JP6728824B2 - Method for producing mesoporous silica nanoparticles - Google Patents

Description

The present invention relates to a method for producing mesoporous silica nanoparticles.

As a material for adsorbing and storing various substances, mesoporous silica nanoparticles having meso-sized pores (mesopores) having a pore diameter of about 2 to 50 nm have been attracting attention, and various manufacturing methods have been conventionally used. Is being considered.

For example, Non-Patent Document 1 (Dengke Shen et al., “Biphase Stratification Approach to Three-Dimensional Dendritic Biodegradable Mesoporous Silica Nanospheres”, NANO LETTERS, American Chemical Society, January 27, 2014, Volume 14, Issue 2, pp. 923-932), an upper layer composed of a solution of tetraethoxysilane (TEOS) using a hydrophobic organic solvent such as 1-octadecene, decahydronaphthalene, or cyclohexene as a solvent, and cationic cetyltrimethylammonium as a template. A method for forming mesoporous silica nanoparticles by self-assembly is disclosed, which utilizes the interface between two lower layers composed of an aqueous solution containing chloride and triethanolamine as a catalyst.

Dengke Shen et al., “Biphase Stratification Approach to Three-Dimensional Dendritic Biodegradable Mesoporous Silica Nanospheres”, NANO LETTERS, American Chemical Society, January 27, 2014, Volume 14, Issue 2, pp. 923-932

However, in the method described in Non-Patent Document 1, a solution of tetraethoxysilane using a hydrophobic organic solvent such as 1-octadecene, decahydronaphthalene, or cyclohexene in the upper layer (by a hydrophobic organic solvent, Diluted silane raw material: In addition, referring to Table 1 in Non-Patent Document 1 described above, the silane raw material is diluted to 5 to 20% by volume.), and mesoporous silica nanoparticles are formed without using an organic solvent. There is no particular description about what to do. In addition, in the method of using such an organic solvent, a step of removing the organic solvent (separation, recovery, disposal, etc. of the organic solvent) is required after the production of the mesoporous silica nanoparticles, which is economical and efficient. Wasn't always enough.

The present invention has been made in view of the problems of the above-mentioned conventional techniques, can produce mesoporous silica nanoparticles without using an organic solvent, and can eliminate the step of removing the organic solvent mesoporous. It is an object of the present invention to provide a method for producing silica nanoparticles.

As a result of repeated intensive studies to achieve the above objects, the present inventors have floated an undiluted silica raw material composed of tetraalkoxysilane on the water surface of an aqueous solution containing a surfactant and a hydrolysis catalyst, By hydrolyzing the silica raw material and generating mesoporous silica nanoparticles in the aqueous solution, it is possible to produce mesoporous silica nanoparticles without using an organic solvent, and it is possible to eliminate the step of removing the organic solvent. The present invention has been completed and the present invention has been completed.

That is, the manufacturing method of the mesoporous silica nanoparticles of the present invention, the water of an aqueous solution containing a surfactant and hydrolysis catalyst, in a state in which floated neat silica raw material consisting of tetraalkoxy silane, Mu said in the aqueous solution The method is characterized in that the silica raw material is hydrolyzed while stirring so that an emulsion of the diluted silica raw material is not formed, and mesoporous silica nanoparticles are produced in the aqueous solution.

In the method for producing mesoporous silica nanoparticles of the present invention, the tetraalkoxysilane preferably has 8 to 16 carbon atoms.

Furthermore, in the method for producing mesoporous silica nanoparticles of the present invention, the temperature condition for producing the mesoporous silica nanoparticles is preferably 20 to 95°C.

According to the method for producing mesoporous silica nanoparticles of the present invention described above, it is possible to produce mesoporous silica nanoparticles without using an organic solvent, and it is possible not only to eliminate the step of removing the organic solvent, When the amount of the aqueous solution is constant with respect to the surface area of the water surface, it is possible to obtain the relationship between the reaction time and the average particle size of the obtained nanoparticles by a unique formula, and the average particle of the nanoparticles with respect to the reaction time. The degree of expansion of the diameter can be easily predicted, and the degree of expansion of the average particle diameter of nanoparticles (the degree of growth of particles due to self-assembly) is controlled by controlling the reaction time so that the size becomes the target size. It is also possible. The reason why such an effect is achieved is not necessarily clear, but the present inventors presume as follows (this point will be briefly described below with reference to the drawings (schematic diagram shown in FIG. 1)). explain.).

FIG. 1 is a drawing schematically showing a state in which a silica raw material 2 floats on the water surface of an aqueous solution 3 in a reaction vessel 1. The symbol I in FIG. 1 conceptually shows the interface between the upper layer (the layer made of the silica raw material 2) and the lower layer (the layer made of the aqueous solution 3), and the arrow A indicates the silica hydrolyzed from the upper layer to the lower layer. It conceptually shows a state in which a raw material is introduced (added) (a state of permeation), that is, conceptually shows a direction in which a hydrolyzed silica raw material is introduced. In the present invention, the silica raw material is hydrolyzed with the undiluted silica raw material 2 made of tetraalkoxysilane floating on the water surface of the aqueous solution 3 containing the surfactant and the hydrolysis catalyst. The “undiluted silica raw material” referred to here is one that is not substantially diluted with an organic solvent and contains 90% by mass or more of tetraalkoxysilane (for example, a stock solution of tetraalkoxysilane). Say. By using tetraalkoxysilane without using an organic solvent in this way, it becomes possible to simplify the composition of the reaction solution and at the same time quantitatively control the amount of silica raw material that comes into contact with the water surface, thereby suppressing the reaction rate to a lower level. It becomes possible. In addition, such a tetraalkoxylane is a water-insoluble liquid before the hydrolysis. In the present invention, such a tetraalkoxysilane is floated on the water surface in an undiluted state to hydrolyze the tetraalkoxysilane in contact with water at the interface I between the layer of the aqueous solution 3 and the layer of the silica raw material 2. (The silica raw material is hydrolyzed in a phase-separated state). When the tetraalkoxysilane is hydrolyzed at the interface I in this way, a silanol group is generated by the hydrolysis, and the hydrolyzed silica raw material permeates into the aqueous solution 3, and the hydrolyzed silica raw material becomes the aqueous solution 3 Will be supplied inside (see arrow A in the figure). In the present invention, as described above, since undiluted tetraalkoxysilane in which the reaction proceeds relatively slowly is used as the raw material, the reaction rate of hydrolysis can be further suppressed, and the aqueous solution 3 The permeation of the silane raw material (raw material after hydrolysis) into the inside slowly occurs through the interface I between the undiluted silane raw material layer 2 and the aqueous solution 3. Further, since such a hydrolysis reaction occurs at the interface I with water, it is speculated that the hydrolysis reaction proceeds at a constant rate in proportion to the area of the water surface, and the supply of the silica raw material into the aqueous solution 3 is almost complete. It is thought to proceed at a constant speed. On the other hand, in the aqueous solution 3, a complex is formed between the hydrolyzed silica raw material and the surfactant to form a complex (particularly after the silica core is formed from the hydrolyzed silica raw material, the silica skeleton is formed). Are considered to be complex at the stage of growth). Then, in such a complex, silanol groups generated by hydrolysis are sequentially condensed to grow silica (silicon oxide) particles in a self-assembled manner. As described above, when the silica particles grow (when the silica is formed), silica (silicon oxide) is not generated in the portion where the surfactant is present. In this way, the surfactant in the aqueous solution 3 functions as a template of pores, and the silica particles 4 in which the surfactant is introduced into the pores are formed. Further, since it is clear that the growth of such particles 4 is proportional to the amount (concentration) of the silica raw material in the aqueous solution 3, when the amount of the aqueous solution with respect to the area of the water surface is constant, the reaction time The degree of growth of the particle diameter of the obtained nanoparticles 4 (the degree of the average particle diameter) is proportional, and the relationship between the reaction time and the average particle diameter can be obtained by a unique mathematical formula. Thus, in the present invention, it is possible to uniquely determine the relationship between the reaction time and the average particle size of the obtained nanoparticles. Therefore, in the present invention, the degree of expansion of the average particle size of the nanoparticles 4 with respect to the reaction time can be easily predicted, and by controlling the reaction time so that the target size is obtained, the average particle size of the nanoparticles 4 The present inventors presume that it is possible to synthesize nanoparticles while controlling the degree of expansion (the degree of particle growth due to self-assembly). In the present invention, since the reaction proceeds as described above, it is not necessary to use an organic solvent in the reaction system, and the amount of the solvent (water) used is also small according to the intended design. It is possible.

