JP2007111855A - Core / shell structure having nanoparticle composite as core, structure using it as a constituent element, and method for preparing them and structure prepared therefrom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a conventional nanoparticle-meso porous composite has a difficulty in the control of a nanoparticle size to be produced, an extreme difficulty in void space control between meso porous and nanoparticle, and furthermore an extreme difficiulty in producing many nanoparticle having different compositions in the interior of mesomeso porous by controlling these sizes. <P>SOLUTION: The core-shell structure 1 employing a nanoparticle composite as a core comprises the core 6 composed of the nanoparticle composite made by directly joining the first nanoparticle 2 and the second nanoparticle 3 which differs from the first nanoparticle and a shell 7 having a diameter of several nanometers to ten several nanometer which covers the core 6 via void space. The first nanoparticle 2 is formed of a metal having a light of absorption edge that is photo-dissolved, metal oxide, a semiconductor, or a high polymer. The second nanoparticle 3 is formed of a metal which is precipitated from solution for solid deposit, metal oxide, the semiconductor, or the high polymer, and is joined the first nanoparticle 2. The void space controls the particle diameter of the first nanoparticle 2, so as to control a desired size. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nanoparticle composite used as a catalyst, an electronic device material, etc., a core / shell structure using the composite, a structure using the same as a constituent element, and a method for preparing the structure prepared from them About.

  Porous materials are widely used for catalysts, adsorbents, surfactants and the like. A porous material is a substance having pores of a fixed shape, a porous material having a pore diameter of 2 nm or less is called a microporous body, and a porous material having a pore diameter of 2 to 50 nm is a mesoporous material. It is called a porous body. As the microporous material, for example, zeolite is well known. Zeolite has crystal pores in which metal atoms such as Si or Al are bonded via oxygen, and has pores with a fixed shape. For example, contact for cracking heavy oil into gasoline using these pores. It is used as a decomposition catalyst and as a molecular sieve adsorbent that allows only linear alkanes to pass through without passing through branched alkanes.

Furthermore, in recent years, porous bodies having larger voids, that is, mesoporous bodies, have been proposed to improve the catalytic function and realize new functions, and active research is being conducted on the preparation of mesoporous bodies made of metal oxides such as silica. Has been. So far, mesoporous materials represented by mesoporous silica have been used to form metal oxide thin films around them, using surfactant micelles and self-organized organic molecular assemblies such as inorganic or organic nanoparticles as templates. Later, it is prepared by removing the template. The pore structure of the mesoporous material can be controlled by controlling the size of the material used as the template and the arrangement structure thereof. The mesoporous material in which the pores are randomly dispersed and the pores are regularly arranged Many mesoporous materials have been realized, such as a mesoporous material having a three-dimensional regular arrangement of spherical pores.
A mesoporous material is a new type of crystal that has not been observed so far, although it does not have regularity at the atomic level, and mesoscale voids are regularly arranged. It is expected to be used as an industrial material such as a material having a function of adsorbing and separating), a catalyst, and a surfactant. In addition, it is highly expected to be used in various fields, such as introducing a collection of various atoms and molecules into voids to enable use as a new electronic device material.

  As a method for generating particles in the internal nanospace of the mesoporous material, a method of generating a metal or semiconductor in the pores by introducing a compound as a raw material into the mesoporous material and reacting it has been generally used so far. It is done. However, in the nanoparticle-mesoporous composite produced by this method, the internal metal or semiconductor nanoparticle size is determined by the pore size inside the porous body (see, for example, Non-Patent Documents 1 and 2).

  On the other hand, nano particles are taken into the core part of the core / shell structure in advance, and only the core part is selectively removed by chemical dissolution or baking, thereby producing hollow particles incorporating the nanoparticles inside the shell. Has been reported (for example, see Non-Patent Documents 3 to 7).

  Recently, the present inventors have realized a core-shell structure having a controlled void inside (see, for example, Non-Patent Document 8). The core-shell structure having a controlled void in the inside controls the void inside the core by accurately etching in nano order by photoetching of CdS inside the core.

A. Fukuoka and 8 others "Novel Templating Synthesis of Necklace- Shaped Mono- and Bimetallic manowires in Hybrid Organic-Inorganic Mesoporus Material", J. AM. CHEM. Soc., 2001, Vol. 123, No. 14, pp. 3373 -3374 S. Besson and 4 others "3D Quantum Dot Lattice Inside Mesoporous Silica Films", Nano Lett., 2002, Vol.2, No.4, pp.409-414 Y. Yin and 3 others "Synthesis and Characterization of Mesoscopic Hollow Spheres of Ceramic Materials with Functionalized Interior Surfaces", Chem. Matter., 2001, Vol.13, No.4, pp.1146-1148 K. Kamata and two others "Synthesis and Characterization of Monodispersed Core-Shell Spherical Colloids with Movable Cores", J. AM. CHEM. Soc., 2003, Vol.125, No.9, pp.2384-2385 P. Mulvaney and 3 others "Silica encapsulation of quantum dots and metal clusters", J. Mater. Chem., 2000, Vol.10, pp.1259-1270 Y. Sun and two others "Template-Enlarged Replacement Reaction: A One-Step Approach to the Large-Scale Synthesis of Metal Nanostructures with Hollow Interiors", Nano Lett., 2002, Vol.2, No.5, pp.481- 485 M. Kim and 3 others "Synthesis of Nanorattles Composed of Gold Nanoparticles with Encapsulated in Mesoporous Carbon and Polymer Shells", Nano Lett., 2002, Vol.2, No.12, pp.1383-1387 T. Torimoto and 7 others "Preparation of Novel Silica-Cadmium Sulfide Composite Nanoparticles Having Adjustable Void Space by Size-Selective Photoetching", J. AM. CHEM. Soc., Vol.125, No.2, 2003, pp.316- 317

  In the conventional nanoparticle-mesoporous composite, there is a problem that it is difficult to control the size of the generated nanoparticle, and it is also extremely difficult to control the gap between the mesoporous material and the nanoparticle. In addition, there is a problem that it is extremely difficult to generate a plurality of nanoparticles having different compositions within the meso-meso porous body by controlling their sizes.

