JP2007169763A - Metal nanoparticles comprising two or more metals and method for forming the same - Google Patents

Abstract

The present invention provides a method for efficiently forming metal nanoparticles comprising two or more metals in a medium using a photochemical reaction.
A method of forming metal nanoparticles composed of two or more kinds of metals in a medium, wherein a radical precursor that generates radicals by photoexcitation and a medium containing two or more kinds of metal ions or metal complexes are excited. A formation method characterized by irradiating light, and metal nanoparticles formed in a medium by the formation method.
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Description

  The present invention relates to a method for producing metal nanoparticles composed of two or more metals in a medium using a photochemical reaction.

  The possibility of various applications of metal nanoparticles, which are nano-sized metal particles, has been pointed out, and research for practical application is actively progressing. In response, methods for producing metal nanoparticles under a variety of conditions have been developed, from the gas phase to solutions, micelles, soft materials such as sols and gels, and solids such as glass.

  Metal nanoparticles created in polymer matrices such as gels, sols, and films have functions as metal nanoparticle-polymer composites, so they can be used as nonlinear optical materials, photoimaging, photopatterning, magnetic materials, and sensors. It is expected (for example, non-patent documents 1 to 3).

  Among metal nanoparticles, those composed of two or more kinds of metals have optical and electrochemical properties that can be adjusted according to the application, and thus can be applied to a wider range of applications.

  Although methods for producing metal nanoparticles composed of one kind of metal in a medium have been extensively studied, it has been said that sufficient research has been conducted on methods for producing metal nanoparticles composed of two or more kinds of metals. It ’s hard.

  Currently, a chemical reduction method is being studied as a method for producing nanoparticles composed of two or more metals (multi-metal nanoparticles), which reduces a solution containing multiple metal ions by a chemical method. Is the method. Alternatively, there is a method in which another metal is deposited around a nucleus prepared in advance by a chemical method.

However, these are all chemical reduction methods, and there are no reports of producing metal nanoparticles composed of two or more metals in a medium using a photochemical reduction method utilizing the spatial resolution of light. Moreover, it is difficult to produce multimetal nanoparticles in a solid medium (resin or the like) by these methods.
Stellacci, CA Bauer, T. Meyer-Friedrichen, W. Wenseleers, V. Alain, SM Kuebler, SJ Pond, Y. Zhang, SR Marder, JW Perry, Adv. Mater. 2002, 14, 194. GB Smith, CA Deller, PD Swift, A. Gentle, PD Garrett, WKJ Fisher, Nanopart. Res. 2002, 4, 157. FP Zamborini, MC Leopold, JF Hicks, PJ Kulesza, MA Malik, RW Murray, J. Am. Chem. Soc. 2002, 124, 8958.

  An object of the present invention is to provide a method for efficiently forming metal nanoparticles composed of two or more metals in a medium using a photochemical reaction. Specifically, an object of the present invention is to provide a method for efficiently forming metal nanoparticles having various structures such as an alloy and a core-shell made of two or more metals in a medium.

  Another object of the present invention is to provide metal nanoparticles obtained by the forming method.

  As a result of intensive studies to solve the above problems, the present inventor has obtained the following knowledge.

  It is known that a radical generally has a much higher reducing power than its parent molecule (radical precursor). For example, the half-wave potential of a benzophenone ketyl radical, which is one of aromatic radicals, is reported as -0.25 V vs. SCE, and has a very high reducing power.

  A radical obtained by treating a radical precursor with a photochemical method (such as lamp or laser irradiation) becomes an active intermediate having a high reducing power and functions as a reducing agent. It has been found that by using this reducing agent, two or more kinds of metal complexes or metal ions coexisting can be reduced simultaneously or successively to produce metal nanoparticles composed of two or more kinds of metals.

  Specifically, for example, by simultaneously reducing a metal complex or metal ion with a radical in a medium, metal nanoparticles composed of two or more kinds of metals can be created, or a metal complex or a radical with a radical in the medium After the metal ions are reduced to form the cores of the metal nanoparticles, the coexisting metal complexes or metal ions are continuously reduced on the surface of the cores to deposit the shells. It has been found that metal nanoparticles composed of two or more types of metal (or multilayer structure type) can be formed.

  In particular, the latter core-shell type metal nanoparticles are composed of a metal that forms a core and a metal that forms a shell (shell) surrounding the metal. When metal ions are reduced on the surface of the core, the metal ions are reduced. It is formed by utilizing the increase in potential.