Further, in the present invention, most of the silica raw material before hydrolysis exists in a state of being separated from the aqueous layer (the layer formed of the aqueous solution 3) (basically, the hydrolysis reaction is performed in a phase-separated state), The present inventors presume that the concentration of the silane raw material in the layer can be kept relatively low and the reaction rate can be kept low. In the present invention, since the undiluted silica raw material 2 made of tetraalkoxysilane insoluble in water is used to hydrolyze the silica raw material through the interface I between the layer of the silica raw material 2 and the layer of the aqueous solution 3, Since the silica raw material after hydrolysis can be slowly introduced into the aqueous solution 3 basically at a constant rate, whereby the mesoporous silica nanoparticles 4 are slowly produced in the aqueous solution 3 at a constant rate. It is also possible to promote the growth of uniform particles. Further, in the present invention, by leaving the undiluted silica raw material made of tetraalkoxysilane insoluble in water in the state of being floated in water, the silica raw material having a substantially constant concentration is always present at the interface of the aqueous solution, The feed rate of the raw material into the aqueous solution 3 can be kept substantially constant regardless of the reaction time (even if the hydrolyzed raw material is introduced into the water, the upper silica raw material layer is undiluted Therefore, it is considered that basically the same concentration of the raw material is sufficiently maintained in the portion in contact with the water surface.For example, when a silica raw material containing 100% by mass of tetraalkoxysilane is used, the reaction is Even if it progresses, a layer of silica raw material consisting of 100% by mass of tetraalkoxysilane always exists on the water surface, and the feed rate of the raw material into the aqueous solution 3 can be kept substantially constant regardless of the reaction time. ). In this respect, when using a silica raw material diluted with a large amount of an organic solvent as described in Non-Patent Document 1, when a part of the silica raw material is hydrolyzed and the reaction proceeds, the upper layer (organic solvent It is considered that the concentration of the silica raw material in the (containing layer) changes greatly, and the reaction rate changes due to this. Therefore, in the method described in Non-Patent Document 1, in order to react at a constant reaction rate, it is considered necessary to control the concentration of the raw material, for example, by replacing the organic layer. The present inventors presume that it is difficult to efficiently control the degree of diameter growth by the reaction time or the like.

As described above, in the present invention, by using an undiluted silica raw material that is not substantially diluted with an organic solvent and contains 90% by mass or more of tetraalkoxysilane as the silica raw material, In addition, it is possible to allow the reaction to proceed efficiently and at a constant rate, which makes it possible to express the relationship between the reaction time and the particle size of the generated mesoporous silica nanoparticles by a simple mathematical expression. In the present invention, the concentration of the silica raw material that permeates the aqueous layer can be suppressed to a relatively low level by floating the silica raw material in water (in a phase-separated state) and causing the reaction. The present inventors presume that it is possible to generate particles while controlling the reaction rate suitable for generation.

As described above, according to the present invention, it is also possible to efficiently control the degree of expansion of the average particle diameter of nanoparticles (the degree of particle growth due to self-assembly) by the reaction time. The present inventors presume that it becomes possible to efficiently manufacture nanoparticles having a design (size, etc.). Further, in the method for producing mesoporous silica nanoparticles of the present invention, the mesoporous silica nanoparticles can be efficiently produced without using an organic solvent, and therefore it is possible to eliminate the step of removing the organic solvent after the production. Therefore, the present inventors presume that the method for producing mesoporous silica nanoparticles of the present invention can reduce the step of removing the organic solvent, and is also an excellent method in terms of efficiency and economy (cost).

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture a mesoporous silica nanoparticle without using an organic solvent, and it becomes possible to provide the manufacturing method of a mesoporous silica nanoparticle which can eliminate the removal process of an organic solvent. ..

It is a schematic diagram which shows typically the state which the silica raw material floats on the water surface of an aqueous solution in a reaction container. 3 is a scanning electron micrograph of the nanoparticles obtained in Example 1. 1 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 1. 3 is a scanning electron micrograph of the nanoparticles obtained in Example 2. 3 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 2. 5 is a scanning electron micrograph of the nanoparticles obtained in Example 3. 5 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 3. 5 is a scanning electron micrograph of the nanoparticles obtained in Example 4. 5 is a graph of nitrogen adsorption/desorption isotherm of nanoparticles obtained in Example 4. 9 is a scanning electron micrograph of the nanoparticles obtained in Example 5. 5 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 5. 7 is a scanning electron micrograph of the nanoparticles obtained in Example 6. 9 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 6. 9 is a scanning electron micrograph of the nanoparticles obtained in Example 7. 9 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 7. 9 is a scanning electron micrograph of the nanoparticles obtained in Example 8. 9 is a graph of nitrogen adsorption/desorption isotherm of nanoparticles obtained in Example 8. 9 is a scanning electron micrograph of the nanoparticles obtained in Example 9. 9 is a graph of a nitrogen adsorption/desorption isotherm of nanoparticles obtained in Example 9. 9 is a scanning electron micrograph of the nanoparticles obtained in Example 10. 9 is a graph of nitrogen adsorption/desorption isotherms of nanoparticles obtained in Example 10. It is a graph which shows the relationship between the particle diameter of the nanoparticles obtained in Examples 4-6, and reaction time.

Hereinafter, the present invention will be described in detail with reference to its preferred embodiments.

