Spherical surface-treated silica aerogel and method for producing the same

Abstract

To provide a spherical porous silica having a large specific surface area and pore volume, and having an amino acid derivative as a coordinating functional group on the surface.SOLUTION: A spherical surface-treated silica aerogel has a specific surface area of 300 to 1000 m2 / g by BET method, has a peak of pore volume and pore radius of 1 to 8 mL / g and 1 to 30 nm by BJH method, respectively, has a volume reference cumulative 50% diameter (D50) value of 1 to 200 μm in particle size distribution measured by Coulter counter method, has an average circularity determined by image analysis method of 0.8 or more, and has at least one kind of amino acid derivative on the surface.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a spherical surface-treated silica aerogel having an amino acid derivative on its surface, and a method for producing the same. [Background technology]

[0002] Porous silica is used, for example, as a column packing material, a metal adsorbent, and an immobilizing agent for amino acids, peptides, proteins, or nucleic acids, by utilizing the affinity between the silanol groups present on the silica surface or between substances introduced onto the silica surface via chemical bonds and metal ions or other molecules.

[0003] Among these, porous silica with a coordinating functional group that exhibits specific affinity with a specific metal ion bound (immobilized) on its surface is widely used as a metal adsorbent for refining organic compounds for medical and electronic materials and recovering rare metals. When used for these purposes, it is common to pack porous silica into a column.

[0004] Amino acids and peptides composed of multiple amino acids are known to be used as coordinating functional groups. For example, according to Non-Patent Document 1, carnosine, a dipeptide composed of β-alanine and histidine, is known to form strong bonds with various metal ions to form complexes.

[0005] The method of introducing a coordinating functional group to the surface of porous silica is generally to first introduce a reactive functional group to the surface of porous silica via a chemical bond, and then fix the introduced reactive functional group and a molecule having a coordinating functional group by a covalent bond. For example, in Patent Document 1, the silanol group on the surface of porous silica is reacted with a surface treatment agent having an epoxy group to introduce an epoxy group, then reacted with a diamine to introduce an amino group, and further the amino group is covalently bonded to a molecule having a coordinating functional group.

[0006] When using porous silica with a coordinating functional group on its surface as a metal adsorbent, it is known that its performance as a metal adsorbent depends not only on the type and amount of the ligand, but also on the physical properties of the porous silica. In general, the larger the specific surface area of ​​the porous silica, the higher the retention due to the increased contact area with the metal ions to be recovered, and the larger the pore volume of the porous silica, the lower the back pressure during liquid passage. Furthermore, since a uniform packed bed can be constructed, it is preferable that the particles are spherical. Therefore, in order to widely use the porous silica as a metal adsorbent, it is preferable to use porous silica that has a large specific surface area and pore volume, is spherical, and has a coordinating functional group on its surface that has affinity for metals. As mentioned above, examples of the coordinating functional group include amino acids and peptides. However, currently existing porous silica does not fully meet these requirements. For example, the specific surface area of ​​the porous silica (silica gel) used in Patent Document 1 is 74 m 2 / g, which means that the specific surface area is not large.

[0007] Spherical silica aerogel is known as a type of spherical porous silica that has a large specific surface area and pore volume. According to Patent Document 2, a W / O type emulsion is made into a dispersion of a gel, and then the dispersion is separated into two layers, an O phase and a W phase, to obtain a dispersion in which the gel is dispersed in the W phase. After that, the silanol groups on the surface of the metal oxide (silica) are reacted with a silylating agent to perform a hydrophobic treatment, and drying shrinkage is suppressed, so that a specific surface area of ​​400 m2 can be obtained without drying and removing the dispersion medium in the gel under supercritical conditions. 2 / g or more, a pore volume of 2 mL / g or more, and a circularity of 0.8 or more can be produced.

[0008] According to Patent Document 3, a W / O type emulsion is used as a dispersion liquid for a gelled body, and then the water in the gelled body is replaced with a solvent. Then, the silanol groups on the surface of the spherical silica aerogel are reacted with a surface treatment agent having a hydrophobic group such as a hydrocarbon group to perform a hydrophobic treatment, thereby suppressing drying shrinkage, and thereby a specific surface area of ​​400 m2 can be obtained without drying and removing the dispersion medium in the gel under supercritical conditions. 2This method can easily produce spherical silica aerogels with a specific surface area of ​​0.1 / g or more, a pore volume of 3 mL / g or more, and a circularity of 0.8 or more. Taking advantage of their large specific surface area and pore volume, the hydrophobized spherical silica aerogels are used as heat insulating agents and cosmetic additives.

