JP4671216B2 - Mesoporous silica nanoparticles having micropores and method for producing the same - Google Patents

Description

  The present invention relates to a porous structure having both micropores and mesopores and a nano-level size of several tens of nanometers used as a catalyst support, molecular sieves, adsorbent, etc. utilizing the chemical and structural characteristics of silica. The present invention relates to a novel silica nanoparticle having a spherical shape and a method for producing the same.

  Silica (silicon oxide) is a chemically stable compound, and is highly safe for the human body and the environment. Amorphous materials containing this as a main component are high-grade products such as windows and tableware glass, and recently optical fiber glass. On the other hand, crystalline materials represented by quartz have been put into practical use as oscillation elements. Silica gel and porous glass are solids that have a secondary particle structure or pore structure formed on silica and have a high surface area and a high pore volume. They are used as adsorbents, carriers, and mold materials in a wide range of industrial fields. In particular, silica gel is used for various applications such as desiccant for packaged food and gas dehumidification, clarifier for beer, filler for chromatography, fluid catalyst carrier, carrier for pulverizing pharmaceutical products.

Porous glass is prepared by dissolving a specific phase in a phase-divided glass structure, whereas in 1992, a surfactant was used as a template to create mesopores with a diameter of 2 nm or more and 1000 m ² / g. A method for creating a porous silica material having a larger specific surface area was developed by Mobil (Non-Patent Document 1). That is, by reacting a silicic acid component using cetyltrimethylammonium bromide (CTAB) as a template, cylindrical pores having a diameter of 2 to 8 nm formed a two-dimensional-hexagonal structure, and MCM-41 type and three-dimensional pores. Two types of mesoporous silica of type MCM-48 linked were synthesized.

  Thereafter, vesicle-like MSU-V (non-patent document 2) using alkyldiamine as a template, SBA-12 type having a three-dimensional hexagonal structure using nonionic decaethylene glycol monooctadecyl ether (non-patent document 3), etc. Various mesoporous silicas have been obtained. Furthermore, by using a block copolymer EOmPOnEOm (m = 33 to 70, n = 5 to 26) composed of hydrophilic ethylene oxide (EO) and hydrophobic propylene oxide (PO) as a template, a pore diameter of 10 nm or more is obtained. A two-dimensional hexagonal mesoporous silica SBA-15 was also obtained (Non-patent Document 4).

  As described above, mesoporous silica having a large specific surface area and a peculiar pore structure has been regarded as promising as a catalyst support or an adsorbent from the beginning, but the material created first is, for example, MCM-41 type is micron. The scale, SBA-15, had a primary particle size of submicron scale, and all had a difficulty in the particle size. For this reason, micronization has been studied with the aim of reducing the diffusion resistance to guest molecules by reducing the particle size and effectively utilizing the pores (for example, Non-Patent Document 5). By reacting tetraethyl orthosilicate (TEOS) dissolved in an aqueous solution of sodium hydroxide in the presence of an extremely low concentration of CTAB, mesoporous silica having an MCM-41 type structure is obtained as spherical particles having an average diameter of 110 nm (non- Patent Document 6).

  Moreover, when the ratio of the silicic acid component dissolved in the alkaline aqueous solution and the surfactant is changed, the diameter of the generated spherical MCM-41 type mesoporous silica particles can be controlled in a wide range of 65 to 740 nm (Non-patent Document 7). At this time, when CTAB is used as a surfactant, particles having a regular pore structure and a disordered spherical shape are obtained, and when dodecylamine is used, an irregular pore structure and a regular spherical shape are obtained. It has also been clarified that morphological particles are produced.

Mesoporous silica of 50 nm or less has also been reported. For example, spherical particles having a diameter of about 20 nm are obtained by performing a TEOS / CTAB / NaOH / H ₂ O reaction for a short time and then diluting with a large excess of water (Non-patent Document 8). Furthermore, recently, mesoporous silica having a diameter of about 20 nm and having a three-dimensional hexagonal structure has been synthesized using the mixed system of the block copolymer P123 and the anionic surfactant as a template (Non-patent Document 9).