  As a result of further research based on this knowledge, the present invention has been completed.

  That is, this invention relates to the method of forming the metal nanoparticle which consists of 2 or more types of metals in the following media, and the metal nanoparticle formed by this formation method.

  Item 1. A method of forming metal nanoparticles composed of two or more metals in a medium, which irradiates a medium containing radical precursors that generate radicals by photoexcitation and two or more metal ions or metal complexes with excitation light. The formation method characterized by the above-mentioned.

  Item 2. Item 2. The method according to Item 1, wherein the radical precursor is bisaryl ketones, arylalkyl ketones, benzoin, benzyl, or quinones.

  Item 3. Item 2. The method according to Item 1, wherein the excitation light is laser light or lamp light and has a wavelength capable of exciting the radical precursor.

  Item 4. Item 2. The forming method according to Item 1, wherein the metals constituting the two or more metal ions or metal complexes are at least two selected from the group consisting of palladium, iron, copper, nickel, gold, silver and platinum.

  Item 5. Item 2. The forming method according to Item 1, wherein the medium is a solid medium or a liquid medium.

  Item 6. Item 2. The forming method according to Item 1, wherein the formed metal nanoparticles composed of two or more metals are an alloy composed of two or more metals or a core-shell structure.

  Item 7. Metal nanoparticles formed in a medium by the formation method according to any one of Items 1 to 6.

  Hereinafter, the present invention will be described in detail.

  The present invention is a method of irradiating a medium containing a radical precursor and two or more metal ions or metal complexes with excitation light to form metal nanoparticles composed of two or more metals in the medium. In other words, two or more types can be obtained by irradiating a medium containing a predetermined radical precursor with excitation light to generate radicals, and simultaneously or successively reducing two or more metal ions or metal complexes with the radicals. This is a method for producing metal nanoparticles composed of the above metals.

Radical Precursor The “radical precursor” used in the present invention is a compound that is directly excited by light irradiation. Hydrogen or halogen is extracted from a medium in which the excited state coexists, or the excited state is bonded. It means a compound having the property of generating radicals by cleavage.

  The radical precursor is not particularly limited as long as it has the above properties, and a wide range of compounds can be used. For example, bisaryl ketones such as benzophenone, 4-methoxybenzophenone, naphthylphenyl ketone, 4-benzoylbiphenyl, bis-biphenyl-4-yl-methanone; arylalkyl ketones such as acetophenone; bis such as diphenylmethane and dinaphthylmethane Arylmethanes; bisarylmethyl halides such as diphenylmethyl chloride and dinaphthylmethyl chloride; benzoins; quinones such as benzoquinone and anthraquinone. Of these, bisaryl ketones, particularly benzophenone or derivatives thereof are preferred from the viewpoint that the photoexcited state has a high ability to extract hydrogen, halogen, and the like, and the generated radical has a relatively high reducing ability for metal ions or metal complexes. It is.

  Specifically, for example, bisaryl ketones, arylalkyl ketones, and the like once generate a triplet excited state when excited by excitation light, and extract hydrogen, halogen, etc. from the coexisting hydrogen or halogen donor. To generate radicals. Bisarylmethanes and the like generate radicals by C—H bond cleavage from an excited state generated by excitation light, and bisarylmethyl halides generate radicals by C-halogen bond cleavage from an excited state caused by excitation light. .

  Metal ions or metal complexes are reduced by electron transfer from the radicals. In this manner, the radical precursor is used as a so-called dopant that generates a radical by photoexcitation and photochemical reaction in a medium and reduces a metal ion or metal complex by the radical.

Metal Ion or Metal Complex The metal ion or metal complex used in the present invention is not particularly limited as long as it accepts electrons and is reduced to a zero-valent metal. Moreover, a metal ion or a metal complex contains 2 or more types of metals.

As a metal which comprises a metal ion or a metal complex, iron, copper, nickel, gold | metal | money, silver, platinum etc. are mentioned, for example. That is, examples of metal ions include iron ions, copper ions, nickel ions, gold ions, silver ions, and platinum ions, and examples of metal complexes include HAuCl ₄ , AgNO ₂ , PtCl ₄ , Cu (CH ₃ COO ) ₂ , FeCl ₃ , AuCl _{3 and the} like. A metal ion or a metal complex can be appropriately selected so as to contain two or more kinds of metals from among the above, depending on the reducing power of the radical.