[0009] It is expected that a spherical silica aerogel with a large specific surface area and pore volume can be easily produced as a metal adsorbent by following the manufacturing method described in Patent Document 2 or 3. However, in order to widely use the spherical silica aerogel as a metal adsorbent for refining compounds for medical and electronic materials and recovering rare metals, it is necessary to introduce a coordinating functional group that shows affinity with metal ions by using the silanol groups on the surface of the spherical silica aerogel as a foothold. For this reason, it is not possible to use the spherical silica aerogel described in Patent Documents 2 and 3, in which the silanol groups on the surface are reacted with a surface treatment agent having a hydrophobic group to perform hydrophobic treatment. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2011-001336 [Patent Document 2] Japanese Patent Application Publication No. 2014-88307 [Patent Document 3] International Publication No. 2012 / 057086 [Non-patent literature]

[0011] [Non-Patent Document 1] EJ Baran, Metal Complexes of Carnosine, Biochemistry (Moscow), Vol. 95, No. 7, 2000, pp. 789-797. Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, in order to provide a metal adsorbent that exceeds the performance of conventional porous silica in terms of metal ion retention, back pressure during liquid passage, and construction of a uniform packed phase, and that can be widely used for refining organic compounds for medical and electronic materials and recovering rare metals, it is desirable to develop porous silica that has a large specific surface area and pore volume, is spherical, and has coordinating functional groups.

[0013] Therefore, an object of the present invention is to provide a porous silica having a large specific surface area and pore volume, a spherical shape, and having an amino acid derivative on its surface as a coordinating functional group. In the present invention, the "amino acid derivative" refers to an amino acid or a peptide in which two or more amino acids are linked by peptide bonds. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to solve the above problems. As a result, they have found that instead of the step of hydrophobizing the silanol groups on the surface in the spherical silica aerogel production method described in Patent Documents 2 and 3, a surface treatment is performed with a surface treatment agent having a reactive functional group, and then an amino acid derivative is introduced, thereby making it possible to produce a spherical surface-treated silica aerogel having a large specific surface area and pore volume, which is spherical, and which has an amino acid derivative, while suppressing drying shrinkage.

[0015] That is, one embodiment of the present invention is a sintered body having a specific surface area of ​​300 to 1000 m by the BET method. 2 / g, the peaks of the pore volume and pore radius measured by the BJH method are 1 to 8 mL / g and 1 to 30 nm, respectively, the volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by the Coulter counter method is 1 to 200 μm, and the average circularity determined by an image analysis method is 0.8 or more, and the spherical surface-treated silica aerogel has at least one amino acid derivative on the surface.

[0016] Another aspect of the present invention is (1) preparing an aqueous silica sol; (2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O type emulsion; (3) A step of gelling the silica sol to convert the W / O type emulsion into a dispersion of a gel; (4) replacing the water in the gel with an organic solvent; (5) treating the gel with a surface treatment agent having a functional group capable of binding to an amino acid derivative; (6) removing the substituted organic solvent (7) modifying the gel with an amino acid derivative; and (8) A step for removing the organic solvent used in the step (7). The method for producing the spherical surface-treated silica aerogel comprises the steps of: Effect of the Invention

[0017] The spherical surface-treated silica aerogel according to one embodiment of the present invention has an amino acid derivative on its surface that has a high affinity for metals, and therefore can be widely used for refining organic compounds for medical and electronic materials. In addition, since it has a large specific surface area and pore volume and is spherical, it has good retention power, low back pressure during liquid flow, and can be used as a column packing material that can construct a uniform packed bed.

[0018] According to a method for producing a spherical surface-treated silica aerogel according to one embodiment of the present invention, a spherical surface-treated silica aerogel having a large specific surface area and pore volume, a spherical shape, and an amino acid derivative can be produced by carrying out a surface treatment using a surface treatment agent having a functional group capable of bonding with an amino acid derivative, followed by the introduction of the amino acid derivative, while suppressing drying shrinkage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments. Furthermore, unless otherwise specified, the expression "A to B" for a numerical range means "A or more and B or less." In such an expression, when a unit is added only to the numerical value B, the unit is also applied to the numerical value A.

[0020] Generally, spherical silica aerogel is a porous silica obtained by drying the solvent contained in wet silica gel while maintaining the solid network and replacing it with air, and has a spherical shape and a porosity of 70% or more. In the present invention, spherical silica aerogel that has been surface-treated with a surface treatment agent is called spherical surface-treated silica aerogel.

[0021] In the present invention, the "specific surface area by the BET method" refers to a value obtained by drying a sample to be measured at a temperature of 150°C for 1 hour or more under a vacuum of 1 kPa or less, measuring the adsorption isotherm only on the nitrogen adsorption side at liquid nitrogen temperature, and analyzing the adsorption isotherm by the BET method. The pressure range used for the analysis is a relative pressure range of 0.1 to 0.25. The "pore volume by the BJH method" refers to a pore volume derived from pores with a pore radius of 1 nm to 100 nm obtained by analyzing the adsorption isotherm on the adsorption side obtained in the same manner as above by the BJH method (Barrett, EP; Joyner, LG; Halenda, PP, J. Am. Chem. Soc. 1951, 73, 373.). "Pore radius peak according to the BJH method" refers to the pore radius value at which a pore distribution curve (volume distribution curve) at the maximum peak value is obtained by analyzing the adsorption isotherm on the adsorption side obtained in the same manner as described above using the BJH method, and plotting the derivative of the cumulative pore volume with respect to the logarithm of the pore radius on the vertical axis and the pore radius on the horizontal axis.