The method for producing mesoporous silica nanoparticles of the present invention, the water surface of an aqueous solution containing a surfactant and a hydrolysis catalyst, in the state of floating undiluted silica raw material consisting of tetraalkoxysilane, to hydrolyze the silica raw material, The method is characterized by producing mesoporous silica nanoparticles in the aqueous solution.

The surfactant according to the present invention is not particularly limited as long as it can be used for forming pores when forming a silicon oxide, and can be used for producing mesoporous silica nanoparticles. A known surfactant can be appropriately used. Among these surfactants, a cationic surfactant is preferable from the viewpoint of high affinity with the silica raw material. Moreover, as such a cationic surfactant, for example, an alkyl ammonium halide having a long-chain alkyl group having 8 to 26 carbon atoms can be preferably used. Further, among such surfactants, an alkyltrimethylammonium halide having a long-chain alkyl group having 9 to 26 carbon atoms such as tetradecyltrimethylammonium halide, hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide is preferable, and tetradecyl Trimethylammonium halide and hexadecyltrimethylammonium halide are more preferable, and tetradecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride are more preferable.

In addition, such a surfactant is introduced into the silica raw material and functions as a template for pore formation, as described above. In general, the surfactant is considered to form a complex with the hydrolyzed silica raw material in the aqueous solution during the reaction (at the stage where the silica skeleton grows after the nucleus of silica is formed). It is considered to be complex). Then, in such a complex, a reaction of condensing silanol groups of the silica raw material proceeds to form a silicon oxide (silica). On the other hand, silicon oxide is not generated in the portion where the surfactant is present in the composite. Therefore, the surfactant is introduced into the silica raw material and functions as a template for pore formation. In addition, such a surfactant can be used alone or in combination of two or more, but as described above, as a template for forming pores in the reaction product of the silica raw material. It is considered that it works, and the type thereof has a great influence on the shape of the pores of the porous body, so that it is preferable to use one type alone from the viewpoint of obtaining more uniform nanoparticles.

Further, the hydrolysis catalyst according to the present invention is not particularly limited as long as it can promote the hydrolysis of tetraalkoxysilane, and a known catalyst for hydrolysis can be appropriately used. As such a hydrolysis catalyst, amines exhibiting weak basicity are preferable from the viewpoint of suppressing rapid progress of hydrolysis reaction and polycondensation reaction at the interface of tetraalkoxysilane and water. Examples of such amines include triethanolamine, triethylamine, trimethylamine, and ammonia. Further, among such amines, from the viewpoint of low volatility, triethanolamine and triethylamine are more preferable, and triethanolamine is particularly preferable. Such a hydrolysis catalyst may be used alone or in combination of two or more kinds.

The aqueous solution according to the present invention contains a surfactant and a hydrolysis catalyst. Water used as a solvent for such an aqueous solution is not particularly limited, and for example, ion-exchanged water may be used. The concentration of the surfactant in such an aqueous solution is not particularly limited, but it is preferably 2 to 25% by mass, more preferably 5 to 20% by mass. If the concentration of such a surfactant is less than the lower limit, the micelle formation of the surfactant is inhibited, and the template function of mesopore formation tends to decrease, while if it exceeds the upper limit, the viscosity of the aqueous solution increases. Therefore, the diffusion of the hydrolyzed silica raw material tends to be non-uniform.

The concentration of the hydrolysis catalyst in the aqueous solution is not particularly limited, but is preferably 0.01 to 5% by mass, and particularly preferably 0.1 to 1% by mass. If the concentration of such a hydrolysis catalyst is less than the lower limit, hydrolysis is difficult to proceed, and the yield of silica nanoparticles finally obtained tends to decrease, while if it exceeds the upper limit, the hydrolysis reaction is accelerated. This tends to make it difficult to control the particle diameter.

Further, the aqueous solution according to the present invention may be any solution as long as it comprises water, a surfactant and a hydrolysis catalyst, and may contain other components as long as the effects of the present invention are not impaired. From the viewpoint of allowing the reaction to proceed more efficiently, the aqueous solution according to the present invention is more preferably substantially composed of only water, a surfactant and a hydrolysis catalyst, and water, a surfactant and hydrolysis. Those consisting only of a catalyst are particularly preferred.

Further, in the present invention, an undiluted silica raw material made of tetraalkoxysilane is used as the silica raw material. Here, the “undiluted silica raw material made of tetraalkoxysilane” is one that is not substantially diluted with an organic solvent, and contains 90% by mass of tetraalkoxysilane (more preferably 95 to 100% by mass, More preferably 97 to 100% by mass, and particularly preferably 100% by mass or more). As described above, the “undiluted silica raw material composed of tetraalkoxysilane” is 90% by mass of tetraalkoxysilane (more preferably 95 to 100% by mass, further preferably 97 to 100% by mass, particularly preferably 100% by mass). ) It is contained in the above proportion. The term "substantially not diluted with an organic solvent" as used herein means that the amount of the organic solvent is preferably 10% by mass or less (more preferably 5% by mass or less, further It is preferably 3% by mass or less, and particularly preferably 1% by mass or less). As described above, the “undiluted silica raw material” is substantially undiluted with the organic solvent (as described above, the amount of the organic solvent is 10% by mass or less even if it is contained in the raw material). However, it is preferable that the content of the organic solvent is 0% by mass, while the content of the tetraalkoxysilane is 90% by mass or more. Since tetraalkoxysilane is basically a liquid at room temperature (25° C.), the silica raw material is basically a liquid material.

In the present invention, the undiluted silica raw material composed of tetraalkoxysilane is used for the production (synthesis) of the mesoporous silica nanoparticles as described above. Here, in the synthesis of mesoporous silica nanoparticles, it is considered that three processes of nucleation, growth of a silica skeleton, and composite of a surfactant and silica act in combination. Then, in order to form good-quality nanoparticles, it is necessary to cause nucleation at an early stage of the reaction and then stably grow the silica skeleton. Here, if the reactivity of the silica raw material is too high, the complexation with the surfactant does not proceed sufficiently and a sufficient porous structure cannot be formed. As described above, in order to form high-quality porous nanoparticles, the growth reaction of the silica skeleton needs to be sufficiently faster than the nucleation, while the complexation of the silica raw material and the surfactant also progresses rapidly. There is a need to. Therefore, in the present invention, mesoporous silica nanoparticles are synthesized by using an undiluted silica raw material composed of tetraalkoxysilane so that the above-mentioned three processes are well-balanced.

Such a tetraalkoxysilane is not particularly limited, but preferably has 8 or more carbon atoms (more preferably 8 to 16, more preferably 8 to 14 and particularly preferably 10 to 14). When the number of carbon atoms is less than the lower limit, the hydrolysis reaction proceeds rapidly and it becomes difficult to control particle growth, or the layer of the silica raw material tends to be immediately mixed with the layer of the aqueous solution. If the upper limit is exceeded, the hydrolysis reaction will not proceed under mild reaction conditions, and the yield of nanoparticles will tend to decrease sharply.

