U.S. patent application number 11/885434 was filed with the patent office on 2008-07-10 for single crytalline noble metal ultrathin-film-like nanoparticle formed in adsorbed micelle film as reaction filed formed at solid-liquid interface, and production method thereof.
This patent application is currently assigned to JAPAN SCIENCE AND TECHNOLOGY AGENCY. Invention is credited to Hideya Kawasaki, Tsuyoshi Kijima.
Application Number | 20080166259 11/885434 |
Document ID | / |
Family ID | 36941345 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080166259 |
Kind Code |
A1 |
Kijima; Tsuyoshi ; et
al. |
July 10, 2008 |
Single Crytalline Noble Metal Ultrathin-Film-Like Nanoparticle
Formed in Adsorbed Micelle Film as Reaction Filed Formed at
Solid-Liquid Interface, and Production Method Thereof
Abstract
It is aimed at creating noble metal nanoparticles having novel
shapes, sizes, and arrangements usable for catalysts, electrodes,
and the like. Micelles made into rod-like shapes having
semicylindrical cross-sections are formed on a carrier substrate in
a self-creating manner and immobilized thereon; noble metal ions
are added and diffused in the micelles to complex the micelles with
noble metal ions; and a reducing agent is subsequently caused to
act thereon to progress a reductive reaction of noble metal within
the immobilized micelles as reaction fields, thereby growing single
crystalline noble metal ultrathin-film nanoparticles on the carrier
substrate by utilizing the fixed micelles having the shapes as
templates, respectively.
Inventors: |
Kijima; Tsuyoshi; (Miyazaki,
JP) ; Kawasaki; Hideya; (Fukuoka, JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
1700 DIAGONAL RD, SUITE 310
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
JAPAN SCIENCE AND TECHNOLOGY
AGENCY
Kawaguchi-shi
JP
|
Family ID: |
36941345 |
Appl. No.: |
11/885434 |
Filed: |
March 1, 2006 |
PCT Filed: |
March 1, 2006 |
PCT NO: |
PCT/JP2006/304415 |
371 Date: |
August 31, 2007 |
Current U.S.
Class: |
420/461 ;
420/462; 420/463; 420/466; 420/501; 420/507 |
Current CPC
Class: |
B22F 1/0055 20130101;
C25B 11/081 20210101; H01M 4/885 20130101; H01M 4/92 20130101; B01J
35/0013 20130101; Y02E 60/50 20130101; B01J 23/38 20130101; H01M
2008/1095 20130101; B01J 37/0215 20130101; B22F 2998/00 20130101;
B22F 2001/0033 20130101; B22F 9/24 20130101; B01J 37/03 20130101;
B22F 1/0018 20130101; B82Y 30/00 20130101; B22F 2998/00 20130101;
B22F 1/0025 20130101 |
Class at
Publication: |
420/461 ;
420/507; 420/501; 420/463; 420/462; 420/466 |
International
Class: |
C22C 5/00 20060101
C22C005/00; C22C 5/02 20060101 C22C005/02; C22C 5/06 20060101
C22C005/06; C22C 5/04 20060101 C22C005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2005 |
JP |
2005-057159 |
Oct 27, 2005 |
JP |
2005-313412 |
Claims
1. A single crystalline noble metal ultrathin-film determinate-form
nanoparticle characterized in that the single crystalline noble
metal ultrathin-film determinate-form nanoparticle is produced in a
solid-liquid interface two-dimensional micelle acting as a reaction
field and formed of one kind or two kinds of surfactants on a
carrier substrate; that the single crystalline noble metal
ultrathin-film determinate-form nanoparticle is constituted of at
least one kind of noble metal selected from a group consisting of
platinum (Pt), gold (Au), silver (Ag), palladium (Pd), rhodium
(Rh), iridium (Ir), and ruthenium (Ru); and that the single
crystalline noble metal ultrathin-film determinate-form
nanoparticle exhibits an ultrathin film shape having a thickness in
a range of 2 to 5 nm, and has an arbitrary contour selected from a
shape of disk, rod, plate, and sheet.
2. The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of claim 1, characterized in that the
carrier substrate is any one of graphite, mica, and silica.
3. The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of claim 1, characterized in that
means for producing the noble metal nanoparticle in the micelle is
provided by a reductive reaction conducted within the micelle as
the reaction field.
