JP4591847B2 - Layered double hydroxide and composition containing the same - Google Patents

Description

  The present invention relates to a layered double hydroxide which has a good dispersibility in an organic solvent and gives a dispersion liquid transparent to visible light.

A compound called layered double hydroxide or hydrotalcite is a layered compound represented by the following general formula.
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] [A ^n- _{x / n} · mH ₂ O]
(Wherein, M ²⁺ is a divalent metal ion, M ³⁺ is a trivalent metal ion, A ^n-in interlayer anion, m is an appropriate real number, n represents a positive integer, x is a positive not exceeding 1 Real number.)
In the above general formula, [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] in the first half is a metal hydroxide layer called a base layer or a host layer of a layered double hydroxide. It has a structure in which layers called an intermediate layer or guest layer composed of anions and water molecules in the latter half of the general formula are alternately stacked.

  This layered double hydroxide is used as an anion exchanger, anion adsorbent, catalyst, precursor of composite metal oxide, and also used as a resin additive such as flame retardant and stabilizer. It has been. Recently, as the expectation for the creation of composite materials at the molecular level or nanometer size has increased, attempts to obtain a dispersion in which the layered double hydroxide layer is exfoliated to the molecular size level are becoming active (Non Patents). Reference 1). There is a possibility that a material called a nanocomposite exhibits excellent characteristics that are not found in conventional composite materials in terms of mechanical characteristics, gas permeability, optical characteristics, and the like.

When using a layered double hydroxide as a raw material for a nanocomposite material, establishment of a technique for peeling and dispersing the layered double hydroxide into a basic single layer in an organic solvent is strongly demanded. The means adopted to peel the layered double hydroxide to the basic layer unit of the inorganic layer is based on inserting an appropriate organic molecular anion between the hydroxide layers to make the inorganic layer oleophilic. It is said. In this respect, the selection of organic molecular ions for modifying the interlayer is extremely important, and the use of dodecyl sulfate and amino acids has been attempted so far. For example, an attempt has been made to obtain a stable dispersion by dispersing a layered double hydroxide whose layer is modified with dodecylsulfuric acid well in butanol (Non-patent Document 2). In addition, a method utilizing the fact that the layered double hydroxide modified with glycine and dispersed in formamide is disclosed (Patent Document 1). However, the dispersion obtained by these methods has remained at a translucent level, and a dispersion that is transparent to visible light has not been obtained.
F. Leroux and J.-P. Besse, 2001, Chemistry of Materials, Vol. 13, pages 3507-3515 M. Adachi-Pagano, C. Foragno and JP. Besse, 2000 Chem. Commun., 2000, 91-92 JP 2003-226681 A

  The object of the present invention is to separate and disperse the basic layer unit of the layered double hydroxide, whereby it is dispersed in an organic solvent at a molecular level or close to the molecular level, and is transparent to visible light. It is to provide a layered double hydroxide that gives a dispersion.

[1]
It is a layered double hydroxide represented by the following formula [1], and has a structure in which a base layer and an intermediate layer are alternately stacked, and A ⁻ of the intermediate layer contains fluorine represented by the following formula [2] A layered double hydroxide characterized by being an imide ion.
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] [A ^n- _{x / n} · mH ₂ O] [1]
( ^Wherein M ²⁺ is a divalent metal ion, M ³⁺ is a trivalent metal ion, m is a real number of 0 or more, n is a positive integer, x is a positive real number not exceeding 1, [M ²⁺ _{1 -x} M ³⁺ _x (OH) ₂ ] is the basic layer, [A ^n- _{x / n} · mH ₂ O] is the intermediate layer)
[R1X] [R2Y] N ^- ... [2]
(Wherein R1 and R2 are alkyl groups having 1 to 12 carbon atoms, all or part of which are substituted with fluorine, and the same or different from each other, X and Y are CO groups or SO ₂ groups that are the same or different from each other)
[2]
[1] The anion of the intermediate layer contains a perfluoroalkyl sulfonic acid imide ion represented by (C ₄ F ₉ SO ₂ ) ₂ N ⁻ , and the basic layer contains [(Mg ₃ Al) (OH) ₈ ] ⁺ The layered double hydroxide described in the above.
[3]
The above [1] or [2] obtained by coprecipitation of a divalent metal salt, a trivalent metal salt, and a fluorine-containing imide salt by mixing them in an aqueous solution under neutral or alkaline conditions. A layered double hydroxide described in any of the above.
[4]
The above is a product produced by precipitation, subsequent aging, washing and drying in an environment in which a fluorine-containing imide salt is used at least 1.2 times the trivalent metal salt and carbon dioxide and carbonate ions are excluded. 3] The layered double hydroxide described in [3].
[5]
An alcohol dispersion of the layered double hydroxide according to any one of [1] to [4] above, wherein the dispersion has a transmittance of 90% or more in a wavelength region of 300 nm to 1100 nm.

