JP2017171509A - Method for producing mesoporous silica nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing mesoporous silica nanoparticles capable of producing mesoporous silica nanoparticles without utilizing organic solvents and capable of eliminating a removing step for organic solvents.SOLUTION: Provided is a method for producing mesoporous silica nanoparticles characterized in that, in a state where non-diluted silica raw material made of tetraalkoxysilane is floated on the water face of an aqueous solution including a surfactant and a hydrolysis catalyst, the silica raw material is subjected to hydrolysis, and the mesoporous silica nanoparticles are produced in the aqueous solution.SELECTED DRAWING: None

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. It 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, published 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, cyclohexene as a solvent, and cationic cetyltrimethylammonium as a template. A method of forming mesoporous silica nanoparticles by self-assembly using a lower layer interface composed of an aqueous solution containing chloride and triethanolamine as a catalyst is disclosed.

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

  However, in such a method described in Non-Patent Document 1, a solution of tetraethoxysilane using a hydrophobic organic solvent such as 1-octadecene, decahydronaphthalene, cyclohexene or the like in the upper layer (with a hydrophobic organic solvent). Diluted silane raw material: In addition, referring to Table 1 in the above Non-Patent Document 1, it 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 using such an organic solvent, after the production of mesoporous silica nanoparticles, an organic solvent removal step (separation, recovery, disposal, etc. of the organic solvent) is required, which is economical and efficient. It was not always enough.

  The present invention has been made in view of the above-described problems of the prior art, can produce mesoporous silica nanoparticles without using an organic solvent, and can eliminate the need for a step of removing the organic solvent. It aims at providing the manufacturing method of a silica nanoparticle.

  As a result of intensive studies to achieve the above object, 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, mesoporous silica nanoparticles can be produced without using an organic solvent, and the organic solvent removal step can be eliminated. As a result, the present invention has been completed.

  That is, the method for producing mesoporous silica nanoparticles of the present invention hydrolyzes a silica raw material in a state where an undiluted silica raw material made of tetraalkoxysilane is floated on the water surface of an aqueous solution containing a surfactant and a hydrolysis catalyst. It is a method characterized by forming mesoporous silica nanoparticles 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, it is preferable that the temperature condition for producing the mesoporous silica nanoparticles is 20 to 95 ° C.

  In addition, according to the method for producing mesoporous silica nanoparticles of the present invention, mesoporous silica nanoparticles can be produced without using an organic solvent, and it becomes possible to eliminate the step of removing the organic solvent. When the amount of aqueous solution with respect to the area of the water surface is constant, the relationship between the reaction time and the average particle diameter of the obtained nanoparticles can be determined by a unique mathematical formula, and the average particle of the nanoparticles with respect to the reaction time The degree of expansion of the average particle diameter of the nanoparticles (the degree of particle growth by self-organization) is controlled by controlling the reaction time so that the degree of diameter expansion can be easily predicted and the target size is achieved. It is also possible. The reason why such an effect is achieved is not necessarily clear, but the present inventors speculate as follows (Note that this point will be simply described below with reference to the drawing (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. In addition, the symbol I in FIG. 1 conceptually shows the interface between the upper layer (layer consisting of silica raw material 2) and the lower layer (layer consisting of aqueous solution 3), and arrow A is silica hydrolyzed from the upper layer to the lower layer. It conceptually shows the state in which the raw material is introduced (added) (the state of permeation), that is, the direction in which the hydrolyzed silica raw material is introduced. In this invention, a silica raw material is hydrolyzed in the state which floated the undiluted silica raw material 2 which consists of tetraalkoxysilane on the water surface of the aqueous solution 3 containing surfactant and a hydrolysis catalyst. The “undiluted silica raw material” as used herein is substantially not diluted with an organic solvent and contains 90% by mass or more of tetraalkoxysilane (for example, a tetraalkoxysilane stock solution). Say. By using tetraalkoxysilane without using an organic solvent in this way, the composition of the reaction solution is simplified, and at the same time, quantitative control of the amount of silica raw material in contact with the water surface is possible, and the reaction rate is kept lower. It becomes possible. Further, such tetraalkoxylane is a liquid insoluble in water at the stage before hydrolysis. In the present invention, such a tetraalkoxysilane is floated on the water surface in an undiluted state, and the tetraalkoxysilane in contact with water is hydrolyzed at the interface I between the aqueous solution 3 layer and the silica raw material 2 layer. (The silica raw material is hydrolyzed in the phase-separated state). Thus, when the tetraalkoxysilane is hydrolyzed at the interface I, a silanol group is generated by hydrolysis, and the hydrolyzed silica raw material permeates into the aqueous solution 3, and the hydrolyzed silica raw material becomes the aqueous solution 3. (See arrow A in the figure). In the present invention, as described above, since the undiluted tetraalkoxysilane in which the reaction proceeds relatively slowly is used as a raw material, the hydrolysis reaction rate can be further reduced, and the aqueous solution 3 The penetration of the silane raw material (the raw material after hydrolysis) slowly occurs through the interface I between the undiluted silane raw material layer 2 and the aqueous solution 3. In addition, since such a hydrolysis reaction is a reaction that occurs at the interface I with water, it is assumed that the hydrolysis proceeds at a constant rate in proportion to the area of the water surface. It is thought that it proceeds at a constant speed. On the other hand, in the aqueous solution 3, the hydrolyzed silica raw material and the surfactant are combined to form a composite (particularly, after the silica core is formed from the hydrolyzed silica raw material, the silica skeleton is formed). Is considered to be compounded at the stage of growth). In such a composite, silica (silicon oxide) particles grow in a self-organized manner by successive condensation of silanol groups generated by hydrolysis. Thus, when the silica particles grow (when 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 for the pores, and the silica particles 4 in which the surfactant is introduced into the pore portions 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, the reaction time is determined when the amount of the aqueous solution relative to the surface area is constant. 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 diameter of the obtained nanoparticles. Therefore, in the present invention, the degree of expansion of the average particle diameter of the nanoparticles 4 with respect to the reaction time can be easily predicted, and by controlling the reaction time so as to have the target size, the average particle diameter of the nanoparticles 4 can be controlled. The inventors speculate that it is possible to synthesize nanoparticles while controlling the degree of expansion (the degree of particle growth by 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) to be used is reduced according to the intended design. It is possible.