4. The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of claim 3, characterized in that the
reductive reaction is achieved by hydrazine.
5. The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of claim 1, characterized in that the
noble metal nanoparticle is picked up in a state carried by the
carrier, by picking up the carrier substrate after the reductive
reaction followed by drying.
6. The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of claim 5, characterized in that the
noble metal particle picked up in the state carried on the carrier
is collected by separating the noble metal particle from the
carrier substrate.
7. The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of claim 1, characterized in that the
noble metal is platinum.
8. A production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle, characterized in that
the method comprises the steps of: preparing a micelle forming
solution containing one kind or two kinds of surfactants at a
micelle concentration; subsequently immersing a carrier substrate
into the micelle forming solution, to cause a micelle formed in a
rod-like shape having a semicircle cross-section to be formed on
and immobilized to the carrier substrate; subsequently adding a
solution containing a noble metal ion into the micelle to thereby
contain the noble metal ion within the micelle; and subsequently
causing a reducing agent to act on the micelle containing therein
the metal ion to thereby progress a reductive reaction within the
immobilized micelle as a reaction field, to produce a single
crystalline noble metal ultrathin-film determinate-form
nanoparticle exhibiting a thin-film shape having a thickness in a
range of 2 to 5 nm and having an arbitrary contour selected from a
shape of disk, rod, plate, and sheet, by utilizing the immobilized
micelle as a template.
9. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the two-dimensional micelle as the reaction
field is adjusted in shape and size, to thereby adjust a shape and
a size of the produced noble metal ultrathin-film determinate-form
nanoparticle.
10. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the noble metal ion is one kind of ion
selected from platinum (Pt), gold (Au), silver (Ag), palladium
(Pd), rhodium (Rh), iridium (Ir), and ruthenium (Ru) ions.
11. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the surfactant for forming the
two-dimensional micelle comprises one kind or two kinds of
surfactants so that the noble metal thinfilm-like particle is
controlled in thickness, shape, and size, by changing the kind of
the surfactant, or the kinds of the surfactants and a mixing ratio
therebetween.
12. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the noble metal ion within the micelle is
changed in concentration, to control the single crystalline
platinum thinfilm-like particle in thickness, size, and the
like.
13. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the carrier is one kind of carrier selected
from graphite, mica, and silica.
14. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the reductive reaction is achieved by
hydrazine.
15. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that the noble metal nanoparticle exhibits a
single two-dimensional film shape grown to have one side dimension
of 50 nm or more.
16. The production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 8,
characterized in that noble metal is platinum.
17. A noble metal catalyst material, characterized in that the
noble metal catalyst material includes the single crystalline noble
metal ultrathin-film determinate-form nanoparticle of claim 1, to
be used as an active ingredient in catalyst design.
18. The noble metal catalyst material of claim 17, characterized in
that the noble metal catalyst material is used in catalyst design
for fuel cell.
19. The noble metal catalyst material of claim 17, characterized in
that the noble metal catalyst material is used for designing a
vehicular exhaust gas purifying catalyst.
20. A noble metal electrode material, characterized in that the
noble metal electrode material includes the single crystalline
noble metal ultrathin-film determinate-form nanoparticle of claim
1, to be used as an electrode designing material for cell or
electrolysis.
21. A noble metal sensor material, characterized in that the noble
metal sensor material includes the single crystalline noble metal
ultrathin-film determinate-form nanoparticle of claim 1, to be used
as a sensor designing material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a novel noble metal
ultrathin-film-like nanoparticle including, as a main component,
noble metal such as platinum usable as: a catalyst to be used in
various chemical reactions; an electrode to be provided for various
electrochemical reactions, such as an electrolysis electrode; and a
fundamental material or functional element for photonics,
electronics, and information technologies such as temperature,
pressure, and gas sensor elements; in various industries and
environmental fields such as fuel cell-oriented catalyst, and
catalyst for treatment of vehicular exhaust gas, utilizing
chemical, electrochemical, and magnetic characteristics of metal
platinum; and also relates to a production method of such a noble
metal ultrathin-film-like nanoparticle.
BACKGROUND ART
[0002] Noble metal elements have excellent workability, heat
resistance, oxidation resistance, corrosion resistance,
electrochemical property, and unique magnetism, and spectroscopic
and chemical natures by virtue of "d" electrons of the elements
themselves, and have been utilized from long ago as materials for
decoration, materials for physical and chemical tools such as
crucible, materials for electric industry such as thermocouples,
electric contacts, and materials for electronic industry such as
paste, and as catalysts, insoluble electrodes, and high-performance
magnets.
