JP2013103860A - Method for producing hollow nanoparticle comprising mesoporous silica shell - Google Patents

Abstract

The present invention provides a simple and highly efficient production method of nano hollow particles composed of silica shells having a mesopore structure with an average pore diameter of 1 to 10 nm.
A surfactant micelle structure is formed on the surface of calcium carbonate by mixing a surfactant aqueous solution with calcium carbonate whose shape is controlled to a nano size, and a mesocorresponding to the micelle structure is formed by reaction of silicon alkoxide. Nano hollow particles made of a silica shell having a pore structure are produced.
[Selection] Figure 6

Description

The present invention relates to a method for producing nano hollow particles comprising a silica shell having a mesoporous structure.

It is known that porous inorganic particles are used as a carrier for the purpose of use in medicine, agricultural chemicals, cosmetics and the like. In particular, silica shells having uniform mesopores of several nanometers and hollow particles having a hollow structure inside the silica shell, a large amount of active ingredients such as drugs, agricultural chemicals, and cosmetics in the above applications are contained in the hollow structure. The active ingredient can be sustainedly released using the mesopore structure. With the development of nanotechnology, by making the hollow particles into nano-sized hollow particles and by changing the shape of the hollow particles in various ways, the sustained release performance can be controlled more precisely. The application range can be expected to expand. Patent documents 1 and 2 are inventions related to the porous inorganic particles.

The technique described in Patent Document 1 uses a particle made of polymethyl methacrylate as a core, forms a layer of a cationic surfactant in the form of micelles on the surface of the core particle, and performs hydrolysis and condensation reaction on the surface of the micelle. A method of producing nano hollow particles comprising silica shells having mesopores corresponding to the alkyl chain length of the surfactant by removing the surfactant and the core particles by adding the silicon alkoxide and heat-treating is there.

The hollow particles composed of silica shells having mesopores described in Patent Document 1 have an average particle size of 0 by producing core particles having a desired diameter and controlling the type and concentration of the surfactant. 0.04 to 2 μm and mesopores having an average pore diameter of 1 to 5 nm. However, the polymethyl methacrylate particles that are core particles are produced only in a spherical form due to their properties, and it is difficult to stably produce a particle diameter of 100 nm or less. Furthermore, since the interaction force between the core particle surface and the surfactant is small, there is a problem that the core particle surface needs to be modified as a pretreatment.

The technique described in Patent Document 2 relates to a method for producing a hollow particle including an outer shell portion having a mesoporous structure containing silica and a hollow portion present inside the outer shell portion, and is hydrophobic. Pressurizing a mixed solution containing an organic compound, a surfactant, and an aqueous solvent by a high-pressure emulsification method to form an emulsion containing emulsion droplets containing the hydrophobic organic compound; and adding silica to the emulsion. A composite silica particle in which a source is added, an outer shell portion having a mesoporous structure containing silica is formed on the surface of the emulsified droplet, and the emulsified droplet is included inside the outer shell portion and the outer shell portion Is a method for producing hollow particles made of silica shells having mesopores, the method comprising the step of precipitating and the step of removing the emulsified droplets from the composite silica particles.

The hollow mesoporous silica particles of the invention described in Patent Document 2 are nano hollow particles having an average pore diameter in the range of 1 to 3 nm and an average particle diameter of 0.005 to 0.2 μm, and 500 to 1500 m. ^Since it has a large specific surface area of ² / g, it is effective to use the nano hollow particles as a catalyst or a drug carrier. However, in order to form the structure, the micelle and the hydrophobic organic compound solution are mixed while the micelle of the surfactant is mixed in a mixture of the surfactant and the aqueous solvent, and the hydrophobic solution is mixed in the aqueous solvent. Many steps are required to form spherical droplets of the organic compound solution, stack the micelles on the surface of the hydrophobic organic compound solution droplets, add a silica source, and form a silica layer on the micelle surface. is there. Furthermore, in order to reduce the droplet diameter, it is necessary to subject the mixed solution of the micelle aqueous solvent and the hydrophobic organic compound solution to high-pressure emulsification multiple times, and a multilayer formed on the surface of the droplets by multiple treatments There was a problem that the micelle structure was destroyed.

JP2010-037150 JP2011-132044

An object of the present invention is to solve the problems of the prior art, and does not require a complicated process or apparatus, is easy to control the form, and has a nano-sized mesoporous structure. It is providing the hollow particle which consists of stably.

  The present inventors have found that the above-mentioned problems can be solved by using calcium carbonate whose shape is controlled in nano size. That is, according to the present invention, the following method is provided.