  In the present invention, since most of the silica raw material before hydrolysis exists in a state separated from the aqueous layer (layer consisting of the aqueous solution 3) (basically, the hydrolysis reaction is performed in a phase separated state), water The present inventors infer that the concentration of the silane raw material in the layer can be kept relatively low and the reaction rate can be kept low. And in this invention, in order to hydrolyze a silica raw material through the interface I of the layer of the silica raw material 2 and the layer of the aqueous solution 3, using the undiluted silica raw material 2 which consists of tetraalkoxysilane insoluble in water, Since the silica raw material after hydrolysis can be slowly slowly introduced into the aqueous solution 3 at a constant rate, and the mesoporous silica nanoparticles 4 are slowly generated in the aqueous solution 3 at a constant rate. It is also possible to promote uniform particle growth. Further, in the present invention, an undiluted silica raw material made of tetraalkoxysilane insoluble in water is floated on water, so that a 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 almost constant regardless of the reaction time (even if a hydrolyzed raw material is introduced in the water, the layer made of the upper silica raw material 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 consisting of 100% by mass of tetraalkoxysilane is used, the reaction Even if it progresses, a silica raw material layer 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 depends on the reaction time. Not can be kept substantially constant.). In this regard, when a silica raw material diluted with a large amount of an organic solvent as described in Non-Patent Document 1 is used, 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 layer) increases greatly, and the reaction rate changes due to this. Therefore, in the method as 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 speculate that it is difficult to efficiently manage the degree of diameter growth by reaction time or the like.

  Thus, in the present invention, by using an undiluted silica raw material that is not diluted with an organic solvent and contains 90% by mass or more of tetraalkoxysilane as a silica raw material. In addition, it is possible to efficiently advance the reaction at a constant rate, and thus it is possible to express the relationship between the reaction time and the particle diameter of the generated mesoporous silica nanoparticles with a simple mathematical formula. In the present invention, the concentration of the silica raw material penetrating into the aqueous layer can be kept relatively low by allowing the silica raw material to float in water (in a phase-separated state) and reacting it. The present inventors speculate that it is possible to produce particles while controlling the reaction rate to be suitable for production.

  As described above, according to the present invention, the degree of expansion of the average particle diameter of the nanoparticles (the degree of particle growth by self-organization) can be efficiently controlled by the reaction time. The present inventors speculate that it is possible to efficiently produce designed (size, etc.) nanoparticles. Further, in the method for producing mesoporous silica nanoparticles of the present invention, 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 speculate that the method for producing mesoporous silica nanoparticles of the present invention can reduce the organic solvent removal step and is excellent in terms of efficiency and economy (cost).

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

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

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

  The method for producing mesoporous silica nanoparticles of the present invention comprises hydrolyzing the silica raw material in a state where an undiluted silica raw material made of tetraalkoxysilane is floated on the water surface of an aqueous solution containing a surfactant and a hydrolysis catalyst. The method is characterized in that mesoporous silica nanoparticles are produced 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 silicon oxide, and can be used for producing mesoporous silica nanoparticles. A known surfactant can be appropriately used. Among such 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 suitably used. Further, among these surfactants, alkyltrimethylammonium halides having a long-chain alkyl group having 9 to 26 carbon atoms such as tetradecyltrimethylammonium halide, hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide and the like are preferable, and tetradecyl is preferred. Trimethylammonium halide and hexadecyltrimethylammonium halide are more preferable, and tetradecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride are more preferable.

  As described above, such a surfactant is introduced into the silica raw material and functions as a template for pore formation. In general, the surfactant is considered to form a composite with a hydrolyzed silica raw material in an aqueous solution during the reaction (after the silica skeleton is formed, the silica skeleton grows). It is thought to be compounded). In such a composite, a reaction in which the silanol group of the silica raw material condenses proceeds to form silicon oxide (silica). On the other hand, silicon oxide is not generated in the part 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. Such surfactants 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. Since it is considered to work and the type greatly affects the shape of the pores of the porous body, it is preferable to use one type alone from the viewpoint of obtaining more uniform nanoparticles.