[0003] Among the noble metal elements, platinum is extremely
important from an industrial aspect as a catalyst having a function
for promoting a chemical reaction similarly to the other metals of
the platinum group, and is being widely used in fields such as
petroleum purification, petrochemical industry, vehicular and
factory exhaust gas purification, synthesis gas production, and
medicine/fat and oil production.
[0004] Metal catalysts represented by a platinum catalyst are each
typically prepared by introducing a metal component into silica,
alumina, zeolite, activated carbon, or the like by an impregnation
method, ion-exchange method, coprecipitation method, or the like by
using a water solution of a metal salt, followed by treatment such
as firing, hydrogen reduction, and the like (non-patent reference
1).
[0005] Namely, metal catalysts are each provided for reactions in a
form of complex particles comprising solid carriers carrying metal
particles on the surfaces thereof, such that activities of the
metal catalysts are changed by the kinds of the metals, as a matter
of course, sizes of carried metal fine particles, kinds of crystal
faces, kinds of carriers, and the like, and control of sizes of
fine particles is particularly important. Diameters of metal fine
particles depend on preparation conditions, and, for example, it
has been reported that an averaged particle size of platinum fine
particles carried on zeolite by adopting
tetraamminedichloroplatinum as a starting material is made 6 nm by
air firing, and 1 nm or less by vacuum firing (non-patent reference
2).
[0006] Further, relationships between activities of metal catalysts
and particle sizes thereof are made different depending on intended
reactions, and there have been also reported a system where an
activity is lowered as a particle size is decreased (example:
dehydrogenation reaction of 2,3-dimethylbutane by Pt/activated
carbon), a system where an activity is rather increased (example:
hydrocracking reaction of methyl-cyclopentane by Pt/alumina), a
system where an activity is maximized at a certain particle size
(isomerization reaction of n-hexane by Pt/CaY), and a system where
an activity is independent of particle sizes (oxidation reaction of
SO.sub.2 and H.sub.2 by a Pt catalyst) (non-patent reference
3).
[0007] Thus, as a preparation method of a platinum catalyst, there
has been reported a method for conducting liquid-phase reduction in
the presence of a protective agent such as polyvinyl-pyrrolidone to
thereby prepare noble metal colloids, in addition to various
modifications of the above-described typical methods (non-patent
reference 4).
[0008] Further, it has been recently reported that platinum
particles and platinum wires each having diameters of 2.5 nm are
obtained by photo-reducing or hydrogen-reducing chloroplatinic acid
introduced into pores of mesoporous silica, such that the former
exhibit an activity several tens times as high as that of the
latter in terms of a hydrogenation reaction of butane (non-patent
reference 5).
[0009] In addition the above-described non-porous metal fine
particles in the shapes of sphere, wire, and the like, there is
being conducted production of mesoporous metals by adopting a
technique of template-based synthesis (non-patent reference 6).
[0010] The template-based method was originated in 1992 from a fact
that Mobil Co., Ltd. succeeded in creating mesoporous silica having
honeycomb mesopores of 2 to 8 nm by adopting a surfactant as a
template (non-patent reference 7). After that, there have been
synthesized many kinds of mesoporic bodies having various metal
oxides or sulfides as frame components other than silica, by
similar techniques (non-patent reference 8).
[0011] Also concerning metals, there has been synthesized
mesoporous platinum in particulate shapes having pore diameters of
about 3 nm by reducing chloroplatinic acid by hydrazine or the like
while adopting micelles of nonionic surfactant as a template
(non-patent reference 9), and there have been also fabricated
mesoporous platinum (non-patent reference 10) and tin (non-patent
reference 11) in a film shape by electrodeposition of micelle
liquid crystal comprising a metal salt and a surfactant.
[0012] There have been obtained porous platinum particles each
having an outer diameter of 50 to 400 nm and comprising a frame
structure made of platinum wires having diameters of 3 nm and
mutually coupled in a three-dimensional network shape, by
impregnating the mesoporous silica MCM-48 having the
three-dimensional pore structure as synthesized by the
above-described surfactant template-based method, followed by
hydrogen reduction at a high-temperature (non-patent reference
12).
