JP2020029394A - Porous silica, functional material and method for manufacturing porous silica - Google Patents

Abstract

The present invention provides porous silica with improved properties and a method for producing the same. The present invention has a first pore P1 and a second pore P2, the first pore has an average pore diameter of 100 to 1000 nm, and the second pore has an average pore diameter of 0. Porous silica PS, which is 5-3 nm. A functional material containing porous silica. A method for producing porous silica by hydrolysis of an alkoxysilane, comprising: (a) preparing a first liquid containing a surfactant, an alkoxysilane, and water; (b) combining the first liquid and a basic liquid. A method for producing porous silica, comprising the step of gelling a first liquid by a dehydration condensation reaction of the first liquid by contacting the first liquid. A method for producing porous silica, which comprises, after step (b), (c) heat-treating a gelled product obtained by gelling the first liquid. In the step (a), when the stoichiometric ratio of alkoxysilane and water is alkoxysilane:water=1:n, n is 20 or less, a method for producing porous silica. [Selection diagram] Figure 2

Description

  The present invention relates to porous silica and a method for producing porous silica, and in particular, porous silica having a hierarchical porous structure, a functional material using porous silica having a hierarchical porous structure, and a porous material having a hierarchical porous structure. The present invention relates to a method for producing porous silica.

  Porous silica having mesopores is generally produced using micelles of a surfactant as a template. Such porous silica is used as an adsorbent or the like.

  For example, Non-Patent Document 1 discloses a porous silica having mesopores. In particular, Non-Patent Document 1 discloses a technique for obtaining porous silica having mesopores in the form of particles of several microns.

  Also, in Patent Document 1, a surfactant having a group having 2 to 7 carbon atoms in a hydrophobic part is dispersed in alkoxysilane, and water adjusted to pH 0 to 2 is added in an amount of 2 to 4 equivalents to alkoxysilane. There is disclosed a technique in which hydrolysis of alkoxysilane proceeds gently to obtain a monolithic mesoporous silica having a pore diameter of 0.5 nm or more and less than 2 nm. In particular, in this technique, in Non-Patent Document 1, only amorphous silica was obtained when a cationic surfactant having a group having 6 carbon atoms in the hydrophobic portion was used, whereas the number of carbon atoms in the hydrophobic portion was small. We have succeeded in reducing the pore size by using a cationic surfactant with a small size as a micelle (template).

  Patent Document 2 discloses that in addition to a surfactant, an alkoxysilane, and water, an alkoxysilane is hydrolyzed in the presence of a water-soluble polymer to have a surfactant, an alkoxysilane, water, and a water-soluble polymer. By bringing the mixed solution into contact with a basic solution, the monolithic mesoporous silica was successfully converted into nanoparticles.

  Patent Document 3 discloses that a metal or a metal compound is impregnated in pores of porous silica by impregnating a liquid containing a metal or a compound having a metal as an elemental composition in pores of porous silica and performing heat treatment. A technique for encapsulating contained fine particles is disclosed. In particular, by using porous silica as a template, formation of particles (for example, W, Cu, Cr, Mn, Fe, Co or Ni, and metal oxides thereof) exhibiting unique properties not seen in a bulk state. Have been successful.

  Patent Literature 4 discloses an anodized porous alumina in which regularly arranged pores are arranged in an ideal triangular lattice in a range of 4 × 4 or more in the vertical and horizontal directions. Non-Patent Document 2 discloses a method for producing porous silica having macropores of several tens of μm in diameter using ice crystals as a template.

Japanese Patent No. 5827735 Japanese Patent No. 5647669 Japanese Patent No. 6165937 JP 2018-3048 A

J. S. Beck, J. C. Vartuli, G. J. Kennedy, C.T.Kresge, W.J.Roth, S. E. Schramm, Chem. Mater., 1994, 6, 1816. H. Nishihara, S. R. Mukai, D. Yamashita, H. Tamon, Chem. Mater Commun., 2005, 17, 683.

  The present inventor has been engaged in research and development on the synthesis of porous silica, particularly porous silica having mesopores having a pore diameter of less than 2 to 50 nm (mesoporous silica), and has achieved various results.

  In particular, the synthesis of porous silica having micropores having a pore diameter of 2 nm or less has been successfully performed using a surfactant having a group having a small number of carbon atoms in a hydrophobic part as a template (see Patent Document 1 and the like).

  Such porous silica having mesopores or micropores can be used in the fields of adsorbents, various catalyst carriers, separation membranes, sensors and the like.

  However, when the porous silica is formed as large particles, it is not possible to efficiently adsorb a substance to intrinsic mesopores or micropores or to carry a functional material such as a catalyst. Therefore, it is conceivable that the mesopores or micropores exposed on the surface function efficiently by increasing the surface area, for example, by reducing the size of the porous silica.

  Therefore, an object of the present invention is to provide a technique capable of improving the characteristics of porous silica. In particular, it is to improve the characteristics of the porous silica by providing macropores in the porous silica and exposing mesopores and micropores on the side surfaces of the macropores. Another object of the present invention is to provide a method for producing such porous silica.

  The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  The outline of a typical invention among the inventions disclosed in the present application will be briefly described as follows.

  Among the inventions disclosed in the present application, the porous silica shown in a typical embodiment has a first pore and a second pore, and the average pore diameter of the first pore is 100 nm. And the average pore diameter of the second pores is 0.5 nm or more and 3 nm or less.

  Among the inventions disclosed in the present application, the functional material described in the representative embodiment has the porous silica.

  Among the inventions disclosed in the present application, a method for producing porous silica described in a typical embodiment is a method for producing porous silica by hydrolysis of an alkoxysilane, wherein (a) a surfactant, A step of preparing a first liquid having an alkoxysilane and water, (b) gelling the first liquid by a dehydration-condensation reaction of the first liquid by contacting the first liquid with a basic liquid; Process.

  Among the inventions disclosed in the present application, according to the porous silica described in the following representative embodiments, the characteristics of the porous silica can be improved.

  Further, according to the method for producing porous silica described in the representative embodiment described below among the inventions disclosed in the present application, porous silica having good characteristics can be produced.

FIG. 3 is a diagram illustrating a process for producing the porous silica according to the first embodiment. FIG. 2 is a diagram schematically illustrating a configuration of a porous silica according to the first embodiment. It is a figure which shows a micelle (template) typically. It is a reaction formula showing the formation reaction (sol-gelation) of porous silica. It is a schematic diagram which shows the formation mechanism of a macropore. FIG. 3 is a diagram illustrating a method of applying a precursor solution to a substrate. It is a SEM image of porous silica (film form) synthesized using C18TAC. It is a SEM image of porous silica (film form) synthesized using C18TAC. It is a figure which shows the nitrogen adsorption / desorption isotherm of the porous silica (film form) synthesize | combined using C18TAC. It is a graph which shows the pore diameter distribution of the porous silica (film form) synthesize | combined using C18TAC. It is a graph which shows the pore diameter distribution of the porous silica (film form) synthesize | combined using C18TAC. 5 is an enlarged SEM image of a cross section of a porous silica film. It is an enlarged SEM image of the upper surface of porous silica. It is a figure which shows the nitrogen adsorption / desorption isotherm of the porous silica (film form) synthesize | combined using C6TAB. It is a graph which shows the pore diameter distribution of porous silica (film form) synthesized using C6TAB. 5 is an SEM image of the porous silica of Comparative Example 1. 9 is an SEM image of the porous silica of Comparative Example 2. 5 is an enlarged SEM image of a cross section of a porous silica film. It is a SEM image of a glass filter. 5 is an enlarged SEM image of a cross section of a porous silica film. FIG. 7 is a diagram illustrating a process for producing the porous silica according to the second embodiment. FIG. 9 is a diagram illustrating another manufacturing process of the porous silica according to the second embodiment. It is a schematic diagram which shows the formation mechanism of a macropore. 8 is an SEM image of porous silica (granular) of Example 4. 9 is an SEM image of the porous silica (granular) of Example 5. It is a schematic diagram which shows the structure of the air purifier of Embodiment 3. FIG. 13 is a diagram illustrating a process of manufacturing a synthetic film of the glass filter and the porous silica film according to the fourth embodiment. FIG. 13 is a diagram illustrating a process of manufacturing a synthetic film of the glass filter and the porous silica film according to the fourth embodiment. 5 is an SEM image of a glass filter having a porous silica film formed on the obtained surface. It is a transmission electron microscope image (TEM image) of the obtained titanium dioxide inclusion porous silica. It is a figure which shows the particle size and the number of titanium dioxide particles. It is a figure which shows the mode of a photocatalytic decomposition reaction experiment of isopropyl alcohol. It is a figure which shows the amount of carbon dioxide generated at the time of the photocatalytic decomposition reaction of isopropyl alcohol. It is a figure which shows the mode of the adsorption filtration experiment of a methylene blue aqueous solution. It is a figure which shows the measurement result (porosity, removal rate, and filtration rate) of Example D and a comparative example. 9 is an SEM image of each sample of Example E. It is a schematic diagram which shows the formation mechanism of a macropore.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It is to be noted that components having the same function are denoted by the same or related reference numerals, and repeated description thereof will be omitted.

(Embodiment 1) Porous silica in film form In this embodiment, porous silica is synthesized by a sol-gel method using a surfactant as a template. Such a synthesis method is sometimes referred to as a molecular template method (template method).