  The hydrolysis catalyst according to the present invention is not particularly limited as long as it can promote hydrolysis of tetraalkoxysilane, and a known hydrolysis catalyst 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 or polycondensation reaction at the interface between tetraalkoxysilane and water. Examples of such amines include triethanolamine, triethylamine, trimethylamine, and ammonia. Of these amines, triethanolamine and triethylamine are more preferable, and triethanolamine is particularly preferable from the viewpoint of low volatility. Such hydrolysis catalysts may be used singly or in combination of two or more.

  The aqueous solution according to the present invention contains a surfactant and a hydrolysis catalyst. The water used as the solvent for such an aqueous solution is not particularly limited, and for example, ion exchange water may be used. Further, the concentration of the surfactant in such an aqueous solution is not particularly limited, but is preferably 2 to 25% by mass, and more preferably 5 to 20% by mass. If the concentration of such a surfactant is less than the above lower limit, the micelle formation of the surfactant is inhibited, and the template function of mesopore formation tends to be reduced. On the other hand, if the upper limit is exceeded, 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 the hydrolysis catalyst is less than the lower limit, hydrolysis does not proceed easily, and the yield of finally obtained silica nanoparticles tends to decrease. On the other hand, if the concentration exceeds the upper limit, the hydrolysis reaction is accelerated. This tends to make it difficult to control the particle diameter.

  Moreover, the aqueous solution concerning this invention should just consist of water, surfactant, and a hydrolysis catalyst, and may contain another component in the range which does not impair the effect of this invention. From the viewpoint of allowing the reaction to proceed more efficiently, the aqueous solution according to the present invention is more preferably composed essentially of water, a surfactant and a hydrolysis catalyst, and water, surfactant and hydrolysis are more preferable. Those consisting only of a catalyst are particularly preferred.

  Moreover, in this invention, the undiluted silica raw material which consists of tetraalkoxysilane is used as a silica raw material. Here, the “undiluted silica raw material comprising tetraalkoxysilane” is substantially not diluted with an organic solvent, and 90% by mass of tetraalkoxysilane (more preferably 95 to 100% by mass, More preferably 97-100% by mass, particularly preferably 100% by mass) or more. Thus, “undiluted silica raw material comprising tetraalkoxysilane” is 90% by mass of tetraalkoxysilane (more preferably 95-100% by mass, still more preferably 97-100% by mass, particularly preferably 100% by mass). ) It contains in the above ratio. Further, "substantially not diluted with an organic solvent" here means that the amount of the organic solvent is preferably 10% by mass or less (more preferably 5% by mass or less, even if it is contained in the raw material). It is preferably 3% by mass or less, particularly preferably 1% by mass or less. As described above, the “undiluted silica raw material” is substantially not diluted with an organic solvent (as described above, the amount of the organic solvent is 10% by mass or less even if contained in the raw material). It is preferable that it contains tetraalkoxysilane in a proportion of 90% by mass or more, and among them, the organic solvent content is most preferably 0% by mass. Since tetraalkoxysilane is basically liquid at room temperature (25 ° C.), the silica raw material is basically a liquid material.

  In the present invention, undiluted silica raw material composed of tetraalkoxysilane as described above is used for the production (synthesis) of mesoporous silica nanoparticles. Here, in the synthesis of mesoporous silica nanoparticles, it is considered that three processes of nucleation, growth of a silica skeleton, and complexing of a surfactant and silica act in a complex manner. In order to form good quality nanoparticles, it is necessary to cause nucleation at the initial stage of the reaction, and then stably grow the silica skeleton. Here, if the reactivity of the silica raw material is too high, the complexing with the surfactant does not proceed sufficiently and a sufficient porous structure is not 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 composite of the silica raw material and the surfactant proceeds rapidly. There is a need to. Therefore, in the present invention, mesoporous silica nanoparticles are synthesized using an undiluted silica raw material made of tetraalkoxysilane so that the above three processes occur in a well-balanced manner.

  Although it does not restrict | limit especially as such a tetraalkoxysilane, It is preferable that carbon number is 8 or more (more preferably 8-16, still more preferably 8-14, especially preferably 10-14). If the number of carbon atoms is less than the lower limit, the hydrolysis reaction proceeds fast and it becomes difficult to control particle growth, or the silica raw material layer tends to be immediately mixed with the aqueous solution layer. When the upper limit is exceeded, the hydrolysis reaction does not proceed under mild reaction conditions, and the yield of nanoparticles tends to decrease rapidly.

Moreover, as said tetraalkoxysilane, following General formula (1):
Si (OR) ₄ (1)
(In Formula (1), a plurality of R's each independently represents an alkyl group.)
It is preferable that it is a compound represented by these. Such an alkyl group selected as R preferably has 2 or more carbon atoms, more preferably 2 to 4 carbon atoms, and particularly preferably 3 carbon atoms. If the number of carbon atoms is less than the lower limit, the silica raw material tends to be immediately mixed in the aqueous solution layer (aqueous layer) and it becomes difficult to form a phase-separated state. Under such reaction conditions, it tends to be difficult to proceed with the hydrolysis reaction. Such an alkyl group may be linear or branched.

  As such tetraalkoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetratetrasilane, from the viewpoint of controlling the activity to such an extent that it has moderate hydrolysis reactivity and does not easily react with moisture in the atmosphere. 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 alone from the viewpoint of controlling the reaction rate.