[0022] The spherical surface-treated silica aerogel according to one embodiment of the present invention has a specific surface area according to the BET method of 300 to 1000 m 2 / g, preferably 300 to 900m 2 / g, and particularly preferably 300 to 800m 2 / g range. When used as a column packing material, the larger the specific surface area, the greater the retention due to the increased contact area with the molecules to be separated (Giaquinto, A.; Liu, Z.; Bach, A.; Kazakevich, Y., Anal. Chem. 2008, 80, 6358-6364.). However,2 If the particle size exceeds 1 / g, the particle size of the primary particles that make up the porous structure (network structure) of the independent particles (secondary particles) of the spherical surface-treated silica aerogel becomes small and is not large enough to form the pore structure of the spherical surface-treated silica aerogel, resulting in the pores being crushed, making production difficult.

[0023] In addition, the spherical surface-treated silica aerogel according to one embodiment of the present invention has a pore volume of 1 to 8 mL / g, preferably 1 to 6 mL / g, as determined by the BJH method. When used as a column packing material, the larger the pore volume, i.e., the higher the porosity, the lower the back pressure during liquid passage, as calculated using the Carman-Kozeny formula. However, if the pore volume exceeds 8 mL / g, the strength of the secondary particles decreases, and the particles are crushed in the column during liquid passage, so it is preferable that the pore volume is within the above range.

[0024] In the spherical surface-treated silica aerogel according to one embodiment of the present invention, when the specific surface area and pore volume are within the above-mentioned preferred ranges, the peak of the pore radius measured by the BJH method is 1 to 30 nm, preferably 5 to 20 nm. When used as a metal adsorbent, the optimal pore radius varies depending on the size of the metal ion to be separated, so that the pore radius may be determined for each metal ion to be separated, taking into account the balance between the specific surface area and the pore volume.

[0025] In the present invention, the "cumulative 50% diameter (D50) value on a volume basis" in the "particle size distribution measured by the Coulter counter method" refers to a cumulative 50% diameter (D50) on a volume basis obtained by dispersing 30 mg of a sample to be measured in 40 mL of ethanol, subjecting the sample to a crushing process by an ultrasonic crusher at 70 W for 10 minutes, and then measuring the cumulative 50% diameter (D50) on a volume basis by the Coulter counter method. The spherical surface-treated silica aerogel according to one embodiment of the present invention has a D50 value in the range of 1 to 200 μm. When used as a metal adsorbent, particles with a particle diameter of 1 μm to 200 μm are preferably used. If the particle diameter is less than 1 μm, an increase in back pressure becomes a problem when applied to a column-packed metal recovery device, and if the particle diameter is larger than 200 μm, the distance traveled by diffusion within the particles becomes long, resulting in a decrease in recovery performance, so it is preferable that the particle diameter is within the above range.

[0026] In the present invention, the "average circularity obtained by image analysis" refers to the arithmetic mean value of the circularity obtained by image analysis of SEM images of 2000 or more spherical, surface-treated silica aerogel particles observed at a magnification of 1000 times by secondary electron detection using a scanning electron microscope (SEM). The "circularity" of each spherical, surface-treated silica aerogel particle is a value calculated by the following formula (1).

[0027] C=4πS / L 2 (1) In formula (1), C represents the circularity. S represents the area (projected area) that the spherical surface-treated silica aerogel particles occupy in the image. L represents the length (perimeter) of the outer periphery of the spherical surface-treated silica aerogel particles in the image. Secondary particles are counted as one particle, and particle groups that form aggregated particles are counted as one particle.

[0028] The individual independent particles constituting the spherical surface-treated silica aerogel according to one embodiment of the present invention have an average circularity of 0.8 or more. As the average circularity increases from 0.8 to 1, the individual particles constituting the spherical surface-treated silica aerogel become closer to a true sphere, the number of agglomerated particles decreases, and a uniform packed bed can be constructed.

[0029] The spherical surface-treated silica aerogel according to one embodiment of the present invention has at least one kind of amino acid derivative on the surface.