Specific combinations include gold ion / copper ion, gold ion / silver ion,
Examples include gold ions / iron ions, platinum ions / iron ions, and the like. More specifically, HAuCl ₄ / Cu (CH ₃ COO) ₂ , HAuCl ₄ / FeCl _{3 and the} like are exemplified. Of these, HAuCl ₄ / Cu (CH ₃ COO) ₂ is preferable.

Medium As the medium on which the metal nanoparticles are formed in the present invention, various solid media or liquid media can be used. The solid medium or liquid medium used in the present invention is not particularly limited as long as it can disperse or dissolve the radical precursor and metal ions, and can generate radicals.

  For example, micelles (for example, polystyrene-poly-4-vinylpyridine, etc.), resins (for example, polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), etc.), zeolites, solid media such as glass, water, organic solvents (for example, It is possible to use a liquid medium such as methanol, ethanol, 2-propanol, benzene, toluene, methyltetrahydrofuran and the like. Whatever solid medium or liquid medium is used, in order to form homogeneous metal nanoparticles therein, radical precursors, radical precursors, and metal ions or metal complexes can be uniformly dispersed or dissolved. preferable.

  The concentration of the radical precursor, metal ion or metal complex in the medium is not particularly limited and can be appropriately selected from a wide range. For example, the concentration of the radical precursor in the medium (for example, PVA) may be, for example, about 5 to 50 mol / L, preferably about 20 to 30 mol / L. The concentration of the metal ion or metal complex in the medium is, for example, about 0.1 to 10 mol / L, preferably about 1 to 5 mol / L. When the concentration of each component in the medium is within the above range, electron transfer from a radical to a metal ion or metal complex is facilitated, and metal nanoparticles can be efficiently formed.

  The method of the present invention is not limited to these concentrations, and can be carried out under a wide range of concentration conditions by combining all metal ions or metal complexes, media, radical precursors, etc. to which the method can be applied. Is possible.

  Examples of the method for dissolving or dispersing the radical precursor and the metal ion or metal complex in the medium (solid medium or liquid medium) include the following methods.

  When a liquid medium is used, the radical precursor and two or more kinds of metal ions or metal complexes may be placed in the liquid medium, mixed uniformly, and dissolved or dispersed.

  When a solid medium is used, particularly when a resin is used, a radical precursor, metal ion or metal complex as a dopant, and a solvent that can dissolve all of the resin (for example, water, formic acid, acetic acid, alcohols, Acetonitrile, DMF, ethylene glycol, or a mixture thereof, etc.), which is molded into a desired shape to remove the solvent.

  The molding method is not particularly limited, and a known method such as injection molding, extrusion molding, spin coating or the like may be employed depending on the shape. The shape can be selected according to the application, and for example, it can be a flat shape such as a film or a sheet, a cube, a rectangular parallelepiped, a sphere, or any other three-dimensional shape. In the case of a three-dimensional shape, in order to improve the strength, a crosslinking agent may be added to the resin as necessary to perform a crosslinking treatment.

  Further, when zeolite is used as the solid medium, the radical precursor, metal ion or metal complex, and hydrogen donor, which are dopants, may be dissolved in a solvent that can dissolve them and incorporated into the zeolite.

Formation of metal nanoparticles Next, the composite material containing a radical precursor and a metal ion or metal complex prepared as described above is irradiated with excitation light to form metal nanoparticles in the medium. .

  The formation method of the present invention is characterized in that metal nanoparticles composed of two or more kinds of metals can be produced in a medium by utilizing a high reduction stress of radicals generated by a photoreaction.

  In order to reduce metal ions or metal complexes to form metal nanoparticles, it is first necessary to generate radicals that function as a reducing agent in a medium. A radical precursor doped in a medium is excited by a light source, and a radical is generated by a photochemical reaction. In the presence of an appropriate metal ion or metal complex, a reduction reaction of the metal ion or metal complex occurs due to electron transfer from the generated radical, and a seed crystal of metal nanoparticles is generated.

In this case, the following two processes are considered as the formation process of the metal nanoparticles. (1) When a radical can simultaneously reduce a plurality of coexisting metal ions or metal complexes (A ^{n +} and B ^{n +} ), an alloy nanoparticle composed of a plurality of metals or an aggregate thereof (A and B) is formed. (See FIG. 1 (a)). (2) When one (A ^{n +} ) of a plurality of metal ions or metal complexes in which radicals coexist can be selectively reduced, a nucleus is formed by the reduction. The coexisting metal ion or metal complex (C ^{n +} ) is further reduced (deposited) on the surface of the nucleus by being further reduced on the surface of the nucleus by radicals. Thereby, the core-shell type or bilayer structure type bimetallic nanoparticles are formed (see FIG. 1B and FIG. 2). In addition, when multiple types of metals are present, multi-layered multi-metal nanoparticles can be formed.