[Specific description]
The present invention will be specifically described below.
In order to realize a transparent dispersion in which the layered double hydroxide is peeled and dispersed to the metal hydroxide layer of the basic layer, the affinity between the organic anion that modifies the interlayer and the dispersion medium molecule and the Size control is an important key. The present invention has achieved a layered double hydroxide that can produce a transparent dispersion in the visible light region when dispersed in alcohol by using a fluorine-containing imide molecular ion as an interlayer modifier. That is, the present invention provides a layered double hydroxide having a fluorine-containing imide molecular ion between layers, and a transparent liquid material in which this is dispersed in an alcohol solvent.

(Layered double hydroxide)
The layered double hydroxide of the present invention is a layered double hydroxide having a base layer of metal hydroxide and an anion between layers, and contains a fluorine-containing imide molecular ion as an anion between layers. Specifically, for example, the metal hydroxide of the base layer contains a divalent metal ion and a trivalent metal ion, and the anion between the layers is represented by the general formula [A ⁿ⁻ _{x / n} · mH. includes a fluorine-containing imide molecule ion represented by ₂ O], those having a basic layer made of a metal hydroxide, a structure in which the intermediate layer are laminated alternately consisting of anions and water molecules.

An example of the layered double hydroxide of the present invention is represented by the following general formula.
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] [A ^n- _{x / n} · mH ₂ O] [1]
In the general formula [1], M ²⁺ is a divalent metal ion derived from the used metal salt, M ³⁺ is a trivalent metal ion derived from the used metal salt, and [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] is a metal hydroxide layer called a layered double hydroxide base layer or host layer. [A ⁿ⁻ _{x / n} · mH ₂ O] in the latter half of the above general formula is an intermediate layer composed of anions and water molecules, and A ⁻ represents a fluorine-containing imide ion. Here, x is a real number not exceeding 1, n is a positive integer, and m is a real number of 0 or more.

Specifically, the divalent metal ions constituting the basic layer of the layered double hydroxide are Mg ²⁺ , Zn ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ^2+, etc. The valent metal ions are Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Co ³⁺ , Ga ^{3+ and the} like. Further, x in the above structural formula is preferably 0.17 to 0.40. A specific example of this basic layer is [(Mg ₃ Al) (OH) ₈ ] ⁺ or the like.

The fluorine-containing imide ion (A ⁻ ) that forms the interlayer anion in the above general formula is given by, for example, a fluorine-containing imide compound represented by the following formula (2).
(Wherein R1 and R2 are alkyl groups having 1 to 12 carbon atoms, all or part of which are substituted with fluorine, which may be the same or different from each other, and X And Y are CO groups or SO ₂ groups, which may be the same or different from each other.

The fluorine-containing imide ion (2) is specifically a perfluoroalkyl sulfonic acid imide ion represented by, for example, (C ₄ F ₉ SO ₂ ) ₂ N ⁻ .

[Preparation of the layered double hydroxide]
The layered double hydroxide can be obtained by mixing a bivalent metal salt, a trivalent metal salt, and a fluorine-containing imide molecular salt in an aqueous solution state under neutral or alkaline conditions and co-precipitation. The amount of fluorine-containing imide molecular salt used may be equivalent to the amount of trivalent metal ions in the aqueous metal salt solution, but is preferably 1.2 times or more than the amount of trivalent metal ions.