In addition, as the tetraalkoxysilane, the following general formula (1):
Si(OR) ₄ (1)
(In formula (1), plural R's each independently represent an alkyl group.)
The compound represented by is preferable. The alkyl group selected as R has preferably 2 or more carbon atoms, more preferably 2 to 4 carbon atoms, and particularly preferably 3 carbon atoms. If the carbon number is less than the lower limit, it tends to be difficult for the silica raw material to be immediately mixed in the aqueous solution layer (aqueous layer) to form a phase separation state, while if the carbon number exceeds the upper limit, it is mild. Under various reaction conditions, it tends to be difficult to proceed with the hydrolysis reaction. In addition, such an alkyl group may be linear or branched.

As such a tetraalkoxysilane, while having an appropriate hydrolysis reactivity, from the viewpoint of controlling the activity to the extent that it does not easily react with moisture in the atmosphere, tetrapropoxysilane, tetraisopropoxysilane, tetra Ethoxysilane is preferable, tetrapropoxysilane and tetraisopropoxysilane are more preferable, and tetrapropoxysilane is particularly preferable. Such tetraalkoxysilanes may be used alone or in combination of two or more, but it is preferable to use one kind alone from the viewpoint of controlling the reaction rate.

Further, as described above, the undiluted silica raw material may have a tetraalkoxysilane concentration (purity) of 90% by mass or more, and may appropriately contain other components other than tetraalkoxysilane that can be used for the production of silica. May be included. Examples of such other components include trialkoxysilane, dialkoxysilane, and monoalkoxysilane.

Further, such an undiluted silica raw material may have a tetraalkoxysilane concentration of 90% by mass or more, but from the viewpoint of making the reaction rate more uniform, it is substantially composed of only tetraalkoxysilane. Those having a tetraalkoxysilane concentration of 95% by mass or more (more preferably 97% by mass or more, further preferably 98% by mass or more, and particularly preferably 99% by mass or more) are preferable. Most preferred are those having a tetraalkoxysilane concentration (purity) of 100% by mass or more. In addition, since such a silica raw material is undiluted, it does not substantially contain an organic solvent (the amount of the organic solvent is preferably 10% by mass or less even if contained in the raw material. ). As an undiluted silica raw material composed of such a tetraalkoxysilane, a commercially available tetraalkoxysilane (for example, a trade name “Tetropropyl Orthosilicate” manufactured by Tokyo Kasei Kogyo Co., Ltd., a concentration of tetrapropoxysilane of 98% by mass) is used as a stock solution. It is also possible to use it as it is.

In the present invention, the undiluted silica raw material composed of the tetraalkoxysilane (hereinafter sometimes simply referred to as “undiluted silica raw material”) is floated on the water surface of the aqueous solution. It is decomposed to generate mesoporous silica nanoparticles in the aqueous solution.

Here, the method of floating the undiluted silica raw material on the water surface of the aqueous solution is not particularly limited, but basically, since the tetraalkoxysilane is insoluble in water, so that an emulsion is not formed in water, It is preferable to employ a method of slowly and slowly adding the undiluted silica raw material to the water surface of the aqueous solution (a method of slowly and slowly developing the undiluted silica raw material on the water surface).

Further, when the undiluted silica raw material is floated on the water surface of the aqueous solution, the silica raw material is present at the interface between the layer (upper layer) made of the undiluted silica raw material and the layer (lower layer) made of the aqueous solution. The hydrolysis reaction can be allowed to proceed, and the hydrolyzed silica raw material can be added (permeated) into the aqueous solution. Then, when the silica raw material thus hydrolyzed is added to the aqueous solution, a nucleus of silica is formed between the silica raw materials in the aqueous solution, and a silica skeleton is grown on the basis of the nucleus to cause surface activity. Complexation with the agent occurs, a complex is formed, condensation of silanol groups of the silica raw material proceeds in the complex, and silica nanoparticles formed by introducing a surfactant into the pores are formed ( It is possible to obtain the mesoporous silica nanoparticles by the synthesis. As described above, a reaction in which the silica raw material is hydrolyzed (the hydrolysis reaction) occurs, and thus the hydrolyzed silica raw material is supplied to generate mesoporous silica nanoparticles in an aqueous solution. In other words, the formation reaction of the mesoporous silica nanoparticles (particle synthesis reaction) proceeds with the hydrolysis reaction.

The temperature condition for producing such mesoporous silica nanoparticles (in the series of reactions of the hydrolysis reaction and the particle synthesis reaction) is preferably 20 to 95°C, and preferably 25 to 80°C. Is more preferable. If such a temperature condition is less than the lower limit, the reaction rate becomes too slow, and it tends to be difficult to efficiently recover a sufficient amount of silica nanoparticles. On the other hand, if the temperature exceeds the upper limit, water vaporization or boiling occurs. Therefore, the reaction rate cannot be kept constant, and it tends to be difficult to obtain homogeneous nanoparticles.

Further, in producing mesoporous silica nanoparticles (in the series of reactions of the hydrolysis reaction and the synthesis reaction of particles), the reaction of producing silica, such as particle growth in an aqueous solution, proceeds more uniformly. It is preferable to allow the reaction to proceed with stirring. The conditions of such stirring are not particularly limited, but it is possible to maintain a state in which the undiluted silica raw material floats on the water surface of the aqueous solution, and an emulsion of the undiluted silica raw material is formed in the aqueous solution. It is preferable to stir slowly so that the magnetic stirrer uses a stirrer having a diameter of about 3 to 10 mm and a length of about 10 to 20 mm when the amount of the aqueous solution is about 10 to 100 mL. It is preferable to stir (rotate at low speed) at a rotation speed of about 100 to 250 rpm (more preferably 120 to 200 rpm). If the number of revolutions is less than the lower limit, it tends to be difficult to uniformly diffuse the silica raw material that has permeated into the aqueous layer (water layer) into the aqueous layer, while if it exceeds the upper limit. The interface between the layer of silica raw material and the layer of aqueous solution (water layer) is disturbed, so that the reaction system cannot be kept homogeneous or an emulsion tends to be produced. It should be noted that the number of revolutions and the like may be appropriately changed depending on the equipment so that the undiluted emulsion of the silica raw material is not formed in the aqueous solution so that the emulsion is slowly stirred.

As described above, in the present invention, the mesoporous silica nanoparticles can be obtained by advancing the reaction under conditions (such as temperature) under which the hydrolysis reaction and the particle synthesis reaction proceed. In the present invention, since the undiluted silane raw material causes the reaction while floating on the water surface of the aqueous solution, as described above, the supply rate of the silane raw material through the water surface is substantially constant regardless of the reaction time. Is believed to be maintained (because the concentration of the silane raw material in contact with the water surface does not change basically). As described above, when the amount of the silica raw material supplied into the water is almost proportional to the reaction time using the undiluted silane raw material, if the raw material is used for forming the nanoparticles, the generated nanoparticles are The volume is also almost proportional to time. Therefore, the relationship between the reaction time and the particle diameter of the obtained mesoporous silica nanoparticles can be predicted by a simple mathematical formula (since the volume of nanoparticles is almost proportional to time, the diameter of nanoparticles is the 1/3 power of the reaction time). It is considered to be proportional to.).

