JP3925936B2 - Method for recovering or collecting metal oxide nanoparticles - Google Patents

Description

  The present invention relates to organically modified fine particles in which hydrocarbons are strongly bonded to the surface of fine particles, particularly organically modified metal oxide fine particles and a method for producing the same, and a method for recovering or collecting fine particles such as nanoparticles, and applied technology thereof. About.

  Fine particles, especially nanometer-sized particles (nanoparticles) exhibit various unique and excellent properties, characteristics, and functions, so they are more accurate and smaller than all current materials and products. It is expected to realize a technology that satisfies the demand for lighter weight. In this way, nanoparticles are made from ceramic nanostructure modifiers, optical functional coating materials, electromagnetic shielding materials, secondary battery materials, fluorescent materials, electronic component materials, magnetic recording materials, polishing materials, and other industrial and industrial materials, It is attracting attention as a material for the 21st century because it enables high-performance, high-performance, high-density, and high-precision products such as pharmaceuticals and cosmetics. From the recent basic research on nanoparticles, the discovery of ultra-high functionality, new physical properties, and the synthesis of new materials by the quantum size effect of nanoparticles has attracted a great deal of interest from industry. However, in order to put nanoparticles into practical use, it is necessary to add a specific function to each fine particle. To that end, the establishment of a technology that modifies the surface of the particle to enable the addition of that function. Is required. Examples of convenient means for adding a function that can be stably used and utilized to the fine particles, particularly nanoparticles, include organic modification, and the modification is particularly required through a strong bond.

There have been many reports on organic / inorganic composite materials and their synthesis research, and research on organic modification of inorganic particles has been conducted. It was something to be implemented. There is no known method for reacting an organic substance with fine particles in the reaction field, that is, water while synthesizing fine particles in water or an aqueous solution. There are many known methods for modifying the surface of inorganic particles in an organic solvent to modify the surface of the particles. However, nano-sized particles are prone to agglomeration, and in particular, particles synthesized in water are placed in an organic solvent. In order to disperse, pretreatment such as using a surfactant is required. Thus, there is no report on a technique for surface modification while synthesizing particles in water.
As methods for surface modification in-situ, reports such as reverse micelle method and hot soap method have been made. In the reverse micelle method, water is suspended in an oil phase using a surfactant to form reverse micelles, and a reactive substrate is added thereto to cause reaction crystallization. The metal oxide particles generated in the suspended aqueous phase are stabilized with a surfactant to stabilize and disperse the nanoparticles. The surfactant is adsorbed on the particle surface and does not bind by reaction. The hot soap method is a method in which the above-described method is performed at a high temperature using only a surfactant without using an oil phase. The metal salt aqueous solution to be reacted is supplied while rapidly stirring, and reaction crystallization is performed. This is a technique that utilizes the fact that the surrounding surfactant is adsorbed simultaneously. An example of organic modification that has been reported so far is adsorption of alkanethiol, and no reactive modification has been performed.
There are many research reports that high-temperature and high-pressure water forms a homogeneous phase with organic substances, and that water functions as an acid or base catalyst in high-temperature and high-pressure fields and the organic synthesis reaction proceeds even without a catalyst. However, there is no report on a method for reacting an inorganic material with an organic material.

It is known that nano-sized highly crystalline particles can be synthesized by using supercritical water as a reaction field for hydrothermal synthesis. However, there has been no report on methods of modifying the surface of the produced nanoparticles in the reaction field or synthesizing organically modified particles by reacting with organic substances. A technique for performing in-situ surface modification while performing CVD in a supercritical fluid is already known. That is, alkanethiol or alcohol is allowed to coexist in a reaction field for synthesizing metal nanoparticles by performing CVD in a supercritical fluid with reference to a method such as the hot soap method. In this method, it is reported that particle growth is suppressed and nanometer-sized particles are generated. In the CVD technique, a reduction reaction by alkanethiol and surface modification occur simultaneously, and the resulting product is a metal Cu and a structure in which alkanethiol is coordinated has been reported. In addition, while using a reducing agent in supercritical water, a method for producing nanoparticles by coordinating thiol groups to metal nanoparticles and suppressing particle growth by synthesizing in the presence of alkanethiol as described above. There is. Some of the results reported that alcohols were not only coordinated but also bonded and in-situ surface modified in the reaction field. However, it is not a reaction crystallization in supercritical “water” but a method belonging to a reaction in-situ surface modification method in an organic solvent.
A method for surface-treating glass or silica gel in water is widely known, and the method is a CNBr activation method or an epoxy activation method. Since both the CNBr method and the epoxy activation method are performed in an alkaline solution, all the nanometer (nm) particles are dissolved, so that oxidation in water using these known reactions is performed. Surface modification of product nanoparticles is not possible.

The conventional organic modification methods are summarized below.
1) Synthesis of organic / inorganic composite materials There is a silane coupling method as a general method for modifying the surface of metal oxides (Non-patent Document 1). ). Surface modification of oxides in water is also known. Methods for surface modification of glass or silica gel in water include CNBr activation method and epoxy activation method. This is a method in which CNBr or epoxy reacts with OH on the surface to give a functional group of CN or epoxy, and the desired functional group is introduced through this. However, it is necessary to set ph necessary for these reactions and to add a catalyst, and there is also generation of acid as a product. In general, since all of these activation methods are carried out in an alkaline solution, all the particles of the order of nm are dissolved, and the surface modification of oxide nanoparticles in water using these well-known reactions is impossible. (Non-Patent Document 6). In any of the above methods, organic modification is performed in an organic solvent. Nano-sized particles have high surface energy and tend to aggregate. As a method of synthesizing particles of 10 nm or less, a solution method such as a sol-gel method or a hydrothermal method is effective as shown in FIG. However, when particles synthesized in a solvent are taken out and dried, they are strongly aggregated and it is extremely difficult to re-disperse them in an organic solvent. It is necessary to gradually change the solvent to an organic solvent. In particular, nanoparticles synthesized in water often have hydrophilic groups, and in order to disperse them in an organic solvent, pretreatment such as using a surfactant is required. Therefore, techniques for surface modification while synthesizing nanoparticles in-situ are important in the synthesis of nanoparticles of 50 nm or less.

2) In-situ surface modification method Reverse micelle method Using a surfactant, water is suspended in the oil phase to form reverse micelles, and a reactive substrate is added to the reaction crystallization. Let For example, when a Cd (NO ₃ ) ₂ aqueous solution and Na ₂ S micelles are mixed, CdS nanoparticles and NaNO ₃ can be generated. In order to stabilize the CdS nanoparticles, a stabilizer such as alkanethiol can be supplied to stabilize the nanoparticles. The surfactant is in a state of being adsorbed on the surface, and there is no binding due to reaction (Non-patent Document 7). Recently, a method using supercritical carbon dioxide as a solvent has also been reported (Non-patent Documents 8 and 9).
Hot Soap Method The above method is performed at a high temperature using a surfactant without using an oil phase. A metal salt aqueous solution to be reacted is supplied while rapidly stirring to cause reaction crystallization, and at the same time, the surrounding surfactant is adsorbed (Non-Patent Document 10). Most of the reported examples so far are adsorption of alkanethiol, and no reactive modification has been performed.
Reactive crystallization in-situ surface modification in supercritical fluids A method has also been proposed in which organic modification is performed simultaneously with thermal decomposition CVD (Chemical Vapor Deposition) in supercritical fluids. In particular, papers that have been surface modified by coexisting alkanethiols in the supercritical hydrothermal synthesis (Technoarch patent) field have also been reported. While Cu (NO _{3) 2} aqueous solution in a supercritical state, the coexistence of hexane thiol, reduction occurs, Cu particles are synthesized, stabilization occurs with hexane thiol in situ. In this case, thiol acts as a reducing agent, and hexanethiol coordinates to the surface of the generated Cu nanoparticles. This is a well-known coordination to a metal (Non-patent Document 11). It is also known to perform surface modification with alcohol while synthesizing SiO ₂ by thermal decomposition in a supercritical organic solvent (Non-patent Document 11).
The inventors have already proposed nanoparticle synthesis in supercritical water that synthesizes nano-sized highly crystalline particles by using supercritical water as the reaction field for hydrothermal synthesis. There is no mention of a method for modifying the surface of the produced particles in the reaction field or synthesizing the organically modified particles by reacting with an organic substance. In addition, there are many research reports that high-temperature high-pressure water forms a homogeneous phase with organic substances, and that in high-temperature and high-pressure fields, water functions as an acid or base catalyst and the organic synthesis reaction proceeds even without a catalyst. However, there is no report on a method of reacting an inorganic material with an organic substance.