  Further, as described above, the undiluted silica raw material only needs to have a tetraalkoxysilane concentration (purity) of 90% by mass or more. You may contain. Examples of such other components include trialkoxysilane, dialkoxysilane, and monoalkoxysilane.

  Further, such an undiluted silica raw material may be one having a tetraalkoxysilane concentration of 90% by mass or more, but from the viewpoint of making the reaction rate more uniform, it is substantially only from tetraalkoxysilane. (A concentration of tetraalkoxysilane of 95% by mass or more (more preferably 97% by mass or more, more preferably 98% by mass or more, particularly preferably 99% by mass or more)) is more preferable. (A concentration (purity) of tetraalkoxysilane of 100% by mass or more) is most preferable. In addition, since such a silica raw material is an undiluted thing, it does not contain an organic solvent substantially (even if it contains in a raw material, it is preferable that the quantity of an organic solvent is 10 mass% or less. ). As an undiluted silica raw material comprising such a tetraalkoxysilane, a commercially available tetraalkoxysilane (for example, trade name “Tetrapropyl Orthosilicate” manufactured by Tokyo Chemical Industry Co., Ltd., tetrapropoxysilane concentration of 98% by mass, etc.) It is also possible to use it as it is.

  In the present invention, the silica raw material is added to the water surface of the aqueous solution in a state where the undiluted silica raw material composed of the tetraalkoxysilane (hereinafter, simply referred to as “undiluted silica raw material”) is floated. Decompose to form mesoporous silica nanoparticles in the aqueous solution.

  Here, the method of floating undiluted silica raw material on the water surface of the aqueous solution is not particularly limited, but basically, tetraalkoxysilane is insoluble in water, so that an emulsion is not formed in water. It is preferable to employ a method in which the undiluted silica raw material is slowly and slowly added onto the water surface of the aqueous solution (a method in which the undiluted silica raw material is slowly and slowly developed 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 at the interface between the layer made of the undiluted silica raw material (upper layer) and the layer made of the aqueous solution (lower layer) It is possible to proceed with the hydrolysis reaction of this, and it is possible to add (permeate) the hydrolyzed silica raw material to the aqueous solution. When the hydrolyzed silica raw material is added to the aqueous solution, silica nuclei are formed by the silica raw materials in the aqueous solution, and the silica skeleton is grown on the basis of the surface activity. As the composite with the agent occurs, the composite is formed, and the condensation of the silanol group of the silica raw material proceeds in the composite to form silica nanoparticles in which the surfactant is introduced into the pores ( Synthesized) and the mesoporous silica nanoparticles can be obtained. In this way, since the reaction of the silica raw material is hydrolyzed (the hydrolysis reaction), and the hydrolyzed silica raw material is supplied to produce mesoporous silica nanoparticles in an aqueous solution. That is, the production 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 hydrolysis reaction and particle synthesis reaction) is preferably 20 to 95 ° C, and preferably 25 to 80 ° C. Is more preferable. If the 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 upper limit is exceeded, water evaporation or boiling occurs. Therefore, the reaction rate cannot be kept constant, and it tends to be difficult to obtain homogeneous nanoparticles.

  Further, when producing mesoporous silica nanoparticles (in the series of reactions of the hydrolysis reaction and the particle synthesis reaction), the reaction for producing silica such as particle growth in an aqueous solution proceeds more uniformly. The reaction is preferably allowed to proceed while stirring. The stirring conditions are not particularly limited, but the undiluted silica raw material can be kept floating on the water surface of the aqueous solution, and an emulsion of the undiluted silica raw material is formed in the aqueous solution. For example, when the amount of the aqueous solution is about 10 to 100 mL, a magnetic stirrer is used with a stirring bar having a diameter of about 3 to 10 mm and a length of about 10 to 20 mm. 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 rotations is less than the lower limit, the silica raw material that has penetrated into the aqueous solution layer (water layer) tends to be difficult to diffuse uniformly into the water layer. There is a tendency that the interface between the silica raw material layer and the aqueous solution layer (water layer) is disturbed so that the reaction system cannot be kept homogeneous or an emulsion is produced. It should be noted that the number of revolutions and the like may be appropriately changed depending on the equipment so as to slowly agitate so that the undiluted silica raw material emulsion is not formed in the aqueous solution.

  As described above, in the present invention, the mesoporous silica nanoparticles can be obtained by allowing the reaction to proceed under conditions (such as temperature) where the hydrolysis reaction and the particle synthesis reaction proceed. In the present invention, the reaction is caused in a state where the undiluted silane raw material floats on the water surface of the aqueous solution. Therefore, as described above, the supply rate of the silane raw material through the water surface is almost constant regardless of the reaction time. (This is because the concentration of the silane raw material in contact with the water surface basically does not change.). As described above, when the undiluted silane raw material is used and the amount of the silica raw material supplied to the water is substantially proportional to the reaction time, if the raw material is all used for the formation of the nanoparticles, 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 with a simple formula (the volume of the nanoparticles is almost proportional to the time, so the diameter of the nanoparticles is the 1/3 power of the reaction time). It is considered to be proportional to.