  Generally, when a surfactant is dissolved in a solution, for example, cylindrical micelles (templates) are formed in accordance with the type and concentration of the surfactant. Here, when an alkoxysilane or the like serving as a silica source is added to the solution, the adsorption and growth reaction of silicate ions proceeds in the gaps of the micelles, and a silica gel skeleton is formed. The silicate state is changed from a sol state to a gel state by the silicate ion adsorption and growth reaction, and is called a sol-gel reaction (see FIG. 4). Thereafter, when the silica gel skeleton (gelled product) is calcined (heat treated), the surfactant used as the template is decomposed and removed, and porous silica is obtained. In other words, a silica skeleton having a plurality of pores (pores, micropores) is obtained.

  Hereinafter, the method for synthesizing the porous silica of the present embodiment will be described in detail. FIG. 1 is a diagram showing a process for producing the porous silica of the present embodiment.

  As shown in FIG. 1A, a precursor solution (sol, sol-state liquid) L1 of porous silica is formed.

  First, a silicon compound serving as a silica source and a surfactant are mixed and stirred. The precursor solution L1 is formed by adding water and stirring in the mixed solution. The precursor solution L1 is in a sol state, and gels (solidifies) by contact with a basic aqueous solution as described later. In addition, the precursor solution L1 gels with stirring (elapse of time).

  An alkoxysilane can be used as the silicon compound serving as a silica source. Alkoxysilane is a compound having an alkoxy group bonded to silicon. As the alkoxysilane, for example, tetraethoxysilane (TEOS) can be used. As a silicon compound serving as a silica source, sodium silicate or the like can be used in addition to alkoxysilane.

As the surfactant, a cationic surfactant is used. Examples of the cationic surfactant of the general formula _{R 1 R 2 R 3 R 4} N + X - can be used surfactant represented by (see FIG. 3). R ₁ is a hydrophobic part, for example, an alkyl group having 1 to 24 carbon atoms, a benzyl group, or a phenyl group; and R ₂ R ₃ R ₄ is, for example, a methyl group, an ethyl group, a propyl group, or a butyl group. is there. X is, for example, a halogen ion such as F, Cl, Br, and I. It is preferable to use a quaternary cationic surfactant as the cationic surfactant. Further, the alkyl group of R ₁ may be linear or branched.

The added water (H ₂ O) serves as a reactant for the hydrolysis of the alkoxysilane. The pH of the water to be added is desirably adjusted to about pH 2, which is the isoelectric point of alkoxysilane. At the isoelectric point, the hydrolysis rate of the alkoxysilane and the gelation rate of the silicate ion are the slowest, so that sufficient time for micelle formation of the surfactant can be secured.

  Further, when the pH of water is about 0 to 1, hydrolysis is accelerated, but the same effect can be obtained because the gelation rate of silicate ions is sufficiently low. Therefore, it is preferable to adjust the pH of the water to be added to a range of 0 to 2. If the pH is 3 or more, the rate of hydrolysis and gelation is too high, so that sufficient time for dissolving the surfactant and forming micelles may not be secured.

  As the acid for pH adjustment, an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid, or an organic acid such as acetic acid can be used.

Here, in order to improve the moldability of the cylindrical micelle (template) serving as the pores of the porous silica, it is preferable to hydrolyze with as little water (solvent) as possible (see FIG. 4). Therefore, the amount of water added to the alkoxysilane (n when the stoichiometric ratio with water is alkoxysilane: water = 1: n) is at least 2 equivalents (eq) and at least 20 equivalents required for the reaction. The range is as follows, more preferably in the range of 2 to 10 equivalents, and still more preferably in the range of 2 to 4 equivalents. In this way, by using a system with a small amount of solvent, the reaction system can be maintained as a mixture of almost pure silicate ions and a surfactant, and the stability of the micelle of the surfactant serving as a template can be secured. , Can promote the sol-gel reaction. For example, porous silica can be synthesized even when a surfactant having less than 8 carbon atoms is used as R ₁ (hydrophobic portion). Therefore, the second pore diameter (average pore diameter, average pore diameter, D2) of the porous silica described below can be reduced. In other words, by adjusting the number of carbon atoms in the hydrophobic portion of the surfactant, the second pore diameter of the porous silica can be easily adjusted.

  Next, as shown in FIG. 1B, a precursor solution (sol) L1 is applied to the substrate SUB. Here, a coating layer of the precursor solution (sol) L1 is formed on the surface of the substrate SUB by immersing the substrate SUB in the precursor solution (sol) L1.

Next, by bringing the precursor solution (sol) L1 on the surface of the substrate SUB into contact with the basic solution L2, silicate ion adsorption and growth reaction (sol-gel reaction) proceeds in the gaps of the micelles, and silica (SiO ₂ ) is formed. Formed (see FIG. 4). For example, as shown in FIG. 1C, the substrate SUB to which the precursor solution (sol) L1 is attached is immersed in the basic liquid L2. As the basic liquid L2, for example, an aqueous ammonia solution can be used.

The precursor solution (sol) L1 attached to the surface of the substrate SUB gels (solidifies) by contacting the basic solution L2 (FIG. 1D). The gel is dried and then fired. By this calcination, the surfactant inside silica (SiO ₂ ) is removed, and porous silica PS can be obtained.

Further, here, the shape of the precursor solution (sol) L1 applied to the surface of the substrate SUB is reflected, and a film-like porous silica PS is formed. As described above, the shape of the applied precursor solution (sol) L1 is reflected on the shape of the porous silica, and the moldability is improved. The thickness of the film can be adjusted by the viscosity of the precursor solution (sol) L1, for example, it may be about 1000nm~10 ⁶ nm.

  A large number of pores corresponding to micelles (templates) made of a surfactant are formed in the porous silica in the form of a film. The holes are, for example, mesopores or micropores.

  In addition, as described later, this porous silica film has a large number of macropores extending in a direction intersecting the direction in which the film extends. In the present application, based on IUPAC standards, pores having a diameter of 2 nm or less are defined as micropores, pores having a diameter of 2 to 50 nm are defined as mesopores, and pores having a diameter of 50 nm or more are defined as macropores.

  That is, the film-like porous silica of the present embodiment has a large number of macropores (micrometer-sized holes) extending in a direction intersecting with the direction in which the film extends, and the side walls of the macropores have And pores (mesopores, micropores) corresponding to micelles (templates). The diameter of the macropore is 100 nm or more and 2000 nm or less. The thickness of the side wall of the macro hole is 100 nm or more and 2000 nm or less.

As described above, according to the present embodiment, macropores having orientation, mesopores and micropores corresponding to micelles (templates) inside silica (SiO ₂ ) constituting side walls of the macropores, Can be formed. Such porous silica having two or more kinds of pores may be referred to as “porous silica having a hierarchical porous structure”.

  FIG. 2 is a diagram schematically illustrating a configuration of the porous silica of the present embodiment. The photograph in FIG. 2 is an SEM image of the porous silica (film) of Example 1 (FIG. 7C) described later.

  As shown in FIG. 2, a plurality of columnar holes (first pores) P1 are formed in a direction substantially perpendicular to the direction in which the film extends (that is, the surface of the substrate SUB). The diameter (minor diameter, average pore diameter, diameter of the columnar cross section) D1 of this hole is 100 nm or more. Further, inside the porous silica PS constituting the side wall of the columnar hole P1, second pores (mesopores or micropores) P2 corresponding to micelles (templates) are formed. The diameter (minor diameter, average pore diameter) of this hole is defined as D2. Part of the second pores (mesopores or micropores) P2 is exposed from the side wall of the columnar hole P1. In other words, a part of the second pores (mesopores or micropores) P2 is connected to the columnar pores P1.

  As described above, according to the porous silica of the present embodiment, the macropores are provided, and the mesopores and the micropores are exposed on the side walls thereof, so that the mesopores and the micropores can function efficiently. For example, when porous silica is used as an adsorbent, the efficiency of adsorbing substances can be improved. Further, even when a functional material such as a catalyst is supported on the porous silica, the efficiency of the catalyst function can be improved by improving the diffusivity of the substrate, and the amount of the catalyst supported can be increased. Thus, the characteristics of the porous silica can be improved.

FIG. 3 is a diagram schematically showing micelles (templates). As is clear from FIG. 3, the micelle diameter is determined based on the carbon number of R ₁ (hydrophobic portion, hydrophobic alkyl chain) of the surfactant. Therefore, the larger the number of carbon atoms, the larger the diameter of the micelle (ie, the diameter of the second pore), and the smaller the number of carbon atoms, the smaller the diameter of the micelle (ie, the diameter of the second pore). Become. For example, when the number of carbon atoms in R ₁ (hydrophobic portion) of the surfactant is 8 or more, the diameter (short diameter) D2 of the second pore is a mesopore of 50 nm or less, but the R 2 of the surfactant is _{When the} number of carbon atoms in ₁ (hydrophobic portion) is less than 8 (the number of carbon atoms is 2 to 7), the diameter (short diameter) D2 of the second pore is a micropore of 2 nm or less. By adjusting the carbon number of R ₁ (hydrophobic portion) of the surfactant in this manner, the diameter (short diameter) D2 of the second pore can be adjusted to, for example, 0.5 nm or more and 3 nm or less.