  In addition, in the conventional core / shell structure, it is possible to create voids inside the hollow particles, but once the structure is completed, the size of the incorporated nanoparticles and the space between the shell and the particles of the hollow particles are reduced. There is a problem that it is difficult to control the size of the gap.

  Thus, the conventional core-shell structure is a structure including one nanoparticle inside the shell, and a structure including a plurality of nanoparticles having different properties inside the core is not known.

  In view of the above problems, the present invention is prepared from a core / shell structure having a core of a nanoparticle composite in which a plurality of nanoparticles having different properties are directly bonded, and a structure having the core / shell structure as a core, and from these. It is an object to provide a method for preparing a structure.

The core-shell structure having the nanoparticle composite of the present invention as a core is a core composed of a nanoparticle composite in which a first nanoparticle and a second nanoparticle different from the first nanoparticle are directly bonded. And a shell having a diameter of several nanometers to several tens of nanometers covering the core via a gap, and the first nanoparticle is photodissolved and has a light absorption edge, a metal, a metal oxide, and a semiconductor Alternatively, the second nanoparticle is made of a polymer solid and is made of a metal, metal oxide, semiconductor, or polymer solid deposited from the solid precipitation solution and bonded to the first nanoparticle. The voids are controlled to a desired size by controlling the particle size of the first nanoparticles.
The shell is preferably made of a material that is not photodissolved. Preferably, the first nanoparticle is a metal chalcogenide semiconductor fine particle, the second nanoparticle is a metal, and the shell is a film having a silicon-oxygen bond as a skeleton. The metal chalcogenide semiconductor fine particles are preferably CdS (cadmium sulfide), and the film having a silicon-oxygen bond as a skeleton is SiO _x (silicon oxide, 0 <x).
The core / shell structure having the nanoparticle composite as a core is composed of two or more nanoparticles having different properties, for example, a nanoparticle composite having a semiconductor-metal junction can be realized as a core. It is promising as a catalyst material for conducting a catalytic reaction.

  Further, a structure having a core / shell structure having the nanoparticle composite of the present invention as a core as a constituent element is a core / shell structure having the nanoparticle composite as a core as a constituent element. . Since this structure has a core / shell structure with a nanoparticle composite as a core, in addition to the effects of the core / shell structure, a wider range of optical sensors, Catalytic reactions, material synthesis, and adsorption of specific substances are possible.

In addition, a method for preparing a core-shell structure using the nanoparticle composite of the present invention as a core is a first method comprising a metal, a metal oxide, a semiconductor, or a polymer solid having a light absorption edge while being photodissolved. A nanoparticle is formed with a controlled particle size, and the surface of the first nanoparticle is chemically modified with a chemical substance having an element bonded to the surface of the first nanoparticle and a group containing a component element of an oxide that does not dissolve in light. Then, a group is introduced into the surface, the group is hydrolyzed to form a film made of the above oxide, and a core-shell structure having the first nanoparticle as a core and the film as a shell is formed, A controlled void is formed inside the core-shell structure by etching the core-shell structure by controlling the wavelength in the photodissolving solution and irradiating light to control the particle size of the first nanoparticles. And solid precipitation containing the constituent elements of the second nanoparticle First nanoparticles having a controlled particle size are deposited by depositing second nanoparticles made of metal, metal oxide, semiconductor or polymer in the shell of the core-shell structure having a controlled void in the solution. By directly joining the nanoparticles, a core composed of a nanoparticle composite in which the first nanoparticles and the second nanoparticles that are photo-dissolved are joined directly, and a few nanometers to several tens of nanometers covering the core via a gap. A core-shell structure having a shell with a nanometer diameter and a void controlled to a desired size by controlling the particle size of the first nanoparticles is obtained.
According to this method, the size of each nanoparticle forming the core can be accurately adjusted in the core-shell structure having the nanoparticle composite as a core.

In the above-described configuration, the second solid nanoparticles are deposited by light irradiation in the shell of the core-shell structure having voids controlled inside by the solid precipitation solution. This solid deposition solution is a metal deposition solution, which deposits metal or metal oxide. The metal deposition solution is a mixed solution containing a metal element constituting the second solid nanoparticles and containing an electron or hole scavenger.
According to this method, a nanoparticle composite in which a second solid nanoparticle is irradiated with light in a shell of a core / shell structure having a controlled void inside and deposited while controlling its size with high precision. A core-shell structure having a core as a core can be prepared.

  Moreover, it is preferable to form it soluble in water or soluble in an organic solvent by adding a chemical substance having a hydrophilic group or a hydrophobic group and further chemically modifying it after hydrolysis. According to this method, a core-shell structure having a nanoparticle composite as a core, which is soluble in water or in an organic solvent, can be prepared.