  Note that the mesoporous silica nanoparticles formed in the aqueous solution in this manner are those in which a surfactant is introduced into the pores. In order to remove such a surfactant, for example, after recovering mesoporous silica nanoparticles formed from the aqueous solution, a step of removing the surfactant may be appropriately performed. Examples of the step of removing such a surfactant include a method of treating with an organic solvent and a method of firing. As a method of treating with such an organic solvent, a method of extracting and removing the surfactant by immersing mesoporous silica nanoparticles in a good solvent having high solubility in the organic component in the pores can be employed. Moreover, in the method by the said baking, the method of heating the said mesoporous silica nanoparticle at 300-1000 degreeC, Preferably it is 400-700 degreeC. Although such heating time may be about 30 minutes, 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 the air, but since a large amount of combustion gas is generated, it may be performed by introducing an inert gas such as nitrogen.

  Thus, in the present invention, mesoporous silica nanoparticles can be obtained. Such mesoporous silica nanoparticles have pores having a so-called mesosize (2 to 50 nm) pore diameter. Moreover, the “nanoparticles” referred to in the present invention may be particles having an average particle diameter in the range of 20 to 500 nm.

  In the present invention, by using the 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 and compounds that can be adsorbed in the pores tend to be limited when mesoporous silica nanoparticles are used as an adsorbent, and on the other hand, exceed the upper limit. As a result, the uniformity of the pore diameter decreases, and the particles tend to be brittle. In addition, such a pore diameter can be obtained by a density functional method based on a nitrogen adsorption / desorption isotherm. That is, based on the nitrogen adsorption / desorption isotherm, a pore size distribution curve is obtained by a density functional method, the pore diameter at the maximum peak is measured from the pore size distribution curve, and the pore diameter at the maximum peak is determined as the nanoparticle. It can be measured as the pore diameter. Here, the nitrogen adsorption / desorption isotherm is obtained by cooling the mesoporous silica nanoparticles to a liquid nitrogen temperature (-196 ° C.) and introducing nitrogen gas, obtaining the nitrogen gas adsorption amount by a constant volume method or a gravimetric method, and then introducing the nitrogen gas. The nitrogen gas pressure is gradually increased, and the adsorption amount of nitrogen gas against each equilibrium pressure can be plotted (for example, the nitrogen adsorption / desorption isotherm is a product name “Autosorb” manufactured by Quantachrome). -1 "can be used to determine the amount of nitrogen gas adsorbed by a gas adsorption method (adopting a constant volume method) at a liquid nitrogen temperature (-196 ° C).

  Further, the mesoporous silica nanoparticles thus obtained preferably have an average particle diameter of 25 to 300 nm (more preferably 30 to 200 nm). If the average particle size is less than the lower limit, it tends to be difficult to collect the nanoparticles by filtration or centrifugation. On the other hand, if the average particle size exceeds the upper limit, strong light scattering may occur or uniform chemical modification inside the particles may occur. By becoming difficult, the application tends to be limited to adsorbents and the like. Such an average particle size is obtained by measuring the particle size (diameter) of any 200 or more particles with a scanning electron microscope (for example, trade name “SU3500” manufactured by Hitachi High-Technologies Corporation), and calculating the average value. Can be obtained. If the particle is not a true sphere, the average value of the diameter of the smallest circumscribed circle of the particle and the diameter of the largest circumscribed circle of the particle is adopted as the “particle diameter” of each particle. In addition, the particle diameter of any 200 or more particles can be calculated by measuring the particle diameter of each particle based on an image obtained by a scanning electron microscope. In addition, the average particle diameter of such mesoporous silica nanoparticles can be easily 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 tends to be large, and the control of physical properties tends to be difficult. . In addition, such a standard deviation is the same as the above-mentioned measurement of the average particle size, and the particle size of any 200 or more particles can be determined by a scanning electron microscope (for example, trade name “SU3500” manufactured by Hitachi High-Technologies Corporation). It can be obtained using the measured data. Such a standard deviation can be easily within the above range by appropriately changing the volume of the aqueous solution, the conditions of stirring 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 a BET (Brunauer-Emmett-Teller) adsorption isotherm using an adsorption isotherm in a range of 0.05 to 0.2 relative pressure from the nitrogen adsorption / desorption isotherm. It can be calculated as a surface area.

Furthermore, the pore volume of the mesoporous silica nanoparticles is not particularly limited, but is preferably 0.2 cm ³ / g or more, and 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 a pore volume can be calculated from a nitrogen adsorption / desorption isotherm by a 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 (the volume occupied by the silica skeleton is 0.5 cm ³ / g). Preferably, it is 40 to 65%. If the porosity is less than the lower limit, the inside and surface of the pores tend not to be used for physical property control. On the other hand, if the upper limit is exceeded, the mechanical strength of the particles tends to decrease, and the application tends to be limited. It is in.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to a following example.

