing method The method for producing a titanic acid nanosheet dispersion according to claim 1, wherein the solid is added as a dispersion obtained by separating and dispersing a solid with a solution containing amines and / or phosphoniums.   A titanic acid nanosheet in which a seed crystal titanate nanosheet is added to a titanic acid nanosheet dispersion stock solution obtained by hydrolysis reaction of titanium alkoxide and / or titanium salt in the presence of amines and / or phosphoniums, and hydrothermally treated. Control method of particle diameter.   Obtained by adding seed crystal titanate nanosheet to titanate nanosheet dispersion stock solution obtained by hydrolysis reaction of titanium alkoxide and / or titanium salt in the presence of amines and / or phosphoniums, and hydrothermally treating again. The titanate nanosheet. 5. The titanate nanosheet according to claim 4, wherein a volume-based average particle diameter measured by a dynamic light scattering method in a dispersion having a TiO ₂ concentration of 1% by mass is 5 to 100 nm.   A titanate nanosheet dispersion containing the titanate nanosheet according to claim 4.