Polymer Frontier 21 Series 15 “Inorganic / polymer nano-interface control”, edited by the Society of Polymer Science, pp.3-23, NTS, 2003 "Formation of Ordered Monolayer of Anionic Silica Particles on a Cationic Molecular Layer", T. Yonezawa, S. Onoue, and T. Kunitake, Chem. Lett., No. 7, 689-690 (1998). "Molecular Imprinting of Azobenzene Carboxylic Acid on a Ti02 Ultrathin Film by the Surface Sol-Gel Process", S. -W. Lee, I. Ichinose, T. Kunitake, Langmuir, Vol. 14, 2857-2863 (1998). "Alternate Molecular Layers of Metal Oxides and Hydroxyl Polymers Prepared by the Surface Sol-Gel Process", I. Ichinose, T. Kawakami, T. Kunitake, Adv. Mater., Vol. 10, 535-539 (1998). "Molecular Imprinting of Protected Amino Acids in Ultrathin Multilayers of Ti02 Gel", S.W.Lee, I.Ichinose, T.Kunitake, Chem. Lett, .No.12, 1993-1994 (1998) Rolf Axen, Jerker Porath, Sverker Ernbvack, "Chemica Coupling of Peptides and Proteins to Polysaccharides by Means of Cyanogen Halides", Nature, Vol. 214, 1967, pp. 1302-1304 A) "Nanoparticle manufacturing, evaluation, application, and latest technology of equipment", pp.16-19, 2002, CM Publishing Ye, X. R., Lin, Y. Wang, C .. Wai, C. M., Adv. Materials, 2003, 15, 316 Ye, X. R., Lin, Y. Wang, C., Wai, C. M., Chem. Comm, 2003, 642 A) “Latest Technology for Manufacturing, Evaluation, Application, and Equipment of Nanoparticles”, pp.19-21, 2002, CMC Publishing Kirk J. Ziegler, R. ChristopherDoty, Keith P. Johnston, and Brian A. Korgel, "Synthesis of Organic Monolayer-Stabilized Copper Nanocrystals in Supercritical Water", J. Am. Chem. Soc., 2001, 123, 7797-7803

Since it has various useful properties and functions, many synthesis methods including supercritical synthesis methods have been proposed and developed for fine particles, especially nanoparticles, which are expected to be useful. However, there is a need for a method for recovering the fine particles and nanoparticles synthesized in this way, and a method for stabilizing the dispersion as fine particles without aggregation after the recovery. Also, when used, it is necessary to disperse well in resin, plastics and solvent. In particular, nanoparticles synthesized in water often have a hydrophilic surface and are not easily recovered from water. In addition, the nanoparticles have a problem that they are not familiar with organic solvents and resins.
In order to satisfy these needs, it is considered that the surface of the nanoparticles needs to be modified with an organic substance according to the purpose. For example, desirable modifications include modification with the same polymer as the resin or imparting the same functional group as the solvent. And if surface modification is possible in water, it will also become easy to isolate | separate and collect | recover nanoparticles from water. However, in order to surface-modify nanoparticles synthesized in water with an organic substance, it is desirable that the water and the organic substance have a homogeneous phase. In this case, the modifier that can be used is an amphiphilic surfactant. Or lower alcohols that can be dissolved in water. Furthermore, even if it is collected by some method, the collected nanoparticles are very easily aggregated, and once aggregated, the nanoparticles are easily redispersed even if a dispersant is used. It ’s difficult. In addition, the surface modification of such nanoparticles is quite difficult.
It is known that water and organic substances form a homogeneous phase in high-temperature and high-pressure fields. For example, alcohols and sugars, carboxylic acids and alcohols, and carboxylic acids and amines undergo dehydration reactions in high-temperature and high-pressure water without any catalyst. I know it will happen. However, it is not known that a reaction occurs between the hydroxyl group on the particle surface and the organic substance under the conditions.

Thus, it is necessary to develop a method for introducing a desired desired functional group at the time of synthesis of nanoparticles in water. As a result of intensive research, the present inventors coexisted organic substances in a high-temperature and high-pressure hydrothermal synthesis field. When the metal oxide particles were synthesized, it was found that fine particles with surface modification in which the organic substance was firmly bonded to the particle surface due to the occurrence of a homogeneous phase reaction between the particle surface and the organic substance were obtained. And since the obtained nanoparticle was organically modified, it discovered that it could collect | recover easily by phase-separating from water with a residual organic substance after cooling. Based on these findings, the present invention has been completed.
In representative aspects, the present invention provides the following.
[1] In the method of collecting or collecting metal oxide nanoparticles,
Using high-temperature and high-pressure water as a reaction field, the surface of the metal oxide nanoparticles reacts with the organic modifier, and the hydrocarbon group which may be substituted or unsubstituted may be covalently bonded, ether bond, ester Via a bond selected from the group consisting of a bond, a bond through an N atom, a bond through an S atom, a metal-C- bond, a metal-C = bond and a metal- (C = O)-bond. The surface of the nanoparticle is organically modified by binding to the surface of the nanoparticle,
(1) precipitating and collecting metal oxide nanoparticles dispersed in an aqueous solution;
(2) The metal oxide nanoparticles dispersed in an aqueous solution are transferred to an organic solvent and recovered, or
(3) collecting metal oxide nanoparticles at the organic solvent phase-water phase interface;
A method for recovering or collecting metal oxide nanoparticles.
[2] The metal oxide nanoparticles are formed by subjecting a metal compound to a hydrothermal reaction using high-temperature and high-pressure water as a reaction field, and the surface of the formed metal oxide nanoparticles and an organic modifier are used. Recovering or collecting according to the above [1], wherein a hydrocarbon group, which may be substituted or unsubstituted, is bonded to the surface of the nanoparticle through a covalent bond. Law.
[3] The recovery or collection method according to [1] or [2] above, wherein the high-temperature and high-pressure water is water under supercritical or subcritical conditions.
[4] The recovery according to any one of the above [1] to [3], wherein the high-temperature high-pressure water is water having a pressure at or above the critical point and / or a temperature condition at or above the critical point. Or collection method.
[5] The above-mentioned [1] to [4], wherein the organically modified metal oxide nanoparticles are synthesized in a reaction field where water exists under a temperature condition of 250 to 500 ° C. and a pressure condition of 10 to 30 MPa. The collection | recovery or collection method as described in any one of these.
[6] When organically modifying the surface of the nanoparticles, metal oxide nanoparticles may be produced in the reaction field in the supercritical hydrothermal synthesis method in the presence of an organic modifier, which may be substituted or unsubstituted. Any one of the above [1] to [5], wherein an organically modified metal oxide nanoparticle having a hydrocarbon group bonded to the surface of the nanoparticle through a covalent bond is synthesized. Collection or collection method as described.
[7] The recovery or collection method according to the above [6], wherein the particle size of the produced particles is adjusted to be smaller than that in the case of supercritical hydrothermal synthesis in the absence of an organic modifier.
[8] The recovery or collection method according to any one of [1] to [7], wherein the hydrocarbon group is a long-chain hydrocarbon having a chain having 1, 2, 3 or more carbon atoms. .
[9] The organic modifier is selected from the group consisting of alcohol, aldehyde, carboxylic acid, amine, thiol, amide, ketone, oxime, phosgene, enamine, amino acid, peptide, and sugar. The collection or collection method according to any one of [1] to [8].
[10] The recovery or collection method according to any one of [1] to [9] above, wherein a solvent that promotes the uniform phase of the organic modifier and water is used as a coexisting substance.
[11] The recovery according to [10], wherein the solvent is selected from the group consisting of methanol, ethanol, propanol, i-propanol, butanol, i-butanol, t-butanol and ethylene glycol. Or collection method.
[12] The recovery or collection method according to any one of [1] to [11] above, wherein the reaction is performed in the presence of an acid.
[13] The recovery or collection method according to [12] above, wherein the acid is selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, bromic acid, formic acid, acetic acid, propionic acid, and toluenesulfonic acid. .
[14] The reaction rate of the organic modifier is controlled by controlling a factor selected from the group consisting of temperature, acid concentration, and reaction time. Any one of [1] to [13] above Collection or collection method.
[15] The average diameter of the nanoparticles is
(1) 100 nm or less,
(2) 50 nm or less,
(3) 20 nm or less,
(4) 10 nm or less, or
(5) The collection or collection method according to any one of [1] to [14] above, wherein the collection or collection method is 5 nm or less.

