JP6881708B2 - Porous silica and its manufacturing method - Google Patents

Description

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

Porous silica has a large specific surface area and can control the size of pores, and is therefore expected to be used as an adsorbent, a catalyst carrier, and the like. Porous silica is usually produced using a mold. For example, Japanese Patent Application Laid-Open No. 2000-220036 (Patent Document 1), Japanese Patent Application Laid-Open No. 2010-070406 (Patent Document 2), Non-Patent Document 1 and the like disclose porous silica produced by using collagen fibers as a template. .. In Japanese Patent Application Laid-Open No. 2016-098119 (Patent Document 3), International Publication No. 2011/108649 (Patent Document 4), Non-Patent Document 2 and Non-Patent Document 3, etc., porous silica produced by using a surfactant as a template. Is disclosed.

Japanese Unexamined Patent Publication No. 2000-220036 JP-A-2010-070406 Japanese Unexamined Patent Publication No. 2016-098119 International Publication No. 2011/108649

Y. Ono et al., "Preparation of Novel Hollow Fiber Silica Using Collagen Fiber as a Template," Chemistry Letters of the Chemical Society of Japan., 475-476 (1999) T. Sawada et al., "Preparation of Mesoporous Silica with Well-Defined Hexagonal Array of Pores by Using Octyltrimethylammonium Chloride," Bulletin of the Chemical Society of Japan., 81 (3), 407-409 (2008) Y. Di et al., "Ultralow Temperature Synthesis of Ordered Hexagonal Smaller Supermicroporous Silica Using Semifluorinated Surfactants as Template," Langmuir, 22, 3068-3072 (2006)

The IUPAC (International Union of Pure and Applied Chemistry) defines pores having a pore diameter of less than 0.7 nm in a porous material such as porous silica as ultramicro pores. Further, pores having a pore diameter of 0.7 to 2 nm are defined as supermicro pores, pores having a pore diameter of 2 to 50 nm are defined as mesopores, and pores having a pore diameter exceeding 50 nm are defined as macropores. Porous silica has the potential to be applied to applications other than adsorbents and catalyst carriers by controlling the size and uniformity of pores. New applications include, for example, gas separation membrane materials, carriers accommodating quantum dots, and the like. In particular, porous silica having ultramicro pores having a pore diameter of less than 0.7 nm is expected to expand its applications. However, the porous silica disclosed in Patent Document 1 cannot form pores having a pore diameter of 2 nm or less because silica does not enter between the molecules of collagen as a template. Further, in Patent Document 2 and Non-Patent Document 1, porous silica having supermicropores is produced using expensive collagen fibers. In Patent Document 3, Patent Document 4, Non-Patent Document 2 and Non-Patent Document 3, a porous silica having supermicropores is produced by using an expensive surfactant. In these cases, it is difficult to put it into practical use because the production cost of the porous silica is high. That is, a technique for inexpensively obtaining porous silica having ultra-micro pores having a uniform pore diameter and having a wide range of uses has not yet been developed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a porous silica having ultramicro pores having a uniform pore diameter, which can be widely used and inexpensively obtained, and a method for producing the same.

The porous silica according to the present invention has ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm.

The porous silica has a plurality of the ultramicro pores and the plurality of macropores, and the total specific surface area of the ultramicro pores occupies 90% or more of the total specific surface area of the porous silica. Is preferable. The porous silica preferably has a particle size of 500 nm or more and 100 μm or less.

The porous silica preferably contains 0.3% by mass or less of carbon.
It is more preferable that the porous silica emits white light when irradiated with ultraviolet rays.

In the toluene adsorption test by the sampling bag method, the porous silica has a toluene concentration of C _{0 in the sampling bag before the test and a toluene concentration of C 30} in the sampling bag 30 minutes after the start of the test. , C ₃₀ / C ₀ is preferably 0.7 or less.

In the method for producing porous silica according to the present invention, insoluble modified collagen and alkoxysilane are mixed in a first acidic solution having a pH of 0.1 to 5 to obtain a complex containing the modified collagen and silica. A method for producing porous silica, which comprises one step, a second step of washing and drying the complex, and a third step of removing the denatured collagen from the complex after the second step. The third step is a step of removing the denatured collagen from the complex by firing the complex at 500 ° C. or higher, and the complex is prepared in a second acidic solution having a temperature of 100 to 150 ° C. and a pH of 0.1 to 5. To remove the denatured collagen from the complex by acid-hydrolyzing the denatured collagen, and at 20-50 ° C. using 0.1 to 10% by mass of enzyme with respect to the denatured collagen. It is at least one selected from the group consisting of steps of removing the denatured collagen from the complex by enzymatically treating the denatured collagen.

In the method for producing porous silica, it is preferable not to perform the second step.
The first step includes a step of dispersing the denatured collagen in the first acidic solution by stirring and / or ultrasonic irradiation, and then adding the alkoxysilane to the first acidic solution. Is more preferable.

According to the present invention, it is possible to provide porous silica having ultramicro pores having a uniform pore diameter, which can be widely used and inexpensively obtained, and a method for producing the same.

It is a drawing substitute photograph which shows the electron microscope image of the porous silica which concerns on Example 1. FIG. (A) is a graph showing the measurement result of the nitrogen adsorption / desorption isotherm of the porous silica according to Example 1, and (b) is the measurement result of the nitrogen adsorption / desorption isotherm of the porous silica according to Comparative Example 2. It is a graph which shows. (A) is a graph showing the measurement result of the t-prot curve of the porous silica according to Example 1, and (b) shows the measurement result of the t-prot curve of the porous silica according to Comparative Example 2. It is a graph. It is a graph showing the dynamic adsorption property of toluene of the porous silica of Example 1 and the porous silica of Comparative Example 2 in comparison. It is a graph showing the static adsorption property of toluene of the porous silica of Example 1 and the porous silica of Comparative Example 2 in comparison. (A) is a drawing-substituting photograph showing a complex obtained by dispersing denatured collagen in a first acidic solution for 30 minutes by stirring and then adding alkoxysilane, and (b) is a drawing-substituting photograph showing the first acidic solution. 6 is a drawing-substituting photograph showing a complex obtained by dispersing denatured collagen in a solution by ultrasonic irradiation for 30 minutes and then adding alkoxysilane. It is a drawing substitute photograph showing the state of light emission of porous silica under ultraviolet (black light) irradiation, and (a) shows the state of light emission of porous silica when irradiated with ultraviolet rays having a wavelength of 254 nm, (b). Shows the state of light emission of the porous silica when irradiated with ultraviolet rays having a wavelength of 365 nm.