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

<Measurement of average particle diameter 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). In such measurement, 200 particles are selected arbitrarily (randomly) from a scanning electron microscope (SEM) image (observed image) of the particles obtained in each example, and the 200 particles The average particle diameter of the nanoparticles and the standard deviation of the particle diameter were determined by measuring the particle diameter (diameter). When the selected particle is not a true sphere, the average value of the diameter of the smallest circumscribed circle of the particle and the diameter of the largest circumscribed circle of the particle 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, the nitrogen adsorption / desorption isotherm was measured using a gas adsorption amount measuring device (trade name “Autosorb-1”) manufactured by Quantachrome. Such nitrogen adsorption / desorption isotherm was measured by determining the amount of nitrogen gas adsorbed by a gas adsorption method (adopting a constant volume method) at a liquid nitrogen temperature (−196 ° C.) (the following average pore diameter and the like). The nitrogen adsorption / desorption isotherm measured by such a method was also used as the nitrogen adsorption / desorption isotherm in the measurement of each characteristic. And the specific surface area was calculated | required by BET (Brunauer-Emmett-Teller) method using the adsorption isotherm of the range of 0.05-0.2 of relative pressure from the obtained nitrogen adsorption-desorption isotherm.

<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, a pore size distribution curve is obtained by the density functional method (density functional method based on the equilibrium adsorption model) using the nitrogen adsorption isotherm. 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 isotherm measured as described above, by using an adsorption isotherm in the range of relative pressure 0.6 to 0.8, by calculating by the t-plot method, The pore volume of the particles obtained in the examples was determined. Further, from the pore volume value 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) ( The voids between the particles are not included, and the void ratio is a void ratio derived from the mesoporous structure.

Example 1
In a 100 mL eggplant flask, a stirrer (diameter 7 mm, length 20 mm: a stirrer of the same size was used in each of the following examples), hexadecyltrimethylammonium chloride (surfactant) 10% by mass. An aqueous solution (60 mL) and a triethanolamine (0.18 g) as a hydrolysis catalyst were added to obtain an aqueous solution containing a surfactant and a hydrolysis catalyst. Next, 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: trade name “manufactured by Tokyo Chemical Industry Co., Ltd.” “Tetrapropyl 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. The same applies to Examples 3 to 6 and 8 to 10 described later. Tetrapropoxysilane was used.) Was slowly added and floated so as not to form an emulsion (after slowly developing), and then at a speed of 150 rpm using a magnetic stirrer while maintaining a temperature condition of 50 ° C. The mixture was then 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). Thereafter, an operation of redispersing in 60 mL of a mixed solution of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol] / [concentrated hydrochloric acid] of 200/1) and collecting by centrifugation was repeated twice (surfactant) Removal process). Subsequently, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol, and finally the nanoparticles were collected as a dispersion (solvent: ethanol). The total amount of nanoparticles obtained was 0.44 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 89 nm, and the standard deviation of the particle diameter was 9.9 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 2, as a result of measurement using a scanning electron microscope (SEM), it was confirmed that the obtained particles were spherical.

Further, the nanoparticles in the dispersion were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a nitrogen adsorption / desorption isotherm was determined. The obtained nitrogen adsorption / desorption isotherm is shown in FIG. As is apparent from the results shown in FIG. 3, type IV hysteris was confirmed in the nitrogen adsorption / desorption isotherm. Further, 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 these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 2)
To a 100 mL eggplant flask, a stirring bar, an aqueous solution (60 mL) containing hexadecyltrimethylammonium chloride (surfactant) in a proportion of 10% by mass and triethanolamine (0.18 g) as a hydrolysis catalyst were added, An aqueous solution containing a surfactant and a hydrolysis catalyst was obtained. Next, after the aqueous solution is heated to 80 ° C., tetraisopropoxysilane (4 mL: trade name manufactured by Tokyo Chemical Industry Co., Ltd.) is placed on the water surface of the aqueous solution while being heated so that the temperature of the aqueous solution can be maintained at 80 ° C. After slowly adding “Tetraisopropyl Orthosilicate”, a stock solution with a purity of 99% by mass (organic solvent content: 0% by mass) without diluting with an organic solvent, so as not to produce an emulsion. (After slowly developing), the mixture was stirred for 10 hours at a speed of 150 rpm using a magnetic stirrer while maintaining the temperature condition of 80 ° 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). Thereafter, an operation of redispersing in 60 mL of a mixed solution of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol] / [concentrated hydrochloric acid] of 200/1) and collecting by centrifugation was repeated twice (surfactant) Removal process). Subsequently, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol, and finally the nanoparticles were collected as a dispersion (solvent: ethanol). The total amount of nanoparticles obtained was 0.11 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 137 nm, and the standard deviation of the particle diameter was 28.3 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 4, 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a nitrogen adsorption / desorption isotherm was determined. The obtained nitrogen adsorption / desorption isotherm is shown in FIG. As is apparent 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 BET specific surface area of the nanoparticles is 1053 m ² / g, the pore diameter is 5.1 nm, the pore volume is 0.97 cm ³ / g, and the porosity is 66%. confirmed. From these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 3)
To a 100 mL eggplant flask, a stirring bar, an aqueous solution (60 mL) containing hexadecyltrimethylammonium chloride (surfactant) in a proportion of 10% by mass and triethanolamine (0.18 g) as a hydrolysis catalyst were added, 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 The mixture was stirred for 48 hours at a speed of 150 rpm using a magnetic stirrer under the conditions of (° 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). Thereafter, an operation of redispersing in 60 mL of a mixed solution of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol] / [concentrated hydrochloric acid] of 200/1) and collecting by centrifugation was repeated twice (surfactant) Removal process). Subsequently, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol, and finally the nanoparticles were collected as a dispersion (solvent: ethanol). The total amount of nanoparticles obtained was 0.11 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 52 nm, and the standard deviation of the particle diameter was 8.2 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 6, 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a 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. 7, 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 1482 m ² / g, the pore diameter is 4.3 nm, the pore volume is 0.82 cm ³ / g, and the porosity is 62%. confirmed. From these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