By modifying the surface of fine particles (especially nanoparticles) with a hydrophilic surface with hydrophobic groups such as organic groups such as hydrocarbons, particles that are difficult to recover from an aqueous medium can be easily and reliably obtained. In addition, the fine particles (particularly, nanoparticles) can be separated and recovered by transferring to the organic medium side without impairing useful properties of the fine particles (particularly, nanoparticles). On the other hand, hydrophobic fine particles (particularly nanoparticles) can be separated and recovered by transferring them to the aqueous medium side such as an aqueous solution by modifying the surface with hydrocarbons having hydrophilic groups. it can.
For metal oxide fine particles (particularly nanoparticles) present in an aqueous medium, it is difficult to form a uniform reaction system with a modifier having an organic group such as a hydrophobic hydrocarbon. In particular, it was impossible to organically modify nanoparticles) without impairing the useful properties of the particles, but this would be possible using the modification of the present invention. Furthermore, since the degree of modification can be controlled, various characteristics specific to each can be imparted by modification.
Other objects, features, excellence and aspects of the present invention will be apparent to those skilled in the art from the following description. However, it is understood that the description of the present specification, including the following description and the description of specific examples and the like, show preferred embodiments of the present invention and are presented only for explanation. I want. Various changes and / or modifications (or modifications) within the spirit and scope of the present invention disclosed herein will occur to those skilled in the art based on the following description and knowledge from other parts of the present specification. Will be readily apparent. All patent documents and references cited herein are cited for illustrative purposes and are not to be construed as a part of this specification. is there.

The present invention uses organic high-temperature high-pressure water as a reaction field to form a bond between the surface of metal oxide fine particles and an organic substance, and organically modified metal oxide fine particles, particularly organic materials that have recently attracted attention due to their unique characteristics. The present invention provides a technique for synthesizing modified metal oxide nanoparticles, organically modified metal oxide fine particles obtained in this way, and utilization / application techniques thereof. The present invention is an organic modification method paying attention to the point that water and an organic substance form a homogeneous phase in a reaction field having a certain phase behavior. The features of this method are conceptually and schematically shown in FIG.
The reaction field for the modification reaction of the present invention preferably includes pressure and / or temperature conditions at or above the subcritical water or critical point of water. Figure 1 shows the density-temperature / pressure dependence of water (left side of Figure 1) and the dielectric constant-pressure dependence of water (right side of Figure 1). It can be seen that a unique reaction environment can be provided when the temperature / pressure region is the reaction field. 2 shows the phase behavior of the water-gas binary system near the critical point of water (left side of FIG. 2) and the phase behavior of the water-organic solvent system (right side of FIG. 2). It is clear that there is a uniform homogeneous phase forming region, and it can be clearly applied to the modification reaction of the present invention.
If a functional group having a high affinity with the solvent or resin to be used in using the nanoparticles is introduced into the particle, it can be dispersed in the solvent or resin at a high concentration, which is excellent.
In the present invention, the particle size can be controlled by performing in-situ surface modification in a hydrothermal synthesis reaction field including a supercritical region.

In the present specification, the term “fine particles” may refer to particles having an average particle size of 1 μm (1,000 nm) or less, preferably nanoparticles. The nanoparticles may generally refer to particles having an average particle size of 200 nm or less, preferably those having a size of 200 nm or less. In some cases, the nanoparticles may have an average particle size of 100 nm or less, and in other cases the average particle size may be 50 nm or less. In a preferred case, the nanoparticles have an average particle size of 20 nm or less, and in other cases, the average particle size is 10 nm or less, or 5 nm or less. It may be a thing. In a preferred case, the nanoparticles preferably have a uniform particle size, but may have a mixture of particles having different particle sizes at a certain ratio.
The particle diameter can be measured by a method known in the art, and can be measured, for example, by TEM, adsorption method, light scattering method, SAXS or the like. In TEM, observation is performed with an electron microscope. When the particle size distribution is wide, it is necessary to pay attention to whether or not the particles entering the field of view represent all particles. In the adsorption method, the BET surface area is evaluated by N ₂ adsorption or the like.
In general, fine particles were produced using a hydrolysis reaction, for example, a hydroxide such as Fe (OH) _3, higher temperatures FeO (OH), equilibrated to Fe ₂ O ₃ is shifted. The molecular arrangement state shifts from a random amorphous state to an aligned crystalline state as the temperature increases. By using the technique of the present invention, it is possible to obtain highly crystalline nanoparticles that are organically modified.
High crystallinity can be confirmed by electron diffraction, electron micrograph analysis, X-ray diffraction, thermogravimetric analysis, and the like. For example, in electron diffraction, a dot is obtained as a diffraction interference image for a single crystal, a ring for a polycrystal, and a halo for an amorphous crystal. In the electron micrograph, the crystal plane is solid if it is a single crystal, and it is polycrystalline if it has such a shape that crystals further appear from above the particles. When polycrystalline primary particles are small and many particles aggregate to form secondary particles, they become spherical. If it is amorphous, it must be spherical. In X-ray diffraction, a sharp peak is obtained if it is a single crystal. The crystallite size can be evaluated from the width of 1/2 height of the X-ray peak using the Sherre equation. If the crystallite size obtained by the evaluation is the same as the particle diameter evaluated from the electron microscope image, it is evaluated as a single crystal. In thermogravimetric analysis, when heated in a dry inert gas with a thermobalance, the weight decreased due to the evaporation of water adsorbed at around 100 ° C, and further decreased to about 250 ° C due to dehydration from within the particles. Is seen. When organic materials are included, even greater weight loss is observed at 250-400 ° C. In the case of particles obtained by the technique of the present invention, even when the temperature is raised to 400 ° C., the maximum weight loss due to dehydration from the inside of the crystal is 10% or less, which is significantly higher than that of metal oxide fine particles synthesized at low temperature. Different. Thus, the fine particles of the organically modified metal oxide fine particles obtained according to the present invention are characterized by high crystallinity, for example, having a sharp peak by X-ray diffraction, and dots or rings by electron diffraction. In other words, dehydration of crystal water is 10% or less per dry particle by thermogravimetric analysis, and / or primary particles have crystal planes in an electron micrograph.

In the case of fine particles, the surface energy and external energy such as gravity and electric field antagonize in relation to the particle size, that is, when particles are separated or dispersed by centrifugal force, gravity sedimentation, electrophoresis, etc. When the diameter is smaller than several hundreds of nanometers, it does not disperse unless a large external force is applied. Below 50 nm, the effect of surface energy becomes even greater, and it will be extremely difficult with only external field energy unless the surface properties or the physical properties of the solvent are controlled. The technique of the present invention can solve this problem.
In particular, when the particle size is 10 nm or less, there is no overlap of quantum states, and the influence of the electronic state on the surface greatly affects the bulk physical properties. For this reason, it has been found that physical properties completely different from those of bulk particles can be obtained, that is, a quantum size effect (Kubo effect) appears. In the case of particles having a size of about 10 nm or less, it can be considered as a completely different substance, but in the technique of the present invention, the fine nanoparticles can be suitably organically modified.
Typical fine particles in the present invention include those having a metal oxide as a main particle structure, and hereinafter referred to as “metal oxide fine particles”.
The “metal” in the metal oxide contained in the metal oxide fine particles is not particularly limited as long as it can typically produce nanoparticles, and is selected from those known to those skilled in the art. Can be used. Typical metals include the group IIIB boron (B)-group IVB silicon (Si)-group VB arsenic (As)-group VIB tellurium (Te) lines in the long-period periodic table. The elements on the line with the boundary as well as those on the left or lower side of the long-period periodic table from the boundary, such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, etc., Group IB elements such as Cu, Ag, Au, etc., Group IIB elements such as Zn, Cd, Hg, etc., Group IIIB elements such as B, Al, Ga, In, Tl, etc. Group IVB elements include Si, Ge, Sn, Pb, Group VB elements such as As, Sb, Bi, Group VIB elements include Te, Po, and Groups IA to VIIA. It is done. Metal oxides include Fe, Co, Ni, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Ti, Zr, Mn, Eu, Y, Examples include oxides such as Nb, Ce, and Ba, such as SiO ₂ , TiO ₂ , ZnO ₂ , SnO ₂ , Al ₂ O ₃ , MnO ₂ , NiO, Eu ₂ O ₃ , Y ₂ O ₃ , Nb ₂ O ₃ , InO, ZnO, Fe ₂ O ₃ , Fe ₃ O ₄ , Co ₃ O ₄ , ZrO ₂ , CeO ₂ , BaO 6Fe ₂ O ₃ , Al ₅ (Y + Tb) ₃ O ₁₂ , BaTiO ₃ , LiCoO ₂ , LiMn ₂ O ₄ , K ₂ O · 6TiO ₂ , AlOOH, and the like.