In the above configuration, preferably, the first nanoparticle made of a light-dissolving solid is CdS (cadmium sulfide), the element bonded to the particle surface is an S (sulfur) element, and the component element of the oxide that is not light-dissolving is Si (silicon). , The group is Si (CH ₃ O) ₃ Si (trimethoxysilyl) group, the chemical is (CH ₃ O) ₃ Si (CH ₂ ) ₃ SH (3-mercaptopropyltrimethoxysilane), hydrolyzed The film to be formed is made of SiO _x (silicon oxide, 0 <x), and the second solid nanoparticles are made of metal, metal oxide, semiconductor, or polymer. According to this method, a core made of CdS nanoparticles having a controlled particle size, a shell made of a SiO _x film covering the core via the controlled voids, and metal or metal oxide nanoparticles deposited in the voids The core / shell structure to be formed can be prepared. The shell is thin enough to allow permeation of solutes and solvents.

Preferably, in the above configuration, the first nanoparticle made of a light-dissolving solid contains CdS, the element bonded to the particle surface contains an S element, the constituent element of an oxide that does not dissolve light contains Si, and the group contains Si ( CH ₃ O) ₃ Si group, the chemical substance is (CH ₃ O) ₃ Si (CH ₂ ) ₃ SH, and the chemical substance having a hydrophilic group is a carboxyl group, quaternary ammonium group, amino group, sulfonic acid group, hydroxyl group The alkyl silane having a group or the like, the chemical substance having a hydrophobic group is n-octadecyltrimethoxysilane, and the second solid nanoparticle is made of a metal, a metal oxide, a semiconductor, or a polymer. According to this method, a core of a nanoparticle composite composed of a CdS nanoparticle having a controlled particle size and a second solid nanoparticle having a controlled particle size made of a metal, a metal oxide, a semiconductor, or a polymer, A shell made of a SiO _x film covering the core is formed. A desired functional group is formed on the shell and can be dissolved in a desired solvent.

  It is preferable that the first nanoparticles have a desired particle size by photodissolving with light having an absorption edge wavelength corresponding to the desired particle size. As the void for the second nanoparticle precipitation, a void formed in advance in the core / shell structure by light irradiation with controlled wavelength is used. According to this method, the light-dissolving nanoparticles that are the core in the core-shell structure absorb light and are light-dissolved, thereby reducing the particle size. When the particle size of the light-dissolving nanoparticle becomes smaller, the absorption edge wavelength of the nanoparticle core that dissolves from the wavelength of the irradiation light shifts to the shorter wavelength side due to the quantum size effect, and the absorption edge wavelength of the nanoparticle core that dissolves from the wavelength of the irradiated light. When becomes short, the core is not photodissolved. In this way, by selecting the wavelength of the irradiation light, the size of the nanoparticles to be photodissolved can be set to a desired size. As a result, the voids for the second nanoparticle deposition can also be set to a desired size. Thereby, since the void size can be controlled to a desired size, a core-shell structure having a nanoparticle composite in which the size of each nanoparticle is freely controlled as a core can be accurately prepared.

Furthermore, a method for preparing a structure having a core / shell structure having the nanoparticle composite of the present invention as a core as a constituent element is a core having a plurality of nanoparticle composites prepared by any of the above methods as a core. -It can be formed by dispersing the shell structure in a solvent and evaporating the solvent gradually to self-assemble.
A two-dimensional structure comprising a core / shell structure having a core of a plurality of nanoparticle composites prepared by any one of the above methods and being developed at the gas-liquid interface. The membrane may be compressed and organized. In addition, a core-shell structure having a plurality of nanoparticle composites prepared by any of the above methods as a core can be arranged using DNA as a template. According to said method, the structure which uses the core-shell structure which made the nanoparticle composite core the component can be prepared.

  Moreover, the method for preparing the nanoparticle composite of the present invention includes the step of removing the shell of the core-shell structure using the nanoparticle composite prepared by any one of the above methods as a core, A nanoparticle composite composed of second nanoparticles is obtained. According to this method, a core / shell structure using a nanoparticle composite as a core, and a core / shell structure using a nanoparticle composite as a core obtained by a method for preparing a structure including the core / shell structure, etc. In addition, the nanoparticle composite can be prepared with high accuracy.

ADVANTAGE OF THE INVENTION According to this invention, the core-shell structure which used the nanoparticle composite_body | complex as a core, and the structure which uses it as a component can be provided. In addition, it is possible to provide a core / shell structure having a nanoparticle composite as a core and a method for preparing a structure having the core / shell structure as a constituent element. Furthermore, by using a core / shell structure having a nanoparticle composite as a core and a method for preparing a structure having the core / shell structure as a constituent element, a nanoparticle composite and a core / shell structure having a nanoparticle as a core are obtained. A preparation method that can be accurately prepared can be provided.
Therefore, according to the present invention, it is easy to prepare nanomaterials necessary for nanodevices such as optical sensors based on novel nanoparticle composites that could not be prepared by the prior art, and catalysts that are extremely efficient compared to conventional catalysts. Can be done.

Hereinafter, the configuration of the core-shell structure having the nanoparticle composite according to the first embodiment of the present invention as a core will be described with reference to the drawings.
The core / shell structure having the nanoparticle composite of the present invention as a core is composed of a nanoparticle composite formed by directly joining a plurality of nanoparticles having different properties, and a shell covering the core.
FIG. 1 is a schematic cross-sectional view showing a configuration of a core-shell structure having a nanoparticle composite according to a first embodiment of the present invention as a core. FIG. 1 shows a core / shell structure having a nanoparticle composite composed of two different types of nanoparticle as a core. As shown in the figure, the core-shell structure 1 having the nanoparticle composite of the present invention as a core includes a core 6 and a shell 7 covering the core 6, and the core 6 includes the first nanoparticles. 2 and a second nanoparticle 3 different from the first nanoparticle 2 is a nanoparticle composite.