Example 4
To a 100 mL eggplant flask, a stirring bar, an aqueous solution (60 mL) containing hexadecyltrimethylammonium chloride (surfactant) in a proportion of 10% by mass and triethanolamine (0.18 g) as a hydrolysis catalyst were added, An aqueous solution containing a surfactant and a hydrolysis catalyst was obtained. Next, 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) is slowly formed on the water surface of the aqueous solution so as not to form an emulsion. 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 a 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). Thereafter, an operation of redispersing in 60 mL of a mixed solution of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol] / [concentrated hydrochloric acid] of 200/1) and collecting by centrifugation was repeated twice (surfactant) Removal process). Subsequently, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol, and finally the nanoparticles were collected as a dispersion (solvent: ethanol). The total amount of nanoparticles obtained was 0.14 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 64 nm, and the standard deviation of the particle diameter was 8.7 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 8, as a result of measurement using a scanning electron microscope (SEM), it was confirmed that the obtained particles were spherical.

Further, the nanoparticles in the dispersion were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a 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 nanoparticles have a BET specific surface area of 935 m ² / g, a pore diameter of 4.3 nm, a pore volume of 0.57 cm ³ / g, and a porosity of 53%. confirmed. From these 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 nanoparticles obtained was 0.29 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 89 nm, and the standard deviation of the particle diameter was 7.0 nm. Further, as is apparent from the scanning electron micrograph 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a 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, type IV hysteris was confirmed in the nitrogen adsorption / desorption isotherm. Further, from the nitrogen adsorption / desorption isotherm, 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 these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

(Example 6)
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 24 hours, and nanoparticles were obtained. The total amount of nanoparticles obtained was 0.78 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 115 nm, and the standard deviation of the particle diameter was 10.4 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 12, 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a nitrogen adsorption / desorption isotherm was determined. The obtained nitrogen adsorption / desorption isotherm is shown in FIG. As is apparent from the results shown in FIG. 13, 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 829 m ² / g, a pore diameter of 4.3 nm, a pore volume of 0.52 cm ³ / g, and a porosity of 51%. confirmed. From these 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: trade name “Tetraethyl Orthosilicate” manufactured by Tokyo Chemical Industry Co., Ltd.), dilute a stock solution of 96 mass% purity (content of organic solvent 0 mass%) with organic solvent The nanoparticle was recovered as a dispersion (solvent: ethanol) in the same manner as in Example 1 except that it was used as is. The total amount of nanoparticles obtained was 0.99 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 90 nm, and the standard deviation of the particle diameter was 10.7 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 14, 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a nitrogen adsorption / desorption isotherm was determined. The obtained nitrogen adsorption / desorption isotherm is shown in FIG. As is apparent 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 nanoparticles have a BET specific surface area of 449 m ² / g, a pore diameter of 3.5 nm, a pore volume of 0.21 cm ³ / g, and a porosity of 29%. confirmed. From these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

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

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 91 nm, and the standard deviation of the particle diameter was 9.4 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 16, 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a nitrogen adsorption / desorption isotherm was determined. The obtained nitrogen adsorption / desorption isotherm is shown in FIG. As is apparent 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 BET specific surface area of the nanoparticles is 1322 m ² / g, the pore diameter is 4.3 nm, the pore volume is 0.91 cm ³ / g, and the porosity is 65%. confirmed. From these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

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

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 126 nm, and the standard deviation of the particle diameter was 10.2 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 18, 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 were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a 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, the nanoparticles have a BET specific surface area of 943 m ² / g, a pore diameter of 4.3 nm, a pore volume of 0.66 cm ³ / g, and a porosity of 57%. confirmed. From these 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), a stirring bar, an aqueous solution (10 mL) containing hexadecyltrimethylammonium chloride (surfactant) in a proportion of 20% by mass, and triethanolamine (0. 10 g) was added to obtain an aqueous solution containing a surfactant and a hydrolysis catalyst. Next, the aqueous solution is heated to 50 ° C., and while being heated so that the temperature of the aqueous solution can be maintained at 50 ° C., tetrapropoxysilane (8 mL) is slowly added on the water surface so as not to form an emulsion and floated. (After slowly developing), the mixture was stirred for 10 hours at a speed of 150 rpm using a magnetic stirrer while maintaining the temperature at 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). Thereafter, an operation of redispersing in 60 mL of a mixed solution of ethanol and concentrated hydrochloric acid (volume ratio of [ethanol] / [concentrated hydrochloric acid] of 200/1) and collecting by centrifugation was repeated twice (surfactant) Removal process). Subsequently, the nanoparticles after centrifugation were dispersed in 10 mL of ethanol, and finally the nanoparticles were collected as a dispersion (solvent: ethanol). The total amount of nanoparticles obtained was 0.17 g.