In particular, when the number of carbon atoms in R ₁ (hydrophobic portion) of the surfactant is less than 8, formation of micelles tends to be difficult. In contrast, in the present embodiment, as described above, the reaction system can be maintained as a mixture of almost pure silicate ions and a surfactant by hydrolyzing with as little water (solvent) as possible. In addition, the stability of the micelle of the surfactant serving as a template can be ensured, and the diameter (short diameter) D2 of the second pore can be reduced.

  Although the mechanism of forming the macropores is not clear, the following mechanism can be considered.

  FIG. 4 is a reaction formula showing a reaction for producing porous silica (sol-gelation). FIG. 5 is a schematic view showing a mechanism of forming macropores.

As shown in reaction formula 1 in FIG. 4, Si (OH) ₄ (silicate ion) is formed by hydrolysis of tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ). Then, as shown in Reaction Formula 2, Si (OH) ₄ undergoes polycondensation to form silica (SiO ₂ ) (dehydration condensation reaction). By adding a surfactant to this reaction system and using micelles as templates, porous silica can be formed.

  The above hydrolysis reaction (reaction formula 1) and polycondensation reaction (reaction formula 2) are summarized as reaction formula 3.

As shown in FIG. 5 (A), when the precursor solution (sol) L1 on the surface of the substrate SUB comes into contact with ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) which is the basic liquid L2, The body solution (sol) L1 gels (solidifies), and SiO ₂ (Gel) is formed. Note that micelles MC are incorporated in this SiO ₂ .

Ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates into the precursor solution (sol) L1 side from the gap of SiO ₂ due to osmotic pressure (FIG. 5B). Then, the precursor solution (sol) L1 gels (solidifies) in the vicinity of the infiltrated ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) (FIG. 5C). Further, ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates, and SiO ₂ grows. As described above, SiO ₂ grows so as to surround the region where the precursor solution (sol) L1 is present and in which ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates (arrow portion in the drawing). . The region where the precursor solution (sol) L1 exists and in which ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates (arrow portion in the figure) is a columnar hole (first hole, macro hole). ) P1. The columnar holes (first holes, macro holes) P1 have orientation and extend in a direction intersecting with the surface of the substrate SUB, more specifically, substantially perpendicularly. In other words, it extends in the thickness direction of the porous silica film.

  Thus, according to the present embodiment, it is possible to obtain porous silica in which macropores and mesopores or micropores are exposed on the side walls of the macropores. In addition, macropores and porous silica having mesopores or micropores exposed on the side walls of the macropores can be obtained by a simple manufacturing process. That is, the growth of silica incorporating the micelles MC and the formation of macropores due to the infiltration of the basic liquid and the contact with the sol, which are thought to be derived from the reaction mechanism, proceed simultaneously, and have a hierarchical porous structure. Porous silica can be easily formed.

  In the step shown in FIG. 1, the precursor solution (sol) L1 was applied to the surface of the substrate SUB by a so-called dip method (immersion method, see FIGS. 1B and 1C). The precursor solution (sol) L1 may be applied by the above method.

  FIG. 6 is a diagram illustrating a method of applying the precursor solution (sol) L1 to the substrate SUB. For example, as shown in FIG. 6A, the precursor solution (sol) L1 may be applied onto the substrate SUB using a spray gun (fog spray) SG. Such application is called spray coating. Further, as shown in FIG. 6B, the precursor solution (sol) L1 may be discharged from the nozzle N onto the rotating substrate SUB and spin-coated. Such application is called spin coating.

  Although there is no limitation on the type of the substrate SUB, for example, a silicon substrate or a glass substrate can be used. In addition to the substrate, a glass filter or the like may be used. The glass filter is an aggregate of glass fibers, for example, one processed into a plate shape.

  As described above, according to the present embodiment, a porous silica having a hierarchical porous structure and in the form of a film can be produced.

  Here, for example, in Patent Document 2, in addition to a surfactant, an alkoxysilane and water, alkoxysilane is hydrolyzed in the presence of a water-soluble polymer such as polyethylene glycol, and this mixed solution is converted into a basic solution. By contacting with a solution, monolithic mesoporous silica has been successfully converted into nanoparticles. In this case, porous silica having two pores of about 2 nm of mesopores derived from a surfactant and about 20 to 50 nm of mesopores corresponding to the particle gap is formed.

  In this case, the difference between the two types of pores is too small. In addition, a water-soluble polymer such as polyethylene glycol is essential. Further, the mesopores corresponding to the particle gap of about 20 to 50 nm have no orientation.

  Further, in the method of forming a hierarchical porous structure using ice crystals as a template as in Non-Patent Document 2, the macropore diameter is as large as several tens of μm, and the difference between the two kinds of pores is too large.

  In comparison with such a method, according to the present embodiment, for example, when used as an adsorbent or a catalyst carrier, it exhibits high substrate diffusivity in macropores, and can be used as a substrate for micropores or mesopores. In order to promote the adsorption, the adsorption efficiency and the catalyst efficiency can be improved. In addition, the macropores can have orientation, and higher substrate diffusion efficiency can be obtained. Thus, porous silica having a hierarchical porous structure having an effective pore diameter difference can be obtained.

  Hereinafter, the present embodiment will be described in more detail based on examples.

(Example 1) Synthesis of porous silica having a hierarchical porous structure and a film shape In a polypropylene container, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) was added as a silica source, followed by 0.0075 mol to 0.038 mol (0.2 to 1 eq) of the cationic surfactant was dispersed and stirred. At this point, the TEOS and the surfactant do not mix. That is, a uniform solution is not obtained. Octadecyltrimethylammonium chloride (C18TAC) or hexyltrimethylammonium bromide (C6TAB) was used as the cationic surfactant.

  Next, about 2.74 g (0.152 mol; 4 eq) of water whose pH was adjusted to about 0 to 2 using hydrochloric acid was added to the above mixed solution, and the mixture was stirred at room temperature to obtain a solution (precursor solution). I got This solution is in the form of a sol. The hydrolysis of TEOS proceeded with stirring for about one hour, and a substantially uniform solution (precursor solution, sol) was obtained. In this example, the stirring time was 6 hours.

  The substrate (silicon substrate) was immersed (dip coated) in this solution (precursor solution, sol), and then immersed in a 25% aqueous ammonia solution. The solution (precursor solution, sol) attached to the surface of the substrate gelled (solidified) at the moment it came into contact with the aqueous ammonia solution. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant. As a result, a porous silica film was obtained.

  The pores of the obtained porous silica were analyzed. The specific surface area (SSA), pore volume (TPV), and average pore diameter (D) were measured. The specific surface area (SSA) was measured by the BET method. The average pore diameter was measured using the GCMC method.

The BET specific surface area of the porous silica using C18TAC was 1,144 m ² / g, and the pore volume was 0.85 cm ³ / g.

  FIGS. 7 and 8 show SEM images of porous silica (in the form of a film) synthesized using C18TAC. In FIG. 7, (A) is an SEM image of the upper surface of the porous silica using C18TAC, and it can be seen that porous silica in the form of a film is obtained. (B) is an SEM image of a cross section of the film-like porous silica, and (C) is an enlarged SEM image thereof. FIG. 8 is an enlarged SEM image of the upper surface of the porous silica.

  As is clear from FIGS. 7B, 7C, and 8, it was observed that a plurality of macropores were opened perpendicularly to the direction in which the film extended (the thickness direction of the film). In addition, in the SEM image of FIG. 8, the SEM image of a portion where the surface of the porous silica was chipped and macropores clearly appeared was taken (the same applies to FIG. 13).

  As described above, the porous silica (film form) synthesized using C18TAC has a hierarchical porous structure having mesopores using surfactant micelles as templates and macropores confirmed by SEM images. It turns out that it is.

  FIG. 9 is a diagram showing a nitrogen adsorption / desorption isotherm of porous silica (in the form of a film) synthesized using C18TAC. In FIG. 9, the graph is bent and the inclination is changed in part (a). Such a portion (a) corresponds to the type IV of the IUPAC classification, and it is presumed that micropores or mesopores are present. Further, also in the portion (b), a bent portion of the graph exists, and a hysteresis loop can be confirmed. This part (b) also corresponds to the above-mentioned type IV, and the existence of larger macropores is also presumed.

FIGS. 10 and 11 are graphs showing the pore size distribution of porous silica (membrane) synthesized using C18TAC. FIG. 10 shows the pore size distribution of micropores or mesopores based on the GCMC method, and FIG. 11 shows the pore size distribution of macropores obtained by the mercury intrusion method. The horizontal axis is the pore diameter (Pore diameter, [nm]), and the vertical axis is the integrated pore volume (dVp, [cm ³ / g]). In FIG. 11, the vertical axis on the right side is the Log differential pore volume (dV / d (logD), [cm ³ / g]).

As shown in FIG. 10, the average pore diameter (GCMC method) was 3.5 nm (mesopore). As shown in FIG. 11, the average pore diameter of the macropores was about 600 nm. Note that the second peak (10 ⁵ nm) shown in FIG. 11 is based on the gap (gap) between the porous silicas, and is not based on the macropores confirmed in the SEM image.

  As described above, it was found that the porous silica (film-like) synthesized using C18TAC was a silica film having a hierarchical porous structure having macropores of 600 nm and mesopores of 3.5 nm.

The BET specific surface area of the porous silica using C6TAB was 626 m ² / g, and the pore volume was 0.65 cm ³ / g.