The first nanoparticle 2 may be any solid as long as it has a light absorption edge, but may be a metal chalcogenide semiconductor, for example, CdS (cadmium sulfide). The core diameter is controlled to a desired value of about several tens of nanometers to about 1 nanometer.
The second non-light-dissolving nanoparticles 3 may be anything as long as they are solids having a composition different from that of the first nanoparticles. For example, metals, metal oxides, semiconductors, polymers, and the like are preferable. The core diameter is controlled to a desired value of about several tens of nanometers to about 1 nanometer. Although not shown, the shell 7 has a large number of micropores (holes having a diameter of several angstroms). Here, the shell 7 may be anything as long as it does not dissolve in light, and may be, for example, SiO _x (silica, 0 <x). The diameter of the shell 7 is controlled to a desired value of about several tens of nanometers to several nanometers depending on the application.

The core-shell structure 1 having the nanoparticle composite of the present invention as a core can be used, for example, for the following applications. When the first nanoparticle 2 of the nanoparticle composite 6 is, for example, a semiconductor that is photodissolved, and the second nanoparticle 3 is a metal, the junction 4 is a semiconductor-metal junction (Schottky junction or shot). This is also called a key barrier), and a diode structure is obtained. The diode structure can also be used as a functional element such as an optical sensor.
In addition, when the first nanoparticle 2 of the nanoparticle composite 6 is a semiconductor and the second nanoparticle 3 is a semiconductor having a forbidden band width different from that of the first semiconductor, the junction 4 is a heterojunction. Since it can be a diode structure, it can be similarly used as a functional element such as an optical sensor.
In addition, the nanoparticle composite 6 has a relatively large specific surface area, and photochemical characteristics such as light absorption and luminescence change greatly depending on the adsorbed chemical species on the surface. It can also be used as a chemical sensor.
Further, when the nanoparticle 3 that is not photo-dissolved in the core-shell structure 1 having the nanoparticle composite 6 as a core is formed as the catalyst metal fine particle having the highest catalytic activity, the micropores existing in the shell 7 are interposed. Thus, a specific substance having a specific structure can be selectively adsorbed and used as a catalyst for treating a polluted gas.

Next, a structure including the core-shell structure 1 having the nanoparticle composite according to the second embodiment of the present invention as a core will be described.
FIG. 2 is a schematic cross-sectional view showing a configuration of a structure 10 having a core-shell structure 1 having a nanoparticle composite as a core according to the second embodiment of the present invention as a constituent element. As shown in FIG. 2, FIG. 2 shows a structure 10 in which a large number of core / shell structures 1 having the nanoparticle composite shown in FIG. This structure 10 is a structure in which the core-shell structure 1 having the nanoparticle composite shown in FIG. 1 as a core is regularly arranged. In the figure, the densely stacked structure is shown, but the present invention is not limited to this, and various shapes of structures are possible.
According to the structure 10, for example, in a specific photocatalytic reaction including a complicated reaction process, a reaction substrate selectively adsorbed on the core-shell structure 1 having a nanoparticle composite as a core is Since it is regularly arranged based on the shape, a reaction field optimal for the photocatalytic reaction can be constructed.

Next, a preparation method according to the third embodiment of the core-shell structure 1 using the nanoparticle composite as a core will be described. Note that FIG. 4 and FIG. 5 are referred to during the description.
FIG. 3 is a diagram showing a process of a method for preparing a core-shell structure 1 having a nanoparticle composite as a core according to the third embodiment of the present invention. First, as shown in FIG. 3A, photodissolved fine particles 2 having a desired particle diameter are prepared. The fine particles 2 may be generated by, for example, a liquid phase precipitation method or a CVD (chemical vapor deposition) method, or may be generated by other means. Next, as shown in FIG. 3B, the surface of the fine particles 2 is covered with a shell 7 made of a substance that does not dissolve light.

For example, when the fine particles 2 are a metal chalcogenide semiconductor, the following method is possible. A case of cadmium sulfide (CdS) will be described as an example.
FIG. 4 is a view schematically showing a process of coating a core made of CdS fine particles with a shell made of SiO _x . As shown in FIG. 4A, the surface of the CdS fine particles 2 is chemically modified using 3-mercaptopropyltrimethoxysilane ((CH ₃ O) ₃ Si (CH ₂ ) ₃ SH), which is one of thiol compounds. Thus, a trimethoxysilyl group (Si (OMe) ₃ ) is introduced into the surface of the CdS fine particles 2 (Si (OMe) ₃ − / CdS). Since 3-mercaptopropyltrimethoxysilane is a thiol compound, it can bind to CdS via S of the thiol compound. Subsequently, by hydrolyzing the trimethoxysilyl group (Si (OMe) ₃ ), the core / shell having the CdS fine particles 2 as the core (core) and the silica (SiO _x ) monolayer as the shell (shell) 7 is used. A structure is formed (SiO _x − / CdS). Since the trimethoxysilyl group introduced on the surface contains Si as a constituent element, a SiO _x film can be formed by hydrolysis. This SiO _x film is not photo-dissolved.

