JP2016121044A - Silica structure and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silica structure excellent in mechanical strength, where mechanical strength is not enough depending on applications or the like thereof although it is known that conventional silica structures has a fixed mechanical strength and can be used for a polishing application.SOLUTION: There is provided a silica structure containing silica and molybdenum and having no communication hole, where silicon atom constituting whole or a surface layer of the silica structure has a Q4 structure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a silica structure and a method for producing the same.

  In recent years, application of silica structures having various structures to applications such as resin fillers and separating materials has been studied.

  For example, it is known that a silica-based bicontinuous structure having uniform macropores can be obtained by phase separation based on spinodal decomposition accompanied by sol-gel reaction of alkoxysilane. The said silica type co-continuous structure can be used for uses, such as a filler of a high performance liquid chromatography (HPLC) column.

  However, since the silica-based co-continuous structure has a structure including communication holes, the mechanical strength is weak, and the silica-based bicontinuous structure cannot usually be used for applications requiring mechanical strength.

For applications that require such mechanical strength, an attempt has been made to apply a silica structure having excellent mechanical strength by not having a communication hole. For example, in Patent Document 1, non-spherical silica fine particles having an average particle diameter measured by a dynamic light scattering method in the range of 5 to 300 nm are dispersed in a dispersion medium, and the solid content concentration is 10 to 60% by mass. A silica sol for polishing, wherein the area of Q4 in the peak area of chemical shift -73 to -120 ppm at the time of ²⁹ Si-NMR spectrum measurement is 88% or more and the area of Q3 is 11% or less The invention concerning is described. According to Patent Document 1, for the polishing silica sol, it is possible to improve the density and density of the silica structure by increasing the siloxane bond of silicon atoms, thereby being suitable for precision polishing of glass substrates and the like, It is described that it has a high polishing rate.

  The Q4 has a silicon atom structure in which four oxygen atoms are bonded, and the Q3 has a silicon atom structure in which three oxygen atoms and one hydroxyl group are bonded. Q1 is a silicon atom structure in which one oxygen atom and three hydroxyl groups are bonded, and Q2 is a silicon atom structure in which two oxygen atoms and two hydroxyl groups are bonded.

  By the way, in Patent Document 1, as a method for producing a silica sol, a step of preparing a solution containing silica hydrogel, a step of washing and removing a salt, a step of obtaining a silica sol, and a first hydrothermal treatment are performed. It includes a step of growing spherical silica fine particles and a step of performing a second hydrothermal treatment to advance the condensation of silanol groups in the silica particles. At this time, it is described that the ratio of the Q4 structure and the Q3 structure can be increased by performing the second hydrothermal treatment in the presence of an alkali species.

JP 2012-111869 A

  In the silica sol (silica structure) described in Patent Document 1, the ratio of the peak area of Q4 is only 89 to 91%. In this case, the silica structure may not necessarily have sufficient mechanical strength depending on its use.

  Then, an object of this invention is to provide the silica structure excellent in mechanical strength.

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, it has been found that the above problems can be solved by utilizing molybdenum, and the present invention has been completed.

  That is, this invention relates to the silica structure which does not have a communicating hole containing a silica and molybdenum. Under the present circumstances, the silicon atom which comprises the whole said silica structure or a surface layer has Q4 structure, It is characterized by the above-mentioned.

  According to the present invention, a silica structure having excellent mechanical strength can be obtained.

2 is a scanning electron micrograph of the silica structure obtained in Example 1. FIG. 3 is a scanning electron micrograph of the silica structure obtained in Example 2. FIG. It is a ²⁹ Si SP NMR chart of the silica structure (a) obtained in Example 2 and wet low-porous silica (b) before molybdenum oxide treatment.

  Hereinafter, embodiments for carrying out the present invention will be described in detail.

<Silica structure>
The silica structure according to the present embodiment contains silica and molybdenum and does not have communication holes. At this time, silicon atoms constituting the entire silica structure or the surface layer have a Q4 structure. The silica structure may further contain an organic compound or the like.

  Since the silica structure does not have communication holes, it has higher mechanical strength than, for example, a silica-based bicontinuous structure having communication holes.

  Moreover, since the silica structure has a Q4 structure because the silicon structure constituting the entire silica structure or the surface layer of the silica structure has a Q4 structure by utilizing molybdenum, high density can be realized. Even higher mechanical strength can be achieved.