  FIGS. 12 and 13 show SEM images of porous silica (in the form of a film) synthesized using C6TAB. FIG. 12 is an enlarged SEM image of a cross section of the porous silica film, and FIG. 13 is an enlarged SEM image of the upper surface of the porous silica.

  As is clear from FIG. 12 and FIG. 13, even in porous silica (C6) using C6TAB, a plurality of macropores are vacant in the direction perpendicular to the direction in which the film extends (in the thickness direction of the film). Observed.

  As described above, the porous silica (film-like) synthesized using C6TAB is a silica having a hierarchical porous structure having micropores using surfactant micelles as templates and macropores confirmed by SEM images. It turns out that it is.

  FIG. 14 is a diagram showing a nitrogen adsorption / desorption isotherm of porous silica (in the form of a film) synthesized using C6TAB. In FIG. 14, the graph is bent and the inclination is changed in the portion (a). Such a portion (a) corresponds to the type I of the IUPAC classification, and the existence of micropores is presumed. Further, also in the portion (b), a bent portion of the graph exists, and a hysteresis loop can be confirmed. This part (b) also corresponds to the above-mentioned type IV, and the existence of larger macropores is also presumed.

  FIG. 15 is a graph showing the pore size distribution of porous silica (membrane) synthesized using C6TAB. FIG. 15 is a pore size distribution of micropores or mesopores based on the GCMC method.

  As shown in FIG. 15, the average pore diameter (GCMC method) was 1.3 nm (micropore). When the pore size distribution of the macropores was examined by the mercury intrusion method, the average pore size of the macropores was about 500 nm.

  As described above, it was found that the porous silica (film-like) synthesized using C6TAB was a silica film having a hierarchical porous structure having macropores of 500 nm and micropores of 1.3 nm.

(Comparative Example 1) Silica synthesized without using a surfactant In forming the solution (precursor solution, sol) of Example 1, a solution was formed without adding a surfactant. That is, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) was added as a silica source to a polypropylene container, and then 2.74 g (0.152 mol) of water whose pH was adjusted to about 0 to 2 using hydrochloric acid. About 4 eq) and stirred at room temperature to obtain a solution (precursor solution, sol). The stirring time was 6 hours.

  The substrate (silicon substrate) was immersed (dip coated) in this solution (precursor solution, sol), and then immersed in a 25% aqueous ammonia solution. The solution (precursor solution, sol) attached to the surface of the substrate gelled (solidified) at the moment it came into contact with the aqueous ammonia solution. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant. Thereby, silica was obtained.

  FIG. 16 shows an SEM image of the silica of this comparative example. As is clear from FIG. 16, when the surfactant was not added, no macropores were formed, and only an aggregate of amorphous silica particles was obtained. Further, since no surfactant was added, no micelles were formed, and neither micropores nor mesopores were formed.

  As described above, when the surfactant was not added, silica having a hierarchical porous structure having macropores and micropores or mesopores could not be formed. From this, it was found that a surfactant was essential for the synthesis of silica having a hierarchical porous structure.

(Comparative Example 2) ... Silica synthesized by gelation and immersion in an aqueous ammonia solution The solution (precursor solution, sol) of Example 1 was spin-coated on a silicon substrate at 1000 rpm to form a coating film. Dry in air. By drying, the coating film gelled and lost fluidity. This gel was immersed in a 25% aqueous ammonia solution. Thereafter, the gel was dried at 60 ° C. and baked at 600 ° C. for 3 hours to remove the surfactant. Thus, porous silica was obtained.

  FIG. 17 shows an SEM image of the porous silica of this comparative example. As is clear from FIG. 17, even when the solution (precursor solution, sol) was gelled and immersed in an aqueous ammonia solution, no macropores were formed. Since the surfactant was added, it is considered that micropores or mesopores were formed using micelles as templates.

  In this way, when the solution (precursor solution, sol) is gelled and then immersed in an aqueous ammonia solution, it is possible to form silica having a hierarchical porous structure having macropores, micropores or mesopores. could not. For this reason, in order to synthesize silica having a hierarchical porous structure, it is essential that the solution (precursor solution, sol) is brought into contact with an aqueous ammonia solution before the solution is gelled after being discharged. I understood.

  In the present specification, gelation means that the viscosity [mPa · s] of the solution becomes 100 [mPa · s] or more, for example, and the viscosity of the solution after stirring is 50 [mPa · s]. It is preferable to make contact with a basic liquid (aqueous ammonia solution) in the following steps.

(Example 2) Relationship between stirring time and film thickness (micropore length) Using octadecyltrimethylammonium chloride (C18TAC) as a cationic surfactant, a film-like porous silica as in Example 1 was used. Was formed. That is, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) was added as a silica source to a polypropylene container, and then a cationic surfactant (C18TAC) was added in an amount of 0.0075 mol to 0.038 mol (0.2 to 1eq) was dispersed and stirred. At this point, the TEOS and the surfactant do not mix. That is, a uniform solution is not obtained.

  Next, about 2.74 g (0.152 mol; 4 eq) of water whose pH was adjusted to about 0 to 2 using hydrochloric acid was added to the above mixed solution, and the mixture was stirred at room temperature to obtain a solution (precursor solution). I got This solution is in the form of a sol.

  Solutions (precursor solutions, sols) with stirring times of 1, 6, and 24 hours were prepared. The hydrolysis of TEOS proceeded with stirring for about one hour, and a substantially uniform solution (precursor solution, sol) was obtained. Further, as the stirring time increased from 1 hour to 6 hours and then to 24 hours, the viscosity of the solution (precursor solution, sol) increased, but the solution did not gel.

  The substrate (silicon substrate) was immersed (dip coated) in the solution after stirring, and then immersed in a 25% aqueous ammonia solution. The solution (precursor solution, sol) attached to the surface of the substrate gelled (solidified) at the moment it came into contact with the aqueous ammonia solution. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant. As a result, a porous silica film was obtained.

  With an increase in the stirring time, it was confirmed that the film thickness of the film-like porous silica increased. When the stirring time is 1 hour, the film thickness is about 20 μm, when the stirring time is 6 hours, the film thickness is about 30 μm, and when the stirring time is 24 hours, the film thickness is about 35 μm. Was.

  Such a change in the film thickness is caused by the fact that the polymerization of the precursor silicate progresses as the stirring time of the solution (precursor solution, sol) increases, and for example, the precursor silicate becomes an oligomer and the viscosity of the sol increases. Thus, by adjusting the stirring time of the solution (precursor solution, sol), it is possible to control the thickness of the film-like porous silica.

  FIG. 18 is an enlarged SEM image of a cross section of the porous silica film. 18A shows the case where the stirring time is 1 hour, FIG. 18B shows the case where the stirring time is 6 hours, and FIG. 18C shows the case where the stirring time is 24 hours.

  From the comparison between (A) and (B) of FIG. 18, it can be confirmed that the length of the macropores tends to be longer when the stirring time is from 1 hour to 6 hours. Also, from the comparison between (B) and (C) of FIG. 18, when the stirring time is changed from 6 hours to 24 hours, the length of the macropore becomes longer, and the columnar macropore becomes opposite to the surface (substrate side). It can be seen that is bent.

Example 3 Porous Silica Formed on a Glass Filter A film-like porous silica was formed in the same manner as in Example 2, except that octadecyltrimethylammonium chloride (C18TAC) was used as a cationic surfactant. That is, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) was added as a silica source to a polypropylene container, and then a cationic surfactant (C18TAC) was added in an amount of 0.0075 mol to 0.038 mol (0.2 to 1eq) was dispersed and stirred. At this point, the TEOS and the surfactant do not mix. That is, a uniform solution is not obtained.

  Next, about 2.74 g (0.152 mol; 4 eq) of water whose pH was adjusted to about 0 to 2 using hydrochloric acid was added to the above mixed solution, and the mixture was stirred at room temperature to obtain a solution (precursor solution). I got This solution is in the form of a sol. The hydrolysis of TEOS proceeded with stirring for about one hour, and a substantially uniform solution (precursor solution, sol) was obtained. In this example, the stirring time was 6 hours.

  A glass filter was immersed (dip coated) in this solution (precursor solution, sol), and then immersed in a 25% aqueous ammonia solution. The solution (precursor solution, sol) attached to the surface of the glass filter gelled (solidified) at the moment it came into contact with the aqueous ammonia solution. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant. As a result, a porous silica film was obtained.

  FIG. 19 is an SEM image of the glass filter, and FIG. 20 is an enlarged SEM image of a cross section of the film-like porous silica.

  Also in the present embodiment, as shown in FIG. 20, a film-like porous silica is formed on a glass filter, and a plurality of macropores are formed in a direction perpendicular to the direction in which the film extends (in the thickness direction of the film). Was observed. The average pore diameter of the macropores is about 500 nm. In addition, the porous silica formed around the fibers of the glass filter can be seen below the porous silica in the form of a film.

(Embodiment 2) Granular porous silica In Embodiment 1, a film-like porous silica is formed, but in the present embodiment, granular porous silica is formed.