  In addition, when carbonate ions are generated by dissolution of carbon dioxide present in the air, or when carbonate ions are present in the starting material and the water used, this is mixed into the product (layered double hydroxide), and this layered double hydroxide. When it is dispersed in a solvent such as alcohol, the peeling phenomenon to the basic unit layer may be difficult to occur. Therefore, the precipitation synthesis of the layered double hydroxide and the subsequent ripening / washing / drying steps are preferably performed in an environment in which carbon dioxide and / or carbonate ions are excluded, such as in a nitrogen stream. Furthermore, it is preferable to remove carbonate ions in advance for water to be used.

The above-described synthesis method by coprecipitation involves preparing an aqueous solution in which divalent and trivalent metal nitrates, chlorides or sulfates are dissolved, and slowly dropping the aqueous solution into an aqueous solution in which a fluorine-containing imide salt is dissolved. A method of precipitation is preferred. In this case, an aqueous NaOH solution or the like is appropriately added so that the pH is always on the neutral or alkaline side.

(Dispersion of layered double hydroxide)
When the layered double hydroxide obtained by the above precipitation synthesis is dispersed in an appropriate organic solvent such as butyl alcohol, each basic layer is very easily peeled off and dispersed in the solvent. When the layered double hydroxide is put into an appropriate alcohol, the basic layer is peeled off by simply stirring, and more preferably, it is easily peeled off by irradiating with ultrasonic waves for a short time and is transparent to visible light. Can be obtained. In addition to butanol, pentanol, hexanol, heptanol, and isomers thereof can be used as the dispersion solvent.

The mechanism of obtaining a layered double hydroxide dispersion transparent to visible light is considered to be closely related to the form of the resulting fluorine-containing imide ion insert and the physicochemical properties of the layer surface. When the layered double hydroxide of the present invention was observed with an electron microscope, the secondary aggregated particles were several μm, but the size of the primary particles constituting the particles was small and the thickness was 10 nm to 30 nm. It was found that the thickness was about 100 nm, and the flatness of each surface was poor, and it took a curved or wavy form. Also, from the X-ray diffraction pattern, the bottom surface spacing of the layered double hydroxide is estimated to be about 22 mm.

A molecular model of the layered double hydroxide of the present invention estimated based on this is shown in FIG. This figure shows a layered double hydroxide containing (C ₄ F ₉ SO ₂ ) ₂ N ⁻ as an interlayer imide ion and [(Mg ₃ Al) (OH) ₈ ] ⁺ as a layered hydroxide host. Yes.

  When the above-mentioned layered double hydroxide of the present invention forms aggregated particles, it is considered that organic solvent molecules easily enter between the particles and become a first factor that causes peptization to primary particles. In addition, as shown in FIG. 1, the perfluorosulfonic acid imide is composed of a polar part and an extremely hydrophobic part in which perfluorosulfonic acid imide is interposed between the basic layers. And high affinity at the molecular level causes swelling due to penetration of solvent molecules between layers. As a result, the layered double hydroxide layer can be peeled off at the basic unit layer level and dispersed as fine particles. This is considered to be a second factor that brings about high dispersibility.

  The layered double hydroxide according to the present invention can be easily peeled and dispersed to the unit of the basic layer, and a dispersion liquid transparent to visible light can be obtained by dispersing the layered double hydroxide in alcohol or the like. Obtainable. Therefore, new possibilities can be opened for molecular design of nanocomposites with functional organic molecules. As a result, it is expected to be used in a wide variety of fields such as resin compounding, paints, cosmetics, and optical functional materials, and at the same time, various applications to nanotechnology, which is a new technology in the future, are possible.

  Examples of the present invention are shown below. The scope of the present invention is not limited to the examples.