[0030] In the present invention, the amino acid in the "amino acid derivative" is a compound having both an amino group and a carboxy group on one molecule. Examples of amino acids include alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. Depending on the number of amino acids bound, peptides are called dipeptides in which two amino acid molecules are bound, tripeptides in which three amino acid molecules are bound, tetrapeptides in which four amino acid molecules are bound, oligopeptides in which up to about 20 amino acid molecules are bound, and polypeptides in which even more amino acids are bound. Examples of dipeptides include carnosine, anserine, homoanserine, kyotorphin, balenine, aspartame, glorin, and valetin. Examples of tripeptides include aizenin, glutathione, leupeptin, melanostatin, ophthalmic acid, norophthalmic acid, etc. Examples of tetrapeptides include tuftsin, endomorphin, morphiceptin, tetragastrin, etc.

[0031] In the present invention, "having an amino acid derivative on the surface" means that the amino acid derivative is introduced to the surface of the spherical silica aerogel via a chemical bond. The type of amino acid derivative introduced to the surface may be one or more, and the number of amino acid derivatives introduced to the surface is not limited. The amino acid derivative may be introduced not only to the outermost surface of the spherical silica aerogel but also into the pores. The amino acid derivative is bonded by dehydration condensation between the amino group introduced on the spherical silica aerogel and the carboxy group of the amino acid derivative, or between the carboxy group introduced on the spherical silica aerogel and the amino group of the amino acid derivative.

[0032] (Manufacturing method) The spherical surface-treated silica aerogel according to one embodiment of the present invention is (1) preparing an aqueous silica sol; (2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O type emulsion; (3) A step of gelling the silica sol to convert the W / O type emulsion into a dispersion of a gel; (4) replacing the water in the gel with an organic solvent; (5) treating the gel with a surface treatment agent having a functional group capable of binding to an amino acid derivative; and (6) removing the substituted organic solvent (7) modifying the gel with an amino acid derivative; and (8) A step for removing the organic solvent used in the step (7). Among these, steps (1) to (3) may be carried out according to known methods described in Patent Documents 2 and 3 to produce a dispersion of the gelled body.

[0033] Step (4) is a step of replacing the water in the gelled body with an organic solvent in order to smoothly proceed with the surface treatment in step (5). For example, the gelled body and liquid components in the gelled body dispersion are filtered using a suction filter or the like, and the gelled body is washed with water and then with an organic solvent, so that the water in the gelled body is replaced with an organic solvent. The organic solvent is preferably one that has affinity with both the gelled body and the surface treatment agent having a functional group capable of binding with the amino acid derivative used in step (5), and is preferably one that does not prevent the gelled body and the surface treatment agent from forming a chemical bond, and is preferably one that does not cause a chemical reaction with the functional group capable of binding with the amino acid derivative to be introduced. Examples of the organic solvent include acetone, methanol, ethanol, and isopropyl alcohol. Of these, ethanol can be preferably used.

[0034] Step (5) is a step of treating the gelled body with a surface treatment agent having a functional group capable of bonding with an amino acid derivative in order to introduce a functional group capable of bonding with an amino acid derivative onto the surface of the spherical silica aerogel. The surface treatment can be carried out by adding a surface treatment agent having a functional group capable of bonding with an amino acid derivative to a dispersion of the gelled body and the organic solvent obtained by dispersing the gelled body in the organic solvent used in step (4) and stirring the mixture for a certain period of time.

[0035] The functional group capable of bonding with an amino acid derivative in the surface treatment agent is the above-mentioned amino group or carboxy group. An example of the surface treatment agent having a functional group capable of bonding with an amino acid derivative is a compound represented by formula (2), but the surface treatment agent having a functional group capable of bonding with an amino acid derivative used in the present invention is not limited to the compound represented by formula 2.

[0036] R n Six (4-n) (2) In formula 2, n represents an integer of 1 to 3, R represents a functional group capable of bonding with an amino acid derivative or a substituent having a functional group capable of bonding with an amino acid derivative as part of its structure, and X represents a group (leaving group) that can be detached from the molecule by cleaving the bond with the Si atom in a reaction with a compound having a hydroxyl group. When n is 2 or more, multiple Rs may be the same or different. When n is 2 or less, multiple Xs may be the same or different.

[0037] The substituent having a functional group capable of binding to an amino acid derivative as part of the structure represented by R is a substituent having one or more functional groups capable of binding to an amino acid derivative at the end or inside of a molecular chain made of a hydrocarbon or a hydrocarbon containing a hetero atom. The number of atoms constituting the molecular chain is not limited, and the molecular chain may have a branched structure in the middle. The functional group capable of binding to an amino acid derivative present in the substituent may be an amino group or a carboxy group.

[0038] Examples of the leaving group represented by X include halogen atoms such as chlorine and bromine, alkoxy groups such as methoxy and ethoxy, groups represented by -NH-SiR3, and groups represented by -OSiR3 (R has the same meaning as R in formula (2)).