  Also in the present embodiment, porous silica is synthesized by a sol-gel method using a surfactant as a template. As described above, generally, when a surfactant is dissolved in a solution, for example, a cylindrical micelle (template) is formed in accordance with the type and concentration of the surfactant. Here, when an alkoxysilane or the like serving as a silica source is added to the solution, the adsorption and growth reaction of silicate ions proceeds in the gaps of the micelles, and a silica gel skeleton is formed. The silicate state is changed from a sol state to a gel state by the silicate ion adsorption and growth reaction, and is called a sol-gel reaction (see FIG. 4). Thereafter, when firing (heat treatment), the surfactant used as a template is decomposed and removed, and porous silica is obtained. In other words, a silica skeleton having a plurality of pores (pores, micropores) is obtained.

  Hereinafter, the method for synthesizing the porous silica of the present embodiment will be described in detail. FIG. 21 is a diagram showing a process for producing the porous silica of the present embodiment.

  A precursor solution (sol, sol-state liquid) L1 of porous silica is formed in the same manner as in the first embodiment. That is, a silicon compound serving as a silica source and a surfactant are mixed and stirred, and water is added to the mixed solution and stirred to form a precursor solution L1.

As for the silica source, the surfactant, and water (H ₂ O) to be added, the same materials as those in the first embodiment can be used.

  Also in the present embodiment, it is preferable to hydrolyze with as little water (solvent) as possible in order to improve the moldability of cylindrical micelles (templates) that become pores of porous silica (see FIG. 4). Therefore, the amount of water to be added to the alkoxysilane is in the range of at least 2 equivalents (eq) required for the reaction and not more than 20 equivalents, more preferably in the range of not less than 2 equivalents and not more than 10 equivalents, and further preferably, The range is from 2 equivalents to 4 equivalents. The reason for using a small solvent system is as described in the first embodiment.

Next, the precursor solution (sol) L1 is formed into droplets and brought into contact with the basic liquid L2. As a result, in the droplets, the adsorption and growth reaction (sol-gel reaction) of silicate ions proceeds in the gaps between the micelles, and granular (for example, substantially spherical) silica (SiO ₂ ) is formed (see FIG. 4). Thus, the shape of the drop of the precursor solution (sol) L1 is reflected on the shape of the porous silica, and the moldability is improved. The size of the particles can be adjusted by the size of the droplets of the precursor solution (sol) L1 dropped into the basic liquid. For example, the diameter of the particles (spherical) is 1000 nm to 5 × 10 ⁶ nm. Degree.

  For example, as shown in FIG. 21, the precursor solution (sol) L1 is sprayed into the basic liquid L2 using a spray gun (mist spray) SG. As the basic liquid L2, for example, an aqueous ammonia solution can be used. Instead of the spray gun (mist spray) SG, a dropper ED as shown in FIG. 22 may be used. By using the dropper ED, the size of the droplet can be increased. In addition, a syringe or the like may be used instead of the dropper ED. FIG. 22 is a diagram showing another manufacturing process of the porous silica of the present embodiment.

The droplet-shaped precursor solution (sol) L1 shown in FIG. 21 and the like is gelled (solidified) by coming into contact with the basic liquid L2. The gel is taken out, dried, and fired. By this firing, the surfactant inside silica (SiO ₂ ) is removed, and granular porous silica PS can be obtained.

  A large number of pores corresponding to micelles (templates) made of a surfactant are formed in the granular porous silica. The holes are, for example, mesopores or micropores.

  In addition, as described later, the granular porous silica has a large number of macropores extending radially from the center of the particle. Stated another way, it has a plurality of columnar macropores extending from the inside of the particle to the outside. In other words, it has a plurality of columnar macropores extending from the outside to the inside (for example, the center) of the particle.

  As described above, the granular porous silica of the present embodiment has a large number of macropores extending radially from the center of the particles, and the side walls of the macropores have pores (meso) corresponding to the micelle (template). Holes, micropores). The diameter of the macropores (short diameter, average pore diameter, diameter of columnar cross section) is 100 nm or more and 2000 nm or less. The thickness of the side wall of the macro hole is 100 nm or more and 2000 nm or less.

As described above, according to the present embodiment, macropores having orientation, mesopores and micropores corresponding to micelles (templates) inside silica (SiO ₂ ) constituting side walls of the macropores, Can be formed.

  Also in the present embodiment, a plurality of columnar holes (first pores) P1 are formed, and inside the porous silica PS constituting the side walls of the columnar holes P1, the second pores corresponding to the micelles (template) are formed. Micropores (mesopores or micropores) P2 are formed. Part of the second pores (mesopores or micropores) P2 is exposed from the side wall of the columnar hole P1. In other words, a part of the second pores (mesopores or micropores) P2 is connected to the columnar pores P1 (see FIG. 2).

  As described above, according to the porous silica of the present embodiment, the macropores are provided, and the mesopores and the micropores are exposed on the side walls thereof, so that the mesopores and the micropores can function efficiently. For example, when porous silica is used as an adsorbent, the efficiency of adsorbing substances can be improved. Further, even when a functional material such as a catalyst is supported on the porous silica, the efficiency of the catalyst function can be improved by improving the diffusivity of the substrate, and the amount of the catalyst supported can be increased. Thus, the characteristics of the porous silica can be improved.

Also in this embodiment, the micelle diameter is determined based on the carbon number of R ₁ (hydrophobic portion, hydrophobic alkyl chain) of the surfactant (see FIG. 3). Therefore, the larger the number of carbon atoms, the larger the diameter of the micelle (ie, the diameter of the second pore), and the smaller the number of carbon atoms, the smaller the diameter of the micelle (ie, the diameter of the second pore). Become. For example, when the number of carbon atoms in R ₁ (hydrophobic portion) of the surfactant is 8 or more, the diameter (short diameter) D2 of the second pore is a mesopore of 50 nm or less, but the R 2 of the surfactant is _{When the} number of carbon atoms in ₁ (hydrophobic portion) is less than 8 (the number of carbon atoms is 2 to 7), the diameter (short diameter) D2 of the second pore is a micropore of 2 nm or less. Thus, by adjusting the carbon number of R ₁ (hydrophobic portion) of the surfactant, the diameter (short diameter) D2 of the second pore can be adjusted to, for example, 0.5 nm or more and 3 nm or less. .

In particular, when the number of carbon atoms in R ₁ (hydrophobic portion) of the surfactant is less than 8, formation of micelles tends to be difficult. In contrast, in the present embodiment, as described above, the reaction system can be maintained as a mixture of almost pure silicate ions and a surfactant by hydrolyzing with as little water (solvent) as possible. In addition, the stability of the micelle of the surfactant serving as a template can be ensured, and the diameter (short diameter) D2 of the second pore can be reduced.

  Although the mechanism of forming the macropores is not clear, the following mechanism can be considered.

FIG. 23 is a schematic view showing a mechanism of forming macropores. The reaction mechanism for forming silica (SiO ₂ ) in the present embodiment is the same as that in the first embodiment (see FIG. 4).

As shown in FIG. 23, when the precursor solution (sol) L1 on the surface of the substrate SUB comes in contact with ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ), which is the basic liquid L2, the precursor solution (sol) (Sol) L1 is gelled (solidified), and SiO ₂ (Gel) is formed. Note that micelles MC are incorporated in this SiO ₂ .

The SiO ₂ in osmotic pressure from the gap, the precursor solution (sol) L1 side ammonia ^{_{(NH 4 OH, NH 4 +}} + OH -) is Komu penetrates. Then, the precursor solution (sol) L1 gels (solidifies) in the vicinity of the infiltrated ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ). Further, ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates, and SiO ₂ grows. As described above, SiO ₂ grows so as to surround the region where the precursor solution (sol) L1 is present and in which ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates (arrow portion in the drawing). . The region where the precursor solution (sol) L1 exists and in which ammonia (NH ₄ OH, NH ₄ ⁺ + OH ⁻ ) infiltrates (arrow portion in the figure) is a columnar hole (first hole, macro hole). ) P1. The columnar holes (first pores, macropores) P1 have an orientation and extend from the outside to the inside (for example, the center) of the granular droplet LD of the precursor solution (sol) L1. I do.

  Thus, according to the present embodiment, it is possible to obtain porous silica in which macropores and mesopores or micropores are exposed on the side walls of the macropores. In addition, macropores and porous silica having mesopores or micropores exposed on the side walls of the macropores can be obtained by a simple manufacturing process. That is, the growth of silica incorporating the micelles MC and the formation of macropores due to the infiltration of the basic liquid and the contact with the sol, which are thought to be derived from the reaction mechanism, proceed simultaneously, and have a hierarchical porous structure. Porous silica can be easily formed.

  Hereinafter, the present embodiment will be described in more detail based on examples.

Example 4 Synthesis of Granular Porous Silica Having Hierarchical Porous Structure A polypropylene container was charged with 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) as a silica source, followed by cations The active surfactant (C18TAC) was dispersed in 0.0075 mol to 0.038 mol (0.2 to 1 eq) and stirred. At this point, the TEOS and the surfactant do not mix. That is, a uniform solution is not obtained.

  Next, about 2.74 g (0.152 mol; 4 eq) of water whose pH was adjusted to about 0 to 2 using hydrochloric acid was added to the above mixed solution, and the mixture was stirred at room temperature to obtain a solution (precursor solution). I got This solution is in the form of a sol. The hydrolysis of TEOS proceeded with stirring for about one hour, and a substantially uniform solution (precursor solution, sol) was obtained. In this example, the stirring time was 6 hours.

  This solution (precursor solution, sol) was put into a spray and sprayed into a 25% aqueous ammonia solution. The droplets of the solution (precursor solution, sol) gelled (solidified) at the moment of contact with the aqueous ammonia solution. In this case, a particle gel (spherical gel) having a diameter of about 100 μm was obtained. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant. Thus, granular porous silica was obtained.