In addition, a core / shell structure having a nanoparticle composite soluble in water or soluble in an organic solvent as a core is formed by the following method.
FIG. 5 is a diagram schematically showing a process of forming a core / shell structure composed of a CdS core and a SiO _x shell so as to be soluble in water or soluble in an organic solvent. As shown in FIGS. 5 (a) and 5 (b), the surface of the CdS fine particles 2 is chemically modified by the same method as in FIG. 4, and then hydrolyzed as shown in FIG. 5 (c). If the surface is chemically modified by adding an alkylsilane compound having an alkyl group having various functional groups (X) such as methoxysilane (X—R—Si (OMe) ₃ ), the surface of the CdS fine particles 2 The silica monolayer can be further chemically modified (X—R— (SiO _x ) — / CdS). Here, the surface characteristics of the CdS fine particles 2 can be controlled by the type of the functional group (X) of the alkyl group. For example, when n-octadecyltrimethoxysilane is used as the alkylsilane compound, a core / shell structure that can be uniformly dissolved in toluene, dimethylformamide, chloroform, carbon tetrachloride or the like can be obtained. If an alkylsilane having a functional group X having a carboxyl group, a quaternary ammonium group, an amino group, a sulfonic acid group, a hydroxyl group or the like is used, a water-soluble core / shell structure can be obtained.

Next, as shown in FIG. 3 (c), the light-dissolving irradiation light 21, which is light of a specific wavelength, is irradiated onto the fine particles 2 in the light-dissolving solution 20 to control the voids 8 of the core / shell structure. To form. Here, when the light 21 having the absorption edge wavelength of the fine particle 2 is irradiated, the fine particle 2 absorbs the light 21, and the surface of the fine particle 2 is dissolved in the photodissolving solution by the light dissolution reaction, and the diameter gradually decreases. For example, when the CdS fine particles 2 are used, the quantum size effect becomes significant when the particle size is about 10 nm or less. As the particle size of the fine particles 2 becomes smaller, the absorption edge wavelength shifts to the short wavelength side, and the absorption edge wavelength becomes light. When shorter than the wavelength of the irradiation light 21 for dissolution, the photodissolution reaction stops, and the particle diameter of the fine particles 2 stops at a constant value.
Thus, the particle diameter of the fine particles 2 is controlled by selecting the wavelength of the irradiation light 21 for photodissolution. Therefore, by determining the particle diameter of the fine particles 2 corresponding to the desired void 8 and irradiating the light 21 having a wavelength corresponding to the particle diameter, the internally controlled void 8 can be formed.

In addition, the control method of the space | gap used for this invention is the size selective light etching method (Document: J. Electrochem. Soc., 145, 1964-1968 (1998), Chem. Lett., Which was already proposed by the present inventors. 379-380 (1999), J. Phys. Chem. B, 215, 6838-6845 (2001)).
This size-selective photoetching method utilizes the fact that semiconductor nanoparticles have an energy gap that increases as the particle size decreases due to the quantum size effect, and that metal chalcogenide semiconductors are oxidized and dissolved by light irradiation under dissolved oxygen. By irradiating semiconductor nanoparticles having a wide particle size distribution with monochromatic light having a wavelength shorter than the absorption edge wavelength, only the semiconductor nanoparticles having a large particle size are selectively photoexcited and dissolved, resulting in a smaller semiconductor. This is a method of aligning the particle size into nanoparticles.

Next, as shown in FIG. 3 (d), the controlled voids 8 formed in the solid precipitation solution 23 in the step of FIG. 3 (c) are separated from the first nanoparticles by a different composition. By depositing the solid, a nanoparticle composite can be prepared with good controllability.
The feature of the present invention is that the nanoparticle composite that becomes the core is formed by depositing another solid having a composition different from that of the first nanoparticle in the controlled void 8 formed in the step of FIG. In forming the body 6.

As a second nanoparticle, a method of depositing a metal or metal oxide that is a solid that does not dissolve light will be described.
As the metal precipitation solution as the solid precipitation solution 23, a solution containing a metal element can be used. For example, a complex solution containing a metal can be used. When the photodissolved nanoparticles already formed are semiconductor CdS or the like, the metal deposition solution is further irradiated with light to reduce and oxidize electrons and holes generated by excitation of the semiconductor. The photocatalytic reaction used can be controlled to deposit metal or metal oxide. When depositing a metal, it is preferable to add a hole scavenger such as alcohol or trietalamine to the metal deposition solution in order to suppress the oxidative action caused by the photogenerated holes in the semiconductor. In this way, the nanoparticle 2 whose particle size is controlled by photoetching by irradiating the metal precipitation solution 23 with light 24 of a specific wavelength and precipitating the metal fine particles 3 in the void 8 portion. Then, the core / shell structure 1 having the nanoparticle composite 6 composed of the metal nanoparticles 3 as a core can be obtained. Thereby, the core-shell structure 1 having the nanoparticle composite as a core can be prepared.

Next, using the preparation method according to the third embodiment of the core-shell structure 1 having the nanoparticle composite as a core, and as another structure, the core / shell structure 1 having only the second nanoparticle as the core A method for preparing the shell structure and the nanoparticle composite will be described.
First, a method for preparing a core / shell structure having only the second nanoparticles 3 as a core will be described. As described in the third embodiment, the core-shell structure 1 having the nanoparticle composite as a core controls the void 8 inside the core 6 by controlling the photodissolution of the nanoparticle 2 that is photodissolved. The size of the nanoparticles 3 can also be controlled and adjusted by depositing nanoparticles 3 having different properties from the nanoparticles 2 in the voids 8. If this is utilized, the core-shell structure which makes only the 2nd nanoparticle 3 a core can be prepared easily.