Hereinafter, embodiments according to the present invention will be described in detail.
In the present specification, the notation in the form of "A to B" means the upper and lower limits of the range (that is, A or more and B or less), and when the unit is not described in A and the unit is described only in B, A The unit of and the unit of B are the same.

The present inventors have investigated a method for producing porous silica which has ultramicro pores having a uniform pore diameter and can be obtained widely and inexpensively. As a result, it was found that porous silica having different pore sizes was produced depending on the type of collagen used as a template. In particular, it has been found that when insoluble modified collagen is used, porous silica having ultramicro pores having a uniform pore diameter and a large surface area can be produced. The mechanism is unknown in detail, but when insoluble denatured collagen is used as a template, alkoxysilane easily penetrates into the template of denatured collagen with a broken higher-order structure, and is partially impaired in the denatured collagen. It is considered that this is a result of the fact that the stable part does not serve as a template and only the part having a stable collagen structure serves as a template. This makes it possible to produce porous silica having ultra-micro pores having a series of particle shapes and a very small pore diameter.

Furthermore, it was found that the porous silica having the ultramicro pores functions as macropores in the gaps between the aggregated silicas. That is, the porous silica according to the present invention has ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm, and exhibits good dynamic adsorption characteristics and static adsorption characteristics. , Can exhibit excellent properties as a catalyst carrier. Furthermore, there is a possibility that new uses will be added as a gas separation membrane material and a carrier for accommodating quantum dots. Utilizing the characteristics of white light emission due to ultraviolet excitation, it can be expected to be used as a cosmetic raw material and a light emitting material described later. The porous silica according to the present invention does not require a special device and uses inexpensive insoluble modified collagen, and is therefore suitable for mass synthesis. Hereinafter, the specific configuration of the porous silica will be described in detail.

≪Porous silica≫
The porous silica according to the present invention has ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm. Further, the porous silica has a plurality of ultramicro pores and a plurality of macropores, and the total specific surface area of the ultramicro pores preferably occupies 90% or more of the total specific surface area of the porous silica. As a result, the porous silica is excellent in dynamic adsorption characteristics due to the presence of ultramicro pores, and is also excellent in static adsorption characteristics due to the presence of macropores, so that the application can be expanded.

Here, the "pore diameter" in the present specification refers to the width (pore diameter) of the pores appearing on the surface of the porous silica. The pore diameter is represented by the diameter of a circle (circle equivalent diameter) having the same area as the projected area obtained when the pores appearing on the surface of the porous silica are projected. However, the pore diameter of the ultramicro pores is not limited to this. Specifically, the pore diameters of the pores (ultramicro pores and macropores) of the porous silica can be determined by the measurement method described later. As used herein, the term "dynamic adsorption property" refers to the ability of porous silica to adsorb this gas when in contact with a flowing gas. The static adsorption property refers to the ability of porous silica to adsorb this gas when it comes into contact with a retained gas.

As shown in FIG. 1, the porous silica is granular silica having a particle size of 500 nm to 100 μm. This granular silica is formed by aggregating silica particles having a particle size of 500 nm to 5 μm as described later. In porous silica, ultramicro pores having a pore diameter of less than 0.7 nm are formed on the surface of the silica particles having a particle size of 500 nm to 5 μm described above. The gap between the particles when these silicas are aggregated becomes macropores having a pore diameter of more than 50 nm. When the particle size of the porous silica is less than 500 nm and when it exceeds 100 μm, it tends to be difficult to have ultramicro pores having a uniform pore diameter.

In addition to the ultramicro pores and the macropores, the porous silica preferably has supermicro pores having a pore diameter of 0.7 to 2 nm and mesopores having a pore diameter of 2 to 50 nm. This is because porous silica, which has a wide range of uses, can be obtained at low cost. However, when it has supermicro pores and mesopores, the dynamic adsorption property of toluene, which will be described later, tends to decrease. Therefore, it is preferable that the porous silica has only ultramicro pores and macropores.

The particle size of the porous silica is determined by using a field emission scanning electron microscope (FE-SEM, trade name: "S-4800", manufactured by Hitachi High Technology Co., Ltd.) and the measurement function attached to the microscope. , It can be measured by the following measurement method.

First, porous silica is obtained by the production method described later, and the porous silica is washed and dried to obtain a dried product. One microscopic image is obtained by photographing an arbitrary one field of view with respect to this dried body at a magnification of 400 times using the above-mentioned FE-SEM. Subsequently, this one microscope image is analyzed by the measurement function attached to the microscope, and the same as the projected area obtained when the shape is projected on all the porous silicas appearing in these microscope images. Find the diameter of the circle that will be the area (diameter equivalent to the circle). Finally, the particle size of the porous silica can be specified by calculating the average value of these equivalent circle diameters.

<Ultra micro hole>
The porous silica according to the present invention has ultramicro pores having a pore diameter of less than 0.7 nm. This pore diameter means the average pore diameter. The pore size of the ultramicro pores of the porous silica is preferably 0.3 nm or more and less than 0.7 nm, and more preferably 0.4 nm or more and 0.6 nm or less. It is difficult to produce ultramicro pores having a pore diameter of less than 0.3 nm. When the pore diameter is 0.7 nm or more, it can no longer be called an ultramicro pore in the classification of IUPAC, and the dynamic adsorption characteristics tend to deteriorate. Since the pore diameter of the ultramicro pores is 0.3 nm or more and less than 0.7 nm, the porous silica may be used as a carrier for quantum dots on the order of sub-nanometers.