The resulting granular porous silica had a BET specific surface area of 1016 m ² / g, a pore volume of 0.92 cm ³ / g, and an average pore diameter (GCMC method) of 3.5 nm (mesopore). Was.

  FIG. 24 shows an SEM image of the porous silica (granular) of this example. In FIG. 24, (A) is an SEM image of the upper surface of porous silica (granular), and it can be seen that granular porous silica has been obtained. The diameter (average) of the particles is about 100 μm. (B) is an SEM image of a cross section of granular porous silica, and (C) is an enlarged SEM image thereof.

  As is clear from FIGS. 24B and 24C, it was observed that a plurality of macropores were open from the surface of the particle toward the inside. Stated another way, it was observed that macropores extending radially from the center of the particle were open. The average pore diameter of the macropores is about 500 nm.

  Thus, it was found that even if the porous silica was granulated, the silica had a hierarchical porous structure having macropores of 500 nm and mesopores of 3.5 nm.

Example 5 Synthesis of Granular Porous Silica Having Hierarchical Porous Structure In the same manner as in Example 4, a solution (precursor solution, sol) was prepared, and this solution (precursor) was prepared. Solution, sol) was placed in a syringe and dropped into a 25% aqueous ammonia solution. The droplets of the solution (precursor solution, sol) gelled (solidified) at the moment of contact with the aqueous ammonia solution. In this case, a particle gel (spherical gel) having a diameter of about 1 mm was obtained. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant. Thus, granular porous silica was obtained.

The resulting granular porous silica had a BET specific surface area of 1007 m ² / g, a pore volume of 0.91 cm ³ / g, and an average pore diameter (GCMC method) of 3.5 nm (mesopore). Was.

  FIG. 25 shows an SEM image of the porous silica (granular) of this example. In FIG. 25, (A) is an SEM image of a cross section of granular porous silica, (B) is an enlarged SEM image of region A1, and (C) is an enlarged SEM image of region A2.

  The diameter (average) of the particles is about 1 mm. As is clear from FIGS. 25A to 25C, in the case of this example, it was also observed that a plurality of macropores were formed from the surface of the particle toward the inside. Stated another way, it was observed that macropores extending radially from the center of the particle were open.

  Specifically, as shown in FIG. 25C, 0.7 μm (700 nm), 1.4 μm (1400 nm), and 2.0 μm (2000 nm) macropores can be confirmed. The average pore diameter of the macropores is about 500 nm.

  Thus, it was found that even if the porous silica was granulated, the silica had a hierarchical porous structure having macropores of 500 nm and mesopores of 3.5 nm.

(Embodiment 3)
In this embodiment, application examples of the porous silica described in the first and second embodiments will be described.

  The porous silica described in the first and second embodiments can be used, for example, as an adsorbent or various catalyst carriers.

  Here, an air purifier will be described as an example of application of porous silica. FIG. 26 is a schematic diagram showing a configuration of the air purifier of the present embodiment.

  The air purifier illustrated in FIG. 26 includes, for example, a suction fan FN, a first filter F1, and a second filter F2. From the air (Air) taken in by the suction fan FN, large dust such as dust is removed by the first filter F1. The fine particles that have passed through the first filter F1 are collected by the second filter F2. The fine particles to be removed include mold and pollen, tobacco smoke, exhaust gas, malodor such as tobacco smell and pet smell, and harmful volatile organic compounds (VOC) such as formaldehyde.

  For example, by using the film-like porous silica described in Embodiment 1 as the second filter F2, fine particles can be adsorbed by macropores, mesopores, or micropores.

  When a laminated film of the glass filter and the porous silica (Example 3) is used, the glass filter can also serve as the first filter F1. Further, by fixing granular porous silica to various filters by bonding or the like, it can be used as the second filter F2.

  Further, by using the film-shaped porous silica in which the photocatalyst is supported as described in Embodiment 1 as the second filter F2, in addition to the adsorption of the fine particles, the fine particles adsorbed by the action of the photocatalyst are used. The particles can be broken down. In particular, if a photocatalyst is synthesized in mesopores or micropores, a quantum dot photocatalyst can be obtained, and if a photocatalyst is synthesized in macropores, a nanophotocatalyst can be obtained.

  When a photocatalyst is used, a light source may be provided near the second filter F2.

  As described above, by using the porous silica described in the first and second embodiments for an air purifier, air can be efficiently purified. In particular, by using the porous silica described in the first and second embodiments, the substrate exhibits high substrate diffusivity in the macropores and promotes the adsorption of the substrate in the micropores or mesopores. Efficiency can be improved.

  The air purifier is only an example of the application example of the porous silica described in the first and second embodiments, and the porous silica described in the first and second embodiments may be used for various purposes. Is possible. For example, the present invention can be applied to filtration membranes, gas separation membranes, chromatography packings, separators, and the like, in addition to the above-mentioned adsorbents and various catalyst carriers.

  As described above, the porous silica described in the first and second embodiments can be widely applied as a functional material (adsorbent, filter, catalyst carrier, filtration membrane, gas separation membrane, chromatography filler, separator) and the like. It is.

(Embodiment 4)
In the present embodiment, a method for producing a porous silica film only on the surface of a glass filter will be described.

  As described above, the glass filter is an aggregate of glass fibers, and for example, there is a glass filter processed into a plate shape. For this reason, the glass filter includes many gaps (voids, holes) between the glass fibers. Therefore, when the plate-like glass filter is immersed (dip-coated) in the precursor solution as in Example 3 described above, a film-like porous silica is formed on the surface of the plate-like glass filter, and The precursor solution also infiltrates a large number of gaps (pores) between glass fibers, and porous silica is generated.

  Therefore, for example, in order to effectively function a large number of gaps (holes) between glass fibers, it is desired to form a porous silica film only on the surface of the glass filter.

  In such a case, a high-viscosity liquid that can be removed by baking or washing, such as liquid paraffin, is infiltrated into the glass filter in advance, that is, a large number of gaps (holes) between glass fibers are filled with the high-viscosity liquid. In this state, the substrate is immersed in a precursor solution to form a porous silica film (see Example 3).

  FIG. 27 and FIG. 28 are views showing a process of manufacturing a composite film of the glass filter of the present embodiment and a porous silica film.

  First, as shown in FIG. 27 (A), a plate-like glass filter GF (see also FIG. 28 (A)) is immersed in liquid paraffin Lp, and liquid paraffin is inserted into a number of gaps (holes) Sp between glass fibers. Lp is impregnated (see also FIG. 28B).

  Thereafter, in the same manner as in Example 1, a precursor solution (sol, sol-state solution) L1 of porous silica is prepared, and the glass filter GF is immersed in the precursor solution (sol) L1 ( 27B), a coating layer of the precursor solution (sol) L1 is formed on the surface of the glass filter GF.

Next, as shown in FIG. 27C, the precursor solution (sol) L1 on the surface of the glass filter GF to which the precursor solution (sol) L1 is attached is brought into contact with a basic liquid (for example, an aqueous ammonia solution) L2 ( FIG. 27 (C). Thereby, the silicate ion adsorption and growth reaction (sol-gel reaction) proceeds in the gaps between the micelles, and silica (SiO ₂ ) is formed (see FIGS. 27D and 4).

Specifically, the precursor solution (sol) L1 attached to the surface of the glass filter GF gels (solidifies) by contacting with the basic liquid L2 (FIGS. 27D and 28C). . The gel is dried and then fired. By this baking, the surfactant inside silica (SiO ₂ ) is removed, and porous silica PS can be obtained (FIG. 27E). Further, by this baking, the liquid paraffin Lp in the many gaps (holes) Sp between the glass fibers is decomposed, vaporized, and removed (FIG. 28D).

In this manner, porous silica having a hierarchical porous structure can be formed on the surface thereof while maintaining a large number of gaps (holes) between glass fibers. More specifically, the glass filter of the present embodiment has columnar macropores having orientation and mesopores corresponding to micelles (templates) inside silica (SiO ₂ ) constituting side walls of the macropores. And a microporous silica portion, and a glass filter portion having a large number of gaps (pores) between glass fibers. Note that the columnar macropores having orientation are also referred to as channels (macrochannels).

(Example A): A porous silica substrate formed only on the surface of a glass filter A glass filter serving as a substrate was immersed in liquid paraffin in advance and liquid paraffin was impregnated.

  Using octadecyltrimethylammonium chloride (C18TAC) as a cationic surfactant, a porous silica film was formed in the same manner as in Example 2. That is, 8 g (0.038 mol; 1 eq) of tetraethoxysilane (TEOS) was added as a silica source to a polypropylene container, and then a cationic surfactant (C18TAC) was added in an amount of 0.0075 mol to 0.038 mol (0.2 to 1eq) was dispersed and stirred. At this point, the TEOS and the surfactant do not mix. That is, a uniform solution is not obtained.

  Next, about 2.74 g (0.152 mol; 4 eq) of water whose pH was adjusted to about 0 to 2 using hydrochloric acid was added to the above mixed solution, and the mixture was stirred at room temperature to obtain a solution (precursor solution). I got This solution is in the form of a sol. The hydrolysis of TEOS proceeded with stirring for about one hour, and a substantially uniform solution (precursor solution, sol) was obtained. In this example, the stirring time was 6 hours.