[1] Nano hollow particles composed of a silica shell having a mesopore structure with an average pore diameter of 1 to 10 nm and a method for producing the same, a mixed solution containing a surfactant and an aqueous solvent, and calcium carbonate particles The dispersion liquid dispersed in a solvent is mixed, and further, silicon alkoxide and a base catalyst are mixed, and silica coating is performed on the surface of the calcium carbonate particles, and then the calcium carbonate particles and the surface activity inside the silica coating particles. A method for producing nano hollow particles comprising silica shells, wherein the agent is removed.

[2] The method for producing nano-hollow particles according to [1], wherein the shape of the nano-hollow particles made of the silica shell is spherical, spheroid, cylindrical, or cubic.

[3] The method for producing nano hollow particles according to [1] or [2], wherein the nano hollow particles comprising the silica shell have an average particle diameter of 30 to 300 nm.

[4] The method for producing nano hollow particles according to any one of [1] to [3], wherein the silica shell has a shell thickness of 3 to 20 nm.

[5] The above-mentioned [1] to [4], wherein the surfactant is one or more surfactants selected from quaternary ammonium salts represented by the following general formula (1) and general formula (2). The manufacturing method of the nano hollow particle in any one.
[R ₁ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ₁ R ₂ (CH ₃ ) ₂ N] ⁺ X ⁻ (2)
(In the formula, R ₁ and R ₂ each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, and X represents a monovalent anion.)

According to the present invention, nano hollow particles composed of silica shells having a mesoporous structure are mixed with a mixed solution containing a surfactant and an aqueous solvent, and a dispersion in which calcium carbonate particles are dispersed in an organic solvent, Further, by mixing a silicon alkoxide and a base catalyst and removing the calcium carbonate particles and the surfactant by heating, nano hollow particles composed of a silica shell having a mesoporous structure can be easily provided.

The calcium carbonate particles can be produced in a spherical, spheroid, cylindrical, or cubic form, and nano-sized particles of 500 nm or less can be easily and stably produced. By using the calcium carbonate particles having various shapes as the core particles, it is possible to produce nano hollow particles reflecting the shape of the core particles without requiring a complicated process.

Furthermore, since the interaction force between the surface of the calcium carbonate particles and the surfactant is large, a micellar surfactant layer is easily formed on the surface of the calcium carbonate particles, and hydrolyzed silicon alkoxide is added to the micelle surface. Can do. Therefore, it is possible to produce silica shells having mesopores corresponding to the alkyl chain length of the surfactant with high efficiency without requiring any pretreatment on the surface of the core particles.

It is a TEM photograph of the nano hollow particle which concerns on Example 1 of this invention. It is a TEM photograph of nano hollow particles concerning Example 2 of the present invention. It is a TEM photograph of the nano hollow particle which concerns on Example 3 of this invention. It is a TEM photograph of the nano hollow particle which concerns on Example 4 of this invention. It is a TEM photograph of the nano hollow particle which concerns on Example 6 of this invention. It is a TEM photograph of the nano hollow particle which concerns on Example 8 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

Nano hollow particles comprising a silica shell having a mesoporous structure obtained by the present invention are hollow mesoporous silica comprising an outer shell portion having a mesoporous structure containing silica and a hollow portion inside the outer shell portion. Particles. The mesopore structure of the silica shell has an average pore diameter determined by a small angle X-ray scattering method of 1 to 10 nm, preferably 1 to 3 nm. The “mesopore structure” is a structure having a pore diameter of 1 to 10 nm and having a plurality of regularly arranged pores. The mesopore structure is formed, for example, by micellization of a cationic surfactant and self-organization of a silica source on the micelle surface.

The shape of the nano hollow particle composed of a silica shell having a mesopore structure is a spherical shape, a spheroid shape, a cylindrical shape, or a cubic shape. Here, “spherical” means not only a sphere but also a shape similar to a sphere surrounded by a surface, and “spheroid” means not only a spheroid but also a spheroid surrounded by a surface. A “cylindrical shape” refers to a shape similar to a cylinder, not limited to a cylinder, and a “cubic shape” refers to a shape similar to a cube surrounded by a face, not limited to a cube. The hollow particles made of silica shells having such a spherical, spheroid, cylindrical, or cubic form are, for example, spherical, spheroid, cylindrical, or cubic form in a dry powder state. Of calcium carbonate particles. The average particle diameter of the hollow particles is the average of the major axis and minor axis in the case of a spheroid, the average of the diameter and length of the bottom surface of the cylinder in the case of a cylinder, and the length of one side in the case of a cube. Say.