When the surface of fine particles, particularly nanoparticles, is organically modified, it is not particularly limited as long as it is a device capable of achieving high-temperature and high-pressure conditions, and can be selected and used from devices widely known to those skilled in the art. For example, either a batch type apparatus or a flow type apparatus can be used. As a typical reactor, the one shown in FIG. 3 may be mentioned, and a system as shown in FIG. 5 may be constructed, but an appropriate reactor can be constructed as needed.
The organic modifier is not particularly limited as long as it can cause hydrocarbons to be strongly bonded to the surface of the fine particles. The application of nanoparticles, including the fields of organic chemistry, inorganic materials, and polymer chemistry, is not limited. Can be selected from organic materials that are widely known in the field of which is expected. Examples of the organic modifier include ether bond, ester bond, bond through N atom, bond through S atom, bond of metal-C-, bond of metal-C = and metal- (C = O). Those that allow the formation of strong bonds such as-bonds. As the hydrocarbon, the number of carbon atoms is not particularly limited, and those having 1 or 2 carbon atoms can be used. From the viewpoint of taking advantage of the characteristics of the present invention, a long chain carbon chain having 3 or more carbon atoms is used. What is hydrogen is preferable, for example, a C3-C20 linear or branched or cyclic hydrocarbon etc. are mentioned. The hydrocarbon may be substituted or unsubstituted. The substituent may be selected from functional groups widely known in the fields of organic chemistry, inorganic materials, polymer chemistry, etc., and one or more substituents exist. May be the same or different from each other.
Examples of organic modifiers include alcohols, aldehydes, ketones, carboxylic acids, esters, amines, thiols, amides, oximes, phosgene, enamines, amino acids, peptides, and saccharides. It is done.
Typical modifiers include, for example, pentanol, pentanal, pentanoic acid, pentanamide, pentanethiol, hexanol, hexanal, hexanoic acid, hexanamide, hexanethiol, heptanol, heptanal, heptanoic acid, heptaneamide, heptanethiol, Examples include octanol, octanal, octanoic acid, octatanamide, octanethiol, decanol, decanal, decanoic acid, decanamide, decanethiol and the like.
Examples of the hydrocarbon group include an optionally substituted linear or branched alkyl group, an optionally substituted cyclic alkyl group, an optionally substituted aryl group, and an optionally substituted aralkyl group. And a saturated or unsaturated heterocyclic group which may be substituted. Examples of the substituent include carboxy group, cyano group, nitro group, halogen, ester group, amide group, ketone group, formyl group, ether group, hydroxyl group, amino group, sulfonyl group, -O-, -NH-,- S- etc. are mentioned.

Reaction mechanism In water, a hydroxyl group generally exists on the surface of a metal oxide. This is due to the following reaction equilibrium.
MO + H ₂ O = M (OH) (1)
Generally, this reaction is exothermic, and the equilibrium shifts to the left on the high temperature side. The reaction with the used surface modifier is as follows and is due to a dehydration reaction.
The left-facing reaction (reverse reaction) is a reaction well known in the hydrolysis of alkoxides and the like, and is a reaction that occurs easily by addition of water even near room temperature. Since this reverse reaction is generally an exothermic reaction, it is suppressed on the high temperature side, and a rightward reaction is more advantageous. This is the same as the temperature dependence of the dehydration reaction of the metal hydroxide of formula (1).
Further, the stability of the product in water is more advantageous as the solvent polarity is lower because the reaction (dehydration) directed to the right has a lower polarity of the product compared to the reaction source system. The dielectric constant of water is lower at higher temperatures. The dielectric constant is 15 or less at 350 ° C. or lower, and the dielectric constant is rapidly decreased to about 1 to 10 near the critical point. For this reason, a dehydration reaction will be accelerated more than a normal temperature effect.

M (OH) + ROH = M (OR) + H ₂ O = M ・ R + 2H ₂ O
M (OH) + RCOOH = M (OCOR) + H ₂ O = MR + H ₂ O + CO ₂
M (OH) + RCHO = M (OH) CR + H ₂ O = MC = R + 2H ₂ O, MCR + 2H ₂ O, MR + H ₂ + CO ₂
M (OH) + RSH = MSR + H ₂ O (reduction)
(These equations are assumed to be (2))
Hydroxyl attack by amines is known to proceed in the presence of a strong acid or substitution by Cl near room temperature, but exchange with OH occurs in high-temperature and high-pressure water. Regarding organic substances, it has been confirmed that amination of hexanol proceeds by catalyzing carboxylic acid between hexaneamide and hexanol, but it is assumed that a similar reaction proceeds. A part of the reaction mechanism of this method is schematically shown in FIG. 7 as an example.
In the case of thiols, the possibility of reduction in the reaction field has been reported, and it is speculated that the thiol addition reaction was caused by partial reduction on the metal oxide surface.

How to set conditions
1) Reaction equilibrium The reaction conditions for organic modification vary depending on the metal species and modifier, but they are organized as follows.
That is, the reaction proceeds when the equilibrium of equation (1) is on the right side and the equilibrium of equation (2) and below is on the right side. Since the respective equilibrium differs depending on the metal species and modifier, the optimum reaction conditions are different. When the temperature is raised, the equilibrium in the equation (2) and below shifts to the right, and particularly at 350 ° C. or higher, it rapidly shifts to the advancing side, while the equilibrium in the equation (1) shifts to the left. For the reaction conditions, refer to the DBs of formulas (1) and (2).
In the presence of a base and an acid, the surface functional group of the metal oxide can be changed to OH, so that the dehydration reaction with the modifier can proceed under the conditions. In that case, since a dehydration reaction is likely to occur in the presence of an acid, the reaction can be advanced by allowing some acid to coexist at a high temperature.

2) Phase equilibrium Since relatively short-chain hydrocarbon alcohols, aldehydes, carboxylic acids, and amines are soluble in water, for example, surface modification of metal oxides with methanol is possible. However, in the case of longer-chain hydrocarbons, phase separation from the aqueous phase causes the reaction between the metal oxide and the organic modifier in the aqueous phase, even if the reaction equilibrium described above is in progress. Sometimes not. That is, introduction of a lipophilic group is relatively easy, but phase behavior needs to be taken into account when targeting C3 or longer chain hydrocarbons.
The phase behavior of hydrocarbons and water has already been reported and can be used as a reference. In general, a homogeneous phase is formed at an arbitrary ratio as long as it is equal to or higher than the critical trajectory of gas-liquid, and therefore, favorable reaction conditions can be set by setting such temperature and pressure conditions.
Further, when it is desired to lower the optimum reaction temperature, it is possible to coexist the third component for making water and organic matter a uniform phase. For example, it is known that the coexistence region of hexanol and water can be formed at a lower temperature by coexistence of ethanol and ethylene glycol that form a homogeneous phase even at a low temperature. By utilizing this, a reaction between a metal oxide and an organic substance can be performed. However, in this case, the selection of the third component is important so that the surface modification reaction by the third component does not occur.
As described above, this method enables long-chain organic modification in water for the first time.

In-situ surface modification during hydrothermal synthesis As described above, the temperature dependence of the hydroxyl group formation on the surface of the metal oxide of formula (1) and the organic modification reaction of formula (2) and below is in the opposite direction. Therefore, especially when the reaction of the formula (1) is on the left side, that is, on the dehydration side, in order to cause a modification reaction, setting of reaction conditions such as the coexistence of acid is extremely important and sometimes difficult.
In contrast, hydrothermal synthesis in-situ surface modification is a method that makes it possible.
Hydrothermal synthesis proceeds through the following reaction pathway.
Al (NO ₃ ) ₃ + 3H ₂ O = Al (OH) ₃ + 3HNO ₃
nAl (OH) ₃ = nAlO (OH) + nH ₂ O
nAlO (OH) = n / 2Al ₂ O ₃ + n / 2H ₂ O
Proceeding through such a reaction route is the same as in the case of using other metal species and sulfates, hydrochlorides and the like. Furthermore, hydrothermal synthesis, for example, using an apparatus as shown in FIG. 18 can be made into particles with a finer particle diameter as shown in FIG. It will be apparent that finer organically modified particles can be obtained with in-situ surface modification techniques. It will also be apparent that the particle size can be controlled by adjusting the temperature and pressure.
As shown here, even if a hydroxyl group is finally desorbed from the surface by a dehydration reaction, a product as a reaction precursor or many hydroxyl groups are generated on the surface. If an organic modifier coexists in this reaction field, it is possible to carry out the reaction under conditions where a hydroxyl group is present. In addition, since the reaction field coexists with an acid that is also a catalyst for proceeding the dehydration reaction, the modification reaction is accelerated. This makes it possible to perform surface modifications that could not be performed on oxides.