[0039] Specific examples of surface treatment agents having a functional group capable of bonding with amino acid derivatives include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, aminophenyltrimethoxysilane, aminophenyltriethoxysilane, 2-(carbomethoxy)ethyltrimethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, etc., but are not limited to the compounds shown above. These are commercially available and can be easily obtained, and desired ones can also be synthesized by known means.

[0040] The conditions of the above surface treatment depend on the type of surface treatment agent having a functional group capable of binding with an amino acid derivative. In the case of using aminopropyltrimethoxysilane, the treatment temperature is set to 50° C., and the treatment can be performed by holding the surface treatment for about 3 hours or more. The amount of the surface treatment agent having a functional group capable of binding with an amino acid derivative is preferably 1 part by mass or more and 200 parts by mass or less per 100 parts by mass of the dry mass of the gelled body, but is not limited to the above range. The surface treatment may use one type of surface treatment agent or multiple surface treatment agents. When one type of surface treatment agent is used, the surface treatment agent is a surface treatment agent having a functional group capable of binding with an amino acid derivative. On the other hand, when multiple surface treatment agents are used, all of them may be surface treatment agents having a functional group capable of binding with an amino acid derivative, or may include a surface treatment agent that does not have a functional group capable of binding with an amino acid derivative.

[0041] Surface treatment using multiple surface treatment agents can be carried out by adding the first surface treatment agent for a certain period of time, and then adding the second or subsequent surface treatment agents. The reaction solvent may be changed by the same procedure as in step (4), or the surface treatment agents may be added directly without changing the reaction solvent.

[0042] Surface treatment using multiple surface treatment agents is effective when introducing functional groups capable of binding to multiple types of amino acid derivatives to the surface or when preventing drying shrinkage. Even in surface treatment using one type of surface treatment agent, drying shrinkage is suppressed, and it is effective for producing spherical surface-treated silica aerogels that have a large specific surface area and pore volume, are spherical, and have functional groups capable of binding to amino acid derivatives. However, if the surface treatment agent having functional groups capable of binding to amino acid derivatives is three-dimensionally bulky, steric hindrance occurs when the silanol groups present on the surface of the gelled body and the surface treatment agent form chemical bonds, and some silanol groups may remain. Therefore, after performing surface treatment with a surface treatment agent having functional groups capable of binding to amino acid derivatives to introduce functional groups capable of binding to the desired amino acid derivatives, hydrophobization treatment with a hydrophobizing agent is performed to convert the remaining silanol groups into hydrophobic functional groups such as hydrocarbon groups and inactivate them, thereby further preventing drying shrinkage. This hydrophobization treatment aimed at inactivating the remaining silanols is generally called end-capping. End-capping may be carried out using a hydrophobizing agent having a hydrophobic functional group.

[0043] Specific examples of hydrophobizing agents used for end capping include alkyl chlorosilanes, alkyl methoxysilanes, alkyl silazanes, and alkyl siloxanes such as dimethyldichlorosilane, trimethylchlorosilane, methyldichlorosilane, methyltrichlorosilane, trimethylmethoxysilane, methyltrimethoxysilane, trimethylsilylimidazole, hexamethyldisilazane, and hexamethyldisiloxane.

[0044] Step (6) is a step of removing the organic solvent used in step (5). For example, the surface-treated gelled body and the liquid component may be filtered using a suction filter or the like, and washed with an organic solvent. The organic solvent is preferably one that can wash the surface treatment agent and does not chemically react with the introduced reactive functional group. Examples of the organic solvent include acetone, methanol, ethanol, and isopropyl alcohol. Of these, ethanol is preferably used.

[0045] The surface-treated gel obtained by filtration is preferably dried in a dryer for 12 hours or more to remove the organic solvent used in step (5), which may inhibit the reaction in step (7), to obtain a spherical surface-treated silica aerogel. The drying temperature is preferably equal to or higher than the boiling point of the solvent and equal to or lower than the decomposition temperature of the surface treatment, and the pressure is preferably normal pressure (101.33 kPa) or reduced pressure.

[0046] The step (7) is a step of introducing an amino acid derivative onto the surface-treated gelled body or spherical surface-treated silica aerogel obtained in the step (6) and reacting the surface-treated gelled body or spherical surface-treated silica aerogel with the amino acid derivative in order to obtain a gelled body or spherical surface-treated silica aerogel having the amino acid derivative on its surface. This step may be carried out by the same method and conditions as known peptide synthesis. Hereinafter, an example using a spherical surface-treated silica aerogel will be described, but the same process can be carried out when a surface-treated gelled body is used. The amino acid derivative and the condensing agent are added to a dispersion of an organic solvent and a spherical surface-treated silica aerogel obtained by dispersing the spherical surface-treated silica aerogel in an organic solvent, and the mixture is stirred for a certain period of time.