  A glass filter impregnated with liquid paraffin was immersed (dip coated) in this solution (precursor solution, sol) and then immersed in a 25% aqueous ammonia solution. The solution (precursor solution, sol) attached to the surface of the glass filter gelled (solidified) at the moment it came into contact with the aqueous ammonia solution. The gel was dried at 60 ° C. and calcined at 600 ° C. for 3 hours to remove the surfactant and liquid paraffin. As a result, a glass filter (composite film, functional film) having a porous silica film formed on the surface was obtained.

  FIG. 29 is an SEM image of a glass filter having a porous silica film formed on the obtained surface. (A) is an SEM image of a cross section in the thickness direction (for example, see FIG. 28 (D)), and the right part is a partially enlarged view. (B) is an SEM image of the surface of the glass filter after the porous silica film on the surface is peeled off.

  As shown in FIG. 29, it was observed that porous silica in the form of a film was formed on the glass filter, and a plurality of macropores were opened perpendicularly to the direction in which the film extended (the thickness direction of the film). . Further, it is confirmed that a large number of gaps between glass fibers remain in the glass filter portion below the film-like porous silica. As described above, in the case of FIG. 20 described in Example 3, the porous silica is also formed around the fibers of the glass filter, and in the case of the present embodiment, in the glass filter portion, It was found that many gaps between the glass fibers were more open. As described above, by pre-soaking the glass filter in liquid paraffin, porous silica is preferentially formed on the surface of the glass filter rather than between the glass fibers, and the growth of the porous silica between the glass fibers is suppressed. Can be.

In the present embodiment, it is possible to obtain a functional film having macropores, mesopores or micropores in silica (SiO ₂ ) constituting side walls of the macropores, and gaps between glass fibers. . The average diameter (average minor diameter) of these holes is micropores <macropores <gap.

(Fifth Embodiment) Production of Porous Silica-Encapsulated Particles Oriented macropores synthesized in the above embodiment, and mesopores and micropores in silica (SiO ₂ ) constituting side walls of the macropores. Fine particles can be synthesized by using a porous silica having the following formulas, and including a material such as a metal in the pores (pores and micropores).

  For example, the porous silica is brought into contact with an aqueous solution of a metal compound, and the aqueous solution of the metal compound penetrates into pores (mesopores or micropores) of the porous silica. Next, after drying the porous silica, the porous silica is fired, and the metal is included in the pores of the porous silica.

  The metal compound aqueous solution to be used is not limited as long as it is a metal compound aqueous solution (a liquid containing a metal or a compound having the metal as an elemental composition) in which a metal or a metal compound is precipitated (residual) by firing. A compound having a particle material as an elemental composition such as an aqueous solution of tungstic peroxide or an aqueous solution of titanium trichloride can be used.

  When the aqueous solution of tungsten peroxide is used, tungsten oxide can be included in the pores of the porous silica. When the above-mentioned aqueous solution of titanium trichloride is used, titanium dioxide can be included in the pores of the porous silica. When a copper salt such as copper acetate or copper nitrate is used, copper oxide can be included in the pores of the porous silica. When an iron salt such as iron chloride or iron nitrate is used, iron oxide can be included in the pores of the porous silica. When a manganese salt such as manganese nitrate is used, manganese oxide can be included in the pores of the porous silica. When a salt such as titanyl sulfate is used, titanium oxide can be included in the pores of the porous silica.

As described above, according to the method for synthesizing fine particles of the present embodiment, it is possible to form porous silica-containing particles by simple processing. In particular, the macropores having orientation become the flow path of the aqueous solution of the metal compound, and the material such as a metal can be efficiently included in the mesopores or micropores of silica (SiO ₂ ) constituting the side walls of the macropores. .

(Example B)
A porous silica film was formed in the same manner as in Example 1. As described above, the porous silica in the form of a film is “porous silica having a hierarchical porous structure”, and is composed of macropores having orientation and silica (SiO ₂ ) constituting the side walls of the macropores. It has mesopores and micropores corresponding to internal micelles (templates) (see FIG. 2 and the like).

  Using porous silica having a hierarchical porous structure as a carrier, titanium dioxide particles are synthesized inside mesopores and micropores.

  Specifically, porous silica (film form) having a hierarchical porous structure was immersed in a 20 wt% titanium trichloride solution, and the solution was sufficiently impregnated.

  Next, porous silica (film-like) having a hierarchical porous structure was taken out, and the surface was washed with ethanol. By this washing, the titanium trichloride solution in the columnar macropores is removed. Thus, the titanium trichloride solution can be mainly present in the mesopores or micropores.

  Next, porous silica (film) having a hierarchical porous structure is dried under reduced pressure, and then calcined in air at 450 ° C. for about 3 hours to form fine titanium dioxide particles in mesopores and micropores. The encapsulated porous silica (film) was obtained.

  FIG. 30 is a transmission electron microscope image (TEM image) of the obtained titanium dioxide-containing porous silica. As shown in FIG. 30A, even after the titanium dioxide particles are included (supported) in the porous silica, columnar macropores can be confirmed. Then, it can be confirmed from FIG. 30B that titanium dioxide particles are included in the side walls (silica matrix) of the macropores. The average particle size of the included titanium dioxide particles is 1.9 nm. FIG. 31 shows the particle size and the number of titanium dioxide particles.

(Embodiment 6) ... Use as a catalyst carrier The porous silica containing a material such as a metal or a metal compound described in Embodiment 5 can be used as a catalyst. That is, porous silica having a hierarchical porous structure can function as a carrier for the catalyst. For example, a combustion catalyst can be obtained by including platinum. A photocatalyst can be obtained by including tungsten oxide or titanium dioxide.

  As described above, according to the porous silica of the fifth embodiment, the metal or metal compound is hardly contained in the columnar macropores, and the metal is only contained in the mesopores or micropores on the side walls of the macropores. And a metal compound, so that the diffusibility of the reactant is high and the accessibility to the supported catalyst is improved. In addition, particles of about 1 to 2 nm can be included in the side wall of the macropore. For example, when bulk porous silica is used as the carrier, the accessibility is poor and the catalyst efficiency is reduced. On the other hand, in the present embodiment, the columnar macropores serve as flow channels, and particles of about 1 to 2 nm can be included in the side walls, so that the catalyst efficiency can be improved.

  Further, in the present embodiment, a plurality of columnar macropores are arranged with good orientation and are considered to have a high light-gathering rate, and are suitable for use as a photocatalyst. That is, light can be efficiently collected and propagated to the supported catalyst by the plurality of columnar macropores, and the photocatalytic ability can be improved by the above-described substrate diffusivity and light-collecting effect.

  In particular, porous silica having a hierarchical porous structure resembles a diatom shell structure. Diatoms are known for their high photosynthetic ability. Specifically, diatoms are efficiently condensed and delivered to chloroplasts by a shell with a hierarchical porous structure composed of silica, which contributes to high photosynthetic ability. Is believed to be Therefore, it is considered that porous silica having a hierarchical porous structure can efficiently collect light by the hierarchical structure and propagate the light to the supported catalyst.

Example C Photocatalytic Decomposition Reaction Experiment of Isopropyl Alcohol FIG. 32 is a diagram showing a photocatalytic decomposition reaction experiment of isopropyl alcohol. First, porous silica (film-form, Sample) containing fine particles of titanium dioxide described in Example B was prepared.

  Next, as shown in FIG. 32, after placing porous silica (film-like) containing fine particles of titanium dioxide on the bottom surface of the glass container, dry air containing 500 ppm of isopropyl alcohol gas was allowed to flow for 60 minutes. Thereafter, the glass container was sealed.

A xenon lamp was irradiated from the upper surface of the glass container. The amount of generated CO ₂ for each irradiation time was quantified by gas chromatography (Agilent, Micro GC 3000).

As a comparative example, commercially available titanium dioxide particles, bulk mesoporous silica particles supporting titanium dioxide were prepared, and the same treatment and CO2 were performed in place of the porous silica (film form) containing fine particles of titanium dioxide. ₂ Quantification of generated amount was performed.

In the present embodiment, isopropyl alcohol is decomposed by a photocatalytic reaction using a xenon lamp as a light source, and CO ₂ is generated. FIG. 33 is a diagram showing the amount of carbon dioxide generated during the photocatalytic decomposition reaction of isopropyl alcohol. The circles indicate the use of bulk mesoporous silica particles carrying titanium dioxide, the diamonds indicate the use of commercially available titanium dioxide particles, and the squares indicate the porous silica (film-like) containing fine titanium dioxide particles. ) Is used. As shown in FIG. 33, when the porous silica (film-like) containing fine particles of titanium dioxide of this example was used, the case of the comparative example (when bulk mesoporous silica particles supporting titanium dioxide were used) was used. , And when using commercially available titanium dioxide particles), it was found that the photocatalytic resolution was significantly active.

(Example D) ... Adsorption filtration experiment of methylene blue aqueous solution FIG. 34 is a diagram showing a state of an adsorption filtration experiment of a methylene blue aqueous solution. First, the porous silica formed on only the surface of the glass filter described in Example A was prepared.

Next, as shown in FIG. 34, the porous silica formed only on the surface of the glass filter was placed in the center of the funnel with the filter, and a 7.2 μmol / dm ³ aqueous methylene blue solution was dropped from above the sample. The methylene blue concentration of the liquid that passed through the sample was measured from the ultraviolet-visible absorption spectrum, and the removal rate of methylene blue was calculated. The filtration rate was also measured at the same time.