[0013] Similarly, there have been obtained mesoporous platinum and
gold (Au) having pore diameters of about 70 nm by adopting aluminum
anode oxide film of porous solid as a template (non-patent
reference 13), and porous gold (Au) by adopting polystyrene latex
(non-patent reference 14).
[0014] There has also been synthesized mesoporous platinum having a
specific surface area of 47 m.sup.2/g by a method adopting
supercritical CO.sub.2 as a solvent and a black lead crystallite as
a template (non-patent reference 15). Further, there has been also
obtained mesoporous platinum having a specific surface area of 150
m.sup.2/g and shell-like pores of an averaged size of 20 nm by
coating hexachloro platinic acid onto surfaces of silica particles
having an averaged diameter of 20 nm, followed by heating reduction
and subsequent removal of silica (non-patent reference 16).
[0015] Meanwhile, particles in hollow tube shapes having outer
diameters of several nm to several hundreds nm and inner diameters
of several angstroms to several tens nm are called "nanotubes", and
the carbon nanotube discovered as a deposited substance on an arc
electrode in 1991 was the first example of an artificial inorganic
nanotube (non-patent reference 17). Thereafter, in addition to
those based on nitride and sulfide by high-temperature synthesis,
there have been reported oxide-based nanotubes one after the other,
such as nanotubes made of vanadium oxide (non-patent reference 18),
silica (non-patent reference 19), titania (non-patent reference
20), and rare earth oxide by the present inventors (non-patent
reference 21), and the like, by the above-described template-based
method.
[0016] Concerning noble metals, there have been fabricated gold
nanotubes (non-patent references 22 and 23) having substantially
uniform inner diameters of about 1 nm or more, and palladium
nanotubes (non-patent reference 24) having thicknesses of 4 to 5
nm, by a two-step electroless plating reaction by adopting a
polycarbonate porous membrane as a template. Further, the present
inventors have developed a technique to reduce chloroplatinic acid
by adopting liquid crystal comprising two kinds of surfactants as a
template, thereby producing nanotubes made of noble metal such as
platinum and palladium having outer diameters of 6 to 7 nm and
inner diameters of 3 to 4 nm (patent-related reference 1 and
non-patent reference 25).
[0017] There have been also reported platinum particles grown in a
two-dimensional or three-dimensional dendric manner by adopting a
surfactant (non-patent reference 26). Y. Song et al have
synthesized spherical platinum particles having diameters of 10 to
70 nm obtained by platinum grown in a three-dimensional dendric
manner, by conducting light irradiation to a water solution
containing sodium dodecyl sulfate (SDS) or Brij-35 (polyoxyethylene
lauryl ether) acting as a surfactant, chloroplatinic acid, and
ascorbic acid. Further, they have found that single crystal
particles in dendric shapes having diameters of about 10 nm are
produced by adding a small amount of tin porphyrin. Furthermore,
there have been obtained disk-like platinum particles in
two-dimensional dendric shapes having diameters of about 50 nm, in
case of adoption of liposome instead of a surfactant.
[0018] In turn, it has been reported that extremely thin film-like
particles (platinum nano-sheets having thicknesses of about 2 to 3
nm) were synthesized by introducing chloroplatinic acid into gaps
(0.335 nm) between graphite layers, and hydrogen-reducing it
(non-patent reference 27).
[0019] According to patent-related references, it has been
reported: to deposit metal nanoparticles including noble metal by
virtue of an action of a surfactant as a reducing agent from a
solution including transition metal ions and noble metal ions in
the presence of the surfactant (patent-related reference 2); or to
dissolve inorganic metal salts in a solution containing a
surfactant, thereby depositing metal nanoparticles having diameters
in an order of nanometer by virtue of a reductive action of the
surfactant (patent-related reference 3).
[0020] It has been further reported to add: a reversed micelle
solution (II) prepared by mutually mixing a nonaqueous organic
solvent containing a surfactant and a pertinent type of metal salt
solution containing noble metal; into a reversed micelle solution
(I) prepared by mutually mixing a nonaqueous organic solvent
containing a surfactant and a water solution of reducing agent;
followed by a reductive reaction, to produce metal nanoparticles in
the resultant solution (patent-related reference 4).
[0021] It has been also reported to dissolve an organo-metallic
compound of fatty acid, a metal complex of amine, or a mixture
thereof in a nonpolar solvent, followed by addition of a reducing
agent for reduction treatment, thereby obtaining metal
nanoparticles in the solution (patent-related reference 5).