  In one embodiment, since the silicon atoms constituting the entire silica structure or the surface layer have a Q4 structure and have little or no silanol groups, they have low surface polarity, low moisture absorption, high resistance. It can have effects such as excellent alkalinity. Thereby, the silica structure can be applied to a wide range of fields such as a resin filler, a catalyst, a coating material, a photonics material, and a column material.

  In one embodiment, since the silica structure contains molybdenum, the silica structure may be applicable to the use of an oxidation reaction catalyst or an optical material.

  In the present specification, the “communication hole” means a hole where an arbitrary point on the outer surface of the silica structure communicates with an arbitrary point on the outer surface different from the arbitrary point inside the silica structure. means. Therefore, independent holes that do not communicate with the inside of the silica structure, for example, holes that exist independently within the silica structure, are not included in the communicating holes.

  By using molybdenum as will be described later, it is possible to control so that only silicon atoms on the surface portion of the silica structure have a Q4 structure selectively. Therefore, in the present specification, the “surface layer of the silica structure” is arbitrarily controllable, but is preferably 10 to 500 nm with respect to the vertical direction of the outer surface, more preferably perpendicular to the outer surface. It means a layer of 50 to 500 nm with respect to the direction, more preferably 100 to 500 nm with respect to the direction perpendicular to the outer surface.

[silica]
In the silica structure, silicon atoms constituting the whole or the surface layer have a Q4 structure. More specifically, when the silicon atoms constituting the entire silica structure have a Q4 structure, the silica substantially consists of a Q4 structure silicon atom, and preferably the silica consists of a Q4 structure silicon atom. On the other hand, when the silicon atoms constituting the surface layer of the silica structure have a Q4 structure, the silica is substantially composed of a surface layer (shell layer) composed of silicon atoms having the Q4 structure and silicon atoms having the Q1 structure. And a core part including at least one selected from the group consisting of a silicon atom having a Q2 structure and a silicon atom having a Q3 structure, and preferably, the silica is a surface layer (shell layer) made of a silicon atom having a Q4 structure And a core portion including at least one selected from the group consisting of a silicon atom having a Q1 structure, a silicon atom having a Q2 structure, and a silicon atom having a Q3 structure. In the present specification, “substantially consisting of a silicon atom having a Q4 structure” means silica having a silanol group content of 5 mol% or less, preferably 1 to 3 mol% in silica. At this time, the value calculated by the ratio of Q4 obtained by ²⁹ Si-CP / MAS NMR measurement and Q3 and Q2 is adopted as the value of “content of silanol groups in silica”.

  When the silicon atoms constituting the entire silica structure have a Q4 structure, the average particle size of the silica structure is preferably 50 to 1000 nm, more preferably 100 to 1000 nm, and 300 to 1000 nm. More preferably. When the average particle diameter of the silica structure is in the above range, it is preferable because the silicon atoms constituting the entire silica structure can be converted into the Q4 structure while maintaining the shape of the precursor. In the present specification, the value of “average particle size” is calculated by measuring the particle size of an arbitrary 100 particles from an image obtained by a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Means the value. In this case, the “particle diameter” means the maximum length of the distance between two points on the particle outline.

  When the silicon atoms constituting the surface layer of the silica structure have a Q4 structure, that is, when the surface layer (shell layer) and the core part are included, the thickness of the shell layer is 10 nm or more as described above. Preferably, it is 50 to 500 nm, more preferably 100 to 500 nm. It is preferable for the thickness of the shell layer to be 10 nm or more because the characteristics based on the silicon atom having the Q4 structure can be suitably expressed.

  On the other hand, the size of the core part is not particularly limited. When the silica structure is particulate, the average particle size of the core is preferably 1000 μm or less, more preferably 10 nm to 500 μm, and even more preferably 10 nm to 100 μm. It is preferable that the average particle size of the core part is 1000 μm or less because it can be suitably used as a resin filler. The “size of the core portion” means a size obtained by subtracting the thickness of the shell layer from the size of the entire silica structure.

[molybdenum]
Molybdenum has a catalytic function and an optical function. Further, by utilizing molybdenum, the structure of silicon atoms constituting silica can be controlled in the production method as described later.