Magnesium chloride and aluminum chloride were weighed so that the molar ratio was Mg: Al = 3: 1, and water was added to make an aqueous solution having a concentration of Mg ⁺ Al = 0.2 mol / L. Separately, 1.2 times the molar amount of perfluoroalkyl sulfonic acid imide potassium salt [(C ₄ F ₉ SO ₂ ) ₂ NK] of aluminum chloride is dissolved in water, and then a 1 mol / L NaOH aqueous solution is added. The pH was adjusted to 10 by adding an appropriate amount. To this was added the magnesium chloride-aluminum chloride aqueous solution at a rate of 30 mL / hour. At this time, 1 mol / L NaOH aqueous solution was appropriately added so that the pH of the mixed solution was always 10. The dispersion obtained after completion of the dropping was aged in a constant temperature bath at 70 ° C. overnight. The coprecipitate obtained above was washed with water, filtered, dried with a vacuum drier, and then ground using an agate mortar to obtain a powder sample. The obtained powder sample was measured with an X-ray diffractometer, and it was confirmed that the layered material had a bottom surface spacing of 21.8 mm. Further, by FI-IR analysis, absorption derived from the perfluoroalkyl sulfonic acid imide molecule and absorption derived from the layered double hydroxide are detected at the same time, and the layered double water having the imide ion between the layers together with the result of the above XRD. It was confirmed to be an oxide. When this layered double hydroxide was added to an appropriate amount of hexanol and irradiated with ultrasonic waves at 100 W for 1 hour, a transparent liquid with no solid phase precipitated at the bottom of the container was obtained by peeling off the basic layer. The concentration of the dispersion at this time was 1 g / L. When the absorption spectrum of this dispersion was measured using a visible ultraviolet spectrophotometer, the transmittance was 90% or more over the entire wavelength range from 300 nm to 1100 nm.

  0.1 g of the powder obtained in Example 1 was added to 100 mL of various alcohols (butanol, pentanol, hexanol, heptanol) and irradiated with ultrasonic waves at 100 W for 1 hour. A transparent liquid without a solid phase was obtained. When these dispersions were measured for absorption spectra using a visible ultraviolet spectrophotometer, they showed a transmittance of 90% or more over the entire wavelength range from 300 nm to 1100 nm.

  A powder was obtained under the same conditions as in Example 1 except that the Mg: Al ratio was changed to 4: 1, 2: 1. The obtained powder sample was measured by an X-ray diffractometer, and confirmed to be a layered material having a bottom surface spacing of 20.8 mm (4: 1) and 21.9 mm (2: 1). When an appropriate amount of the above alcohol was added to the layered double hydroxide and stirred, a transparent liquid without a solid phase precipitated at the bottom of the container was obtained by peeling off the basic layer. When the absorption spectrum of this dispersion was measured using a visible ultraviolet spectrophotometer, the transmittance was 90% or more over the entire wavelength range from 300 nm to 1100 nm.

Schematic diagram showing the structure of the layered double hydroxide of the present invention

Claims (5)

It is a layered double hydroxide represented by the following formula [1], and has a structure in which a base layer and an intermediate layer are alternately stacked, and A ⁻ of the intermediate layer contains fluorine represented by the following formula [2] A layered double hydroxide characterized by being an imide ion.
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] [A ^n- _{x / n} · mH ₂ O] [1]
( ^Wherein M ²⁺ is a divalent metal ion, M ³⁺ is a trivalent metal ion, m is a real number of 0 or more, n is a positive integer, x is a positive real number not exceeding 1, [M ²⁺ _{1 -x} M ³⁺ _x (OH) ₂ ] is the basic layer, [A ^n- _{x / n} · mH ₂ O] is the intermediate layer)
[R1X] [R2Y] N ^- ... [2]
(Wherein R1 and R2 are alkyl groups having 1 to 12 carbon atoms, all or part of which are substituted with fluorine, and the same or different from each other, X and Y are CO groups or SO ₂ groups that are the same or different from each other) Anions of the intermediate _{layer, (C 4 F 9 SO 2} ) 2 N - include perfluoroalkyl sulfonic acid imide ion represented by the claims 1 basic layer comprises ⁺ _{[(Mg 3 Al) (OH)} 8 ] The layered double hydroxide described in 1. 3. The method according to claim 1, wherein the bivalent metal salt, the trivalent metal salt, and the fluorine-containing imide salt are obtained by coprecipitation by mixing in an aqueous solution under neutral or alkaline conditions. The layered double hydroxide described in the above. A fluorine-containing imide salt is produced by precipitating and subsequent aging, washing and drying in an environment in which 1.2 times or more of a trivalent metal salt is used and carbon dioxide and carbonate ions are excluded. 3. The layered double hydroxide described in 3. The transparent dispersion of the layered double hydroxide according to any one of claims 1 to 4, which exhibits a transmittance of 90% or more in a wavelength region of 300 nm to 1100 nm.