When confirming the existence of ultramicro pores in the pores of the porous silica, a gas adsorption method is used. In this embodiment, as shown in FIG. 2A, a graph of nitrogen adsorption / desorption isotherms of porous silica is obtained based on a gas adsorption method using nitrogen. Specifically, by graphing the horizontal axis as the relative pressure (P / P ₀ ) and the vertical axis as the gas adsorption amount (ml / g), the nitrogen adsorption / desorption isotherm of the porous silica can be obtained. .. Next, this nitrogen adsorption / desorption isotherm is compared with the six types of IUPAC isotherms (I-VI types), and the nitrogen adsorption / desorption isotherms correspond to the IUPAC isotherm classification I (IUPAC I type). Make sure that. From this, it can be seen that the porous silica has micropores having a pore diameter of 2 nm or less. “P” in the relative pressure (P / P ₀ ) represents the pressure of the adsorbent (nitrogen) in the adsorption equilibrium, and “P ₀ ” represents the saturated vapor pressure of the adsorbate (nitrogen) in the adsorption temperature.

Further, whether or not the porous silica has ultramicro pores having a pore diameter of less than 0.7 nm can be confirmed by obtaining a t-prot curve based on the above-mentioned gas adsorption method. The t-prot curve can be obtained by graphing the horizontal axis as the thickness of the adsorbed gas (t, the unit is nm) and the vertical axis as the amount of gas adsorbed (ml / g). As shown in FIG. 3A, by confirming that there is no bending in this t-plot curve, it can be seen that ultramicro pores having a pore diameter of less than 0.7 nm are present in the porous silica.

The reason for using the gas adsorption method when confirming the presence of ultramicro pores in porous silica is as follows. That is, ultramicro pores having a pore diameter of less than 0.7 nm cannot be clearly observed in shape or contour because the pores are too small even when using an electron microscope such as SEM or TEM. Therefore, it is difficult to clearly specify the pore diameter. Therefore, the existence of ultra-micro pores is substantially confirmed by using the gas adsorption method, and the pore diameter is also specified by using the t-plot method (obtaining a t-plot curve).

<Macro hole>
The porous silica according to the present invention has macropores having a pore size of more than 50 nm. This pore diameter also means the average pore diameter in the same manner as the ultramicro pores. The pore size of the macropores of the porous silica is preferably more than 50 nm and 500 nm or less, and more preferably 50 nm or more and 100 nm or less. When the pore diameter of the macropore is 50 nm or less, it can no longer be called a macropore in the classification of IUPAC.

The presence of macropores in the porous silica can be confirmed by observing the porous silica using the above FE-SEM. In the present embodiment, it is possible to confirm the existence of macropores by observing the porous silica at a magnification of 10000 times, and it is possible to measure the pore diameter of the macropores. The pore diameter of the macropores is determined from all the macropores present in 50 to 100 porous silicas in the observation field. Specifically, by using the measurement function attached to the FE-SEM, the equivalent circle diameter, which is the same area as the projected area obtained when the shape is projected onto the macro hole, is obtained and obtained. It can be specified by the average value of these circle-equivalent diameters.

<Surface area / specific surface area>
The porous silica preferably has a specific surface area of 500 to 1000 m ² / g. As a result, excellent properties can be exhibited as an adsorbent and a catalyst carrier. Further, in the porous silica, the total specific surface area of the ultramicropores preferably occupies 90% or more of the total specific surface area of the porous silica. More preferably, the total specific surface area of the ultramicropores occupies 90% or more and 95% or less of the total specific surface area of the porous silica.

If the occupancy of the total specific surface area of the ultramicro pores is less than 90% of the total specific surface area of the porous silica, the adsorption characteristics and the characteristics as a catalyst carrier may be affected. Even if the total specific surface area of the ultramicro pores exceeds 95% of the total specific surface area of the porous silica, the adsorption characteristics and the characteristics as a catalyst carrier may be affected.

The total specific surface area of the porous silica can be measured by using the BET method. Specifically, a commercially available specific surface area / pore distribution measuring device (for example, trade name: "BELSORP-mini", manufactured by Microtrac Bell Co., Ltd.) is used, and the relative pressure (P / P ₀ ) is 0.01 to. By measuring the adsorption amount (ml / g) of the test gas (for example, nitrogen) with respect to the porous silica in the range of 0.05, the specific surface area of the entire porous silica can be calculated. The occupied area of the ultramicro pores with respect to the total surface area of the porous silica can be calculated from the t-prot method based on the specific surface area of the entire porous silica described above. What the "P" and "P ₀ " of the relative pressure (P / P ₀ ) represent is as described above.

The nitrogen adsorption / desorption isotherm, t-prot curve, specific surface area of porous silica, etc. for measuring the average pore size of the above-mentioned ultramicro pores are, for example, a specific surface area / pore distribution measuring device (trade name: "BELSORP-mini"). , Manufactured by Microtrack Bell Co., Ltd.).

<Containing carbon>
The porous silica preferably contains 0.3% by mass or less of carbon. In particular, porous silica is excited by ultraviolet rays having a wavelength of 240 to 370 nm by containing 0.05 to 0.3% by mass of carbon, and emits light of various wavelengths as fluorescence to emit white light. Is preferable. In this case, carbon will be present inside the ultramicropores of the porous silica. As a result, the porous silica can be widely used, for example, as a raw material for cosmetics and luminescent materials. As will be described later, the carbon present inside the ultramicropores of the porous silica is derived from the insoluble modified collagen.

The porous silica more preferably contains 0.08 to 0.24% by mass of carbon. When the carbon content of the porous silica is less than 0.05% by mass and more than 0.3% by mass, white light emission tends not to be sufficiently observed. If the carbon content of the porous silica exceeds 0.3% by mass, the adsorption characteristics and the characteristics as a catalyst carrier may be affected.

The mechanism by which porous silica containing 0.05 to 0.3% by mass of carbon emits white light when irradiated with ultraviolet rays is unknown in detail, but the following mechanism can be considered. That is, when the porous silica is irradiated with ultraviolet rays, the carbon present inside the ultramicro pores absorbs the ultraviolet rays, so that the energy state of the carbon is excited from the ground state to the excited state. When the excited carbon returns to the ground state, it emits (emits) energy as silica light or phosphorescence, but the light emission appears as light of various colors because the amount of energy is not constant. As a result, when the porous silica containing 0.05 to 0.3% by mass of carbon is irradiated with ultraviolet rays, it is considered that the porous silica emits white light.