The technology of the present invention is not based on the premise of equilibration to the oxide by achieving a high temperature field such as synthesizing the precursor once and then synthesizing the metal oxide or metal hydroxide by hydrolysis or the like. Further, the surface of the fine particles can be organically modified without using a radical polymerization substrate, for example, an oxidizing substance, a material sensitive to temperature, light, or the like. Therefore, organic modification of metal particles and particles having different redox states can be performed.
In the present invention, a phase state in which water and an organic substance form a homogeneous phase is used, and an attempt is made to synthesize an inorganic-organic composite substance. A highly crystalline metal having a size of several to 50 nm or less, While synthesizing metal oxide nanoparticles, the surface is modified with organic molecules. At that time, by using a high-temperature high-pressure hydrothermal synthesis method, it was a conventional problem,
1) Surface organic modification is performed while synthesizing nanoparticles with high crystallinity.
2) It becomes possible to form a single layer polymer film,
As a result, 1) nanoparticles recovered from the reaction solvent, which had been an industrial issue until now, 2) stably dispersed and retained in the solvent at a high concentration for a long period of time, 3) uniformly dispersed at a high concentration with the polymer,
4) It is possible to arrange nanoparticles in two dimensions.

Various nanoparticle synthesis methods such as CVD, PVD, spray pyrolysis, sol-gel, reverse micelle, hot soap, and supercritical hydrothermal synthesis have been developed. However, nanoparticles have extremely high surface energy and easily aggregate, so that the physical properties of the original nanoparticles are often not expressed. There is also a need for a method of recovering nanoparticles. Furthermore, there is a need for a method of stabilizing the dispersion after recovery. Also, when used, it is necessary to disperse well in resin, plastics and solvent. In order to satisfy these needs, it is necessary to modify the surface of the nanoparticle with an organic substance according to the purpose. It is desirable to modify the same polymer as the resin and the same functional group as the solvent. These are solved by the present invention.
There are several proposals for the method of surface modification of nanoparticles. However, with weak bonds such as conventional coordination of thiols to metal surfaces and adsorption of surfactants to metal oxides, semiconductor properties, fluorescence properties, and luminescence properties that are manifested as nano-sized particles In some cases, dielectric characteristics and the like are lost. If a metal or metal oxide and an organic molecule can be covalently bonded, unprecedented characteristics of nanoparticles can be extracted. For example, in BaTiO ₃ , the adsorption method causes a dielectric loss in the adsorbed layer, but it is significantly reduced in the covalently bonded molecule.
As a technique for organic modification by forming a covalent bond, there is a method using a silane coupling agent, but a Si atomic layer is formed on the surface of the nanoparticle, and the semiconductor characteristics, fluorescence characteristics, and emission characteristics of the nanoparticles are the same as above. In some cases, dielectric characteristics and the like are lost. There is also a method of introducing a functional group using a chloro compound, but there is a possibility that the nanoparticles are dissolved under the modification reaction conditions (high pH, low pH). The present invention can solve these problems. According to the present invention, a high-temperature and high-pressure hydrothermal synthesis method can also be used, and organic modification is possible while synthesizing highly crystalline nanoparticles. In the high-temperature and high-pressure hydrothermal synthesis field, by coexisting organic substances, metal oxide particles can be synthesized, and the surface of the particles and the organic substances can be combined to form a strong surface modification that binds the organic substances to the surface. to make. The particle size can be sufficiently smaller than 50 nm, and the crystallinity is extremely high. High-temperature and high-pressure water forms a homogeneous phase with organic substances. Then, organic / inorganic bonds are formed on the surface of the generated particles. Since no other reaction such as a polymerization reaction occurs, modification of only one layer is possible. And by surface modification, crystal growth is suppressed and nanoparticles can be synthesized. In addition, an in situ high-temperature heat treatment effect is obtained during synthesis, and crystallinity is high.
In the present invention, it is not required to use an organic-inorganic composite as a precursor as a nanoparticle synthesis means, and the applicable range is remarkably excellent.
As a result, the following effects are expected.

1) Nanoparticles can be recovered from the aqueous phase.
Nanoparticles synthesized in supercritical water are usually suspended in water. However, the surface modification method of the present invention allows the oil phase to be transferred and is completely separated from the water.
Nanoparticle recovery was extremely difficult. Addition of flocculants and methods using surfactants and adsorbents have been empirically used, but in order to further disperse and disperse nanoparticles from these methods, new methods have been introduced. A decentralized technology was needed.
According to the method of the present invention, such operation is not required, and particle recovery is possible as it is. 2) Good dispersion of nanoparticles in organic solvent. In principle, extremely high concentration dispersion is possible.
Hydrophilic titania particles are suspended in water, but transferred from water to the chloroform phase by the surface modification of the present invention.
The surface modification can be performed while crystal precipitation is performed without performing the surface modification operation or the surface modification operation with a surfactant as in the prior art. In the conventional method, the introduction of the modifying group is limited, but any modifying group can be introduced. Therefore, the most suitable solvent for the resin or solvent can be selected. By using the same molecule as the resin and solvent, it becomes possible to achieve the ultimate high concentration dispersion and dispersion without using the solvent and resin.
3) Interfacial alignment by surface modification with controlled coverage It was observed that when the coverage was lowered by reaction control, it was aligned at the interface between water and oil. Therefore, in addition to particle recovery, nanoparticle arrangement using the technique of the present invention is possible.
4) Continuous control of dispersibility By surface modification of nanoparticles dispersed in water using the method of the present invention, precipitation can be easily performed using an appropriate solvent system such as a solution of water: ethanol = 50: 50. It becomes possible to make it. By controlling the degree of surface modification, it is possible to continuously change the concentration at which precipitation begins. For example, specifically, a phenomenon as shown in FIG. 19 can be achieved.
5) Display of selective recognition ability It is possible to create nanoparticles modified with functional groups that do not form chemical bonds with each other, or nanoparticles modified with functional groups that form chemical bonds. Such surface modification can impart the ability to bond with each other and can form higher-order structures of nanoparticles using the technology of the present invention.

Nanoparticles, for example, SiO ₂ is a pigment, a catalyst support, high temperature materials, honeycomb, in applications such as corrosion-resistant material, pigment Fe ₂ O _3, for applications such as magnetic materials, CeO ₂ abrasives, catalyst supports, ion For applications such as conductors and solid electrolytes, TiO ₂ is used for applications such as photocatalysts, pigments and cosmetics, Y ₂ O ₃ is used for applications such as pigments and catalyst carriers, InO is used for applications such as transparent conductors, and ZnO is For applications such as photoconductor materials, conductive materials, pigments, electronic materials, SiO ₂ for applications such as catalyst supports, zeolites, fillers, beads, etc., SnO ₂ for applications such as conductive materials, conductors, sensors, etc. ₂ O ₃ for applications such as magnetic materials, Cu and Ag and Al for applications such as electrodes and catalyst materials, Ni for applications such as electrodes, magnetic materials and catalyst materials, Co and Fe for magnetic materials and catalyst materials, etc. Ag / Cu for electrodes, catalyst materials, etc., and B ₄ C, AlN, TiB ₂ etc. for high temperature materials and high strength Applied to applications such as materials.
Nanoparticles and thin films having nanoparticles in a specific arrangement have been found to exhibit unique and excellent characteristics. For example, a single-layered array of nanoparticles is known to be capable of being densely packed like magnetic nanoparticles and exhibit excellent functions as a near-field memory element, and is applied to magnetic tapes and the like. It exhibits excellent properties and is useful. In addition, since the quantum size effect can be obtained, for example, in the case of nano phosphors arranged in a dispersion pattern, products such as quantum effect phosphors, quantum effect light emitters, and LSI high-density mounting bases can be provided. . A multi-layered arrangement of nanoparticles such as titania exhibits excellent functions such as low light scattering and a photocatalytic effect, such as a wet photoelectric conversion element and a high-performance photocatalytic coating. A particle-dispersed film can be provided with excellent functions such as a reinforcing effect and a flame-retardant effect, and can be used as a semiconductor sealing agent. Typical nanoparticles and microparticles, their preparation, and particle size can be understood with reference to FIG.

Fine particles (including nanoparticles) whose surfaces are organically modified according to the present invention function as particles that meet user needs. For example, it is useful as a high-concentration barium titanate-dispersed resin for semiconductor packaging, a nanoparticle-dispersed ink for inkjet, a battery material, a catalyst material, a lubricant, and the like, which can be prepared as follows.
Electronic components such as semiconductors must be packaged with a high dielectric constant resin in order to eliminate electrical disturbance from outside the package. For this purpose, a barium titanate particle-dispersed thermosetting resin is used. In high-concentration barium titanate-dispersed resins for packaging such as the present semiconductor, it has been required to disperse barium titanate particles at a high concentration. Although it is possible to disperse the titanium dioxide in the resin using a surfactant, there is a problem that dielectric loss occurs at the interface. By using the organic modified fine particle production technology of the present invention, it is possible to synthesize strongly-bonded surface-modified particles, and ultimately, by introducing the same monomer as the resin, a material in which the resin and the inorganic material are integrated is obtained. Can be synthesized.
Since nanoparticles exhibit excellent physical properties such as hue, color development, and durability, they are used in inks for high-tech equipment, for example, nanoparticle-dispersed inks for inkjet. An ink jet printer using ink in which nanoparticles are dispersed is expected to be used for manufacturing wiring, circuit diagrams, and the like by ink jet. However, for that purpose, it is necessary to synthesize nanoparticles suitable for it and disperse them in a solvent at a high concentration. The production technique of the organic modified fine particles of the present invention makes it possible to synthesize particles having the same polymer as the ink solvent.