1 and 2, for example, A ^{n +} / A _atom means a process in which a single metal ion (A ^{n +} ) is reduced to become a metal atom (A _atom ), and A ^{n +} / A _metal is It means a process in which metal ions are reduced and deposited on the metal surface (A _meta ).

  In the case of (2) above, that is, when metal ions or metal complexes are reduced on the surface of the metal nanoparticles in the medium to grow metal nanoparticles, in the case of (1) above, that is, metal ions or Compared with the case where a metal complex is reduced to form a metal atom, the reduction potential is significantly increased (reduced easily). This phenomenon is not limited to the case where the same metal ion or metal complex is reduced. That is, even metal ions or metal complexes that are usually difficult to reduce can be easily reduced on the metal surface.

In this regard, for example, Kaushik Mallik, Madhuri Mandal, Narayan Pradhan, and Tarasankar Pal.Nano lett. 2001, 6, 319, the reduction potential of Au ^III / Au _{atom (aqueous)} is −1.5 V in _aqueous solution. (vs. NHE), but the reduction potential of Au ^III / Au _{metal (aqueous)} has been reported to be +1.5 V (vs. NHE), which can be easily understood.

  According to the forming method of the present invention, metal nanoparticles composed of two or more kinds of metals having various shapes and ratios can be produced according to the process.

  The wavelength of the excitation light from the light source can be appropriately selected and set by those skilled in the art according to the structure and properties of the radical precursor, the type of metal ion or metal complex to be reduced, and the like. For example, the wavelength of the excitation light is usually in the range of about 180 nm to 800 nm, particularly about 180 to 532 nm. As a specific example, when benzophenone is used as a radical precursor, the wavelength of excitation light that excites benzophenone to a triplet excited state may be usually about 180 to 360 nm.

  As a light source of excitation light, laser light such as Nd: YAG laser and excimer laser, lamp light such as mercury lamp and Xe-lamp, and the like are used. Laser light includes pulsed light and continuous-wave light, both of which can be used. In addition, the lamp light is usually only continuous wave light, but it can also be used in a pulsed manner by mechanical means. Laser irradiation is preferable because it can not only produce metal nanoparticles with higher efficiency than light irradiation by a lamp, but also obtain the spatial resolution of the laser.

  In this manner, metal nanoparticles composed of two or more kinds of metals having an average particle diameter of about 1 to 100 nm, particularly about 4 to 10 nm are formed in the medium. Confirmation of generation of metal nanoparticles and measurement of size can be performed using a scanning electron microscope (TEM).

  In the present invention, a radical precursor is photoexcited. In order to avoid damage to the medium, it is necessary that the absorption light wavelength of the medium is out of the absorption light wavelength of the radical precursor. For example, when a radical precursor (for example, benzophenone) is excited with a 355 nm laser, a medium that does not absorb at 355 nm is selected. Since there are relatively many media that do not absorb at 355 nm, a wide range of media can be selected. Such a radical precursor is used as a dopant.

  Examples of the medium include those described above, and can include radical precursors in which the excited radical precursors can react, and any and all polymer matrices, porous materials, solids, solutions It is possible to use soft materials.

  For example, when the solid medium has a planar shape such as a film or sheet, metal nanoparticles can be formed by irradiating a solid medium containing a radical precursor and a metal ion or metal complex with excitation light. .

  Furthermore, if a solid medium containing a radical precursor and a metal ion or metal complex is covered with a mask (photomask) having a predetermined pattern and irradiated with excitation light, only the portion irradiated with light on the solid medium is irradiated. In addition, a circuit pattern made of metal nanoparticles can be formed on the solid medium. In other words, in this method, the narrow width can be arbitrarily controlled depending on the irradiation width of the excitation light, and even a very fine line with a width of about the diffraction limit of light (about half the wavelength) can be freely wired. Can do. The line width of the metal nanoparticles can be arbitrarily controlled up to the diffraction limit of light, for example, a line width of about 133 nm when a light source of 266 nm is used. Note that the irradiation width of the excitation light can be arbitrarily selected by using a lens or the like. The line width can be confirmed using a scanning electron microscope (TEM), an optical microscope or the like. Since the site | part in which the metal nanoparticle was formed has electrical conductivity, it can be utilized for a wide range of uses.