[0047] The amino acid derivative to be reacted here may have either the amino group or the carboxyl group protected by a protecting group. A protecting group is used to suppress reactions other than the desired reaction, and is preferably protected. For example, when an amino group is introduced onto a spherical surface-treated silica aerogel, the amino group on the amino acid derivative is masked by a protecting group in order to selectively react with the carboxyl group on the amino acid derivative. Examples of protecting groups for the amino group on the amino acid derivative include tert-butoxycarbonyl, 9-fluorenylmethyloxycarbonyl, benzyloxycarbonyl, phthaloyl, nosyl, and allyloxycarbonyl groups, and the 9-fluorenylmethyloxycarbonyl group is preferred because of its ease of deprotection and the ease of calculation of the amount of amino acid derivative introduced. These are commercially available and easily available, and the desired one can also be synthesized by known means.

[0048] Condensing agents include N,N-dicyclohexylcarbodiimide, N,N-diisopropylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, (1H-benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate, and 1-[bis(dimethylamino)methylene]-1H-benzotriazolium-3-oxide hexafluorophosphate. These are commercially available and easily available, and desired ones can also be synthesized by known means.

[0049] Additives may be added as necessary. For example, additives for accelerating the reaction include 1-hydroxybenzotriazole and 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine. These are commercially available and easily available, and desired products can also be synthesized by known means.

[0050] A base may be added as necessary. As the base, known bases such as triethylamine, diisopropylethylamine, pyridine, and N,N-dimethylaminopyridine can be used without limitation. These are commercially available and easily available, and desired ones can also be synthesized by known means.

[0051] The organic solvent can be used without any particular limitation as long as the spherical surface-treated silica aerogel can be dispersed and the condensation agent and additives can be dissolved in the organic solvent. From the viewpoint of the solubility of the condensation agent and additives and the efficiency of the condensation reaction, N,N-dimethylformamide is preferred.

[0052] The above condensation reaction conditions depend on the types of amino acid derivatives, condensing agents, and additives, but when using a spherical silica aerogel with an amino group introduced as the spherical surface-treated silica aerogel, amino group-protected alanine as the amino acid derivative, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium-3-oxide hexafluorophosphate as the condensing agent, 1-hydroxybenzotriazole as the additive, diisopropylethylamine as the base, and N,N-dimethylformamide as the solvent, the treatment temperature is set to 25°C and the mixture is stirred for about 30 minutes or more. The amounts of the amino acid derivative, condensing agent, additive, and base used are determined according to the amount of functional groups capable of binding to the amino acid derivatives introduced on the silica aerogel. The amounts of the amino acid derivative, condensing agent, additive, and base are preferably 1 mol or more and 50 mol or less per 1 mol of the functional group, but are not limited to the above ranges.

[0053] Step (8) is a step of removing the organic solvent used in step (7). For example, the spherical surface-treated silica aerogel having an amino acid derivative on its surface and the liquid component may be filtered using a suction filter or the like, and washed with an organic solvent. The organic solvent is preferably one that can wash away the condensation agent, additives, and base used, and is preferably one that does not chemically react with the condensation agent, additives, and base used. Examples of the organic solvent include methanol, ethanol, isopropyl alcohol, and N,N-dimethylformamide. Of these, ethanol and N,N-dimethylformamide are preferably used.

[0054] The gel obtained by filtration and having the surface modified with the amino acid derivative may be dried. For example, by drying in a dryer for 12 hours or more, a spherical surface-treated silica aerogel having the surface modified with the amino acid derivative can be obtained. The temperature during drying is preferably equal to or higher than the boiling point of the solvent and equal to or lower than the decomposition temperature of the surface treatment, and the pressure is preferably normal pressure (101.33 kPa) or reduced pressure.

[0055] In this production method, the spherical surface-treated silica aerogel according to one embodiment of the present invention can be obtained through the above steps (1) to (8).

[0056] (Additional notes regarding manufacturing method) In this manufacturing method, the spherical surface-treated silica aerogel of the present invention can also be obtained by carrying out steps (5) to (8) on spherical silica aerogel manufactured by a known method such as supercritical drying. The spherical silica aerogel is dispersed in an organic solvent, surface-treated with the surface treatment agent used in step (5), the organic solvent is removed in the same manner as in step (6), treated with the amino acid derivative or condensation agent used in step (7), and the organic solvent is removed in the same manner as in step (8), to obtain a spherical surface-treated silica aerogel having an amino acid derivative on its surface, which has the same physical properties as the spherical surface-treated silica aerogel having an amino acid derivative on its surface manufactured by steps (1) to (8). The treatment conditions for the treatment by the supercritical drying method are not particularly limited, and conditions under which the solvent in the gelled body can be completely replaced by supercritical carbon dioxide can be appropriately adopted. Such treatment conditions are, for example, 40°C, 9 MPa, a treatment time of 6 hours, and replacement is repeated five times while updating the supercritical carbon dioxide.