  On the other hand, it has been found that mesoporous materials have inferior catalytic ability and adsorption characteristics compared to zeolite due to their amorphous skeleton and large pore size. For this reason, it has been studied to provide micropores in the amorphous pore walls to achieve functionalization. In the above MCM-41 and SBA-15, the micropores are formed in the pore walls. It was clarified by analysis of the adsorption isotherm (Non-Patent Documents 10 and 11). Furthermore, it has also been found that the pore volume of the micropores can be controlled by changing the charging ratio of tetraethoxysilane and P123 used in the reaction (Non-patent Document 12).

  In addition to the academic literature listed above, various proposals for mesoporous silica have been made in the patent literature in recent years. That is, surfactant and sodium silicate are mixed to obtain mesoporous silica from a composite of surfactant and silica (Patent Documents 1 and 2), or silica is reacted by reaction of silicon alkoxide and acid. The reaction process for precipitation is carried out in two stages, and the acid concentration in each stage is adjusted very strictly, so that mesoporous silica having pores with acid resistance and excellent smoothness and orientation is formed into a thin film. (Patent Document 3) has been proposed. The silica obtained by these proposals is evaluated in that it is formed into a film-like material rich in pore distribution structure and acid resistance, and has a characteristic not found in conventional silica. However, none of them describe or suggest the preparation of mesoporous silica particle sizes into nanometer-scale ultrafine particles that have recently attracted attention and are evaluated by the particle size itself.

C. T.A. Kresge and 4 others, Nature, 359, p. 710-712 (1992) P. T.A. Tanev and 1 other, Science, 271, 1267 (1996) D. Zhao and four others, Am. Chem. Soc. , 120, 6024 (1998) D. Zhao and 6 others, Science, 279, 548 (1998) Y. F. Lu and 5 others, Nature, 398, 223-226 (1999) Q. Cai and five others, Chem. Mater. 13, 258-263 (2001) R. I. Nooney and 4 others, Chem. Mater. 14, 4721-4728 (2002) C. D. Fowler and three others, Adv. Mater. 13, 649-652 (2001) K. Suzuki and two others. Am. Chem. Soc. 126, 462-463 (2004) Y. Long and three others, Langmuir, 14, 6173 (1998) M.M. Kruk and three others, Chem. Mater. 12, 1961 (2000) K. Miyazawa and one other person, Chem. Commun. 12, 2121-2122 (2000) Tsuyoshi Kijima, “Development of functional fine particles and nanomaterials”, Frontier Publishing Co., Ltd., p. 57-68 (2004) T.A. Kijima and 3 others, Langmuir, 18, 6453-6457 (2002) Tsuyoshi Kijima and 6 others, Angew. Chem. Int. Ed. 43, 228-232 (2004)

JP-A-8-34607 JP 2001-261326 A JP 2004-99381 A JP 2004-034228 A

  As described above, in the conventional technology related to mesoporous silica, in order to take advantage of mesoporous silica such as a large specific surface area and a unique pore structure, it has both micropores and mesopores along with the technology for controlling the particle size to 100 nm or less. In addition, technologies for creating silica have been developed individually, but these have remained independent technologies, and it has not been possible to provide a material that satisfies both requirements by fusing both technologies. That is, it is desired to develop a new technique for creating fine mesoporous silica having both micropores and mesopores and having a particle size of 100 nm or less.