FIG. 6 is a diagram showing a process of a method for preparing a core / shell structure using the second nanoparticle 3 of the present invention as a core. As shown in FIGS. 6A to 6D, after preparing the core-shell structure 1 having the nanoparticle composite as a core by the same method as in the third embodiment, FIG. As shown in FIG. 5, the core-shell structure 15 having the nanoparticle 3 as a core can be obtained by removing the second nanoparticle 3 by using a liquid 26 for etching the photodissolved nanoparticle 2 so that the second nanoparticle 3 is not etched. Is obtained. The solution 26 for etching the light-dissolving nanoparticles 2 may be a selective etching solution that cannot etch the second nanoparticles 3.
Here, the 2nd nanoparticle 3 can be made into the nanoparticle which is not photodissolved, or the nanoparticle which is not photodissolved. In the case where the second nanoparticle 3 is a nanoparticle that is photodissolved, and when the first nanoparticle 2 is removed by photoetching, the second nanoparticle 3 may be photoetched under the condition that the second nanoparticle 3 is not photoetched. . Thereby, the core-shell structure 15 having the nanoparticles 3 as the core can be easily prepared from the core-shell structure 1 having the nanoparticle composite as the core.

  The core / shell structure 15 thus prepared can be used, for example, for the following applications. When the second nanoparticle 3 is a catalyst metal fine particle having a shape having the highest catalytic activity, a specific substance having a specific structure can be selectively adsorbed through the micropores of the shell 7 and contamination is caused. It can be used as a catalyst for treating gas and the like.

Next, a method for preparing the nanoparticle composite according to the present invention will be described.
FIG. 7 is a diagram showing a process of a method for preparing a nanoparticle composite according to the present invention. As shown in FIG. 7 (a) to FIG. 7 (d), after preparing the core-shell structure 1 having voids controlled inside by the same method as in FIG. 3, as shown in FIG. 7 (e). If the shell 7 is removed by using the shell etching solution 25, the nanoparticle composite 6 is obtained. Thereby, the nanoparticle composite 6 can be easily prepared from the core-shell structure 1 having the nanoparticle composite as a core.

Next, a method for preparing a structure using the core-shell structure 1 having the nanoparticle composite shown in FIG. 2 as a core will be described.
A plurality of core-shell structures 1 having the nanoparticle composite shown in FIG. 1 as a core are organized by a self-assembly method to prepare a structure 10 having a desired shape.
In this case, the following self-organization method can be applied.
(1) Three-dimensional organization method A core-shell structure having a nanoparticle composite as a core is obtained by dispersing the core-shell structure 1 having a nanoparticle composite as a core in a solvent and gradually evaporating the solvent. Self-organized by van der Waals force between 1 (see: Science, 270, 1335-1338 (1995)).
(2) Two-dimensional organization method The core-shell structure 1 having a nanoparticle composite as a core is developed at the gas-liquid interface to produce a two-dimensional particle film, and the produced two-dimensional particle film is compressed to form a tissue. (Reference: Langmuir, 15, 1853-1858 (1999)).
(3) One-dimensional organization method Using DNA as a template, a core-shell structure 1 having a nanoparticle composite as a core is arranged along the DNA (reference: J. Phys. Chem. B, 103, 8799-8803). (1999)).

Next, these self-assembled structures are bonded between shells by heat treatment, chemical treatment with a crosslinking agent molecule or the like, or direct reaction between shells to stabilize the structures. For example, when the shell is SiO _x , the structure is stabilized by cross-linking between the SiO _x thin films with tetraethoxysilane.

  In the above description, the method of structuring using the core-shell structure 1 having the nanoparticle composite as a core has been described. However, the second nanoparticle 3 shown in FIG. You may structure using the core-shell structure 15 and the nanoparticle composite body 6 shown in FIG.7 (e).

In addition, after preparing a structure of a desired shape by the above method using the structure before forming a controlled void inside, a desired void is formed by size selective photoetching method, and the inside of the void is formed. You may prepare the structure 10 which makes the core-shell structure 1 which made the nanoparticle composite a core deposit by depositing the nanoparticle which is not photodissolved.
Further, the structure 10 having the nanoparticle composite 6 as a constituent is prepared by removing the shell of the structure 10 having the core / shell structure 1 having the nanoparticle composite as a core as a constituent, by etching. Also good.

Next, examples will be described.
By chemically modifying the surface of cadmium sulfide (CdS) nanoparticles with 3-mercaptopropyltrimethoxysilane ((CH ₃ O) ₃ Si (CH ₂ ) ₃ SH), which is one of the thiol compounds, trimethoxy is obtained. After introducing a silyl group ((CH ₃ O) ₃ Si—) onto the surface of the nanoparticle, the surface of the cadmium sulfide (CdS) nanoparticle is covered with a silica layer by hydrolyzing the trimethoxysilyl group and between the shells. A structure having a core / shell structure as a constituent element was formed by cross-linking with a Si—O—Si bond.
By irradiating the obtained core-shell structure with monochromatic light (488 nm), size-selective photoetching is applied to the cadmium sulfide (CdS) nanoparticles inside the core-shell structure, and cadmium sulfide (CdS) nanoparticles. Was reduced to about 3.5 nm.
As a metal deposition solution, an appropriate amount of K is used so that Au is photodeposited in a mixed solution of methanol and H ₂ O (volume ratio is 1: 1) by 5 wt% (wt%) of the core / shell structure. [Au (CN) ₂ ] was added.
To this solution, a core / shell structure having a controlled void inside with CdS as a core and silica layer as a shell is added, and a 400 W mercury lamp (λ> 350 nm) is used as an irradiation light for metal deposition. By irradiating for 5 hours, Au (gold) having a diameter of about 4 nm was photo-deposited inside the void. At this time, Ar (argon) was used as the atmospheric gas.
Thereby, the core-shell structure 1 which made the nanoparticle composite_body | complex which consists of CdS and Au a core was able to be prepared.