Battery materials, for example, electrode materials such as Li-ion batteries and capacitor materials, are mixed with carbon materials to make materials for products. The battery material needs to be well dispersed with carbon and solvent. In general, a treatment using a dispersant is required, but a material that can be uniformly dispersed with a solvent can be synthesized by using the organic modified fine particle production technique of the present invention without using any dispersant.
The supported metal catalyst is activated when the electron orbit of the metal interacts with the oxide catalyst to cause charge transfer. Therefore, by using the organic modified fine particle production technology of the present invention capable of mixing different types of materials on the order of nanometers, it becomes possible to prepare a catalyst having a high density of active sites where metal and oxide come into contact with each other. Become.
In addition, the lubricant is used to reduce the friction acting between the solids, but it can be expected that the lubricant acts as a nano-bearing because the lubricant is contained in the lubricant. Specifically, the shear force is converted into the rotational kinetic energy of the bearing to prevent it from being transmitted as a shear force to the other surface. Conventionally, an organic polymer has been used as a lubricant, but the oxide nanoparticle having a strong structure can be dispersed in the organic modified fine particle production technique of the present invention.
The present invention will be described in detail with reference to the following examples, which are provided merely for the purpose of illustrating the present invention and for reference to specific embodiments thereof. These exemplifications are for explaining specific specific embodiments of the present invention, but are not intended to limit or limit the scope of the invention disclosed in the present application. In the present invention, it should be understood that various embodiments based on the idea of the present specification are possible.
All examples were performed or can be performed using standard techniques, except as otherwise described in detail, and are well known and routine to those skilled in the art. .

[Organic modification of metal oxide fine particles in high temperature and high pressure water]
The experiment was conducted using a 5cc tubular autoclave (Tube Bomb Reactor). 0.1 g of TiO ₂ nanoparticles were charged into a reaction tube together with _2.5 cc of pure water and 0.1 cc of hexanal. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. It took 1.5 min to raise the temperature. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The product was collected by repeating water washing and chloroform washing twice. The recovered product is shown on the right side of FIG. When hexanal was not used, the recovered product was suspended in water as shown on the left side of FIG. This is because a hydrophilic group is generated. In addition, it turns out that such a remarkable difference is not seen only by mixing a modifier without making it react, and it is not based on the physical adsorption of a modification group. Further, according to IR spectrum measurement of the obtained particles, surface hydroxyl groups were decreased, and Ti—OR, Ti— (C═O) —R and Ti—R bonds were observed. From the above, formation of a covalent bond by reaction was confirmed.
Thus, the surface modification of the metal oxide can be performed by using high-temperature and high-pressure water as a reaction solvent.

[Organic modification of metal oxide fine particles in high temperature and high pressure water]
In the same manner as in Example 1, an experiment was conducted using a 5 cc tubular autoclave (Tube Bomb Reactor). 0.1 g of SiO ₂ nanoparticles were charged into a reaction tube together with _2.5 cc of pure water and 0.1 cc of hexylamine. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. It took 1.5 min to raise the temperature. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The product was collected by repeating water washing and chloroform washing twice. When hexylamine was not used, the recovered product was suspended in water as in Example 1. This is because a hydrophilic group is generated. On the other hand, when the modification was performed, particles gathered at the interface between chloroform and water. Thus, it was found that when the modification was not complete and a sufficient wetting angle could not be obtained for both water and chloroform, it did not shift to the chloroform phase but gathered at the interface. Controlled organic modification in high temperature and high pressure water demonstrates the potential for metal oxide collection at the interface. In this case as well, it can be seen that such a remarkable difference is not seen only by mixing the modifying agent without reacting, and it is not due to physical adsorption of the modifying group. Further, according to IR spectrum measurement of the obtained particles, CH ₂ and CH ₃ peaks were observed on the surface (FIG. 9). From the above, formation of a covalent bond by reaction was confirmed.

[Amino acid modification of metal oxide fine particles in high temperature and high pressure water]
The reaction is carried out by an experiment using a 5 cc tubular autoclave (Tube Bomb Reactor).
A reaction tube is charged with 0.1 g of SiO ₂ nanoparticles together with _2.5 cc of pure water and 100 mg of cysteine. Preheat the reaction tube in a heating furnace set to 400 ° C. The pressure when assuming pure water is 390 bar. It takes 1.5min to raise the temperature. React for 10 min. The reaction is stopped by putting the reaction tube into cold water. The recovered particles are completely dispersed in water and are better dispersed than in a state suspended before the reaction. This indicates that SiO ₂ does not aggregate due to the addition of the hydrophilic group, and the dispersibility is improved.
Similar to Examples 1 and 2, such a remarkable difference is not observed only by mixing the modifying agent without reacting, and it is understood that it is not due to physical adsorption of the modifying group. Moreover, according to the IR spectrum measurement of the obtained particles, COOH and NH ₂ groups are decreased, and a bond of Si—NR and SiO— (CO) R is observed on the surface. From the above, formation of a covalent bond by reaction can be confirmed.

[Organic modification of metal oxide fine particles coexisting with acid in high-temperature and high-pressure water]
The reaction was carried out by an experiment using a 5 cc tubular autoclave (Tube Bomb Reactor).
0.1 g of Al ₂ O ₃ nanoparticles were charged into a reaction tube together with _2.5 cc of 0.1 M H ₂ SO ₄ aqueous solution and 0.1 cc of hexanal. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. It took 1.5 min to raise the temperature. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The product was collected by repeating water washing and chloroform washing twice. A similar experiment was conducted, and an experiment was conducted in which hexanol was used instead of chloroform.
In the case where pure water is used without adding acid, the recovered product is in a state of being precipitated at the bottom of the chloroform phase (lower phase). This was the same result as when no surface treatment experiment was performed. On the other hand, when surface modification was carried out in the presence of an acid, it was partially suspended in the chloroform phase. When recovered with hexanol, it was partially suspended in hexanol and partially collected at the interface between hexanol (upper phase) and water. This indicates that the surface treatment reaction proceeds by the coexistence of the acid. Even in a reaction system in which organic modification is unlikely to proceed, the reaction can proceed by coexisting an acid. A similar experiment was performed on ZnO, which was difficult to modify, and it was confirmed that the modification was possible in the presence of an acid as described above.

[Long-chain organic modification of metal oxide fine particles in high-temperature and high-pressure water]
The reaction was conducted using a 5 cc tubular autoclave (Tube Bomb Reactor).
0.1 g of SiO ₂ nanoparticles were charged into a reaction tube together with 1.5 cc of pure water and 1 cc of dodecanal. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. It took 1.5 min to raise the temperature. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The product was collected by repeating water washing and chloroform washing twice. A similar experiment was performed with hexanal.
When dodecanal was not used, the recovered product was suspended in water, but when modified, particles gathered at the interface between chloroform and water at 400 ° C, and the modification was achieved. It has been shown. When hexanal was used, the reaction proceeded well at 300 ° C. and 400 ° C., but a slight progress of the reaction was confirmed even at 200 ° C. However, when dodecanal was used, good surface modification was possible at 400 ° C, but the reaction did not proceed at all at 200 ° C. Even at 300 ° C., the progress of the reaction was lower than that of hexanal.
There are sufficient reports on the phase behavior of alkane-water systems, and the phase behavior of dodecane-water systems is considered to be due to the formation of a heterogeneous phase at low temperatures.

[Organic modification of metal oxide fine particles in high temperature and high pressure water]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). TiO ₂ nanoparticles 0.1g was charged into a reaction tube together with 2.5cc pure water and 0.1cc hexanoic acid. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The product was collected by repeating water washing and chloroform washing twice. The recovered product is shown in FIG.
When hexanoic acid was not used and surface modification was not performed, the recovered product was suspended in water (upper phase) as shown in the left of FIG. However, when the surface was modified with hexanoic acid, the nanoparticles moved to the chloroform phase (lower phase). When surface modification is not performed, hydrophilic groups (OH groups) are generated on the surface of TiO ₂ nanoparticles, whereas surface modification with hexanoic acid results in the introduction of hydrophobic groups on the particle surface. It suggests that. In addition, such a remarkable difference is not seen only by mixing a modifier without making it react, and it turns out that the result obtained here is not based on the physical adsorption of a modification group. Further, according to IR spectrum measurement of the obtained particles, as shown in FIG. 11, peaks of CH ₃ and CH ₂ bonds were observed. From the above, formation of a covalent bond by reaction was confirmed.
Thus, the surface modification of the metal oxide can be performed by using high-temperature and high-pressure water as a reaction solvent. Similar results have been obtained with hexanamide.