The carbon content in the porous silica is determined using a fully automatic elemental analyzer (organic trace element analysis: CHN analysis) (trade name "vario MACRO cube", manufactured by Elementer Japan Co., Ltd.) under the following conditions. It can be obtained by measuring.
Combustion temperature: 1150 ° C
Reduction temperature: 850 ° C
Standard substance: Sulfanilamide standard product (manufactured by Elementer Japan Co., Ltd.).

<Action>
(Dynamic adsorption characteristics)
The porous silica according to the present invention can have excellent dynamic adsorption characteristics. The dynamic adsorption property refers to the ability of porous silica to adsorb this gas when it is brought into contact with a flowing gas as described above. The dynamic adsorption characteristic is the time during which the porous silica is brought into contact with a predetermined amount of flowing gas (the gas to be adsorbed) and the porous silica can continue to completely adsorb the gas (adsorption failure). It can be obtained by measuring the time to reach). Therefore, it can be said that the longer the time during which the porous silica can continue to completely adsorb the gas, the better the dynamic adsorption characteristics.

In the present embodiment, the dynamic adsorption property of the porous silica can be specifically evaluated by the following method. First, 100 mg of a porous silica sample dried overnight in the air at 105 ° C. is placed in a glass tube, and a pretreatment is performed in which the sample is heated at 150 ° C. for 2 hours while flowing dry air through the glass tube. Then, the sample is cooled to 30 ° C. to prepare a sample for adsorption test. Furthermore, a treatment tank called a saturator containing toluene is placed in an ice bag maintained at 0 ° C., and dry air, which is a carrier gas, is flowed through the treatment tank to perform a dynamic adsorption characteristic test containing about 450 ppm of toluene. Prepare gas for use. In the dynamic adsorption characteristic test, the time required for the sample to break through adsorption is measured by flowing the test gas through the glass tube at a flow rate of 50 ml / min with respect to 100 mg of the sample placed in the glass tube. To do.

As shown in FIG. 4, the porous silica according to the present invention, for example, in Example 1 described later, took about 120 minutes to reach adsorption rupture. As described above, since the porous silica has a property of completely adsorbing the test gas continuously for a long period of time, it can be suitably used as an adsorbent, a catalyst carrier, a gas separation membrane material, and the like.

(Static adsorption characteristics)
The porous silica according to the present invention can exhibit excellent static adsorption characteristics. The static adsorption property refers to the ability of porous silica to adsorb this gas when it comes into contact with a gas that has stagnated as described above. The static adsorption characteristics can be specifically evaluated by the sampling bag method described later. According to this method, the amount of toluene adsorbed on porous silica can be measured by comparing the toluene concentration in the sampling bag (Tedlar® bag) before and after the test, and the larger the amount of adsorption, the more static. It can be said that it has excellent adsorption characteristics.

The method for evaluating the static adsorption characteristics using the sampling bag method is as follows. First, a commercially available Tedlar (registered trademark) bag having a volume of 3 L or more is prepared, and 100 mg of a porous silica sample pretreated by the same method as when evaluating the dynamic adsorption characteristics is applied to the Tedlar (registered trademark) bag. Contain. Subsequently, 3 L of a static adsorption characteristic test gas containing about 80 ppm of toluene is introduced into this Tedlar (registered trademark) bag using air in a standard state (20 ° C., 65% RH) as a carrier gas. Further, after leaving it in that state for a predetermined time, the gas for static adsorption characteristic test is taken out, and the toluene concentration in this gas is measured by a gas detector tube (trade name "toluene gas detector tube 122L", manufactured by Gastec Co., Ltd.). To do. Thereby, the static adsorption characteristic of the porous silica can be evaluated by calculating how much the toluene concentration of the toluene gas for the static adsorption characteristic test is reduced from 80 ppm before the test.

In the toluene adsorption test by the sampling bag method described above, the porous silica according to the present invention has a toluene concentration of C ₀ in the sampling bag before the test and a toluene concentration in the sampling bag 30 minutes after the start of the test. _When it is set to 30, it is preferable to have an adsorption characteristic in which _{C 30} / C _{0 is 0.7 or less.} At this time, it can be evaluated that the porous silica is excellent in static adsorption characteristics. In particular, it is more preferable to have an adsorption characteristic in which _{C 30} / C _{0 is 0.6 or less.} The ideal value (lower limit value) of C ₃₀ / C _{0 is 0.}

As shown in FIG. 5, for example, in Example 1 described later, a tedler bag introduced with 3 L of a static adsorption characteristic test gas containing 100 mg of porous silica and about 80 ppm of toluene has a toluene concentration in a sampling bag before the test. When C ₀ and the toluene concentration in the sampling bag 30 minutes after the start of the test were C ₃₀ , C ₃₀ / C ₀ was 0.7 or less. As described above, the porous silica has excellent static adsorption characteristics and can be suitably used as an adsorbent, a catalyst carrier, a gas separation membrane material and the like. In FIG. 5, the toluene concentration in the sampling bag when X minutes have passed since the start of the test is represented as _{C x.}

Based on the above, the porous silica according to the present invention exhibits good dynamic adsorption characteristics and static adsorption characteristics by having ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm. It can exhibit excellent properties as an adsorbent and a catalyst carrier. Further, there is a possibility that new applications will be expanded as the above-mentioned cosmetic raw materials, light emitting materials, gas separation membrane materials, carriers for accommodating quantum dots, and the like.

≪Manufacturing method of porous silica≫
The first method for producing porous silica according to the present invention is to obtain a complex containing modified collagen and silica by mixing insoluble modified collagen and alkoxysilane in a first acidic solution having a pH of 0.1 to 5. It comprises a step, a second step of washing and drying the complex, and a third step of removing denatured collagen from the complex after the second step. As a result, porous silica having ultra-micro pores having a uniform pore diameter can be obtained at low cost. In the complex obtained in the first step, silica derived from alkoxysilane is aggregated using the modified collagen as a template, and the hydroxyl group, carboxyl group and amino group in the modified collagen and the silanol group of the silica are bonded by hydrogen bond or ionic bond. Has a structure.