  Although it does not restrict | limit especially as said molybdenum, In addition to molybdenum metal, molybdenum trioxide, the partial reduction body of the molybdenum compound mentioned later, etc. are contained.

  The molybdenum-containing form is not particularly limited, and may be included in a form that adheres to the surface of silica, or may be included in a form in which a part of silicon having a silica structure is substituted, or a combination thereof. It may be.

  The content of molybdenum in the silica structure is preferably 20% by mass or less, more preferably 0.001 to 10% by mass, and 0.01 to 5% by mass with respect to the mass of the silica structure. More preferably, it is% or less. A molybdenum content of 20% by mass or less is preferable because the Q4 bond rate of silica is improved.

[Organic compounds]
In one embodiment, the silica structure may include an organic compound. The organic compound has a function of adjusting the surface physical properties of the silica structure.

  Although it does not restrict | limit especially as an organic compound, Organosilane and a polymer are mentioned.

  Examples of the organic silane include alkyltrialkoxysilanes, dialkylalkoxysilanes, and trialkylalkoxysilanes.

  Examples of the polymer include a hydrophobic polymer and a polymer having a functional group.

  Among these, the organic compounds are methyltrimethoxysilane, 3-glycitoxypropyltrimethoxysilane, trimethylmethoxysilane, phenyltrimethoxysilane, 3-mercaptopropyltomethoxysilane, 3-glycitoxypropyltrimethoxysilane, hexyltri. Methoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, polymethyl (meth) acrylate, polystyrene and polyester are preferred, and phenyltrimethoxysilane, hexyltrimethoxysilane and polymethyl (meth) acrylate are preferred. More preferred. In addition, the said organic compound may be contained independently or may contain 2 or more types.

  It does not restrict | limit especially as a containing form of an organic compound, You may be connected with the silica by the covalent bond, and you may coat | cover the silica.

  The content of the organic compound is preferably 20% by mass or less, and more preferably 10 to 0.01% by mass with respect to the mass of the silica structure. It is preferable that the content of the organic compound is 20% by mass or less because the physical properties derived from the silica structure can be easily expressed.

[Properties of silica structure]
The specific surface area of the silica structure is preferably at ^8m 2 / g or less, and more preferably 0~5m ² / g. It is preferable that the specific surface area of the silica is 8 m ² / g or less because the mechanical strength of the silica structure is excellent. In the present specification, the value measured by the BET method is adopted as the value of “specific surface area”.

  When the silica structure has pores therein, the pore diameter is preferably 500 nm or less, more preferably 10 to 400 nm, and even more preferably 50 to 300 nm. It is preferable that the pore size inside the silica structure is 500 nm or less because the mechanical strength of the silica structure is excellent. The pore diameter inside the silica structure can be appropriately controlled by adjusting the production conditions, for example, the specific surface area of the silicon compound as a raw material, the firing temperature, the firing time, and the like. Moreover, in this specification, "the hole diameter inside a silica structure" means the distance between two points where the numerical value becomes the maximum on the outline of a hole.

  The shape of the silica structure is not particularly limited, and any shape such as a spherical shape, an elliptical shape, a cylindrical shape, a polygonal column shape, a needle shape, a rod shape, a fiber shape, a plate shape, a disc shape, a flake shape, a scale shape, an irregular shape, etc. The shape can also be taken. Among these, from the viewpoint of application of the resin filler, the shape of the silica structure is preferably spherical, fiber-like, or plate-like, and more preferably spherical.

  As described above, the silicon atoms constituting the entire silica structure or the surface layer have a Q4 structure and do not have a silanol group, and thus exhibit high alkali resistance, low moisture absorption, and low surface polarity. As a result, the silica structure undergoes little or no hydrolysis even in a basic aqueous solution. In addition, in the silica structure, adsorption of water vapor does not occur or hardly occurs. Furthermore, the silica structure can be used as it is without surface modification.

  In addition, since the surface modification of the silica structure is not required, it is possible to reduce the particle size and the like, for example, it is possible to realize thin film molding and the like, which can contribute to downsizing of the product.

  Further, as described above, the silica structure can be applied to the use of an oxidation reaction catalyst and an optical material by including molybdenum. At this time, since the silica structure has high alkali resistance, hydrothermal stability, etc., for example, when the silica structure is used as an oxidation reaction catalyst, high catalytic reaction efficiency can be obtained.