The mesoporous silica nanoparticles thus formed in the aqueous solution have the surfactant introduced into their pores. In order to remove such a surfactant, for example, a step of removing the surfactant may be appropriately performed after collecting the mesoporous silica nanoparticles formed from the aqueous solution. Examples of the step of removing such a surfactant include a method of treating with an organic solvent and a method of baking. As a method of treating with such an organic solvent, a method of immersing the mesoporous silica nanoparticles in a good solvent having a high solubility for the organic component in the pores and extracting and removing the surfactant can be adopted. In addition, examples of the method by firing include a method of heating the mesoporous silica nanoparticles at 300 to 1000°C, preferably 400 to 700°C. Such heating time may be about 30 minutes, but it is more preferable to heat for 1 hour or more from the viewpoint of completely removing the surfactant. The firing can be performed in air, but a large amount of combustion gas is generated, so an inert gas such as nitrogen may be introduced.

Thus, in the present invention, mesoporous silica nanoparticles can be obtained. Note that such mesoporous silica nanoparticles have pores having a so-called mesosize (2 to 50 nm) pore diameter. Further, the "nanoparticles" referred to in the present invention may be particles having an average particle size in the range of 20 to 500 nm.

In the present invention, by using the above-mentioned surfactant, the mesoporous silica nanoparticles obtained can have a pore diameter of 2 to 10 nm (more preferably 3 to 7 nm). If the pore diameter is less than the lower limit, the types of nanoparticles or compounds that can be adsorbed in the pores tend to be limited when the mesoporous silica nanoparticles are used as an adsorbent, while the upper limit is exceeded. And the uniformity of the pore diameter decreases, and the particles tend to become brittle. It should be noted that such a pore diameter can be obtained by the density functional theory based on the nitrogen adsorption/desorption isotherm. That is, based on the nitrogen adsorption-desorption isotherm, the pore diameter distribution curve is obtained by the density functional theory, the pore diameter at the maximum peak is measured from the pore diameter distribution curve, and the pore diameter at the maximum peak is the nanoparticle. Can be measured as the pore diameter of Here, the nitrogen adsorption/desorption isotherm is obtained by cooling the mesoporous silica nanoparticles to liquid nitrogen temperature (-196° C.) and introducing nitrogen gas, and determining the adsorption amount of nitrogen gas by the constant volume method or the gravimetric method. The nitrogen gas pressure is gradually increased, and the adsorption amount of nitrogen gas with respect to each equilibrium pressure can be obtained by plotting (for example, the nitrogen adsorption/desorption isotherm is a measurement device manufactured by Quantachrome, under the trade name “Autosorb”). It can be measured by determining the adsorption amount of nitrogen gas by a gas adsorption method (using a constant volume method) at a liquid nitrogen temperature (-196° C.) using "-1".

The mesoporous silica nanoparticles thus obtained preferably have an average particle size of 25 to 300 nm (more preferably 30 to 200 nm). When the average particle size is less than the lower limit, it tends to be difficult to recover nanoparticles by filtration or centrifugation, while on the other hand, when the average particle size exceeds the upper limit, strong light scattering occurs, or uniform chemical modification of the inside of the particles occurs. Due to the difficulty, applications tend to be limited to adsorbents and the like. For such an average particle diameter, the particle diameter (diameter) of arbitrary 200 or more particles is measured with a scanning electron microscope (for example, trade name "SU3500" manufactured by Hitachi High-Technologies Corporation), and the average value is calculated. It can be obtained by When the particles are not true spheres, the average value of the diameter of the smallest circumscribing circle of the particles and the diameter of the largest circumscribing circle of the particles is adopted as the “particle diameter” of each particle. In addition, the particle size of any 200 or more particles can be calculated by measuring the particle size of each particle based on an image obtained by a scanning electron microscope. The average particle size of such mesoporous silica nanoparticles can be easily controlled within the above range by appropriately controlling the reaction time according to the type of raw material used.

Further, the mesoporous silica nanoparticles obtained by the present invention preferably have a standard deviation of particle diameter of 30 nm or less, more preferably 15 nm or less. When the standard deviation of the particle diameter exceeds the upper limit, the difference in the structural characteristics (surface area, outer surface area, mesopore length, etc.) of individual mesoporous silica nanoparticles becomes large, and it tends to be difficult to control the physical properties. .. In addition, such a standard deviation is the same as the above-mentioned measurement of the average particle diameter, and the particle diameter of arbitrary 200 or more particles by a scanning electron microscope (for example, trade name "SU3500" manufactured by Hitachi High-Technologies Corporation). It can be obtained by using the measured data. Such a standard deviation can be easily set within the above range by appropriately changing the volume of the aqueous solution, the stirring conditions during the reaction, and the like according to the type of raw material used.

Further, the but are not particularly limited specific surface area of mesoporous silica nanoparticles, preferably at ^{50 m} 2 / g or more, more preferably 70~1500m ² / g. Such a specific surface area is obtained by using an adsorption isotherm in a relative pressure range of 0.05 to 0.2 from a nitrogen adsorption/desorption isotherm and using a BET (Brunauer-Emmett-Teller) adsorption isotherm. It can be calculated as the surface area.

Further, the pore volume of the mesoporous silica nanoparticles is not particularly limited, but is preferably 0.2 cm ³ /g or more, more preferably 0.3 cm ³ /g or more. If the pore volume is less than the lower limit, the amount of nanoparticles or compounds that can be adsorbed in the pores tends to be insufficient. Such pore volume can be calculated from the nitrogen adsorption/desorption isotherm by t-plot test.

In addition, such mesoporous silica nanoparticles have a porosity of 20 to 75% when the density of the silica skeleton is assumed to be 2 g/cm ³ (volume occupied by the silica skeleton is 0.5 cm ³ /g). It is more preferably 40 to 65%. If the porosity is less than the lower limit, it tends to be impossible to utilize the inside or surface of the pores for physical property control, while if the porosity exceeds the upper limit, the mechanical strength of the particles tends to decrease, and the application tends to be limited. It is in.

Hereinafter, the present invention will be described more specifically based on Examples, but the present invention is not limited to the following Examples.

First, a method of evaluating the characteristics of the particles obtained in each example will be described.

<Measurement of average particle size and standard deviation of particles>
The average particle size and standard deviation of the particles obtained in each example were measured by observation with a scanning electron microscope (SEM). For such measurement, a trade name "SU3500" manufactured by HITACHI was used as a scanning electron microscope (SEM). Further, in such a measurement, from the scanning electron microscope (SEM) image (observation image) of the particles obtained in each example, 200 particles were arbitrarily (randomly) selected, and the 200 particles were selected. The average particle diameter of the nanoparticles and the standard deviation of the particle diameters were determined by measuring the particle diameter (diameter) of. When the selected particles are not true spheres, the average value of the diameter of the smallest circumscribing circle of the particles and the diameter of the largest circumscribing circle of the particles is adopted as the “particle diameter” of each particle. ..