The nano hollow particles made of silica shells of the present invention are nano hollow particles made of silica shells having a mesoporous structure, in which a mixed liquid containing a surfactant and an aqueous solvent, and calcium carbonate particles are dispersed in an organic solvent. Nano hollow particles composed of a silica shell having a mesoporous structure obtained by mixing the dispersed liquid, further mixing silicon alkoxide and a base catalyst, and removing the calcium carbonate particles and the surfactant by heating.

Here, the “organic solvent” is not particularly limited as long as it is soluble in silicon alkoxide and water and can further promote the hydrolysis of silicon alkoxide, such as alcohols, glycols, glycol esters, acetone. And the like, and simple solvents such as aliphatic carbons and aromatic hydrocarbons, or a mixed solvent of two or more of these, and alcohols are preferable.

The “silicon alkoxide” is not particularly limited as long as silica can be precipitated by hydrolysis thereof. For example, tetraethoxysilane, trimethoxysilane, tetramethoxysilane, triethoxysilane, tripropoxysilane, tetrapropoxysilane, Butoxysilane, tributoxysilane, or the like can be used. In addition, examples of the “base catalyst” include ammonia and amines.

The surfactant is preferably one or more surfactants selected from quaternary ammonium salts represented by the following general formula (1) and general formula (2).
[R ₁ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ₁ R ₂ (CH ₃ ) ₂ N] ⁺ X ⁻ (2)
(In the formula, R ₁ and R ₂ each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, and X represents a monovalent anion.)

In addition, in the manufacturing method of patent document 2, as above-mentioned, it turned out that manufacture of the nano hollow particle which consists of a silica shell which has a mesopore structure is not easy. The inventors of the present application have found that the above reason is that the mesopore structure is destroyed by a plurality of high-pressure emulsification treatments necessary to obtain nano-sized hollow particles.

A method for producing nano hollow particles comprising a silica shell having a mesoporous structure according to the present invention (hereinafter sometimes abbreviated as “production method of the present invention”) will be described. According to the production method of the present invention, for example, nano hollow particles having an average pore diameter of 1 to 10 nm, preferably 1 to 3 nm, and an average particle diameter of 5 to 200 nm can be easily produced.

[Adjustment of liquid mixture]
In the production method of the present invention, first, a mixed solution containing a surfactant and an aqueous medium is prepared. Adjustment of a liquid mixture is performed by adding surfactant to an aqueous medium, for example. The temperature of the mixed liquid during stirring is preferably maintained at 0 to 90 ° C. from the viewpoint of preventing evaporation of the aqueous medium and suppressing variation in the concentration of the surfactant in the mixed liquid.

[Preparation of dispersion containing calcium carbonate]
A dispersion in which calcium carbonate as a dry powder is dispersed in an organic solvent is prepared. The dispersion can be adjusted, for example, by adding calcium carbonate to an organic solvent and stirring. There is no restriction | limiting in particular about the kind of stirrer used for the said stirring. Examples of the stirrer include a homomixer, a homogenizer, and an ultrasonic disperser. As a commercially available stirrer, for example, Disper (manufactured by PRIMIX), Clearmix (manufactured by M-Technique), Cavitron (manufactured by Taiheiyo Kiko) and the like can be used. The temperature of the mixed liquid during stirring is preferably maintained at 0 to 90 ° C. from the viewpoint of preventing evaporation of the aqueous medium and suppressing variation in the concentration of the surfactant in the mixed liquid.

As the surfactant used in the production method of the present invention, one or more surfactants selected from quaternary ammonium salts represented by the following general formula (1) and general formula (2) are preferable.
[R ₁ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ₁ R ₂ (CH ₃ ) ₃ N] ⁺ X ⁻ (2)
(In the formula, R ₁ and R ₂ each independently represents a linear or branched alkyl group having 4 to 22 carbon atoms, and X represents a monovalent anion.)

R ₁ and R ₂ in the above general formula (1) and general formula (2) are each independently preferably from 6 to 18 carbon atoms, more preferably carbon from the viewpoint of improving the utilization rate of the hydrophobic organic compound. It is a linear or branched alkyl group of formula 8-16. Examples of the alkyl group having 4 to 22 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, and various hexadecyl groups. , Various octadecyl groups, various eicosyl groups, and the like.

X in the general formula (1) and the general formula (2) is preferably a monovalent anion such as a halogen ion, hydroxide ion, nitrate ion, or sulfate ion from the viewpoint of forming highly regular mesopores. One or more selected from ions. X is more preferably a halogen ion, still more preferably a chlorine ion or a bromine ion, and still more preferably a bromine ion.

Examples of the alkyltrimethylammonium salt represented by the general formula (1) include butyltrimethylammonium chloride, hexyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethyl Ammonium chloride, stearyltrimethylammonium chloride, butyltrimethylammonium bromide, hexyltrimethylammonium bromide, octyltrimethylammonium bromide, decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide Bromide, stearyl trimethyl ammonium bromide, cetyltrimethylammonium bromide (CTAB), and the like.