[0057] The amount of amino acid derivative introduced by surface treatment is a value calculated from the carbon content (C amount), nitrogen content (N amount), and sulfur content (S amount) measured by elemental analysis. The C amount, N amount, and S amount are measured by performing an oxidation treatment at a temperature of 1150°C while flowing oxygen and helium, and quantifying the amount of carbon dioxide, nitrogen oxides, and sulfur oxides generated. If the amino acid derivative contains nitrogen or sulfur, the amount of amino acid derivative is calculated as the amount of element / (the number of elements contained in one molecule of amino acid derivative).

[0058] The type of amino acid derivative introduced can be identified by infrared spectroscopy (IR) or nuclear magnetic resonance (NMR). For example, IR identifies amide groups and other organic functional groups that are generated when amino acids are modified onto the silica aerogel surface. NMR can identify the amino acid derivative introduced onto the surface by analyzing C nuclei. Furthermore, Si nuclei can provide information on the bonds around the Si atoms in the silica.

[0059] The amount of the amino acid derivative introduced can be controlled by the amount of the surface treatment agent used in step (5), and is preferably 0.1 mmol / g or more. However, when used as a metal adsorbent, the amount of the amino acid derivative can be determined in consideration of the strength of the affinity with the metal ion to be separated, and is not limited to the above range.

[0060] (Application) The spherical surface-treated silica aerogel according to one embodiment of the present invention has an amino acid derivative, which is a coordinating functional group, on its surface, and can be widely used for refining organic compounds for medical and electronic materials and recovering rare metals. In addition, when packed in a column, it has a large specific surface area and pore volume, and is spherical, so it has good retention of biomolecules, low back pressure during liquid flow, and can form a uniform packed bed, making it suitable for use as a column-packed metal adsorbent.

[0061] In addition, it can be used as a column packing material for the separation, analysis, and purification of biomolecules such as peptides, proteins, and nucleic acids, which was a use of porous silica gel with coordinating functional groups. Furthermore, since it has amino acid derivatives on its surface, it can be used as a biocompatible material or an additive for cosmetics. EXAMPLES

[0062] In the following, examples are shown to specifically explain the present invention. However, the present invention is not limited to these examples. The examples and comparative examples were evaluated by the following methods.

[0063] [Production of spherical surface-treated silica aerogel] <Evaluation method> The specific surface area by the BET method, the pore volume by the BJH method, and the peak of the pore radius by the BJH method were measured using a BELSORP-mini manufactured by BEL Japan Co., Ltd. in accordance with the above definitions.

[0064] Measurement of the cumulative 50% volumetric diameter (D50) was performed using a BECKMAN COULTER Multisizer 3 in accordance with the above definition. The disruption process using an ultrasonic disrupter was performed using a BRANSONIC 1510J-DTH (output 70 W).

[0065] The average circularity was measured according to the above definition using S-5500 (accelerating voltage 3.0 V, secondary electron detection) manufactured by Hitachi High-Technologies Corporation.

[0066] The amount of amino acid derivative introduced was calculated from the amount of C and N according to the above definition. The C value and N value were measured using a fully automatic elemental analyzer (elementar vario MICRO cube) at a temperature of 1150°C while flowing oxygen and helium.

[0067] <Example 1> (Production of gelled body (steps (1) to (4))) While stirring 70 g of sulfuric acid (concentration 9.2 g / 100 mL) with a stirrer, sodium silicate (concentration SiO2 16.4 g / 100 mL, Na2O 5.4 g / 100 mL, SiO2 moles / Na2O moles = 3.2) was gradually added until the pH reached 2.9, to prepare an aqueous silica sol with a pH of 2.9 (step (1)). 140 g of this silica sol was taken out, and 130 g of heptane and 1.5 g of sorbitan monooleate were added, and the mixture was stirred for 1.5 minutes at 5600 rpm / min using a homogenizer (IKA, T25BS1) to form a W / O emulsion (step (2)). The obtained emulsion was gelled at 70 ° C for 1 hour while stirring with a stirring blade (step (3)). 77 g of isopropyl alcohol and 60 g of ion-exchanged water were added, and the O phase and W phase were separated while stirring with a stirring blade. Subsequently, 4.8 g of a 0.5 mol / L aqueous solution of sodium hydroxide was added. The gel was aged at 70° C. for 1 hour. This slurry solution was filtered, and the resulting cake was washed with ion-exchanged water and then with ethanol to obtain a gel in which ethanol had been permeated (step (4)).

[0068] (Surface treatment (steps (5) and (6))) The gel was dispersed in 100 g of ethanol, and while stirring with a stirring blade, aminopropyltrimethoxysilane (9.8 g, 5.0 mmol / g) was gradually added and stirred at 50°C for 3 hours (step (5)). This slurry was filtered, and the resulting cake was washed with ethanol and then heated and dried under vacuum pressure at 150°C for 12 hours or more to obtain a spherical surface-treated silica aerogel having amino groups (step (6)).