  Among the above documents, the template synthesis method using a surfactant described in the non-patent document is applied to other material systems other than silica, and various types of metal oxides and sulfides as skeleton components have been used. A large number of mesoporous materials have been synthesized and developed to synthesize inorganic and polymer nanotubes (see Non-Patent Document 13). In the synthesis of nanoporous nanotube materials using such a surfactant as a template, a single surfactant is used as a template component with almost no exception. On the other hand, the present inventors use a nematic liquid crystal phase obtained by mixing a nonionic surfactant and a cationic surfactant as a reaction field, so that wire-like silver bromide having a diameter of about 1 μm and oxidation are obtained. Finding that tin can be obtained, gaining knowledge that the composite surfactant system is effective for the synthesis of nanostructures (see Non-Patent Document 14), and based on this knowledge, consists of two types of surfactants Developed a method for reducing chloroplatinic acid using liquid crystal as a template, and succeeded in producing noble metal nanotubes such as platinum and palladium with an outer diameter of 6 to 7 nm and an inner diameter of about 3 to 4 nm. (See Patent Document 4). Furthermore, X-ray diffraction experiments and structural model calculations revealed that liquid crystals effective for the generation of such precious metal nanotubes are composed of cylindrical micelles made by combining two types of surfactants. Published in academic literature (Non-Patent Literature 15).

  Therefore, the present inventors have introduced the above-mentioned conventional techniques, and have conducted various research reports on the listed nanotubes and the prior art in mind, while the template synthesis method based on the composite surfactant system is used. In addition, in order to create a new mesoporous silica having a different pore shape, micropores and mesopores, and having a particle size of 100 nm or less, the types of silica source and reducing agent used, and reaction conditions are more intensive. As a result of further research, it was added in advance to the molecular structure formed by mixing two components of two types of nonionic surfactants or ionic surfactants and a relatively large class of nonionic surfactants with a hydrophilic part size. By slowly reacting a silicic acid source such as TEOS, a porous structure having silica as a skeleton and having both micropores and mesopores and a diameter of several tens of nm Has a size of Noreberu novel silica nanoparticles exhibited spherical form was investigated to grow.

That is, as a result of intensive studies, the present inventors have succeeded in solving and achieving the above-described problem by the invention in which the technical configuration described below is taken.
That is, the first invention is (1) a porous structure composed of a silica skeleton having micropores having a diameter of 0.2 to 0.5 nm, and mesopores having a diameter of 4 to 5 nm arranged in a hexagonal shape, and a diameter of 40 to Silica nanoparticles having a spherical shape of 80 nm.

Hereinafter, the second invention presents the method for producing silica nanoparticles of the first invention.
That is, the second invention is (2) one kind of silicon compound selected from the group consisting of organic or inorganic silicon compounds such as tetraethyl orthosilicate and tetramethyl orthosilicate, and polyoxyls such as nonaethylene glycol monohexadecyl ether. Two types of nonionic surfactants selected from the group consisting of ethylene alkyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan esters such as polyoxyethylene sorbitan monostearate, and polyoxyethylene alkyl phenyl ethers A reaction mixture composed of two surfactants, one ionic surfactant and one ionic surfactant, and water, or an acid such as nitric acid and an alcohol such as dodecyl alcohol, or either one of them. Counter By preparing and reacting the mixture, a porous structure having a skeleton composed of silica having micropores with a diameter of 0.2 to 0.5 nm, and mesopores with a diameter of 4 to 5 nm arranged in a hexagonal form and a diameter. 2. The method for producing silica nanoparticles according to claim 1, wherein silica nanoparticles having a spherical shape of 40 to 80 nm are produced and recovered.

Hereinafter, the third to sixth inventions present inventions related to the use of the silica nanoparticles of the first invention.
That is, the third invention, (3) characterized in that said the use of silica nanoparticles described as adsorbent (1), absorbent comprising shea Rikanano particles.
A fourth invention is (4) the adsorbent, characterized in Rukoto be used as molecular sieves adsorbent, wherein (3) absorbent comprising silica nanoparticles according to claim.
A fifth invention is (5) (1), characterized by using the silica particles described as a filler in sections, filler made of sheet Rikanano particles.
A sixth invention is (6) the filler is used as a filler for chromatography, characterized in Rukoto, the (5) filler consisting of silica nanoparticles according to claim.