<Measurement of specific surface area>
The specific surface area of the particles obtained in each example was measured as follows. First, a nitrogen adsorption/desorption isotherm was measured using a gas adsorption amount measuring device (trade name “Autosorb-1”) manufactured by Quantachrome. In addition, such a nitrogen adsorption/desorption isotherm was measured by determining the adsorption amount of nitrogen gas by the gas adsorption method (using the constant volume method) at the liquid nitrogen temperature (-196° C.) (the following average pore diameter, etc.). The nitrogen adsorption/desorption isotherm measured by such a method was used as the nitrogen adsorption/desorption isotherm during the measurement of the respective characteristics of 1.). Then, from the obtained nitrogen adsorption/desorption isotherm, the specific surface area was determined by the BET (Brunauer-Emmett-Teller) method using the adsorption isotherm in the relative pressure range of 0.05 to 0.2.

<Measurement of pore diameter>
The pore diameter of the particles obtained in each example was determined as follows. That is, from the nitrogen adsorption-desorption isotherm measured as described above, the pore diameter distribution curve is obtained by the density functional method (density functional method based on the equilibrium adsorption model) using the adsorption isotherm of nitrogen, and the pore diameter is calculated. The pore diameter (pore diameter) at the maximum peak of the distribution curve was determined by measuring the pore diameter of the particles obtained in each example.

<Measurement of pore volume and porosity>
The pore volume of the particles obtained in each example was determined as follows. That is, first, from the nitrogen adsorption/desorption isotherms measured as described above, the adsorption isotherms in the relative pressure range of 0.6 to 0.8 are used to calculate by the t-plot method. The pore volume of the particles obtained in the examples was determined. Further, from the value of the pore volume obtained as described above, the porosity of each particle (when the density of the silica skeleton is 2 g/cm ³ (that is, the volume occupied by the silica skeleton is 0.5 cm ³ /g)) Porosity between particles is not included. The porosity is calculated by calculating the porosity derived from the mesoporous structure.

(Example 1)
In a 100 mL round-bottomed flask, a stirrer (diameter 7 mm, length 20 mm: a stirrer of the same size was used in each of the following examples) and hexadecyltrimethylammonium chloride (surfactant) 10% by mass. Aqueous solution (60 mL) and triethanolamine (0.18 g) as a hydrolysis catalyst were added to obtain an aqueous solution containing a surfactant and a hydrolysis catalyst. Then, after heating the aqueous solution to 50° C., while heating the aqueous solution so that the temperature of the aqueous solution can be maintained at 50° C., tetrapropoxysilane (4 mL: manufactured by Tokyo Kasei Kogyo Co., Ltd. "Tetropropyl Orthosilicate", a stock solution having a purity of 98% by mass (content of organic solvent: 0% by mass) was used as it was without being diluted with an organic solvent. Tetrapropoxysilane was used) was slowly added and floated so as not to form an emulsion (after slowly developing), and then a magnetic stirrer was used to rotate at a speed of 150 rpm while maintaining a temperature condition of 50°C. Then, the mixture was stirred for 10 hours to form nanoparticles in the aqueous solution. During such stirring, the state in which tetrapropoxysilane floated on the water surface of the aqueous solution was maintained.

The nanoparticles thus produced were collected by centrifugation (4000 rpm, 1 hour). Then, the operation of re-dispersing in a mixed liquid of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol]/[concentrated hydrochloric acid] of 200/1) of 60 mL and collecting by centrifugation was repeated twice (surfactant Removal process). Next, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol to finally collect the nanoparticles as a dispersion liquid (solvent: ethanol). The total amount of the obtained nanoparticles was 0.44 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement using such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 89 nm, and the standard deviation of the particle diameter was 9.9 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 2, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 3, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the nanoparticles have a BET specific surface area of 974 m ² /g, a pore diameter of 4.3 nm, a pore volume of 0.63 cm ³ /g, and a porosity of 56%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 2)
A stirrer, an aqueous solution (60 mL) containing 10 mass% of hexadecyltrimethylammonium chloride (surfactant) and triethanolamine (0.18 g) as a hydrolysis catalyst were added to a 100 mL eggplant flask. An aqueous solution containing a surfactant and a hydrolysis catalyst was obtained. Next, after heating the aqueous solution to 80° C., while heating the aqueous solution so that the temperature of the aqueous solution can be maintained at 80° C., tetraisopropoxysilane (4 mL: trade name of Tokyo Kasei Kogyo Co., Ltd. After slowly adding "Tetraisopropyl Orthosilicate", a stock solution having a purity of 99% by mass (content of the organic solvent of 0% by mass without diluting it with an organic solvent) was slowly added so as not to form an emulsion and floated. (After slowly developing), while maintaining the temperature condition of 80° C., stirring was performed at a speed of 150 rpm for 10 hours using a magnetic stirrer to form nanoparticles in the aqueous solution. During such stirring, the state in which tetrapropoxysilane floated on the water surface of the aqueous solution was maintained.

The nanoparticles thus produced were collected by centrifugation (4000 rpm, 1 hour). Then, the operation of re-dispersing in a mixed liquid of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol]/[concentrated hydrochloric acid] of 200/1) of 60 mL and collecting by centrifugation was repeated twice (surfactant Removal process). Next, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol to finally collect the nanoparticles as a dispersion liquid (solvent: ethanol). The total amount of the obtained nanoparticles was 0.11 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of measurement by such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 137 nm and a standard deviation of particle diameter of 28.3 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 4, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 5, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the nanoparticles have a BET specific surface area of 1053 m ² /g, a pore diameter of 5.1 nm, a pore volume of 0.97 cm ³ /g, and a porosity of 66%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 3)
A stirrer, an aqueous solution (60 mL) containing 10 mass% of hexadecyltrimethylammonium chloride (surfactant) and triethanolamine (0.18 g) as a hydrolysis catalyst were added to a 100 mL eggplant flask. An aqueous solution containing a surfactant and a hydrolysis catalyst was obtained. Then, under room temperature (25° C.) conditions, tetrapropoxysilane (4 mL) was slowly added and floated on the water surface of the aqueous solution so as not to form an emulsion (after slowly developing), and then at room temperature (25° C.). (°C) condition, the mixture was stirred using a magnetic stirrer at a speed of 150 rpm for 48 hours to form nanoparticles in the aqueous solution. During such stirring, the state in which tetrapropoxysilane floated on the water surface of the aqueous solution was maintained.