<First step>
In the first step, insoluble modified collagen and alkoxysilane are mixed in a first acidic solution having a pH of 0.1 to 5 to obtain a complex containing modified collagen and silica.

The insoluble modified collagen serves as a template for producing porous silica. As the insoluble denatured collagen, any insoluble and denatured collagen may be used. For example, by heat-treating and heat-denaturing leather powder derived from the skin of animals such as cows, pigs, chickens, ostriches, and fish, fibers are aggregated and denatured collagen having a broken fiber structure can be obtained. This denatured collagen, unlike gelatin, is insoluble. Gelatin is generally considered to be a heat-denatured product of collagen, but since it is heat-extracted with an aqueous solvent during the production process, it is completely dissolved by heating in an aqueous solvent at 50 ° C. for 1 hour, for example. At this time, the transmittance of gelatin at a concentration of 10% by mass (PAGI method, wavelength 570 nm) is 80% or more in almost all cases, and usually 90% or more. On the other hand, denatured collagen does not dissolve in an aqueous solvent by heating at 50 ° C. for 1 hour. The transmittance of this denatured collagen at a concentration of 10% by mass (PAGI method, wavelength 570 nm) is 0%.

As used herein, the term "insoluble" means that the solubility in water is 1% or less in the method for dissolving gelatin. That is, "insoluble" means that the solubility in water is 1% or less when the mixture is kept at room temperature for 30 minutes and then heated at 50 ° C. for 1 hour. Purified water, ion-exchanged water, distilled water, or the like is used as this water. Furthermore, the above-mentioned "denatured collagen" means that a part of the fibrous structure such as collagen-like sequence or triple helix structure that characterizes collagen is broken and denatured, but it is completely denatured to a single-stranded polypeptide such as gelatin. It means the state that is not done. Insolubilized gelatin obtained by introducing various cross-linking treatments such as thermal dehydration cross-linking and chemical cross-linking using glutaraldehyde into gelatin can also be used as an insoluble material.

Alkoxysilane is a silica source for producing porous silica. Conventionally, the alkoxysilane has an organic functional group (alkyl group, vinyl group, epoxy group, styryl group, methacrylic group, acrylic group, amino group, isocinanurate group, ureido group, mercapto group, isocyanate group, etc.) and an alkoxy group. Any known one can be used. Among these, it is preferable to use tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane and the like. Since it takes time to form a complex when the substituent becomes large, it is more preferable to use tetramethoxysilane or tetraethoxysilane as the alkoxysilane.

The mass of alkoxysilane is preferably 3 to 15 times the mass of insoluble modified collagen. Alkoxysilane is more preferably 5 to 10 times the mass of insoluble modified collagen.

The solvent used for the first acidic solution having a pH of 0.1 to 5 should not be limited as long as it is a solution having a pH of 0.1 to 5, but an aqueous solution having a pH of 0.1 to 5 is preferable. When the first acidic solution is an aqueous solution, the water as the solvent is not particularly limited, but purified water, ion-exchanged water, distilled water and the like can be preferably used. At least one of an inorganic acid and an organic acid can be used as the acid of the first acidic solution. Examples of the inorganic acid include hydrochloric acid and sulfuric acid, and examples of the organic acid include formic acid and acetic acid. These acids may be used alone or in admixture of two or more.

The mass of the first acidic solution is preferably 80 to 150 times the mass of the insoluble denatured collagen. The mass of the first acidic solution is more preferably 100 to 120 times the mass of the insoluble denatured collagen. The pH can be adjusted by adding an appropriate amount of the above-mentioned inorganic and organic acids, preferably acids such as hydrochloric acid, sulfuric acid and acetic acid. When the first acidic solution has a pH of 0.1 to 5, granular silica particles having a smaller particle size tend to aggregate around the template (insoluble denatured collagen). The pH of the preferred first acidic solution is 0.1 to 1. When the pH of the first acidic solution exceeds 5, the efficiency of forming a complex tends to decrease. Even when the pH is less than 0.1, the efficiency of forming the complex tends to decrease.

As a method of mixing alkoxysilane and insoluble modified collagen in the first acidic solution, alkoxysilane may be added to the first acidic solution, and then insoluble modified collagen may be added, but the first acidic solution It is preferable to add insoluble modified collagen therein, followed by alkoxysilane. In particular, in the present invention, the first step includes a step of dispersing the denatured collagen in the first acidic solution by stirring and / or ultrasonic irradiation, and then adding alkoxysilane to the first acidic solution. Is preferable.

For example, FIG. 6A shows a complex obtained by dispersing denatured collagen in a first acidic solution by stirring and then adding alkoxysilane to the first acidic solution. FIG. 6B shows a complex obtained by dispersing denatured collagen in a first acidic solution by ultrasonic irradiation and then adding alkoxysilane to the first acidic solution. The complex shown in FIG. 6B has better dispersibility than the complex shown in FIG. 6A, and a complex having a smaller diameter and a larger surface area can be obtained. From this, it is more preferable that the first step includes a step of dispersing the denatured collagen in the first acidic solution by ultrasonic irradiation and then adding alkoxysilane to the first acidic solution.

<Second step>
In the second step, the complex is washed and dried. As a method for washing and drying the complex, conventionally known methods can be used. Further, in the method for producing porous silica according to the present invention, it is preferable not to carry out the second step when maintaining the acidic atmosphere of the first step in the third step described later.

<Third step>
In the third step, the denatured collagen is removed from the complex after the second step. The third step is a step of removing denatured collagen from the complex by firing the complex at 500 ° C. or higher (step A), and contacting the complex with a second acidic solution at 100 to 150 ° C. and pH 0.1 to 5 The step of removing the denatured collagen from the complex by acid-hydrolyzing the denatured collagen (step B), and the denatured collagen at 20 to 50 ° C. using 0.1 to 10% by mass of an enzyme with respect to the denatured collagen. Is at least one selected from the group consisting of a step (step C) of removing denatured collagen from the complex by enzymatically treating.