  Furthermore, according to the method for forming metal nanoparticles composed of two or more kinds of metals of the present invention, metal nanoparticles composed of two or more kinds of metals (particularly, bimetallic nanoparticles composed of two kinds of metals) in a medium (particularly a solid medium) (Fine particles) is characterized in that the fine lines become stable over time (for example, see Test Example 1 and FIG. 3). That is, the fine lines of metal nanoparticles composed of two or more kinds of metals formed by excitation light irradiation are prevented from diffusing in the medium, and the line width of the fine lines immediately after the formation is maintained for a long time.

  For this reason, the reason is not clear, but in the case of metal nanoparticles (especially bimetallic nanoparticles) made of two or more types of metals created by reducing two or more types of metals, there are metal ions that coexist around them. This is considered to be because diffusion is hindered by the formation of a layer made of a secondary product formed from the above. For example, in the optical micrograph on the left of FIG. 3, another layer is formed outside the outline of the line of the character “6”.

  On the other hand, a thin line of metal nanoparticles made of a kind of metal formed in the same manner does not form the above layer, and the metal nanoparticles easily diffuse in the medium over time. Line weighting will occur.

  Therefore, if the method of the present invention is used, a stable fine line can be formed over time. For example, by applying this method to a laser printer, a metal nanofiber made of ultrafine lines can be obtained using a laser printer. It is also possible to print on the basis of a circuit of particles. This can be applied to the creation of very thin computers and electronic paper.

  In the method of the present invention, whether or not metal nanoparticles composed of two or more kinds of metals are formed can be confirmed as follows. Characteristic surface plasmon absorption is confirmed by the formation of metal nanoparticles composed of two or more metals. Surface plasmon absorption is considered to be specific to metal nanoparticles composed of two or more kinds of metals or to the metal constituting the shell. Thereby, it can confirm that the nanoparticle produced | generated.

  Moreover, it can be examined by powder X-ray diffraction whether metal nanoparticles are generated or whether the generated metal nanoparticles are crystalline or amorphous.

  The present invention is a method of irradiating a medium containing a radical precursor and two or more kinds of metal ions or metal complexes with excitation light to form nanoparticles composed of two or more kinds of metals in the medium. That is, a metal nanoparticle composed of two or more kinds of metals by radical generation using excitation light in a medium containing a predetermined radical precursor, and simultaneously or stepwise reducing metal ions or metal complexes. Can be generated. Nanoparticles having various shapes and metal ratios can be prepared by the method of the present invention.

  In the method of the present invention, a thin wire composed of metal nanoparticles composed of two or more kinds of metals can be easily formed. Fine wires made of nanoparticles with a width of about the diffraction limit of light (about half the wavelength) can be freely wired. For example, it is possible to print on the basis of a circuit made of ultrafine lines using a laser printer.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1
In the following way, gold / copper bimetallic nanoparticles are produced with high efficiency in polyvinyl alcohol (PVA) medium. Hydrogen extraction ability is available, and benzophenone, which has a strong reducing power as a result of hydrogen extraction, is used as a dopant. It was. A PVA film containing benzophenone, HAuCl ₄ and Cu (OOCCH ₃ ) ₂ was formed. As a solvent for film formation, formic acid which dissolves benzophenone, HAuCl ₄ and PVA well was used. A formic acid solution containing benzophenone (5 to 15 mM), HAuCl ₄ (1 mM), Cu (OOCCH ₃ ) ₂ (1 to 5 mM) and PVA (5 wt%) was formed on a quartz plate by a casting method. The produced PVA film showed a light blue color derived from absorption of Cu ²⁺ and PVA complex.

When this PVA film was irradiated with a 355 nm laser to excite benzophenone, the triplet excited state of benzophenone extracted hydrogen from PVA to generate a benzophenone ketyl radical. Gold nanoparticles were generated by electron transfer from radicals to HAuCl ₄ and gold / copper bimetallic nanoparticles were formed by reducing copper ions on the surface of the gold nanoparticles (see FIG. 2).

  UV-Vis absorption spectra of the formed gold / copper bimetallic nanoparticles were measured, and characteristic surface plasmon absorption was observed. In addition, the formation of gold / copper bimetallic nanoparticles was directly confirmed by a scanning electron microscope (TEM). According to TEM observation, the average size (average particle diameter) of the produced nanoparticles was about 2 nm.