Examples of the dialkyldimethylammonium salt represented by the general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, dihexyldimethylammonium bromide, dioctyldimethylammonium bromide, didodecyldimethylammonium bromide, ditetradecyl. Examples thereof include dimethylammonium bromide.

Among these quaternary ammonium salts, from the viewpoint of forming regular mesopores, the alkyltrimethylammonium salt represented by the general formula (1) is particularly preferable, and alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is more preferable. preferable.

These surfactants may be used alone or in admixture of two or more at any ratio. The content of the surfactant in the mixed solution containing calcium carbonate may be appropriately adjusted according to the surface area of the calcium carbonate in the mixed solution, but the yield of nano hollow particles composed of silica shells having a mesoporous structure And from a viewpoint of improving dispersibility, it is preferable in it being 0.1-100 mmol / L. More preferably, it is 10-85 mmol / L.

[Formation of silica-containing mesoporous structure and removal of calcium carbonate]
In the production method of the present invention, a silica source is added to the mixed liquid containing calcium carbonate prepared as described above, and an outer shell portion having a mesoporous structure containing silica is formed on the surface of calcium carbonate, Composite silica particles containing an outer shell and calcium carbonate existing inside the outer shell are deposited. The shell thickness of the silica shell can be changed by the addition ratio of silicon alkoxide and calcium carbonate (silicon alkoxide / CaCO ₃ ). Then, the calcium carbonate particles and the surfactant are removed by heating to obtain nano hollow particles composed of a silica shell having a mesoporous structure.

A surfactant aqueous solution is prepared by mixing cetyltrimethylammonium bromide (CTAB) with distilled water to a concentration of 10 to 85 mmol / L. Meanwhile, cubic calcium carbonate particles are dispersed in ethanol as core particles and mixed with the CTAB aqueous solution. Tetraethoxysilane (TEOS) and a 28% aqueous ammonia solution (NH ₄ OH) were added to the mixed solution, and a CTAB film and a silica coating were applied to the calcium carbonate surface by a sol-gel method to obtain core-shell particles. The core-shell particles were dispersed in distilled water, and the core particles were dissolved and removed using a 3N hydrochloric acid aqueous solution to obtain nano hollow particles composed of silica shells having mesopores. Table 1 below shows the blending amounts of various reagents, the reaction conditions, the shell thickness of the manufactured nano hollow particles of silica shell, the average pore diameter of the silica shell, and the specific surface area of the hollow particles. The silica shell thickness was measured from the TEM observation results, the average pore diameter of the silica shell was calculated by X-ray small angle scattering, and the specific surface area was calculated using the BET equation.

1 to 6 show TEM photographs of nano hollow particles produced under the conditions of Examples 1, 2, 3, 4, 6, and 8. It can be seen that a mesopore structure is formed in the silica shell. When cetyltrimethylammonium bromide (CTAB) is added to the calcium carbonate dispersion, mesopores are formed in the silica shell, but no mesopores are formed in the silica shell under the conditions where CTAB is not added (Comparative Example 1). ).

Claims (5)

Nano hollow particles composed of silica shells having a mesopore structure with an average pore diameter of 1 to 10 nm and a method for producing the same, a mixed liquid containing a surfactant and an aqueous solvent, and calcium carbonate particles as an organic solvent Mix the dispersed dispersion, mix silicon alkoxide and base catalyst, apply silica coating on the surface of the calcium carbonate particles, and then remove the calcium carbonate particles and the surfactant inside the silica coating particles. A method for producing nano-hollow particles comprising a silica shell having a mesoporous structure. The method for producing nano hollow particles according to claim 1, wherein the shape of the nano hollow particles made of the silica shell is spherical, spheroid, cylindrical, or cubic. The nano hollow particle according to claim 1 or 2, wherein the nano hollow particle composed of a silica shell having a mesoporous structure has an average particle diameter of 30 to 300 nm. The method for producing nano hollow particles according to any one of claims 1 to 3, wherein a shell thickness of the silica shell having the mesopore structure is 3 to 20 nm. The said surfactant is 1 or more types of surfactant chosen from the quaternary ammonium salt represented by following General formula (1) and General formula (2), Nano in any one of Claims 1-4 A method for producing hollow particles.
[R ₁ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ₁ R ₂ (CH ₃ ) ₂ N] ⁺ X ⁻ (2)
(In the formula, R ₁ and R ₂ each independently represent a linear or branched alkyl group having 4 to 22 carbon atoms, and X represents a monovalent anion.)