  As a comparative example, a porous silica formed only on the surface of the glass filter was pulverized into powder, and then compression-molded to a thickness of 60 μm or 90 μm (see FIG. 35). These samples were also filtered in the same manner as in FIG. 34, and the removal rates and the filtration rates were measured. In each sample, the porosity of the porous silica formed only on the surface of the glass filter was 51%. In the sample of the comparative example, the porosity of the sample having a thickness of 60 μm was 54%, and the porosity of the sample having a thickness of 90 μm was 68%.

  FIG. 35 is a diagram illustrating measurement results (porosity, removal rate, and filtration rate) of the present example and a comparative example.

As shown in the figure, the 90 μm pellet (Sparse Pellet) has a high porosity of 68%, and thus has a high filtration rate of 8.2 dm ³ / min · cm, but tends to have a low removal rate of 88%. The 60 μm pellet (Dense Pellet) had a low porosity of 54% and a low filtration rate of 1.9 dm ³ / min · cm, but had a high removal rate of 99% and tended to be high. On the other hand, although the sample of this example has a low porosity of 51%, it has a filtration rate of 8.9 dm ³ / min · cm and a removal rate because of the flowability of the vertically oriented macrochannel. Showed a high value of 99%. As described above, it was found that the porous silica formed only on the surface of the glass filter of this example was useful as a filter material capable of high removal rate and rapid filtration.

(Embodiment 7) Control of macropore diameter In this embodiment, control of the pore diameter of columnar macropores in porous silica having a hierarchical porous structure will be described. The pore diameter of the columnar macropores in the porous silica having a hierarchical porous structure can be controlled by the amount of water contained in the precursor sol.

(Example E)
For example, in Example 1, the ratio of TEOS: water was set to 1: 4. In this case, the diameter of the upper portion of the columnar macropore was about 414 nm. On the other hand, when the amount of TEOS: water is 1:10 and 1:12 and porous silica having a hierarchical porous structure is formed in the same manner as in Example 1, the pore diameter at the top of the columnar macropores Was 650 nm and 950 nm, respectively (FIG. 36). FIG. 36 is an SEM image of each sample of this example.

  As described above, it has been found that the diameter of the columnar macropores can be controlled by controlling the amount of water in the precursor sol.

Such a phenomenon can be considered as follows. FIG. 37 is a schematic view showing a formation mechanism of a macropore. If the amount of water in the precursor sol is large, for example, generation than formation mechanism of macropores described with reference to FIG. 5 in the first embodiment (corresponding to FIG. _{37 (A)), SiO 2} (Gel) The amount of water (H ₂ O) and ethanol discharged by (solidification) increases. Specifically, as shown in FIG. 37B, it is considered that the amount of water discharged from the precursor sol in the portion serving as the side wall of the macropore increases, and the pore diameter of the macropore increases (D1a <D1b). ).

As described above, the invention made by the inventor has been specifically described based on the embodiments and examples. However, the present invention is not limited to the above-described embodiments and examples, and does not depart from the gist thereof. Various changes are possible.
[Appendix 1]
A method for producing porous silica by hydrolysis of an alkoxysilane,
(A) preparing a first liquid having a surfactant, an alkoxysilane, and water;
(B) contacting the first liquid with a glass filter filled with a first material between glass fibers;
(C) a step of immersing the glass filter in a basic liquid;
(D) heat-treating the gelled product obtained by gelling the first liquid;
Has,
The method for producing porous silica, wherein the first material filled between the glass fibers is removed in the step (d).
[Appendix 2]
The method for producing porous silica according to Supplementary Note 1, wherein
The porous silica obtained by the step (d) is
Having a first pore and a second pore,
The first pore is a macropore,
The second pores are mesopores or micropores having a smaller average pore diameter than the macropores,
A method for producing porous silica, wherein a gap between the glass fibers is larger than the macropore.
[Appendix 3]
A method for producing porous silica by hydrolysis of an alkoxysilane,
(A) preparing a porous silica having a first group of pores having orientation in a first direction and a second group of pores formed inside the side wall of the first pore;
(B) contacting the porous silica with a liquid containing a metal or a compound having the metal as an elemental composition to impregnate the second pore group of the porous silica with the liquid;
(C) removing the liquid in the first pore group of the porous silica by washing;
(D) a step of performing heat treatment after the step (c) to form fine particles containing the metal or the metal compound in the second pores of the porous silica. For producing porous silica.
[Appendix 4]
A first group of pores having an orientation in a first direction, and a second group of pores formed inside a side wall of the first pore;
The first pore is a macropore,
The second pores are mesopores or micropores having a smaller average pore diameter than the macropores,
Porous silica, wherein the second pores include fine particles containing a metal or a metal compound.
[Appendix 5]
A method for producing porous silica by hydrolysis of an alkoxysilane,
(A) preparing a first liquid having a surfactant, an alkoxysilane, and water;
(B) contacting the first liquid with a basic liquid to cause the first liquid to gel by a dehydration-condensation reaction of the first liquid;
After the step (b),
(C) a step of heat-treating the gelled product obtained by gelling the first liquid;
Has,
In the step (a), when the stoichiometric ratio between the alkoxysilane and the water is alkoxysilane: water = 1: n, n is 20 or less;
The porous silica obtained in the step (c) has a first group of pores having an orientation in a first direction and a second group of pores formed inside a side wall of the first hole. And
A method for producing porous silica, wherein the average pore diameter of the first pore group is adjusted according to the amount n of the water.

  The present invention relates to porous silica and a method for producing porous silica, and in particular, porous silica having a hierarchical porous structure, a functional material using porous silica having a hierarchical porous structure, and a porous material having a hierarchical porous structure. It is effective when applied to a method for producing porous silica.

A1 area A2 area D1 Diameter of first pore (diameter, minor diameter, average pore diameter, diameter of columnar cross section)
D2 Diameter of second pore (diameter, minor axis)
ED Dropper F1 First filter F2 Second filter FN Suction fan L1 Precursor solution (sol, sol-state liquid)
L2 Basic liquid LD Droplet MC Micellar N Nozzle P1 Columnar hole (first hole, macro hole)
P2 Second pore (mesopore or micropore)
PS Porous silica SG Spray gun (mist spray)
SUB board

Claims (14)

Having a first pore and a second pore,
The average pore diameter of the first pores is 100 nm or more and 2000 nm or less,
The porous silica, wherein the average pore diameter of the second pores is 0.5 nm or more and 3 nm or less. The porous silica according to claim 1,
Porous silica, wherein the first pores are macropores and the second pores are mesopores or micropores. The porous silica according to claim 1,
The porous silica is in the form of a film,
The first pores are a plurality of columns extending in the thickness direction of the membrane,
Porous silica, wherein the average pore diameter of the first pores is a columnar minor diameter. The porous silica according to claim 1,
The porous silica is granular,
The first pores are a plurality of pillars extending from the inside of the granule to the outside.
The plurality of columnar first pores are provided radially,
Porous silica, wherein the average pore diameter of the first pores is a columnar minor diameter.   A functional material comprising the porous silica according to claim 3. A method for producing porous silica by hydrolysis of an alkoxysilane,
(A) preparing a first liquid having a surfactant, an alkoxysilane, and water;
(B) a step of causing the first liquid to gel by a dehydration condensation reaction of the first liquid by contacting the first liquid with a basic liquid;
A method for producing porous silica, comprising: The method for producing porous silica according to claim 6,
After the step (b),
(C) a step of heat-treating the gelled product obtained by gelling the first liquid;
Has,
The porous silica obtained by the step (c) is
Having a first pore and a second pore,
The average pore diameter of the first pores is 100 nm or more and 2000 nm or less,
The method for producing porous silica, wherein the average pore diameter of the second pores is 0.5 nm or more and 3 nm or less. The method for producing porous silica according to claim 7,
The method for producing porous silica, wherein the first pores are macropores, and the second pores are mesopores or micropores. The method for producing porous silica according to claim 6,
In the step (a), when the stoichiometric ratio of the alkoxysilane and the water is alkoxysilane: water = 1: n, n is 20 or less. The method for producing porous silica according to claim 6,
The surfactant is a cationic surfactant represented by R ₁ R ₂ R ₃ R ₄ N ⁺ X ⁻ ,
A method for producing porous silica, wherein the R ₁ having a hydrophobic alkyl chain has 4 to 22 carbon atoms. The method for producing porous silica according to claim 6,
The surfactant is a cationic surfactant represented by R ₁ R ₂ R ₃ R ₄ N ⁺ X ⁻ ,
A method for producing porous silica, wherein the above-mentioned R ₁ which is a hydrophobic alkyl chain has 2 to 7 carbon atoms. The method for producing porous silica according to claim 6,
In the step (b),
(B1) a step of applying the first liquid on a substrate;
(B2) a step of immersing the substrate in a basic liquid;
A method for producing porous silica, comprising: The method for producing porous silica according to claim 12,
In the step (b1),
(B1) A method for producing porous silica, which comprises a step of dip coating, spray coating, or spin coating the first liquid on a substrate. The method for producing porous silica according to claim 6,
The method for producing porous silica, wherein the step (b) is a step of dropping a droplet of the first liquid into the basic liquid.