  The nanoparticles in the dispersion thus obtained were observed with a scanning electron microscope (SEM), and the average particle size and standard deviation were determined. 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 average particle diameter of the obtained nanoparticles was 178 nm, and the standard deviation of the particle diameter was 15.0 nm. Further, as apparent from the scanning electron micrograph shown in FIG. 20, as a result of measurement using a scanning electron microscope (SEM), it was confirmed that the obtained particles were spherical.

Further, the nanoparticles in the dispersion were recovered by heating and distilling off the ethanol dispersion medium and dried, and then a nitrogen adsorption / desorption isotherm was determined. The nitrogen adsorption / desorption isotherm obtained 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. From these results and the types of raw materials used, it was confirmed that the obtained particles were mesoporous silica nanoparticles.

[About each nanoparticle obtained in Examples 1-10]
The properties of the nanoparticles obtained in each example are shown in Table 1. In Table 1, TPOS represents tetrapropoxysilane, TIPOS represents tetraisopropoxysilane, and TEOS represents tetraethoxysilane. Moreover, the graph which shows the relationship between the particle diameter of the nanoparticle obtained in Examples 4-6 and reaction time is shown in FIG.

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

  Further, as is clear from the description in Table 1, when Example 1 and Example 3 are compared, the temperature conditions (reaction temperature) during stirring and the stirring time (reaction time) are different, but the reaction temperature is 50 ° C. In the case of (Example 1), it was confirmed that it was possible to grow particles more efficiently than in the case of reacting at room temperature (Example 3). Furthermore, as is clear from the description in Table 1, when Example 1 and Example 5 are compared, the amount of tetrapropoxysilane used is different, but the nano-particles obtained in Example 1 and Example 5 are different. When comparing the structural characteristics of the particles, it is clear that they are almost equivalent, and as in the present invention, an undiluted silane raw material (undiluted tetrapropoxysilane) is floated on the water surface (development). It was found that the reaction rate hardly depends on the addition amount of the silane raw material if the conditions such as temperature and water amount are constant. Such a result shows that when the undiluted silane raw material (undiluted tetrapropoxysilane) is floated on the water surface (in an unfolded state), if the water surface area is the same, the silane to the water layer This is probably because the supply of the raw material is almost constant regardless of the amount of silica raw material used. As described above, it is assumed that the supply of the silane raw material to the water layer becomes almost constant when the temperature or the like is constant because the hydrolysis reaction rate 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 diameter (particle diameter) was obtained 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 examining 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 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 floated on the surface of the water (in the expanded state), the supply of the silane raw material to the water layer takes time to react. Regardless, it is thought to be almost constant. The reason why the supply of the silane raw material into the aqueous solution is almost constant is presumed to be because the reaction rate of hydrolysis depends on the area of the water surface. In addition, from these results, the particle size of the mesoporous silica nanoparticles can be precisely controlled only by controlling the reaction time by floating the undiluted silica raw material consisting of tetraalkoxysilane on the water surface of the aqueous solution and allowing the reaction to proceed. Obviously, it is possible to control (or predict). From these results, it is possible to synthesize desired mesoporous silica nanoparticles in an aqueous solution only by managing the reaction time by floating and reacting an undiluted silica raw material made of tetraalkoxysilane on the water surface of 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, etc., and the desired particle size can be efficiently obtained. The present inventors speculate that these nanoparticles can be produced.

  Further, as is clear from the results shown in Table 1, from the results of Example 4 and Example 8, the amount of the formed particles was determined depending on the amount of the aqueous solution (aqueous layer) even under the same reaction conditions and reaction time. The average particle size is different, and the average particle size of the nanoparticles obtained in Example 8 is about 1. with respect to the average particle size of the nanoparticles obtained in Example 4 while maintaining the properties such as porosity. It was found that it was expanded 4 times. Similarly, from the results of Example 5 and Example 9, the average particle diameter of the formed particles differs depending on the amount of the aqueous solution (aqueous layer) even under the same reaction conditions and reaction time. It was found that the average particle size of the nanoparticles obtained in Example 9 was expanded to about 1.4 times while maintaining the properties such as the porosity with respect to the average particle size of the obtained nanoparticles. . 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 thought to do. From the results of Examples 8 and 9 and the like, 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 became clear that it was possible to make it.

  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, since the method for producing mesoporous silica nanoparticles of the present invention can produce mesoporous silica nanoparticles without using an organic solvent, for example, mesoporous silica nanoparticles used for adsorbents, catalyst carriers, etc. It is particularly useful as a method for producing

  DESCRIPTION OF SYMBOLS 1 ... Reaction container, 2 ... Silica raw material, 3 ... Aqueous solution, 4 ... Silica particle, I ... Interface of upper layer and lower layer, A ... Direction where the silica raw material hydrolyzed from upper layer to lower layer is introduced.

Claims (3)

  The silica raw material is hydrolyzed with the undiluted silica raw material made of tetraalkoxysilane floating on the water surface of the aqueous solution containing the surfactant and the hydrolysis catalyst, and mesoporous silica nanoparticles are generated in the aqueous solution. A process for producing mesoporous silica nanoparticles characterized by   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 a temperature condition for producing the mesoporous silica nanoparticles is 20 to 95 ° C.