(Step A)
In step A, the denatured collagen is completely thermally decomposed by calcining the complex at 500 ° C. or higher. In this step, it is preferable to bake the complex at 600 ° C. or higher. The time for firing may be such that the complex is heated in the air for about 1 to 5 hours. The upper limit of the firing temperature in this step is 700 ° C. Even if the temperature exceeds 700 ° C., it becomes difficult to obtain effects such as shortening the time for complete thermal decomposition of denatured collagen.

(Step B)
The step B may be any step of acid hydrolysis as long as the denatured collagen can be removed from the complex. For example, a second acidic solution having a pH of 0.1 to 5 can be applied to the complex. The complex may be sprayed with a second acidic solution having a pH of 0.1 to 5. Further, the complex may be immersed in a second acidic solution having a pH of 0.1 to 5. From the viewpoint of efficiently removing denatured collagen from the complex, it is preferable to immerse the complex in a second acidic solution having a pH of 0.1 to 5 in this step. Further, from the viewpoint of completely acid-hydrolyzing the denatured collagen, it is more preferable to stir the second acidic solution in a state where the complex is immersed in the second acidic solution having a pH of 0.1 to 5.

The second acidic solution is preferably an aqueous solution having a pH of 0.1 to 5, and can be prepared by the same method as the first acidic solution described above. The pH of the preferred second acidic solution is 0.1 to 1. Furthermore, at least one of an inorganic acid and an organic acid can be used as the acid. Examples of the inorganic acid include hydrochloric acid, sulfuric acid and nitric acid, and examples of the organic acid include formic acid and acetic acid. These acids may be used alone or in admixture of two or more. Hydrochloric acid is preferably used as the acid in the second acidic solution.

When the pH of the second acidic solution exceeds 5, the efficiency of acid hydrolysis of denatured collagen tends to decrease. Further, the temperature at which the complex is brought into contact with the second acidic solution having a pH of 0.1 to 5 is preferably 100 to 150 ° C. If the temperature at which the complex is brought into contact with the second acidic solution is less than 100 ° C., the efficiency of acid hydrolysis tends to decrease. The stirring of the second acidic solution may be carried out until the denatured collagen is removed from the complex, for example, 10 to 48 hours, preferably 20 to 30 hours.

(C step)
In step C, denatured collagen is removed from the complex by using various proteases such as pepsin and a predetermined enzyme such as collagenase, which is a collagen-degrading enzyme, and subjecting the enzyme to an enzymatic reaction at an active temperature. The pH of the solution in which the enzyme is dissolved may be any pH at which the enzyme is not inactivated, and in the case of pepsin, for example, the pH is preferably 0.1 to 5.

If the amount of the enzyme is less than 0.1% by mass with respect to the denatured collagen, it takes a long time to remove the denatured collagen, resulting in poor efficiency. When the amount of the enzyme exceeds 10% by mass with respect to the denatured collagen, the effect of removing the denatured collagen by the enzyme treatment tends to be saturated. Further, when the temperature of the enzyme treatment is lower than 20 ° C. and higher than 50 ° C., the enzyme tends to be inactivated, so that the efficiency of removing denatured collagen decreases. The preferred amount of enzyme is 1-5% by weight with respect to denatured collagen, and the preferred enzyme treatment temperature is 30-40 ° C.

The removal of the denatured collagen from the complex is a removal step by calcination (that is, step A) from the viewpoint of obtaining a porous silica having a larger specific surface area among the above-mentioned steps of calcination, acid hydrolysis treatment and enzyme treatment. Is the most preferable. On the other hand, when at least one of the steps of acid hydrolysis treatment and enzyme treatment (that is, step B or step C) is performed, there is an advantage that the pores of the porous silica are less likely to collapse and shrink. From the viewpoint of efficiently obtaining porous silica, it is preferable to carry out both the acid hydrolysis treatment and the enzyme treatment (that is, the B step and the C step) in the third step. Either of them may be performed first.

Here, in the method for producing porous silica according to the present invention, in the third step, the complex is brought into contact with a second acidic solution having a temperature of 100 to 150 ° C. and a pH of 0.1 to 5 for a time of firing the complex at 500 ° C. or higher. By adjusting the time for acid hydrolysis of the denatured collagen and the time for enzymatically treating the denatured collagen at 20 to 50 ° C. with 0.1 to 10% by mass of the enzyme, the ultramicropores are formed. Porous silica can be produced by leaving a part of carbon derived from denatured collagen inside. In particular, when the residual carbon is contained in the porous silica in an amount of 0.05 to 3% by mass, the porous silica emits white light when irradiated with ultraviolet rays as described above, and is therefore used as a raw material for cosmetics and luminescent materials. It can be used for a wide range of purposes.

<Use>
The porous silica obtained by the production method of the present invention has ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm. Further, silica particles having a particle size of 500 nm to 5 μm are aggregated to form granular silica having a particle size of 500 nm to 100 μm. Further, since the specific surface area of the porous silica is 500 to 1000 m ² / g, it can exhibit excellent properties as an adsorbent and a catalyst carrier. Since the production method of the present invention does not require a special device and uses inexpensive insoluble modified collagen, it is suitable for mass synthesis of porous silica. Since the porous silica obtained by the production method of the present invention exhibits good dynamic adsorption characteristics and static adsorption characteristics, it can exhibit excellent characteristics as an adsorbent and a catalyst carrier. Furthermore, new uses may be added as the above-mentioned cosmetic raw materials, light emitting materials, gas separation membrane materials, carriers for accommodating quantum dots, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

≪Test 1≫
<Manufacturing of porous silica>
(Example 1)
First, collagen T-1034 (manufactured by Nitta Gelatin Co., Ltd.) was prepared as an insoluble denatured collagen as a template. Further, tetraethoxysilane (TEOS) was prepared as a silica source. Next, hydrochloric acid is added to ion-exchanged water to prepare a 4.2% by volume hydrochloric acid aqueous solution (pH 0.63), 1 g of the above-mentioned collagen is added to the aqueous hydrochloric acid solution, and the mixture is stirred for 30 minutes to disperse the above-mentioned collagen. Got 9 ml of TEOS was added to this dispersion solution, and the mixture was stirred at room temperature (25 ° C.) for 24 hours to obtain a complex containing denatured collagen and silica (first step). This complex has a structure in which silica particles derived from tetraethoxysilane are aggregated using insoluble modified collagen as a template. Then, the solution containing the complex was filtered, washed with ion-exchanged water, and left at room temperature overnight to obtain a dried complex (second step).