The present invention provides silica nanoparticles having pores with a specific structure having micropores and mesopores by the above-mentioned specific process, and is provided for various uses, as compared with conventional ones. It is expected that the special effects described will be exhibited or that various functions will be exhibited.
1) When this is used as a packing material or molecular sieve for chromatography, etc., micropores and mesopores act efficiently and synergistically to create molecules and substances with different sizes from several to several nanometers. A remarkable effect such as precise separation due to the difference in size is expected.
2) When this is used as an adsorbent, micropores and mesopores work efficiently and synergistically to remove molecules and substances with different sizes from several to several nanometers simultaneously. Expected to be effective.
3) When this is used as a material separation material, only molecules and ions with an inner diameter of 2 to 4 nm can penetrate into the inside of the particle, so that endocrine disrupting substances such as nonylphenol and phthalate esters and amino acids are compared. It is easy to separate a substance having a small target size from a substance having a high molecular weight such as protein.

  The invention of this application has the above-described features, and will be specifically described below with reference to the accompanying drawings. However, these examples merely disclose one aspect of the present invention, and are not intended to limit the present invention. That is, the aim of the present invention is to provide a novel silica nanoparticle having a spherical structure with a porous structure having both a micropore and a mesopore and a nano-level size of several tens of nanometers in diameter. What is provided is as described above.

  In addition, the outline of the production method is the above structural structure obtained by reacting a silicate component with a structure obtained by mixing at least two kinds of surfactants and an aqueous solution of a silicate compound under appropriate conditions as a template. This is to induce silica nanoparticles having characteristics, and the optimum temperature and mixing conditions for constructing the template vary depending on the characteristics of the target silicic acid species and the surfactant used. On the other hand, the examples are disclosed as an aid for easily carrying out the present invention, and are merely an example of the embodiment, and the silicic acid species and the production method constituting the present invention are also included. It should not be limited by this example.

  FIG. 1 and FIG. 4 are transmission electron microscope observation photographs of the silica nanoparticles of the present invention. According to this, the silica nanoparticles of the present invention are spherical with a particle size of 40 to 80 nm and mesopores with a diameter of about 5 nm. It is observed that the porous body has both 0.3 nm micropores.

Example 1;
Two kinds of surfactant nonaethylene glycol monododecyl ether CH ₃ (CH ₂ ) ₁₁ (CH ₂ CH ₂ O) ₉ OH (C ₁₂ EO ₉ ) 0.29 g and polyoxyethylene sorbitan monostearate ( (Tween 60) 0.65 g and 0.54 ml of water were mixed at 60 ° C. with a shaker for 20 minutes, followed by addition of 0.47 ml of tetraethyl orthosilicate (TEOS, specific gravity 0.93, 95 wt%) at the same temperature. The mixture was shaken and mixed for 2 minutes and then cooled to 0 ° C. to obtain a paste-like liquid crystal (LC) phase having a molar ratio of TEOS / C ₁₂ EO ₉ / Tween 60 / H ₂ O = 4: 1: 1: 60. After this LC phase was aged at 0 ° C. for 24 hours, 0.31 g of ammonium acetate was added, followed by 10 ml of water to prevent the LC phase from being destroyed by ethanol caused by hydrolysis of TEOS, and at 40 ° C. for 3 days. It was allowed to stand and gelled. The produced soft gel was washed with water, and then the supernatant was removed by centrifugation (rotation speed: 3000 rpm). Further, the remaining solid phase was washed twice with water and ethanol, and then centrifuged to obtain a solid product. Finally, it was heated to 400 ° C. at a rate of temperature increase of 3 ° C./min and baked at the same temperature for 10 minutes to remove the surfactant in the mold.
A transmission electron micrograph of the silica particles synthesized as described above is shown in FIG. The obtained silica has mesopores with an inner diameter of about 4 to 5 nm, and is a block-shaped nanoparticle with an outer diameter of about 60 nm having a micropore with a diameter of about 0.3 nm in the skeleton. The pore size distribution curve of this silica particle also gave a maximum at about 4.3 nm ((Fig. 2). The X-ray diffraction pattern of the liquid crystal used as the precursor shows that the hexagonal structure acts as a template. This suggests (Figure 3).