[0022] Moreover, it has been reported to add a reducing agent into
a metal salt solution containing a surfactant, and to irradiate
light thereto, followed by a reaction under still standing in a
dark place, thereby growing metal nanorods in the solution
(patent-related reference 6).
[0023] Furthermore, it has been also reported to cause metal
nanoparticles to be attached onto a substrate without using a
crosslinking agent, and to grow nanoparticles on the substrate by
utilizing the attached nanoparticles as nuclei, to coat a surface
of the substrate (patent-related reference 7).
[0024] Referenced literatures/publications:
[0025] Non-patent reference 1: Hiroh Tominaga, and 1 other,
Chemical Outline, "Catalyst Design", edited by Chemical Society of
Japan, 1982, pp. 50-63,
[0026] Non-patent reference 2: Masayuki Uchida, and 2 others,
Catalyst, 22, 310 (1977)
[0027] Non-patent reference 3: Hiromichi Arai, and 1 other,
"Ultra-fine particle-Its chemistry and function", Asakura
Publishing Co., Ltd., 1993, pp. 124-128
[0028] Non-patent reference 4: N. Toshima, and 1 other, Bull. Chem.
Soc. Jpn., 65, 400 (1992)
[0029] Non-patent reference 5: A. Fukuoka, and 7 others, Catalysis
Today, 66, 23-31 (2001)
[0030] Non-patent reference 6: Yoshiaki Fukushima, Ceramics, 36,
917-919 (2001)
[0031] Non-patent reference 7: C. T. Kresge, and 4 others, Nature,
359, pp. 710-712 (1992)
[0032] Non-patent reference 8: Takeshi Kijima, and 1 other, J. Soc.
Inorg. Mater, 8, pp. 3-16 (2001)
[0033] Non-patent reference 9: G. S. Attard, and 4 others, Angew.
Chem. Int. Ed. 36, 1315-1317 (1997)
[0034] Non-patent reference 10: G. S. Attard, and 5 others,
Science, 278, 838-840 (1997)
[0035] Non-patent reference 11: A. H. Whitehead, and 3 others,
Chem. Comm., 331-332 (1999)
[0036] Non-patent reference 12: H. J. Shin, and 3 others, J. Am.
Chem. Soc., 123, 1246-1247 (2001)
[0037] Non-patent reference 13: H. Masuda, and 1 other, Science,
268, 1466-1468 (1995)
[0038] Non-patent reference 14: O. D. Velev, and 3 others, Nature,
401, 548 (1999)
[0039] Non-patent reference 15: H. Wakayama, and 1 other, Chem.
Comm., pp. 391-392 (1999)
[0040] Non-patent reference 16: Michihiro Asai, and 2 others,
Industrial Material, 50, pp. 27-30 (2002)
[0041] Non-patent reference 17: S. Iijima, Nature, 364, pp. 56-58
(1991)
[0042] Non-patent reference 18: M. E. Spahr, and 5 others, Angew.
Chem. Int. Ed, 37, pp. 1263-65 (1998)
[0043] Non-patent reference 19: M. Adachi, and 2 others, Langmuir,
15, 7097 (1999)
[0044] Non-patent reference 20: H. Imai, and 4 others, J. Mater.
Chem., 9, 2971 (1999)
[0045] Non-patent reference 21: M. Yada, and 4 others, Adv. Mater.,
14, 309-313 (2002)
[0046] Non-patent reference 22: C. R. Martin, and 3 others, J.
Phys. Chem. B, 105, pp. 11925-11934 (2001)
[0047] Non-patent reference 23: K. B. Jirage, and 2 others, Anal.
Chem., 71, 4913-4918 (1999)
[0048] Non-patent reference 24: V. Badri, and 1 other, Int. J.
Hydrogen Energy, 25, 249-253 (2000)
[0049] Non-patent reference 25: Takeshi Kijima, and 6 others,
Angew. Chem. Int. Ed., 43, 228-232 (2004)
[0050] Non-patent reference 26: Y. Song, and 11 others, J. Amer.
Chem. Soc., 126, 635-645 (2004)
[0051] Non-patent reference 27: M. Shirai, and 2 others, Chem.