The structure 10 having the core-shell structure 1 with the nanoparticle composite as a core obtained in Example 1 as a constituent element is removed by etching with a NaOH solution in which the shell (SiO _x ) is diluted. A structure having the nanoparticle composite 6 as a constituent element was prepared.

The CdS in the structure having the core-shell structure 1 having the nanoparticle composite as a core obtained in Example 1 as a constituent element is removed by etching using HCl, whereby Au is used as the core. A core / shell structure 15 having a void inside the SiO _x shell was prepared. FIG. 8 is a transmission electron micrograph of the structure 15 prepared in Example 3 and having a core-shell structure with Au as a core as a constituent element. In the figure, the black solid portion is Au nanoparticles as a core, the thin ring-shaped black portion around it is silica (SiO _x ) as a shell, and the white portion therebetween is a void. As is apparent from the figure, a core / shell structure 15 having a controlled void inside Au as a core is formed. The diameters of the core Au nanoparticles and the shell are about 4 nm and about 7 nm, respectively, and the void size is about 3 nm from these differences. This value is in good agreement with the average particle size of CdS before etching of 3.5 nm.

FIG. 9 is a diagram showing light absorption characteristics of a core-shell structure having the nanoparticle composite of the present invention as a core. In the figure, the vertical axis represents the light absorption by the reflection measurement of the core-shell structure with the nanoparticle composite as the core, that is, the Kubelka-Munk function (arbitrary scale), and the horizontal axis represents the wavelength (nm).
The light absorption (see (1) in FIG. 9) of the core-shell structure 1 using a nanoparticle composite composed of CdS and Au as a core is a core-shell structure having a controlled void inside the core-shell structure 1. Compared with the light absorption of the body (see (3) in FIG. 9), the photodeposition of Au on the CdS particles reduces the short wavelength side absorption of 500 nm or less, which is characteristic of CdS, and is about 500 nm by Au. From the above visible light, it can be seen that the absorption in the infrared region is increased. Although not shown in the figure, the light absorption of the nanoparticle composite composed of CdS and Au also had substantially the same characteristics as the light absorption of the core-shell structure having the nanoparticle composite composed of CdS and Au as the core.
The light absorption (see (2) in FIG. 9) of the core-shell structure 15 having voids inside with the core of Au prepared by removing CdS from the nanoparticle composite 6 composed of CdS and Au It is clear that the light absorption on the short wavelength side of 500 nm or less derived from CdS is reduced by the removal of CdS.
Thus, in the nanoparticle composite 6 composed of CdS and Au of the present invention, the core-shell structure 1 using the nanoparticle composite 6 as a core, and the core-shell structure 5 using Au as a core, It can be seen that the light absorption characteristics in the visible light region are greatly changed as compared with the core-shell structure having CdS as the core.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. Needless to say, the nanoparticle composite composed of two different nanoparticle is not limited to the above examples.

1 is a schematic cross-sectional view showing a configuration of a core-shell structure having a nanoparticle composite according to a first embodiment of the present invention as a core. It is a schematic cross section which shows the structure of the structure which uses the core-shell structure 1 which made the nanoparticle composite_body | complex by the 2nd Embodiment of this invention a core, and is a component. It is a figure which shows the process of the preparation method of the core-shell structure 1 which made the nanoparticle composite_body | complex by 3rd Embodiment based on this invention a core. The step of coating the shell of SiO _x core of CdS fine particles is a diagram schematically illustrating. The core-shell structure made of CdS core and SiO _x shell-soluble or organic solvent in water to form a soluble illustrates schematically. It is a figure which shows the process of the preparation method of the core-shell structure which used the 2nd nanoparticle of this invention as the core. It is a figure which shows the process of the preparation method of the nanoparticle composite_body | complex which concerns on this invention. FIG. 6 is a transmission electron micrograph of a structure prepared in Example 3 and including a core-shell structure having Au as a core as a constituent element. It is a figure which shows the light absorption characteristic of the core-shell structure which made the nanoparticle composite_body | complex of this invention a core.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core-shell structure which used nanoparticle composite as a core 2 1st nanoparticle 3 2nd nanoparticle 4 Junction part 6 Core (nanoparticle composite)
7 Shell 8 Void 10 Structure 15 having a core / shell structure with a nanoparticle composite as a core 15 Core / shell structure 20 having only a second nanoparticle as a core 20 Light dissolving solution 21 Light irradiation Light 23 Metal deposition solution 24 Metal deposition irradiation light 25 Shell etchant 26 Photodissolved nanoparticle etchant

Claims (17)