Example 2;
Two kinds of surfactant nonaethylene glycol monododecyl ether CH ₃ (CH ₂ ) ₁₁ (CH ₂ CH ₂ O) ₉ OH (C ₁₂ EO ₉ ) 0.29 g and polyoxyethylene sorbitan monostearate ( 0.65 g of Tween 60) and 0.54 ml of water were mixed at 60 ° C. with a shaker for 20 minutes, and then tetraethyl orthosilicate (TEOS, specific gravity 0.93, 95 wt%) 0.12 to 0.94 ml In addition, the mixture was shaken and mixed for 2 minutes at the same temperature, then cooled to 20 ° C., and a paste-like liquid crystal having a molar ratio TEOS / C ₁₂ EO ₉ / Tween 60 / H ₂ O = 1-8: 1: 1: 60 (LC ) Phase was obtained. After this LC phase was aged at 20 ° C. for 24 hours, 0.31 g of ammonium acetate was added, followed by 10 ml of water to prevent the LC phase from being destroyed by ethanol caused by hydrolysis of TEOS, and at 20 ° C. for 7 days. It was allowed to stand and gelled. The produced soft gel was processed in the same manner as in Example 1 to obtain a solid product. Finally, it was heated to 400 ° C. at a rate of temperature increase of 3 ° C./min and baked at the same temperature for 10 minutes to remove the surfactant in the mold.
As in Example 1, the transmission electron micrograph of the silica synthesized as described above shows block-like nanoparticles having an outer diameter of about 60 nm having mesopores having an inner diameter of about 4 nm and micropores having a diameter of about 0.3 nm. It was shown that it was generated (FIG. 4). Moreover, the pore diameter distribution curve of the product heat-processed in the temperature range of 100-800 degreeC changed like FIG. From this result and the thermogravimetric / differential thermal analysis curve of the untreated sample (FIG. 6), mesopores having a diameter of about 4 nm are formed around 180 ° C. where the main part of the surfactant decomposes and burns, and the remaining components burn. It is considered that micropores having a diameter of 2 nm or less are generated around 280 ° C. Furthermore, the X-ray diffraction pattern of the 400 ° C. fired product also gave a slightly broad long-period peak with d = 6.1 nm, and it was confirmed that a regular arrangement of mesopores with an inner diameter of 4 nm and a wall thickness of 1 nm was formed. .

Example 3;
Two kinds of surfactant nonaethylene glycol monododecyl ether CH ₃ (CH ₂ ) ₁₁ (CH ₂ CH ₂ O) ₉ OH (C ₁₂ EO ₉ ) 0.29 g and polyoxyethylene sorbitan monostearate ( Tween 60) 0.65 g and water 0.54 ml were mixed uniformly at 60 ° C. with a shaker for 20 minutes, and then tetramethyl orthosilicate (TMOS, specific gravity 0.93, 95 wt%) 0.12-0. After adding 94 ml and shaking and mixing at the same temperature for 2 minutes, the mixture was cooled to 20 ° C. and paste-like liquid crystal having a molar ratio TMOS / C ₁₂ EO ₉ / Tween 60 / H ₂ O = 1-8: 1: 1: 60 ( LC) phase was obtained. This LC phase was left open at 20 ° C. for 3 days to gel. 0.31 g of ammonium acetate was added to the resulting hard gel, washed with water, and then treated in the same manner as in Example 1 to obtain a solid product. Finally, it was heated to 400 ° C. at a rate of temperature increase of 3 ° C./min and baked at the same temperature for 10 minutes to remove the surfactant in the mold.
The product gives an X-ray diffraction pattern and a nitrogen adsorption isotherm shown in FIG. 7B, and is a porous silica body having both mesopores having a diameter of 2 to 4 nm and micropores having a diameter of 1 nm or less by t-plot analysis. all right. Even when water was added to the paste-like liquid crystal (LC) phase and the same operation as in Example 1 was performed, similar results were obtained as in the system in which no water was added, as shown in FIG. 7B.