Comm., pp. 623-624 (1999)
[0052] Patent-related reference 1: JP-A-2004-034228
[0053] Patent-related reference 2: JP-A-2000-54012
[0054] Patent-related reference 3: JP-A-2003-105401
[0055] Patent-related reference 4: JP-A-2003-239006
[0056] Patent-related reference 5: JP-A-2005-81501
[0057] Patent-related reference 6: JP-A-2005-97718
[0058] Patent-related reference 7: JP-A-2005-187915
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0059] Since noble metal elements, particularly Pt, are finite
resources present in extremely small amounts, developments have
been conducted to effectively utilize them, under three guidelines:
(1) to increase surface areas of a Pt material contributing to
reactions, by decreasing particle diameters of the material
(particle diameter control), and by uniformly dispersing the
material (devise of carrying manner); (2) to devise a structure
(form) of the Pt material; and (3) to search for a new material
other than Pt.
[0060] Under such circumstances for development, there have been
extremely numerously developed synthesis techniques for obtaining
products controlled at a nano-level based on the template-based
synthesis method, as referred to in the above-mentioned literatures
and publications. As a result, it has been succeeded in obtaining
fine products such as wires in nanometer sizes, particulate or
film-like madreporic bodies having pores in a honeycomb shape or a
three-dimensional network shape, nanotubes, two-dimensional or
three-dimensional dendric particles, and single crystalline
spherical particles having diameters of 10 nm, in a manner to show
results corresponding to the development objects (1) and (2),
thereby exhibiting a prima facie significance. However, the
production amounts of noble metal elements, particularly Pt
material, are extremely low such that it will be considerably hard
to sufficiently deal with a demand to be expected from now on
mainly based on fuel cells insofar as in view of the existent
amount of the resource and the development level at present. Thus,
it is worried that the situation is urgent.
[0061] As such, although it has been made possible to obtain
particles in nano-sizes by the above-described various techniques
to obtain the prima facie result, there has been demanded a
technique contributing to more effective utilization of the metals
in extremely small amounts. By virtue of such a technique, it can
be expected to exemplarily realize improved material designs such
as enhanced freedom degrees of material selection and higher
performances, in various technical fields utilizing noble metal
elements.
[0062] Further, in case of the template-based synthesis methods
each configured to utilize a molecule aggregate structure to be
formed in a solution, there are such exemplary problems that
particles caused in the course of production of platinum particles
relatively tend to aggregate, and that the molecule aggregate is
subjected to a structural change thereof. There is thus demanded a
new technique for solving such problems.
[0063] Metal catalysts are typically provided in forms of complex
particles comprising solid carriers and metal particles carried on
surfaces of the solid carriers, and activities of the metal
catalysts vary depending on sizes of the carried metal fine
particles, kinds of crystal faces, kinds of the carriers,
dispersibilities, and coating ratios, respectively. As such, there
is demanded a metal particle carrying method capable of
simultaneously realizing not only control of size, form, and the
like of metal particles, but also a higher dispersibility and a
higher coating ratio.
[0064] As described above, it has been considerably problematic to
use a lot of expensive platinum in practical use of recently
noticed solid polymer fuel cells, and it is desired to immediately
develop a platinum particle carrier including the metal catalyst in
a remarkably decreased amount so as to increase an efficiency of
platinum. For example, there is an estimation result that the
amount of platinum in the world is insufficient if 10,000,000 fuel
cell vehicles are manufactured, insofar as platinum is kept to be
used at the rate in the present state. Thus, to decrease the usage
amount of platinum, it is naturally an important factor to devise a
platinum carrying manner, by exemplarily controlling a form of
platinum nanoparticles. However, even when it becomes possible to
control the form of platinum nanoparticles, expensive catalyst
materials are uselessly consumed when the particles are stacked one
above the other upon deposition onto a surface of a carrier.
Therefore, in case of depositing particles onto a surface of a
carrier, it is extremely important not only to control the form of
particles but also to carry the particles thinly on the carrier
surface as single layers without stacking the particles one above
the other, and there is demanded such a controlling technique.
Means for Solving the Problem
[0065] The present inventors intend to provide a solution to the
demand, in view of the related art including the above-mentioned
various investigations and reports and the prior art concerning
platinum nanoparticles. Namely, there have been earnestly conducted
investigations of a method for immobilizing surfactant micelles at
a solid/solution interface (solid-liquid interface two-dimensional
micelles), and kinds of metal sources and reducing agents to be
utilized, as well as reaction conditions, so as to create noble
metal nanoparticles having novel forms different from the
conventional, by virtue of a novel synthetic method utilizing, as a
template, surfactant micelles immobilized at the solid/solution
interface.