Comparative Example 1
In Example 1, gold nanoparticles were prepared in the same manner as in Example 1 except that the PVA film was not doped with HAuCl ₄ .

  However, in this PVA film, formation of ketyl radicals was confirmed, but formation of copper nanoparticles was not confirmed.

  Thereby, in Example 1, the nucleus of the gold nanoparticle is first generated from the gold ion that is easily reduced to a radical, and the copper ion whose reduction potential is increased by being present on the surface thereof is reduced, whereby the gold / copper bimetal. It was found that nanoparticles were formed.

Example 2
In Example 1, gold / copper bimetallic nanoparticles were prepared in a PVA medium in the same manner as in Example 1 except that a CW-light source such as an Xe-lamp or a mercury lamp was used as the excitation light instead of the laser.

  As a result, it was confirmed that gold / copper bimetallic nanoparticles were generated in the same manner when the CW-light source was used.

Example 3
A two-dimensional circuit composed of gold / copper bimetallic nanoparticles in the medium was prepared as follows.

Using the method described in Example 1, various films doped with HAuCl ₄ , Cu (OOCCH ₃ ) ₂ and radical precursors were prepared. In the light irradiation method, a laser (or CW light) having a wavelength of 355 nm was locally irradiated. Alternatively, a photomask was placed on the film and a laser beam with a wavelength of 355 nm (or CW light) was irradiated as a whole.

Radiation precursors are excited by irradiation with light at 355 nm, and HAuCl ₄ is reduced by the radicals. Further, stepwise reduction at the nucleus surface creates gold / copper bimetallic nanowires in the film. It was.

  In addition, the generation of gold / copper bimetallic nanoparticles was directly confirmed by a transmission electron microscope (TEM). The width of the gold / copper bimetallic nanoparticle fine wire could be determined by TEM or optical microscope observation. Note that the width of the thin line when the photomask is used reflects the width of the thin line provided in the photomask.

Comparative Example 2
Various films doped with HAuCl ₄ and radical precursors were prepared using the method described in Example 1. In the light irradiation method, a laser (or CW light) having a wavelength of 355 nm was locally irradiated. Alternatively, a photomask was placed on the film and a laser beam with a wavelength of 355 nm (or CW light) was irradiated as a whole.

Radiation precursors were excited by irradiation with light of 355 nm, and the reduction of HAuCl ₄ by the radicals produced gold nanoparticle fine lines in the film.

Test example 1
The film on which the thin line in Example 3 and Comparative Example 2 was formed was left at 25 ° C. in the air for 1 week. Thereafter, when both fine lines were observed using an optical microscope, as shown in FIG. 3, in the fine line of Example 3, the diffusion of the metal nanoparticles hardly occurred and the line width immediately after the formation of the fine line was maintained. . On the other hand, in the thin wire of Comparative Example 2, the metal nanoparticles were diffused and were larger than the line width immediately after forming the thin wire.

  Therefore, according to the method of the present invention, fine wires made of nanoparticles having a width of about the diffraction limit of light (about half the wavelength) can be freely wired, and the fine wires become stable over time. For example, it is possible to print a circuit made of ultrafine lines on a substrate using a laser printer.

It is the figure which showed typically the mechanism of the reduction | restoration by this invention. It is the figure which showed typically the specific example of the mechanism of the reduction | restoration by this invention. It is an optical micrograph after leaving the fine line of Example 3 and the thin line of Comparative Example 2 for one week.

Claims (7)

  A method of forming metal nanoparticles composed of two or more metals in a medium, which irradiates a medium containing radical precursors that generate radicals by photoexcitation and two or more metal ions or metal complexes with excitation light. The formation method characterized by the above-mentioned.   The formation method according to claim 1, wherein the radical precursor is bisaryl ketones, arylalkyl ketones, benzoin, benzyl, or quinones.   The forming method according to claim 1, wherein the excitation light is laser light or lamp light and has a wavelength capable of exciting the radical precursor.   2. The forming method according to claim 1, wherein the metal constituting the two or more kinds of metal ions or metal complexes is at least two kinds selected from the group consisting of palladium, iron, copper, nickel, gold, silver, and platinum. .   The forming method according to claim 1, wherein the medium is a solid medium or a liquid medium.   The forming method according to claim 1, wherein the formed metal nanoparticles composed of two or more kinds of metals are an alloy composed of two or more kinds of metals or a core-shell structure.   Metal nanoparticles formed in a medium by the forming method according to claim 1.

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