Next, the obtained complex was calcined at 600 ° C. for 5 hours to obtain the porous silica of Example 1 (third step).

(Comparative Example 1)
An attempt was made to produce the porous gelatin of Comparative Example 1 by replacing the template in Example 1 with commercially available gelatin (trade name: "alkali-treated gelatin", manufactured by Kishida Chemical Co., Ltd.) and assuming that the others were the same as in Example 1. However, since gelatin did not function as a template, porous silica could not be obtained. From this, it can be seen that gelatin does not function as a template. Further, since the collagen T-1034 used in Example 1 is heat-denatured, it may contain a hot water-soluble fraction (gelatin), but this warm water-soluble fraction is porous. It was also found that it did not inhibit the synthesis of silica.

(Comparative Example 2)
The template in Example 1 was replaced with a commercially available collagen fiber (trade name: "Hide Powder", manufactured by Sigma-Aldrich), and the same as in Example 1 was used to produce the porous silica of Comparative Example 2.

<Specification of pore structure of porous silica>
(Hole diameter distribution)
First, the porous silica of Example 1 and the porous silica of Comparative Example 2 were evacuated at 300 ° C. for 3 hours in a closed container as pretreatment, respectively. Then, using a specific surface area / pore distribution measuring device (trade name: "BELSORP-mini", manufactured by Microtrac Bell Co., Ltd.), a nitrogen adsorption isotherm and a t-prot curve were obtained under the following measurement conditions, and Examples were obtained. The pore structures of the porous silica of No. 1 and the porous silica of Comparative Example 2 were identified. The results are shown in FIGS. 2 and 3.
Measurement temperature: Liquid nitrogen temperature (77K)
Sample (porous silica) amount: 30 mg
Adsorbed gas: Nitrogen.

As shown in FIGS. 2 (a) and 2 (b), the nitrogen adsorption / desorption isotherms of the porous silicas of Example 1 and Comparative Example 2 all showed IUPAC type I, and thus Examples 1 and 2. It was found that all of the porous silicas of Comparative Example 2 had micropores having a pore diameter of less than 2 nm. Further, as shown in FIG. 3A, since the t-plot curve of the porous silica of Example 1 is not bent, the porous silica of Example 1 has an ultra having an average pore diameter of less than 0.7 nm. It was found to have micropores. On the other hand, as shown in FIG. 3B, the t-plot curve of the porous silica according to Comparative Example 2 was found to be bent, and the average pore size was calculated to be 0.76 nm. Quality silica did not have ultra-micropores.

The angle of the curve of the nitrogen adsorption isotherm of the porous silica of Example 1 is steeper than that of the nitrogen adsorption isotherm of the porous silica of Comparative Example 2 (a) and 2 (Fig. 2). It is understood from the comparison with b). This also suggests that the porous silica of Example 1 has high uniformity of the pore diameter of the ultramicro pores.

Next, the porous silica of Example 1 was observed at a magnification of 400 times using FE-SEM (trade name: "S-4800", manufactured by Hitachi High-Technologies Corporation). Further, before the observation, Pt was deposited on the surface of the porous silica. As a result, according to FIG. 1, which is an observation image, granular silica having a particle size of 500 nm to 100 μm formed by aggregating silica particles having a particle size of 500 nm to 5 μm was confirmed. Further, in FIG. 1, it was observed that the gaps between the aggregated silica particles of granular silica existed as macropores having a pore diameter of more than 50 nm. Therefore, it can be seen that the porous silica of Example 1 has ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm.

(Surface area / specific surface area)
Next, the specific surface area of the porous silica of Example 1 was determined by the BET method based on the amount of nitrogen adsorbed in the range of relative pressure of 0.01 to 0.05 using the above-mentioned specific surface area / pore distribution measuring device. Calculated. As a result, the specific surface area of the porous silica of Example 1 was 685 m ² / g.

Furthermore, based on the above-mentioned method for measuring the surface area, it was found that in the porous silica of Example 1, the total specific surface area of the ultramicropores occupies 94% of the total specific surface area of the porous silica. ..

<Dynamic adsorption characteristics>
The dynamic adsorption characteristics of the porous silica of Example 1 and the porous silica of Comparative Example 2 were evaluated by the above-mentioned method. The result is shown in FIG.

As shown in FIG. 4, the porous silica (white circle) of Example 1 took about 120 minutes to reach adsorption rupture. On the other hand, the porous silica (black circle) of Comparative Example 2 took about 105 minutes to reach adsorption rupture. Therefore, the porous silica of Example 1 has a property of completely adsorbing toluene for a longer period of time than that of Comparative Example 2, and can be suitably used as an adsorbent, a catalyst carrier, a gas separation membrane material, or the like. It is understood that it can be done.

<Static adsorption characteristics>
The static adsorption characteristics of the porous silica of Example 1 and the porous silica of Comparative Example 2 were evaluated by the above-mentioned method. The result is shown in FIG.

As shown in FIG. 5, in the porous silica (black circle) of Example 1, the toluene concentration in the sampling bag before the test was C ₀ , and the toluene concentration in the sampling bag 30 minutes after the start of the test was C ₃₀ . When this was done, C ₃₀ / C ₀ was 0.6, which was 0.7 or less. On the other hand, in the porous silica (double circle) of Comparative Example 2, C ₃₀ / C ₀ was 0.78. Therefore, it is understood that the porous silica of Example 1 has better static adsorption characteristics than Comparative Example 2, and can be suitably used as an adsorbent, a catalyst carrier, a gas separation membrane material, and the like.