[Organic modification of metal oxide fine particles with amino acids in high temperature and high pressure water]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). TiO ₂ nanoparticles 0.1g was charged into a reaction tube together with 2.5cc pure water and 100mg aspartic acid. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The recovered particles were completely dispersed in water and were more well dispersed (right side in FIG. 12) than in a state suspended in water before the reaction (left side in FIG. 12). This indicates that TiO ₂ does not aggregate due to the addition of the hydrophilic group, and the dispersibility is improved.
Similar to Examples 2 and 6, such a remarkable difference is not observed only by mixing the modifying agent without reacting, and it is understood that it is not due to physical adsorption of the modifying group. Further, according to IR spectrum measurement of the obtained particles, COOH and NH ₂ groups were decreased, and Ti—NR, TiO— (CO) R and Ti—R bonds were observed on the surface. From the above, formation of a covalent bond by reaction was confirmed.

[Organic modification of long-chain hydrocarbons in metal oxide fine particles in high-temperature and high-pressure water]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). 0.1 g of SiO ₂ nanoparticles were charged into a reaction tube together with 1.5 cc of pure water and 1 cc of decanoic acid. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. Reacted for 10 min. The reaction was stopped by putting the reaction tube into cold water. The product was collected by repeating water washing and hexadecane washing twice. The recovered product is shown on the right side of FIG. When decanoic acid was not used, the recovered product was suspended in water, but when modified, it was dispersed in hexadecane as shown on the right side of FIG. It has been shown.
Similar experiments were performed for decanal and decanamine, and similar results were obtained. The state of organically modified nanoparticles with decanamine is shown on the left side of FIG. These indicate that surface modification with a long-chain organic substance that hardly dissolves in water near room temperature is possible.

[In-situ organic modification in high-temperature and high-pressure hydrothermal synthesis (1)]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). Hydrogen peroxide was added to a 0.01 mol / l Mn (NO ₃ ) ₂ aqueous solution to a concentration of 0.05 mol / l, and 2.5 g was charged into the reaction tube, and 0.1 cc of hexanol was further charged. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. The reaction was performed for 10 min and the product was recovered. The recovered product is shown in FIG. When hexanol was not used, the recovered product was suspended in water as shown in FIG. 14 a), because a hydrophilic group was generated. On the other hand, when it was modified, it was completely separated from the aqueous phase as shown in Fig. 14 b).
In general, it is technically difficult to recover nanoparticles generated in an aqueous solution from an aqueous phase, but separation and recovery from an aqueous solution can be easily performed by this method. Moreover, although the hexanol modification to the metal oxide produced | generated previously is not easy, it has shown that the organic modification to the oxide nanoparticle surface is possible by in-situ surface modification.

[In-situ organic modification in high-temperature and high-pressure hydrothermal synthesis (2)]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). Hydrogen peroxide was added to a 0.01 mol / l Zn (NO ₃ ) ₂ aqueous solution so that the concentration was 0.05 mol / l, and 2.5 g was added to the reaction tube, and 0.1 cc of hexanol was further charged. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. The reaction was performed for 10 min and the product was recovered. When hexanol is not used, the recovered product is in a state suspended in water because a hydrophilic group is generated. On the other hand, when it was modified, it was completely separated from the aqueous phase. In addition to Zn (NO ₃ ) ₂ , Zn (COOH) ₂ was also used in the same manner.
In any case, as shown in Example 4, it was difficult to modify ZnO unless an acid was allowed to coexist. However, this method shows that surface modification in-situ is possible. In particular, in the case of formate, the acid produced is HCOOH, but it is known that it decomposes into H ₂ + CO ₂ at high temperature, and does not function as an acid. Nevertheless, the reason why a good surface modification could be achieved is thought to be because the dehydration reaction between the hydroxyl group OH at the initial stage of crystal formation and the organic modifier progressed well.
A TEM photograph of the particles obtained by this method is shown in FIG. In FIG. 15, it was observed that the surface modification (lower side) was uniform fine particles compared to the case where the surface modification was not performed (upper side). It can be seen that by performing the surface modification, particle growth is suppressed and fine particles are obtained.

[In-situ organic modification in high-temperature and high-pressure hydrothermal synthesis (3)]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). Hydrogen peroxide was added to a 0.01 mol / l Mn (NO ₃ ) ₂ aqueous solution to a concentration of 0.1 mol / l, and 2.5 g was charged into the reaction tube, and 0.1 cc of hexanol was further charged. The reaction tube was put in a heating furnace set to 400 ° C. in advance and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. The reaction was performed for 10 min and the product was recovered. The recovered product is shown in Fig. 16 b). When hexanol was not used, the recovered product was suspended in water as shown in FIG. 16 a), because a hydrophilic group was generated. On the other hand, when it was modified, it was completely separated from the aqueous phase.

[In-situ organic modification in high-temperature and high-pressure hydrothermal synthesis (4)]
The experiment was conducted by using a 5cc tube type autoclave (Tube Bomb Reactor). Hydrogen peroxide was added to a 0.01 mol / l Ce (NO ₃ ) ₂ aqueous solution to a concentration of 0.1 mol / l, and 2.5 g was added to the reaction tube, and further 0.1 cc of hexanoic acid was charged. The reaction tube was put in a heating furnace set in advance at 200, 300 and 400 ° C. and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. The reaction was performed for 10 min and the product was recovered. The recovered product is shown in FIG. When hexanoic acid was not used, the recovered product was suspended in water as shown in FIG. 17 a), because a hydrophilic group was generated. The treatment did not proceed at 200 ° C (Fig. 17 b)), but it was completely separated from the aqueous phase at 300 and 400 ° C as shown in Fig. 17 c) and d).
When modifying with hexanoic acid that is insoluble in water, the process does not proceed at a low temperature of 200 ° C because it does not form a uniform layer with water, but the process proceeds at 300 ° C or 400 ° C. It is possible to form a homogeneous phase with the modifier. It also shows that there are cases where it is essential to perform the treatment in a high temperature range where the reaction can proceed sufficiently.

[In-situ organic modification in high-temperature, high-pressure hydrothermal synthesis (5)]
By a procedure analogous to Example 9-12 was conducted _{Fe 2 O 3, NiO, ZnO} , for Co ₂ O _3, hexanol, hexanoic acid, hexyl amine, hexanal, and the reaction under hexanethiol coexist. The obtained results are collectively shown in Tables 1 to 4.

Each notation in the above table means the following: None: No modifier, W: Aqueous phase, Int .: Interfacial phase between aqueous and organic phase, O: Organic phase, a little: A little present, little : Just a little, w: from interface to aqueous phase with slight vibration, o: from interface to oil phase with slight vibration, more: more, thick layer: thin layer, thin layer, white: white, black: black, red: red, green: green, yellow: yellow, brown: brown, gray: gray, NP: nanoparticles, L: thickness of interface phase, subscript indicates processing temperature, S: in organic phase The solubility of NP is shown, and the subscript indicates the treatment temperature.
Table 5 shows the results of comparison as a whole.

Similarly, ZnO was surface-modified. The effect of surface modification is sufficiently obtained. However, in the case of hexanol, it could not be said that sufficient surface modification was obtained in any case.
Therefore, in-situ organic modification was performed. The experimental method was the same as in Examples 8 and 9. That is, the experiment was conducted by performing the reaction using a 5 cc tubular autoclave (Tube Bomb Reactor). Hydrogen peroxide was added to a 0.01 mol / l Zn (NO ₃ ) ₂ aqueous solution to a concentration of 0.1 mol / l, and 2.5 g was charged into the reaction tube, and 0.1 cc of hexanol was further charged. The reaction tube was put in a heating furnace set in advance at 200, 300 and 400 ° C. and heated. The pressure when assuming pure water is 390 bar. The heating required 1.5 min. The reaction was performed for 10 min and the product was recovered. When hexanol was not used, the recovered product was in a state of being suspended in water and an oil phase, but the particles were transferred to the oil phase due to surface modification using hexanol. A sufficient surface modification effect is obtained.
Thus, it has been shown that sufficient surface modification can be performed by surface modification in situ even when the surface modification cannot be sufficiently performed on the particles once generated.
Tables 6 and 7 collectively show the results obtained by similarly subjecting ZnO, CeO ₂ , Al ₂ O ₃ , SnO ₂ , and SiO ₂ nanoparticles to surface modification treatment. Table 6 shows a comparison of the results of surface modification of each metal oxide fine particle, and Table 7 shows the results of in situ modification. In the table, ◯ indicates that particles have been transferred to the organic phase, and x indicates clearly that particles have not been transferred to the organic phase. Δ indicates that the organic modification has progressed, though insufficient.