<Method for producing silica structure>
The method for producing the silica structure is not particularly limited, and a known technique can be appropriately applied. From the viewpoint that the structure of the silicon atom can be suitably controlled, production using a flux method preferably using molybdenum is preferable. The method can be applied.

More specifically, a preferred method for producing a silica structure includes a firing step of firing a silicon compound having a specific surface area of less than 10 m ² / g in the presence of a molybdenum compound.

[Baking process]
The firing step is a step of firing a silicon compound having a specific surface area of less than 10 m ² / g in the presence of a molybdenum compound.

(Silicon compound)
The silicon compound is not particularly limited, and a known compound can be used. Specific examples of silicon compounds include artificial non-porous silica such as dry nonporous silica, wet low porosity silica, fumed silica, fused silica, silica gel, etc .; natural silicon compounds such as biosilica; derivatives of these silicon compounds, etc. Is mentioned.

  Examples of the silicon compound derivative include composites of a silicon compound and an organic compound. Specific examples include a silicon compound complex in which silica is modified with organosilane, a silicon compound complex in which a polymer is adsorbed on the surface of the silicon compound, and the like.

  When the silicon compound derivative contains an organic compound, the content of the organic compound is preferably 40% by mass or less, and more preferably 0.1 to 20% by mass with respect to the mass of the silicon compound derivative. A content of the organic compound of 40% by mass or less is preferable because a silica structure can be efficiently formed.

  Among these, it is preferable to use an artificial synthetic silicon compound, and it is more preferable to use at least one selected from the group consisting of dry non-porous silica, wet low-porous silica, fumed silica, and fused silica. In addition, a silicon compound may be used independently or may be used in combination of 2 or more type.

  The shape of the silicon compound is not particularly limited, and for example, spherical, amorphous, aspect structures (wires, fibers, ribbons, tubes, etc.), sheets, monoliths, and the like can be suitably used.

The specific surface area of the silicon compound is less than 10 m ² / g, preferably 0.01 to 9 m ² / g, more preferably 0.01 to 8 m ² / g. When the specific surface area of the silicon compound is 10 m ² / g or more, the resulting silica may have communication holes, and a silica structure having no communication holes may not be obtained.

  Moreover, the size in the minimum direction of the particle diameter of the silicon compound is not particularly limited. In one embodiment, the size in the minimum direction of the particle diameter is preferably less than 1000 nm, and more preferably 100 to 900 nm. When the size in the minimum direction of the particle diameter is less than 1000 nm, the resulting silica structure may have a Q4 structure in the silicon atoms constituting the whole. In another embodiment, the size in the minimum direction of the particle diameter is preferably 1000 nm or more, and more preferably 1500 nm to 1000 μm. When the size in the minimum direction of the particle diameter is 1000 nm or more, in the obtained silica structure, silicon atoms constituting the surface layer may have a Q4 structure. In addition, macroscopic monoliths and bulk silicon compounds can also be suitably used. In the silica structure obtained by using these, the silicon atoms constituting the surface layer can have a Q4 structure. In the present specification, the “size in the smallest direction of the particle diameter” means the distance between two points at which the numerical value is the smallest on the contour line forming the particle.

(Molybdenum compound)
As will be described later, the molybdenum compound has a function as a dehydration catalyst for silanol groups.

The molybdenum compound is not particularly limited, molybdenum oxide, a compound containing molybdenum metal acid radical anions consisting of binding with oxygen (MoO x ^_n-) and the like.

The compound containing the acid radical anion _(MoO ^{x n-),} is not particularly limited, molybdic _{acid, H 3 PMo 12 O 40,} H 3 SiMo 12 O 40, NH 4 Mo 7 O 12 and the like.

  Of the molybdenum compounds described above, molybdenum oxide is preferably used from the viewpoint of cost. Moreover, the above-mentioned molybdenum compound may be used independently or may be used in combination of 2 or more type.

  Although the usage-amount of a molybdenum compound is not restrict | limited in particular, It is preferable that it is 0.03-3.0 mol with respect to 1 mol of silicon compounds, and it is more preferable that it is 0.08-0.7 mol. When the amount of the molybdenum compound used is in the above range, it is preferable because silicon atoms having a Q4 structure are easily obtained.