The nanoparticles thus produced were collected by centrifugation (4000 rpm, 1 hour). Then, the operation of re-dispersing in a mixed liquid of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol]/[concentrated hydrochloric acid] of 200/1) of 60 mL and collecting by centrifugation was repeated twice (surfactant Removal process). Next, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol to finally collect the nanoparticles as a dispersion liquid (solvent: ethanol). The total amount of the obtained nanoparticles was 0.11 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement by such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 52 nm and a standard deviation of the particle diameter of 8.2 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 6, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. 7. As is clear from the results shown in FIG. 7, IV type hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the nanoparticles have a BET specific surface area of 1482 m ² /g, a pore diameter of 4.3 nm, a pore volume of 0.82 cm ³ /g, and a porosity of 62%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 4)
A stirrer, an aqueous solution (60 mL) containing 10 mass% of hexadecyltrimethylammonium chloride (surfactant) and triethanolamine (0.18 g) as a hydrolysis catalyst were added to a 100 mL eggplant flask. An aqueous solution containing a surfactant and a hydrolysis catalyst was obtained. Then, after heating the aqueous solution to 50° C., while slowly heating the aqueous solution so that the temperature of the aqueous solution can be maintained at 50° C., tetrapropoxysilane (8 mL) was slowly added onto the water surface of the aqueous solution so that an emulsion was not formed. After adding and floating (after slowly developing), the mixture was stirred for 5 hours at a speed of 150 rpm using a magnetic stirrer while maintaining the temperature condition of 50° C. to form nanoparticles in the aqueous solution. During such stirring, the state in which tetrapropoxysilane floated on the water surface of the aqueous solution was maintained.

The nanoparticles thus produced were collected by centrifugation (4000 rpm, 1 hour). Then, the operation of re-dispersing in a mixed liquid of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol]/[concentrated hydrochloric acid] of 200/1) of 60 mL and collecting by centrifugation was repeated twice (surfactant Removal process). Next, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol, and finally the nanoparticles were collected as a dispersion liquid (solvent: ethanol). The total amount of the obtained nanoparticles was 0.14 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement with such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 64 nm and a standard deviation of the particle diameter of 8.7 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 8, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 9, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the BET specific surface area of the nanoparticles is 935 m ² /g, the pore diameter is 4.3 nm, the pore volume is 0.57 cm ³ /g, and the porosity is 53%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 5)
Nanoparticles were collected as a dispersion (solvent: ethanol) in the same manner as in Example 4 except that the time for stirring the aqueous solution was changed from 5 hours to 10 hours to obtain nanoparticles. The total amount of the obtained nanoparticles was 0.29 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement by such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 89 nm and a standard deviation of the particle diameter was 7.0 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 10, as a result of measurement by a scanning electron microscope (SEM), it was confirmed that the obtained particles were spherical.

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 11, IV type hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, it is found that the BET specific surface area of the nanoparticles is 1023 m ² /g, the pore diameter is 4.3 nm, the pore volume is 0.68 cm ³ /g, and the porosity is 58%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 6)
The nanoparticles were collected as a dispersion liquid (solvent: ethanol) in the same manner as in Example 4 except that the time for stirring the aqueous solution was changed from 5 hours to 24 hours to obtain nanoparticles. The total amount of the obtained nanoparticles was 0.78 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement using such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 115 nm and a standard deviation of particle diameter of 10.4 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 12, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 13, IV type hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, it is found that the BET specific surface area of the nanoparticles is 829 m ² /g, the pore diameter is 4.3 nm, the pore volume is 0.52 cm ³ /g, and the porosity is 51%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 7)
Instead of using tetrapropoxysilane (4 mL), tetraethoxysilane (4 mL: product name “Tetraethyl Orthosilicate” manufactured by Tokyo Kasei Kogyo Co., Ltd., a stock solution with a purity of 96% by mass (content of organic solvent 0% by mass) was diluted with an organic solvent. The nanoparticles were recovered as a dispersion liquid (solvent: ethanol) in the same manner as in Example 1 except that the nanoparticles were used as they were. The total amount of the obtained nanoparticles was 0.99 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement by such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 90 nm and a standard deviation of particle diameter of 10.7 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 14, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 15, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the BET specific surface area of the nanoparticles was 449 m ² /g, the pore diameter was 3.5 nm, the pore volume was 0.21 cm ³ /g, and the porosity was 29%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 8)
Nanoparticles as dispersion (solvent: ethanol) were obtained in the same manner as in Example 4 except that the amount of the aqueous solution containing hexadecyltrimethylammonium chloride (surfactant) at a ratio of 10 mass% was changed from 60 mL to 20 mL. Were collected to obtain nanoparticles. The total amount of the obtained nanoparticles was 0.15 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of the measurement with such a scanning electron microscope (SEM), it was confirmed that the obtained nanoparticles had an average particle diameter of 91 nm and a standard deviation of the particle diameter of 9.4 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 16, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 17, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the nanoparticles have a BET specific surface area of 1322 m ² /g, a pore diameter of 4.3 nm, a pore volume of 0.91 cm ³ /g, and a porosity of 65%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 9)
Nanoparticles as dispersion (solvent: ethanol) were obtained in the same manner as in Example 5 except that the amount of the aqueous solution containing hexadecyltrimethylammonium chloride (surfactant) at a ratio of 10% by mass was changed from 60 mL to 20 mL. Were collected to obtain nanoparticles. The total amount of the obtained nanoparticles was 0.39 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of such a scanning electron microscope (SEM) measurement, it was confirmed that the obtained nanoparticles had an average particle diameter of 126 nm and a standard deviation of particle diameter of 10.2 nm. Further, as is clear from the scanning electron microscope photograph shown in FIG. 18, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 19, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, it is found that the BET specific surface area of the nanoparticles is 943 m ² /g, the pore diameter is 4.3 nm, the pore volume is 0.66 cm ³ /g, and the porosity is 57%. confirmed. From the above results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 10)
In a 60 mL cylindrical sample bottle (35 mm in diameter), an agitator, an aqueous solution (10 mL) containing hexadecyltrimethylammonium chloride (surfactant) at a ratio of 20% by mass, and triethanolamine (0. 10 g) was added to obtain an aqueous solution containing a surfactant and a hydrolysis catalyst. Then, after heating the aqueous solution to 50° C., tetrapropoxysilane (8 mL) was slowly added to the surface of the water while heating so that the temperature of the aqueous solution could be maintained at 50° C. After that (after slowly developing), the mixture was stirred at a temperature of 50° C. at a speed of 150 rpm for 10 hours using a magnetic stirrer to form nanoparticles in the aqueous solution. During such stirring, the state in which tetrapropoxysilane floated on the water surface of the aqueous solution was maintained.

The nanoparticles thus produced were collected by centrifugation (4000 rpm, 1 hour). Then, the operation of re-dispersing in a mixed liquid of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol]/[concentrated hydrochloric acid] of 200/1) of 60 mL and collecting by centrifugation was repeated twice (surfactant Removal process). Next, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol to finally collect the nanoparticles as a dispersion liquid (solvent: ethanol). The total amount of the obtained nanoparticles was 0.17 g.

The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM) to determine the average particle size and standard deviation. A scanning electron micrograph of such nanoparticles is shown in FIG. As a result of such a scanning electron microscope (SEM) measurement, it was confirmed that the obtained nanoparticles had an average particle diameter of 178 nm and a standard deviation of particle diameter of 15.0 nm. Further, as is clear from the scanning electron micrograph shown in FIG. 20, it was also confirmed that the obtained particles were spherical as a result of measurement by a scanning electron microscope (SEM).