[0066] As a result, it has been discovered that it is possible to
adopt one kind or two kinds of surfactants as well as a carrier
substrate to form two-dimensional micelles at solid-liquid
interfaces and to reduce by hydrazine a platinum chloride salt
previously incorporated into the micelles, in a manner to utilize
the micelles immobilized at the graphite carrier surface as
reaction fields to reduce platinum ions, thereby producing or
growing thinfilm-like particles (thickness: about 2 to 5 nm) each
in a shape of disk, rod, plate, or sheet which is extremely thin
and has a single crystalline frame of platinum.
[0067] It has been appreciated that forms of platinum nanoparticles
or the like to be produced by utilizing interiors of micelles as
reaction fields, strongly depend on metal salt concentrations in
the micelles. The concentrations of metal salt such as noble metal,
particularly chloroplatinic acid in micelles which dictate particle
forms in this technique, can be changed by using two kinds of
surfactants and by varying the mixing ratio thereof, thereby
succeeding in enabling control of forms, sizes, and arrangements of
metal particles on the carrier substrate surface, and in
simultaneously depositing the metal particles thinly as single
layers, respectively.
[0068] In the present invention, it is required that micelles are
formed by one kind or two kinds of surfactants, and the micelles
are utilized as reaction fields, and it is desirable to use two
kinds of surfactants. This is because, although it is difficult to
arbitrarily control micelles as reaction fields and metal salt
concentrations in the micelles in case of adoption of one kind of
surfactant, this can be facilitated by combining two kinds of
surfactants with each other to facilitate controlling of forms,
sizes, arrangements, and the like of particles on the carrier
substrate surface.
[0069] It has been appreciated that platinum ultrathin-film-like
particles to be produced by virtue of micelles immobilized on a
substrate according to the technique of the present invention are
particles controlled in particle form, size, and arrangement
relative to the substrate, which particles are different from those
bulk particles in indeterminate forms to be deposited from the
interior of a solution by the solution reduction method and duly
carried, and are different from those particles to be produced from
simple micelles which are molecule aggregate templates in varying
structures. According to the technique of the present invention, it
is possible to produce extremely thin platinum particles on a solid
substrate, each having a size of several tens nanometers or more
and a thickness of only several nanometers. Because a platinum
catalyst provides a reaction only on the surface thereof and the
interior of the catalyst does not participate in the reaction, the
technique of the present invention is extremely useful in improving
a reactivity since platinum particles are thinly carried on a
carrier surface in a single layer form. Further, as compared with
simple particle forms, the thinfilm-like noble metal nanoparticles
exhibit functions and effects of increased surface energies at
peripheral portions, thereby resultingly allowing the noble metal
nanoparticles to be expected as a catalyst material having a higher
catalytic ability.
[0070] The technique of the present invention is configured to
reduce an extremely small amount of platinum source (only an amount
concentrated on a solid surface) concentrated in solid-liquid
interface two-dimensional micelles to thereby carry platinum
particles on the substrate surface in one step, and is thus capable
of remarkably decreasing a usage amount of a platinum source as
compared with the conventional technique to be conducted in two
steps ("production of platinum particles"+"carriage of platinum
particles onto solid surface").
[0071] The technique carried out for platinum has been applied to
other metals and investigations therefor have been advanced,
thereby resultingly obtaining a knowledge that metals other than
platinum (Pt) such as gold (Au), silver (Ag), palladium (Pd),
rhodium (Rh), iridium (Ir), ruthenium (Ru) and the like can also be
subjected to the synthesis as described above. The present
invention has been carried out based on such a knowledge, and is
configured in the manner described in the following items (1)
through (21).
[0072] (1) A single crystalline noble metal ultrathin-film
determinate-form nanoparticle characterized in that the single
crystalline noble metal ultrathin-film determinate-form
nanoparticle is produced in a solid-liquid interface
two-dimensional micelle acting as a reaction field and formed of
one kind or two kinds of surfactants on a carrier substrate;
[0073] that the single crystalline noble metal ultrathin-film
determinate-form nanoparticle is constituted of at least one kind
of noble metal selected from a group consisting of platinum (Pt),
gold (Au), silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir),
and ruthenium (Ru); and
[0074] that the single crystalline noble metal ultrathin-film
determinate-form nanoparticle exhibits an ultrathin film shape
having a thickness in a range of 2 to 5 nm, and has an arbitrary
contour selected from a shape of disk, rod, plate, and sheet.