From the above, it is considered that the porous silica of Example 1 can exhibit excellent properties as an adsorbent and a catalyst carrier. Furthermore, the production of the porous silica of Example 1 does not require a special device and uses inexpensive insoluble modified collagen, and is therefore suitable for mass synthesis of the porous silica.

≪Exam 2≫
<Manufacturing of porous silica>
(Example 2)
The third step of Example 1 is replaced with the step of removing the denatured collagen from the complex by contacting the complex with a second acidic solution at 70 ° C. and pH 0.63 and acid-hydrolyzing the denatured collagen. Produced the porous silica of Example 2 in the same manner as in Example 1.

(Example 3)
In the third step of Example 1, the complex was brought into contact with a second acidic solution at 70 ° C. and pH 0.63 to acid hydrolyze the denatured collagen, and the denatured collagen was denatured with 5% by mass of pepsin. Instead of the step of removing the denatured collagen from the complex by enzymatically treating the collagen, the porous silica of Example 3 was produced in the same manner as in Example 1 except for the steps.

<Specification of pore structure of porous silica>
The pore structure of the porous silica of Examples 2 to 3 was specified by the same method as the measurement method for the porous silica of Example 1 described above. Presence or absence of ultramicro pores and their average pore diameter, presence or absence of macropores and their average pore diameter, specific surface area, occupied area of ultramicro pores with respect to total surface area, occupation of macropores with respect to total surface area of the porous silica of Examples 2 to 3. Table 1 shows the area, dynamic adsorption characteristics (time until adsorption rupture), and static adsorption characteristics (C ₃₀ / C _0). For reference, Table 1 also shows data such as the presence or absence of ultramicro pores in Example 1 and their average pore diameters.

From the above, the porous silicas of Examples 2 to 3 can exhibit excellent properties as an adsorbent and a catalyst carrier by having ultramicro pores having a pore diameter of less than 0.7 nm and macropores having a pore diameter of more than 50 nm. It is thought that it can be done. Further, the production of the porous silica of Examples 2 to 3 does not require a special device and uses inexpensive insoluble modified collagen, and is therefore suitable for mass synthesis of the porous silica.

≪Test 3≫
<Manufacturing of porous silica>
Porous silicas of Examples 4 to 8 were produced by changing the firing time in the third step of Example 1 and using the same method as in Example 1 for other matters. In Example 4, the firing time in the third step was set to 4 hours, and porous silica having a carbon content of 0% in the ultramicro pores was produced. In Example 5, the firing time was set to 2 hours and 10 minutes to produce porous silica having a carbon content of 0.08% in the ultramicro pores. In Example 6, the firing time was set to 2 hours to produce porous silica having a carbon content of 0.1% in the ultramicro pores. In Example 7, the firing time was 1.5 hours, and porous silica having a carbon content of 0.15% in the ultramicro pores was produced. In Example 8, the firing time was set to 1 hour, and porous silica having a carbon content of 0.24% in the ultramicro pores was produced.

<White emission due to ultraviolet irradiation of porous silica>
The porous silicas of Examples 4 to 8 were irradiated with black light (ultraviolet rays) having a wavelength of 254 nm and a wavelength of 365 nm. The result is shown in FIG. In FIG. 7, (a) shows the state of light emission of the porous silica when irradiated with ultraviolet rays having a wavelength of 254 nm, and (b) shows the state of light emission of the porous silica when irradiated with ultraviolet rays having a wavelength of 365 nm. .. The spots shown in FIGS. 7 (a) and 7 (b) are Example 8 (carbon content 0.24%), Example 7 (carbon content 0.15%), and Example 6 (carbon content 0.15%) in order from the left. Porous silica of Example 5 (carbon content 0.08%) and Example 4 (carbon content 0%). In both the wavelength of 254 nm and the wavelength of 365 nm, the strongest light emission was confirmed in Example 5 (carbon content 0.08%), and no light emission was confirmed in Example 4 (carbon content 0%).

Although the embodiments and examples of the present invention have been described above, it is planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. ..

The embodiments and examples disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims rather than the above-described embodiment, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

Claims (8)

Pore size a porous silica perforated macropores Ultra-micro pores and pore diameter of less than 0.7nm exceeds 50 nm,
The porous silica has a plurality of the ultramicro pores and a plurality of the macropores.
The total specific surface area of the ultramicropores is 90% or more of the total specific surface area of the porous silica. The porous silica according to claim 1 , wherein the porous silica has a particle size of 500 nm or more and 100 μm or less. The porous silica according to claim 1 or 2 , wherein the porous silica contains 0.05% by mass or more and 0.3% by mass or less of carbon. The porous silica according to claim 3 , wherein the porous silica emits white light when irradiated with ultraviolet rays. In the toluene adsorption test by the sampling bag method, the porous silica has a toluene concentration of C _{0 in the sampling bag before the test and a toluene concentration of C 30} in the sampling bag 30 minutes after the start of the test. , The porous silica according to any one of claims 1 to 4 , which has an adsorption property in which _{C 30} / C _{0 is 0.7 or less.} The first step of obtaining a complex containing the modified collagen and silica by mixing insoluble modified collagen and alkoxysilane in a first acidic solution having a pH of 0.1 to 5;
The second step of washing and drying the complex, and
A method for producing porous silica, which comprises a third step of removing the denatured collagen from the complex after the second step.
The third step is a step of removing the denatured collagen from the complex by firing the complex at 500 ° C. or higher, and the complex is placed in a second acidic solution having a temperature of 100 to 150 ° C. and a pH of 0.1 to 5. The step of removing the denatured collagen from the complex by contacting and acid-hydrolyzing the denatured collagen, and using 0.1 to 10% by mass of enzyme with respect to the denatured collagen at 20-50 ° C. A method for producing porous silica, which is at least one selected from the group consisting of steps of removing the denatured collagen from the complex by enzymatically treating the denatured collagen. In the method for producing porous silica according to claim 6,
A method for producing porous silica without performing the second step. The first step includes the step of dispersing the denatured collagen in the first acidic solution by stirring and / or ultrasonic irradiation, and then adding the alkoxysilane to the first acidic solution. The method for producing porous silica according to claim 6 or 7.

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