As can be seen from comparison between Tables 1 to 7, similar in situ surface modification effects are also obtained in ZnO, CeO ₂ , TiO _{2 and the} like.

[In-situ organic modification in high-temperature and high-pressure hydrothermal synthesis (6)]
In the same manner as in Examples 8 and 9, Fe ₂ O ₃ , Co ₂ O ₃ , NiO, ZnO, and TiO _{2 were} synthesized in the presence of hexanol, hexanoic acid, hexylamine, hexanal, and hexanethiol. The results obtained are summarized in Table 7. Based on the case where no surface modifier was used, the magnitude of the effect of surface modification was represented by an index of 1 to 10.

From the above table, it was found that the degree of progress of the surface modification reaction differs depending not only on the temperature but also on the reactants. Even when surface modification is not performed, there are cases where ZnO and NiO are dispersed in water and have sufficient hydrophilic groups, and TiO ₂ is dispersed in the oil phase and there are few hydrophilic groups. Therefore, even when surface modification is performed in situ in the field of particle generation, the stability and reactivity of functional groups on the particle surface are different. In the case of aldehyde modification or amine modification, a surface modification better at 300 ° C than at 400 ° C may be obtained. These results are because a hydrolysis reaction occurs in a high temperature field. That is, the optimum condition includes 300 ° C. to 400 ° C. If the temperature is too high, it is considered that the influence of the reverse reaction appears.

  The present invention relates to organic modified fine particles (particularly nanoparticles) in which hydrocarbons are strongly bonded to the surface of the fine particles, in particular organic modified metal oxide fine particles, a method for producing the same, and recovery or collection of fine particles such as nanoparticles. A variety of unique, superior properties, characteristics and functions of nanoparticles, ceramic nanostructure modifiers, optical functional coating materials, electromagnetic wave shielding materials, secondary battery materials, fluorescent materials, electronic Promote use as industrial and industrial materials such as component materials, magnetic recording materials, and abrasive materials, and pharmaceutical and cosmetic materials. It will be apparent that the invention may be practiced otherwise than as particularly described in the foregoing description and examples. Many modifications and variations of the present invention are possible in light of the above teachings, and thus are within the scope of the claims appended hereto.

The diagram on the left shows the relationship between pressure and temperature and the density of water, and the diagram on the right shows the relationship between the dielectric constant of water, pressure and temperature. The phase behavior (left side) of the water-gas binary system near the critical point of water and the phase behavior (right side) of the water-organic solvent system are shown. 1 shows a typical reactor utilized for organic modification. Typical nanoparticles that are sought to be utilized are shown along with their typical manufacturing methods and particle sizes. The structure of the typical reaction system apparatus utilized for the organic modification of this invention is shown. The characteristics of the organic modification method of the present invention are schematically shown. The mechanism of the modification reaction of the present invention is schematically shown. A case where metal oxide fine particles (TiO ₂ nanoparticles) are surface-modified with hexanal by the method of the present invention (right side) and unmodified particles (left side) are shown in comparison. The IR spectrum of the modified particle when the metal oxide fine particle (SiO ₂ nanoparticle) is surface-modified with hexylamine by the method of the present invention is shown. A case where metal oxide fine particles (TiO ₂ nanoparticles) are surface-modified with hexanoic acid by the method of the present invention (right side) and unmodified particles (left side) are shown in comparison. The IR spectrum of the modified particles when metal oxide fine particles (TiO ₂ nanoparticles) are surface-modified with hexanoic acid by the method of the present invention is shown. A case where metal oxide fine particles (TiO ₂ nanoparticles) are surface-modified with aspartic acid by the method of the present invention (right side) and unmodified particles (left side) are shown in comparison. A case where metal oxide fine particles (SiO ₂ nanoparticles) are surface-modified with decanoic acid (right side) and a case where the surface is modified with decanamine (left side) by the method of the present invention is shown in comparison. A case where metal oxide fine particles are hydrothermally synthesized by the method of the present invention and the surface thereof is in-situ organically modified in the presence of hexanol (right side) and unmodified particles (left side) are shown in comparison. The TEM photograph of the metal oxide fine particles (lower side) organically modified by the method of the present invention is shown in comparison with unmodified particles (upper side). A case where metal oxide fine particles are hydrothermally synthesized by the method of the present invention and the surface thereof is in-situ organically modified in the presence of hexanol (right side) and unmodified particles (left side) are shown in comparison. The result of in-situ organic modification of metal oxide fine particles (CeO ₂ nanoparticles) by changing the treatment temperature by the method of the present invention is shown. The relationship between the typical device configuration and the size of the particles obtained under each condition when hydrothermal synthesis is performed using subcritical or supercritical high-temperature and high-pressure water as a reaction field is shown. It shows that the metal oxide fine particles organically modified by the method of the present invention exhibit properties such as a characteristic dispersibility with respect to a medium by adjusting the affinity with a solvent.

Claims (15)

In the method of collecting or collecting metal oxide nanoparticles,
Using high-temperature and high-pressure water as a reaction field, the surface of the metal oxide nanoparticles reacts with the organic modifier, and the hydrocarbon group which may be substituted or unsubstituted may be covalently bonded, ether bond, ester Via a bond selected from the group consisting of a bond, a bond through an N atom, a bond through an S atom, a metal-C- bond, a metal-C = bond and a metal- (C = O)-bond. The surface of the nanoparticle is organically modified by binding to the surface of the nanoparticle ,
(1) precipitating and collecting metal oxide nanoparticles dispersed in an aqueous solution;
(2) The metal oxide nanoparticles dispersed in an aqueous solution are transferred to an organic solvent and recovered, or
(3) collecting metal oxide nanoparticles at the organic solvent phase-water phase interface;
A method for recovering or collecting metal oxide nanoparticles. The metal oxide nanoparticles are formed by subjecting a metal compound to a hydrothermal reaction using high-temperature and high-pressure water as a reaction field, and reacting the surface of the formed metal oxide nanoparticles with an organic modifier, The recovery or collection method according to claim 1, wherein a hydrocarbon group which may be substituted or unsubstituted is bonded to the surface of the nanoparticle through a covalent bond. The recovery or collection method according to claim 1 or 2, wherein the high-temperature and high-pressure water is water under supercritical or subcritical conditions. The recovery or collection method according to any one of claims 1 to 3, wherein the high-temperature and high-pressure water is water having a pressure at or above the critical point and / or a temperature condition at or above the critical point. The organically modified metal oxide nanoparticles are synthesized in a reaction field where water exists under a temperature condition of 250 to 500 ° C and a pressure condition of 10 to 30 MPa. Collection or collection method. In the organic modification of the nanoparticle surface, metal oxide nanoparticles may be produced in the reaction field in the supercritical hydrothermal synthesis method in the presence of an organic modifier, which may be substituted or unsubstituted. 6. A method for recovering or collecting organically modified metal oxide nanoparticles in which a hydrocarbon group which may be bonded is bonded to the surface of the nanoparticles via a covalent bond. . The recovery or collection method according to claim 6, wherein the particle size of the produced particles is adjusted to a smaller particle size than in the case of supercritical hydrothermal synthesis in the absence of an organic modifier. The recovery or collection method according to any one of claims 1 to 7, wherein the hydrocarbon group is a long-chain hydrocarbon having a chain having 1, 2, 3 or more carbon atoms. The organic modifier is selected from the group consisting of alcohol, aldehyde, carboxylic acid, amine, thiol, amide, ketone, oxime, phosgene, enamine, amino acid, peptide, and sugar. 9. The collection or collection method according to any one of 8. The recovery or collection method according to any one of claims 1 to 9, wherein a solvent that promotes uniform phase formation of the organic modifier and water is used as a coexisting substance. The method according to claim 10, wherein the solvent is selected from the group consisting of methanol, ethanol, propanol, i-propanol, butanol, i-butanol, t-butanol and ethylene glycol. The recovery or collection method according to any one of claims 1 to 11, wherein the reaction is carried out in the presence of an acid. 13. The recovery or collection method according to claim 12, wherein the acid is selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, bromic acid, formic acid, acetic acid, propionic acid, and toluenesulfonic acid. The recovery or collection method according to any one of claims 1 to 13, wherein the reaction rate of the organic modifier is controlled by controlling a factor selected from the group consisting of temperature, acid concentration and reaction time. The average diameter of the nanoparticles is
(1) 100 nm or less,
(2) 50 nm or less,
(3) 20 nm or less,
(4) 10 nm or less, or
(5) The recovery or collection method according to any one of claims 1 to 14, which is 5 nm or less.

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