A core composed of a nanoparticle composite in which a first nanoparticle and a second nanoparticle different from the first nanoparticle are directly bonded;
A shell having a diameter of several nanometers to several tens of nanometers covering the core via a gap,
The first nanoparticles are made of a metal, a metal oxide, a semiconductor or a polymer solid having a light absorption edge while being photodissolved,
The second nanoparticles are made of a metal, metal oxide, semiconductor, or polymer solid deposited from the solid deposition solution and bonded to the first nanoparticles.
A core / shell structure having a nanoparticle composite as a core, wherein the void is controlled to have a desired size by controlling a particle size of the first nanoparticle.   The core / shell structure having a nanoparticle composite as a core according to claim 1, wherein the shell is made of a material that does not dissolve in light.   The first nanoparticle is a metal chalcogenide semiconductor fine particle, the second nanoparticle is a metal, and the shell is a film having a silicon-oxygen bond as a skeleton. A core-shell structure using the nanoparticle composite described in 1 above as a core. 4. The nano of claim 3, wherein the metal chalcogenide semiconductor fine particles are CdS (cadmium sulfide), and the film having a silicon-oxygen bond as a skeleton is SiO _x (silicon oxide, 0 <x). Core / shell structure with particle composite as the core.   A core / shell structure having a nanoparticle composite as a core, comprising a core / shell structure having the nanoparticle composite according to any one of claims 1 to 4 as a core. Structure as element. Along with photodissolution, first nanoparticles made of a metal, metal oxide, semiconductor or polymer solid having a light absorption edge are formed with a controlled particle size,
The group is introduced into the surface by chemically modifying the surface of the first nanoparticle with a chemical substance having an element that binds to the surface of the first nanoparticle and a group that includes a constituent element of an oxide that does not dissolve light. ,
This group is hydrolyzed to form a film composed of the oxide, and a core-shell structure is formed in which the first nanoparticle is a core and the film is a shell.
The core / shell structure is etched by controlling the wavelength in the photodissolved solution and irradiating with light to control the particle diameter of the first nanoparticles, thereby forming a controlled void inside the core / shell structure. Forming,
The second nano-particle made of metal, metal oxide, semiconductor or polymer in the shell of the core-shell structure having a controlled void in the solid precipitation solution containing the constituent element of the second nanoparticle. By precipitating the particles and directly bonding them to the first nanoparticles having a controlled particle size,
A core composed of a nanoparticle composite in which the first nanoparticle and the second nanoparticle that are photodissolved are directly joined, and a shell having a diameter of several nanometers to several tens of nanometers covering the core via a void; A core-shell structure having a nanoparticle composite as a core, characterized in that a core-shell structure having a void controlled to a desired size by controlling the particle size of the first nanoparticle is obtained. Body preparation method.   The method for preparing a core-shell structure using the nanoparticle composite as a core according to claim 6, wherein the second nanoparticles are precipitated by light irradiation.   The method for preparing a core-shell structure using a nanoparticle composite as a core according to claim 6, wherein the solid precipitation solution is a metal precipitation solution and deposits a metal or a metal oxide.   9. The nanoparticle composite according to claim 8, wherein the metal deposition solution is a mixed solution containing a metal element constituting the second nanoparticle and an electron or hole scavenger. A method for preparing a core-shell structure.   [7] The method according to claim 6, wherein after the hydrolysis, a chemical substance having a hydrophilic group or a hydrophobic group is added and further chemically modified to be soluble in water or soluble in an organic solvent. Of a core-shell structure using a nanoparticle composite of the above as a core. The first nanoparticle is CdS (cadmium sulfide), and the element bonded to the surface of the first nanoparticle is an S (sulfur) element.
The component element of the oxide that does not dissolve light is Si (silicon), and the group is a (CH ₃ O) ₃ Si (trimethoxysilyl) group containing Si,
The chemical substance is (CH ₃ O) ₃ Si (CH ₂ ) ₃ SH (3-mercaptopropyltrimethoxysilane),
The coating is SiO _x (silicon oxide, 0 <x),
The core / shell structure having the nanoparticle composite as a core according to claim 6, wherein the second nanoparticle is made of a solid of metal, metal oxide, semiconductor or polymer. Method. The first nanoparticles are CdS;
The element bonded to the surface of the first nanoparticle is S element,
The component element of the oxide that does not dissolve in light is Si, and the group is a (CH ₃ O) ₃ Si group containing Si,
The chemical substance is (CH ₃ O) ₃ Si (CH ₂ ) ₃ SH,
The chemical substance having a hydrophilic group is an alkylsilane having a carboxyl group, a quaternary ammonium group, an amino group, a sulfonic acid group, a hydroxyl group, and the like.
The chemical substance having a hydrophobic group is n-octadecyltrimethoxysilane,
The core / shell structure having the nanoparticle composite as a core according to claim 10, wherein the second nanoparticle is made of a metal, metal oxide, semiconductor, or polymer solid. Method.   The said 1st nanoparticle is made into a desired particle size by carrying out photodissolution with the light of the absorption edge wavelength corresponding to a desired particle size, The any one of Claim 6, 11, 12 characterized by the above-mentioned. Of a core-shell structure using a nanoparticle composite of the above as a core.   A core-shell structure having a plurality of nanoparticle composites prepared by the method according to any one of claims 6 to 13 as a core is dispersed in a solvent, and the solvent is gradually evaporated to be self-organized. A method for preparing the structure comprising obtaining a core / shell structure having the nanoparticle composite as a core as a constituent element.   A core-shell structure having a plurality of nanoparticle composites prepared by the method according to any one of claims 6 to 13 as a core is developed at a gas-liquid interface, and the core A method for preparing a structure comprising a core-shell structure having a nanoparticle composite as a core, wherein a two-dimensional film comprising a shell structure is compressed and organized.   A core-shell structure having a plurality of nanoparticle complexes prepared by the method according to any one of claims 6 to 13 as a core is arranged using DNA as a template, and the nanoparticle complex is a core A method for preparing a structure having the core-shell structure as a constituent.   A nano-particle comprising the first nano-particle and the second nano-particle by removing the shell of the core-shell structure having the nano-particle composite prepared by the method according to any one of claims 6 to 13 as a core. A method for preparing a nanoparticle composite, comprising obtaining a particle composite.