[0069] (Introduction of Amino Acid Derivatives (Steps (7) and (8))) Spherical surface-treated silica aerogel (0.10 g), N-[(9H-fluoren-9-ylmethoxy)carbonyl]-L-alanine (0.14 g), 1-[bis(dimethylamino)methylene]-1H-benzotriazolium-3-oxide hexafluorophosphate (0.17 g), 1-hydroxybenzotriazole (0.07 g), and diisopropylethylamine (0.15 mL) were added to N,N-dimethylformamide (2 mL) and stirred at 25° C. for 30 minutes (step (7)). The slurry was filtered to obtain a cake. 20% piperidine / N,N-dimethylformamide (2 mL) was added to the cake and stirred at 25° C. for 10 minutes. The slurry was filtered, and the resulting cake was washed with N,N-dimethylformamide (2 mL × 2), and then vacuum-dried at 50°C for 12 hours or more under vacuum pressure to obtain a spherical surface-treated silica aerogel having alanine as an amino acid derivative (step (8)). The results of the physical property evaluation of the obtained spherical surface-treated silica aerogel are shown in Table 1.

[0070] <Example 2> The production of spherical surface-treated silica aerogel having amino groups was carried out in the same manner as in Example 1. In the step of introducing the amino acid derivative, the same procedure as in Production Example 1 was carried out except that N,1-bis[(9H-fluoren-9-ylmethoxy)carbonyl]-L-histidylglycine was used as the amino acid derivative, and spherical surface-treated silica aerogel having carnosine as the amino acid derivative was obtained. The results of the physical property evaluation of the obtained spherical surface-treated silica aerogel are shown in Table 1.

[0071] [Table 1]

[0072] <Metal adsorption capacity evaluation> The metal adsorption ability of the spherical surface-treated silica aerogel obtained in Example 2 and the commercially available hydrophobized spherical silica aerogel as Comparative Example 1 was evaluated. A metal salt was dissolved in an organic solvent to prepare a solution with a metal concentration of 1000 ppm. Silica (50 mg) was added to the obtained solution (5 mL), stirred for 5 minutes, and filtered using a membrane filter (0.45 μm, made of PTFE). 1 mL of the recovered solution was dried and solidified, and dilute nitric acid (1%, 50 mL) was added to dissolve the residue, and the amount of metal adsorbed to the silica was measured using an inductively coupled plasma emission spectrometer (iCAP 6500 DUO manufactured by Thermo Fisher). The amount of metal adsorbed to the silica was calculated based on the amount of metal obtained from the solution obtained by passing the sample solution through a membrane filter.

[0073] As metal salts, copper (I) acetate monohydrate, palladium acetate, and nickel acetate were used, and acetonitrile was used as a solvent. Comparative Example 1 was a porous spherical silica aerogel (Airica MT-10 manufactured by Tokuyama Corporation) (BET specific surface area 633 m 2 / g, pore volume 4.02 mL / g, pore radius peak 17.2 nm, D50 value 10 μm, average circularity 0.8 or more, surface functional group methyl) was used.

[0074] [Table 2]

[0075] The spherical surface-treated silica aerogel having an amino acid derivative on its surface obtained in Example 2 of the present invention exhibited high adsorption capacity for the three metals. The silica used in the comparative example did not exhibit high adsorption capacity for all of the three metals.

Claims

1. BET specific surface area: 300 to 1000 m ２ / g, with peaks of pore volume and pore radius measured by the BJH method being 1 to 8 mL / g and 1 to 30 nm, respectively, with a volume-based cumulative 50% diameter (D50) value being 1 to 200 μm in a particle size distribution measured by a Coulter counter method, with an average circularity of 0.8 or more determined by an image analysis method, and having at least one amino acid derivative on the surface.

2. (1) preparing an aqueous silica sol; (2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O type emulsion; (3) A step of gelling the silica sol to convert the W / O type emulsion into a dispersion of a gel; (4) replacing the water in the gel with an organic solvent; (5) treating the gel with a surface treatment agent having a functional group capable of binding to an amino acid derivative; (6) Removing the substituted organic solvent (7) modifying the gel with an amino acid derivative; and (8) A step of removing the organic solvent used in the step (7).

2. The method for producing a spherical surface-treated silica aerogel according to claim 1, comprising the steps of:

3. A metal adsorbent comprising the spherical surface-treated silica aerogel according to claim 1.

4. A column packing material comprising the spherical surface-treated silica aerogel according to claim 1.

5. A biocompatible material comprising the spherical surface-treated silica aerogel according to claim 1.

6. A cosmetic additive comprising the spherical surface-treated silica aerogel according to claim 1.

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