(Baking)
By firing the silicon compound in the presence of a molybdenum compound, a silica structure can be obtained. At this time, the obtained silica structure contains silica and molybdenum and does not have communication holes. Moreover, the silicon atom which comprises the whole silica structure or a surface layer has Q4 structure.

  When the silicon compound is baked in the presence of the molybdenum compound, the molybdenum compound forms an adhesion film on the surface of the resulting silica pores. When the silica having such an adhesion film is baked at a higher temperature, the molybdenum compound sublimes and a dehydration reaction of silanol in the silica occurs. As a result, the entire silica structure or the surface layer can be synthesized (flux method).

In the above-described flux method, the silica structure that can obtain the physical properties of the silicon compound as a raw material can be affected. In one embodiment, when the specific surface area of the silicon compound is less than 10 m ² / g, the specific surface area of the silica obtained depending on this also becomes small, and a silica structure having no communication holes can be obtained.

  In the above flux method, since the molybdenum compound forms an adhesion layer on the silica surface, silanol dehydration reaction, in other words, conversion of silicon atoms having Q2 structure and Q3 structure to silicon atoms having Q4 structure. Is likely to occur.

  At this time, when the silicon compound includes a composite of the silicon compound and the organic compound, the organic compound can disappear through the firing. As a result, for example, independent pores that do not communicate with the obtained silica structure can be formed.

  The physical properties such as the shape and average particle size of the silicon compound can also affect the resulting silica structure. In one embodiment, when a particulate silicon compound having a relatively small average particle size (for example, less than 1000 nm) is used, the resulting silica can also be particulate. When the flux method is applied to such silica, silicon atoms constituting the entire silica structure obtained can have a Q4 structure. This is because silica, which has a relatively small particle size, has a relatively large area on which a molybdenum compound adhesion film can be formed, and the dehydration reaction of silanol proceeds not only to the entire surface but also to the inside of the silica to form a structure. This is because conversion to Q4 structure silicon atoms can occur in all the silicas to be processed.

  On the other hand, in one embodiment, when a particulate silicon compound having a relatively large average particle size (for example, 1000 nm or more) is used, the resulting silica can also be particulate. When the flux method is applied to such silica, silicon atoms constituting the surface layer of the obtained silica structure can have a Q4 structure. This is because the silanol dehydration reaction does not easily proceed to the center due to the large average particle size, and the conversion to a silicon atom having a Q4 structure may remain in the surface layer of silica. In addition, since the molybdenum compound cannot adhere to the central part of the particle silica, the effect of the flux method cannot be obtained.

  However, the physical properties of the resulting silica structure can be controlled by appropriately controlling the silicon compound and molybdenum compound used, the amount used, and the firing conditions.

  In addition, the manufacturing method according to the present embodiment can manufacture a silica structure by a simple process of firing dry solid powders, discharge of solvent / waste liquid, expensive equipment, complicated process, post-treatment, etc. Therefore, it can be said that the manufacturing method does not involve environmental load.

  The atmosphere in firing is not particularly limited, and examples thereof include an air atmosphere, an oxygen atmosphere, an inert atmosphere such as nitrogen and argon, and the like. Among these, an air atmosphere is preferable from the viewpoint of cost.

  The firing temperature is not particularly limited, but is preferably 600 ° C. or higher, more preferably 600 to 1300 ° C., and still more preferably 800 to 1300 ° C. A firing temperature of 600 ° C. or higher is preferable because a silica structure can be suitably formed with sublimation of the molybdenum compound.

  The time taken to raise the temperature to the firing temperature is preferably 1 to 10 hours. The holding time at the firing temperature is preferably 5 minutes to 24 hours. Furthermore, the firing holding time is preferably 10 minutes to 3 hours.

  The firing method is not particularly limited, and for example, a firing furnace or the like can be used.

[Molybdenum removal process]
The method for producing a silica structure may further include a molybdenum removal step of removing at least a part of molybdenum as necessary after the firing step.

  As described above, since molybdenum is sublimated during firing, the molybdenum content in the silica structure can be controlled by controlling the firing time, firing temperature, and the like.

  However, the molybdenum content in the silica structure can also be controlled by the molybdenum removal step.

  Molybdenum can adhere to the surface in the silica structure. The molybdenum can be removed by washing with an aqueous ammonia solution or an aqueous sodium hydroxide solution.