Further, the nanoparticles in the dispersion liquid were collected by heating the ethanol dispersion medium to be distilled off, dried, and then the nitrogen adsorption/desorption isotherm was determined. The obtained nitrogen adsorption/desorption isotherm is shown in FIG. As is clear from the results shown in FIG. 21, type IV hysteris was confirmed in the nitrogen adsorption/desorption isotherm. From the nitrogen adsorption/desorption isotherm, the nanoparticles have a BET specific surface area of 1145 m ² /g, a pore diameter of 4.0 nm, a pore volume of 0.79 cm ³ /g, and a porosity of 61%. confirmed. Based on these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

[Regarding each nanoparticle obtained in Examples 1 to 10]
Table 1 shows the characteristics and the like of the nanoparticles obtained in each example. In Table 1, TPOS represents tetrapropoxysilane, TIPOS represents tetraisopropoxysilane, and TEOS represents tetraethoxysilane. Further, a graph showing the relationship between the particle diameter of the nanoparticles obtained in Examples 4 to 6 and the reaction time is shown in FIG.

As is clear from the results shown in Table 1, in the method for producing mesoporous silica nanoparticles of the present invention (Examples 1 to 10), it was confirmed that mesoporous silica nanoparticles can be produced without using an organic solvent. ..

Further, as is clear from the description in Table 1, comparing Example 1 and Example 3, the temperature conditions during stirring (reaction temperature) and stirring time (reaction time) were different, but the reaction temperature was 50°C. It was confirmed that in the case of (Example 1), the particles can be grown more efficiently than in the case of reacting at room temperature (Example 3). Further, as is clear from the description in Table 1, comparing Example 1 and Example 5 shows that the amounts of tetrapropoxysilane used are different, but the nano-particles obtained in Example 1 and Example 5 are different. When the structural characteristics of the particles are compared, it is clear that they are almost the same, and as in the present invention, the undiluted silane raw material (undiluted tetrapropoxysilane) is floated on the water surface (expansion). It was found that the reaction rate hardly depends on the addition amount of the silane raw material when the conditions such as the temperature and the amount of water are constant when the reaction is carried out. Such a result shows that when the undiluted silane raw material (undiluted tetrapropoxysilane) is allowed to react on the water surface (in the unfolded state) when the water surface area is the same, the silane to the water layer is the same. It is considered that the supply of the raw material is almost constant regardless of the amount of the silica raw material used. As described above, the reason why the supply of the silane raw material to the water layer becomes almost constant when the temperature and the like are constant is presumed that the reaction rate of hydrolysis depends on the area of the water surface.

Furthermore, as is clear from the results shown in Table 1 and FIG. 22, the relationship between the reaction time and the particle size (particle diameter) was shown for Examples 4 to 6 in which the reaction liquid composition was the same and only the reaction time was changed. As a result of the examination and plotting, from the obtained graph (FIG. 22), assuming that the particle diameter is d and the reaction time is t, the following relational expression:
d=39.9×(t) ^1/3
It was found that it can be approximated by (which can be approximated by a relational expression proportional to the 1/3 power of the reaction time). Such a result shows that when the undiluted silane raw material (undiluted tetrapropoxysilane) is allowed to react on the water surface (in the expanded state), the silane raw material is supplied to the water layer at the reaction time. It is thought that this is because it becomes almost constant regardless of the value. The reason why the supply of the silane raw material into the aqueous solution is almost constant is supposed to be that the reaction rate of hydrolysis depends on the area of the water surface. Further, from such results, by allowing an undiluted silica raw material made of tetraalkoxysilane to float on the water surface of the aqueous solution to allow the reaction to proceed, it is possible to precisely control the particle size of the mesoporous silica nanoparticles simply by controlling the reaction time. Obviously, it will be possible to control (or predict). From these results, by floating an undiluted silica raw material made of tetraalkoxysilane on the water surface of the aqueous solution and reacting it, only by controlling the reaction time, the desired mesoporous silica nanoparticles are synthesized in the aqueous solution. Therefore, according to such a method, for example, it is not necessary to control the particle size by controlling the concentration of the silica raw material in the aqueous solution or to control the pH, and to efficiently obtain the desired particle size. The present inventors presume that these nanoparticles can be produced.

Further, as is clear from the results shown in Table 1, it can be seen from the results of Example 4 and Example 8 that, even if the reaction conditions and reaction times are the same, the particles formed are different depending on the amount of the aqueous solution (aqueous layer). The average particle diameter is different, and the average particle diameter of the nanoparticles obtained in Example 8 is about 1. while maintaining the characteristics such as porosity with respect to the average particle diameter of the nanoparticles obtained in Example 4. It turned out that it was expanded four times. Similarly, from the results of Example 5 and Example 9, the average particle size of the particles formed was different depending on the amount of the aqueous solution (aqueous layer) even under the same reaction conditions and reaction times. It was found that the average particle size of the nanoparticles obtained in Example 9 was expanded about 1.4 times the average particle size of the obtained nanoparticles while maintaining properties such as porosity. .. In addition, in Examples 8 and 9, as compared with Examples 4 and 5, the reaction basically proceeds under the condition that the concentration of the silica raw material (hydrolyzed silica raw material) introduced into the aqueous solution is higher. It is supposed to do. From the results of Examples 8 and 9 as described above, according to the present invention, the concentration of the silica raw material (hydrolyzed silica raw material) introduced into the aqueous solution is set to a higher concentration, and the nanoparticles are grown more efficiently. It has become clear that it is also possible to do.

As described above, according to the present invention, it is possible to produce mesoporous silica nanoparticles without using an organic solvent, and to provide a method for producing mesoporous silica nanoparticles that can eliminate the step of removing the organic solvent. It becomes possible to do.

Thus, the method for producing mesoporous silica nanoparticles of the present invention can produce mesoporous silica nanoparticles without using an organic solvent. It is particularly useful as a method for producing

1... Reaction vessel, 2... Silica raw material, 3... Aqueous solution, 4... Silica particles, I... Interface between upper layer and lower layer, A... Direction of introducing hydrolyzed silica raw material from upper layer to lower layer.

Claims (3)

On the water surface of an aqueous solution containing a surfactant and a hydrolysis catalyst, in a state in which an undiluted silica raw material composed of tetraalkoxysilane is floated , stirring is performed so that an emulsion of the undiluted silica raw material is not formed in the aqueous solution. while, the silica raw material allowed hydrolysis method of mesoporous silica nanoparticles, characterized in that to produce the mesoporous silica nanoparticles in the aqueous solution. The method for producing mesoporous silica nanoparticles according to claim 1, wherein the tetraalkoxysilane has 8 to 16 carbon atoms. The method for producing mesoporous silica nanoparticles according to claim 1 or 2, wherein the temperature condition for producing the mesoporous silica nanoparticles is 20 to 95°C.