As disclosed in the above embodiment, mesoporous silica comprising a specific fine size and specific mesoporous pore structure of the present invention, unique to a combination of two types of surfactants shea Li Ca formation reaction It is obtained under the conditions.

  The silica nanoparticles provided by the present invention are typically used as a catalyst carrier or catalyst, and when subjected to a chemical reaction, function as a reactor having a reaction field and a reaction channel due to its unique pore structure. Compared to conventional silica that does not have such a pore structure, it is expected to have an excellent catalytic effect. Furthermore, the unique pore structure of the present invention has a molecular sieving effect, which is expected to function as a selective separating agent for various molecules, and is important as a unit operation in chemical engineering operations. It is expected to be used greatly for separation operations. In addition to the separating agent, it has an adsorption action due to its unique fine pores, and is expected to be used greatly as an excellent adsorbent. The above is a list of typical uses of the silica of the present invention. However, the use mode is not limited to this, and it will be established as one of the basic materials of industrial materials and will be used greatly in various fields. It is expected that

1 is a transmission electron micrograph of the product obtained in Example 1. FIG. 2 is a pore size distribution curve of the product obtained in Example 1. FIG. The X-ray diffraction pattern of the silica precursor liquid crystal obtained in Example 1. 3 is a transmission electron micrograph of the product obtained in Example 2. FIG. (A) 100 ° C., (b) 200 ° C., (c) 400 ° C., and (d) 800 ° C. heat-treated pore diameter distribution curves obtained in Example 2. The thermogravimetric / differential thermal analysis curve of the production | generation (unprocessed) obtained in Example 2. FIG. X-ray diffraction pattern (top) and nitrogen adsorption isotherm (bottom) of the product obtained in Example 3.

Claims (6)

  It consists of a silica skeleton having micropores with a diameter of 0.2 to 0.5 nm, and has a porous structure in which mesopores with a diameter of 4 to 5 nm are arranged in a hexagonal form and a spherical shape with a diameter of 40 to 80 nm. Silica nanoparticles.   One silicon compound selected from the group consisting of organic or inorganic silicon compounds such as tetraethyl orthosilicate and tetramethyl orthosilicate, polyoxyethylene alkyl ethers such as nonaethylene glycol monohexadecyl ether, and polyoxyethylene fatty acid esters , Two types of nonionic surfactants selected from the group consisting of polyoxyethylene sorbitan esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene alkylphenyl ether, and one type of nonionic surfactant and ionic surfactant Prepare a reaction mixture consisting of two types of surfactants in combination with water, or a mixture of water and an acid such as nitric acid and an alcohol such as dodecyl alcohol, or any one of them. Therefore, the skeleton is constituted by silica having micropores having a diameter of 0.2 to 0.5 nm, and a porous structure in which mesopores having a diameter of 4 to 5 nm are arranged in a hexagonal form and a spherical shape having a diameter of 40 to 80 nm are provided. 2. The method for producing silica nanoparticles according to claim 1, wherein the silica nanoparticles are produced and recovered. Characterized in that the silica particles of claim 1 for use as an adsorbent, the adsorbent consisting of shea Rikanano particles. The adsorbent comprising silica nanoparticles according to claim 3 , wherein the adsorbent is used as an adsorbent for molecular sieves. Characterized in that the silica particles of claim 1 for use as a filler, the filler consisting of shea Rikanano particles. 6. The filler comprising silica nanoparticles according to claim 5 , wherein the filler is used as a chromatography filler.

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