  At this time, the molybdenum content can be controlled by appropriately changing the concentration, usage amount, cleaning site, cleaning time, and the like of the aqueous ammonia solution and aqueous sodium hydroxide solution used.

[Organic compound layer forming step]
In one embodiment, the method for producing a silica structure may further include an organic compound layer forming step. The organic compound layer forming step is usually performed after the firing step or after the molybdenum removing step.

  The method for forming the organic compound layer is not particularly limited, and known methods can be appropriately employed. For example, the method of apply | coating the coating liquid containing an organic compound to a silica structure, and drying is mentioned.

  In addition, what was mentioned above can be used as an organic compound which can be used for formation of an organic compound layer.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Manufacture of silica structure>
[Example 1]
A silica structure was synthesized by the flux method.

More specifically, nonporous silica fine particles as a silicon compound: SO-E2 (manufactured by deflagration of metallic silicon, average particle size: 0.5 μm, specific surface area: 5.5 m ² / g, stock 0.7 g (manufactured by Admatechs Co., Ltd.) and 0.3 g of molybdenum oxide (made by Wako Pure Chemical Industries, Ltd.), which is a molybdenum compound, were mixed in a mortar to obtain 1 g of a mixture. 1 g of the obtained mixture was fired at 800 ° C. for 1 hour in a ceramic electric furnace ARF-100K type (with AMF-2P type temperature controller) (manufactured by Asahi Rika Seisakusho Co., Ltd.) as a firing device. Molybdenum oxide was almost sublimated to obtain 0.69 g of silica structured powder.

  When SEM observation was performed using a surface observation apparatus VE-9800 (manufactured by Keyence Corporation), the shape of the obtained silica structure was spherical, similar to the shape of the silicon compound, and had no communication holes. Was confirmed (FIG. 1).

Moreover, the structure of the silicon atom of the silica structure was evaluated. More specifically, ²⁹ Si CP / MAS NMR measurement was performed using JNM-ECA600 (manufactured by JEOL Ltd.). At this time, the chemical shift reference was obtained by separately measuring polydimethylsilane by the CP / MAS method. As a result, peaks derived from Q2, Q3, and Q4 were not observed within the range of 80 to 120 ppm. This indicates that the obtained silica structure is composed of silicon atoms having a Q4 structure. More specifically, in ²⁹ Si CP / MAS NMR measurement, when silica contains a silicon atom based on the Q2 and Q3 structures, that is, when it has a silanol group, a signal is observed due to the spin transfer of protons of the silanol group. . However, when silica does not have a silanol group, no spin transfer of protons of the silanol group occurs, and thus no signal is observed including the Q4 structure. That is, no peak is observed in the ²⁹ Si CP / MAS NMR measurement of silica composed of Q4 bonds having no silanol group. In addition, when ²⁹ Si CP / MAS NMR measurement was performed using the above-described silicon compound (nonporous silica fine particles), a peak derived from the Q3 bond was confirmed from the obtained data.

  Furthermore, the molybdenum in the obtained silica structure was analyzed. When energy dispersive X-ray analysis (TEM-EDS analysis) was performed, it was found that molybdenum was simultaneously present on the silica surface of the silica structure and in the silica.

  Further, the molybdenum content in the obtained silica structure was measured. More specifically, fluorescent X-ray quantitative evaluation was performed using a fluorescent X-ray measurement apparatus ZSX100e (manufactured by Rigaku Corporation). From the obtained data, the molybdenum content in the silica structure was 0.5% by mass.

[Example 2]
Wet low-porous silica as a silicon compound: Seahoster KE-P250 (average particle size: 2.6 μm, specific surface area: 1 to 5 m ² / g, manufactured by Nippon Shokubai Co., Ltd.) and molybdenum oxide as a molybdenum compound ( 0.15 g (manufactured by Wako Pure Chemical Industries, Ltd.) was mixed in a mortar to obtain 1 g of a mixture. 1 g of the obtained mixture was fired at 900 ° C. for 1 hour in a ceramic electric furnace ARF-100K type (with AMF-2P type temperature controller) (manufactured by Asahi Rika Seisakusho Co., Ltd.) as a firing device. Molybdenum oxide was almost sublimated to obtain 0.84 g of silica structured powder.

  When SEM observation was performed in the same manner as in Example 1, it was confirmed that the obtained silica structure had a spherical shape similar to the shape of the silicon compound and had no communication holes (FIG. 2). .

Moreover, when the structure of the silicon atom of the silica structure was evaluated by ²⁹ Si CP / MAS NMR measurement in the same manner as in Example 1, the peaks derived from Q2, Q3, and Q4 were entirely observed within the range of 80 to 120 ppm. It became very weak. This indicates that silanol groups in the silica structure were largely lost as a result of the molybdenum oxide treatment.

In addition, ²⁹ Si SP NMR measurement was performed. At this time, as in the ²⁹ Si CP / MAS NMR measurement, a chemical shift reference was obtained by separately measuring polydimethylsilane by the CP / MAS method. As a result, the peaks derived from Q2 and Q3 almost disappeared, and only the signal of Q4 was shown (FIG. 3a). This indicates that the silica structure has a core-shell structure, and the shell layer (outermost layer) is composed of silicon atoms having a Q4 structure. More specifically, in the ²⁹ Si SP NMR measurement, the shell layer (outermost layer) is detected preferentially for dense particles regardless of the presence of silanol groups. Therefore, in the ²⁹ Si SP NMR measurement, there was no peak derived from Q2 and Q3, and only a signal derived from the peak derived from Q4 was shown. Thus, it can be seen that the shell layer (outermost layer) consists of silicon atoms having a Q4 structure.

In addition, when the ²⁹ Si CP / MAS NMR measurement and the ²⁹ Si SP NMR measurement are comprehensively taken into consideration, it can be understood that the dehydration reaction of the silanol group occurred only in the shell layer (outermost layer) of the silica structure by the molybdenum oxide treatment. This is because the core portion cannot contact with molybdenum oxide, so that no dehydration reaction of silanol groups occurs.

In addition, when ²⁹ Si SP NMR measurement was performed using the above-mentioned silicon compound (wet low-porous silica), a peak derived from Q3 bond was confirmed in the outermost layer from the obtained data (FIG. 3b).

  When molybdenum in the silica structure was analyzed in the same manner as in Example 1, it was found that molybdenum was simultaneously present on the silica surface of the silica structure and in the silica composed of Q4-bonded silicon atoms.

  Moreover, when the content of molybdenum in the silica structure obtained by the same method as in Example 1 was measured, the molybdenum content in the silica structure was 0.4% by mass.

<Example 3>
A silica structure was produced in the same manner as in Example 1.

  0.2 g of the obtained silica structure powder was dispersed in 5 mL of 10% aqueous ammonia. The dispersion was stirred at room temperature for 3 hours, then washed with water and dried to obtain 0.19 g of powder of silica structure.

  The obtained silica structure was subjected to X-ray photoelectron spectroscopy (XPS) measurement. More specifically, measurement was performed using Quantera SXM (manufactured by PHI Co., Ltd.) under the conditions of a voltage of 1.0 V, a current of 20 μA, and a beam diameter of 105 μm. As a result, molybdenum was not detected on the surface of the silica structure. Thereby, it turns out that the molybdenum which exists in the silica structure surface was removed by ammonia washing.

  Moreover, when the content of molybdenum in the silica structure was measured in the same manner as in Example 1, the molybdenum content in the silica structure was 0.3% by mass. Thus, it can be seen that molybdenum present in the silica is not removed by the ammonia cleaning.

Claims (5)

A silica structure having no communication hole, including silica and molybdenum,
A silica structure in which silicon atoms constituting the entire silica structure or a surface layer have a Q4 structure.   The silica structure according to claim 1, wherein the molybdenum content is 20% by mass or less based on the mass of the silica structure. A method for producing a silica structure having no communication holes, comprising a firing step of firing a silicon compound having a specific surface area of less than 10 m ² / g in the presence of a molybdenum compound,
The silica structure comprises silica and molybdenum;
The manufacturing method in which the silicon atom which comprises the whole said silica structure or a surface layer has Q4 structure.   The manufacturing method of Claim 3 which further includes the molybdenum removal process of removing at least one part of the said molybdenum after the said baking process.   The manufacturing method according to claim 3 or 4, wherein the silicon compound is at least one selected from the group consisting of dry non-porous silica, wet low-porous silica, fumed silica, and fused silica.

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