[0075] (2) The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of item (1), characterized in that
the carrier substrate is any one of graphite, mica, and silica.
[0076] (3) The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of item (1), characterized in that
means for producing the noble metal nanoparticle in the micelle is
provided by a reductive reaction conducted within the micelle as
the reaction field.
[0077] (4) The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of item (3), characterized in that
the reductive reaction is achieved by hydrazine.
[0078] (5) The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of any one of items (1) through (3),
characterized in that the noble metal nanoparticle is picked up in
a state carried by the carrier, by picking up the carrier substrate
after the reductive reaction followed by drying.
[0079] (6) The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of item (5), characterized in that
the noble metal particle picked up in the state carried on the
carrier is collected by separating the noble metal particle from
the carrier substrate.
[0080] (7) The single crystalline noble metal ultrathin-film
determinate-form nanoparticle of any one of items (1) through (6),
characterized in that the noble metal is platinum.
[0081] (8) A production method of a single crystalline noble metal
ultrathin-film determinate-form nanoparticle, characterized in that
the method comprises the steps of:
[0082] preparing a micelle forming solution containing one kind or
two kinds of surfactants at a micelle concentration;
[0083] subsequently immersing a carrier substrate into the micelle
forming solution, to cause a micelle formed in a rod-like shape
having a semicircle cross-section to be formed on and immobilized
to the carrier substrate;
[0084] subsequently adding a solution containing a noble metal ion
into the micelle to thereby contain the noble metal ion within the
micelle at solid-liquid interfaces; and
[0085] subsequently causing a reducing agent to act on the micelle
containing therein the metal ion to thereby progress a reductive
reaction within the immobilized micelle as a reaction field, to
produce a single crystalline noble metal ultrathin-film
determinate-form nanoparticle exhibiting a thin-film shape having a
thickness in a range of 2 to 5 nm and having an arbitrary contour
selected from a shape of disk, rod, plate, and sheet, by utilizing
the immobilized micelle as a template.
[0086] (9) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of item (8),
characterized in that the two-dimensional micelle as the reaction
field is adjusted in shape and size, to thereby adjust a shape and
a size of the produced noble metal ultrathin-film determinate-form
nanoparticle.
[0087] (10) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of item (8),
characterized in that the noble metal ion is one kind of ion
selected from platinum (Pt), gold (Au), silver (Ag), palladium
(Pd), rhodium (Rh), iridium (Ir), and ruthenium (Ru) ions.
[0088] (11) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of item (8),
characterized in that the surfactant for forming the
two-dimensional micelle comprises one kind or two kinds of
surfactants so that the noble metal thinfilm-like particle is
controlled in thickness, shape, and size, by changing the kind of
the surfactant, or the kinds of the surfactants and a mixing ratio
therebetween.
[0089] (12) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of item (8),
characterized in that the noble metal ion within the micelle is
changed in concentration, to control the single crystalline
platinum thinfilm-like particle in thickness, size, and the
like.
[0090] (13) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of item (8),
characterized in that the carrier is one kind of carrier selected
from graphite, mica, and silica.
[0091] (14) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of item (8),
characterized in that the reductive reaction is achieved by
hydrazine.
[0092] (15) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of any one of
items (8) through (14), characterized in that the noble metal
nanoparticle exhibits a single two-dimensional film shape grown to
have one side dimension of 50 nm or more.
[0093] (16) The production method of a single crystalline noble
metal ultrathin-film determinate-form nanoparticle of any one of
items (8) through (15), characterized in that noble metal is
platinum.
[0094] (17) A noble metal catalyst material, characterized in that
the noble metal catalyst material includes the single crystalline
noble metal ultrathin-film determinate-form nanoparticle of any one
of items (1) through (7), to be used as an active ingredient in
catalyst design.
[0095] (18) The noble metal catalyst material of item (17),
characterized in that the noble metal catalyst material is used in
catalyst design for fuel cell.
[0096] (19) The noble metal catalyst material of item (17),
characterized in that the noble metal catalyst material is used for
designing a vehicular exhaust gas purifying catalyst.
[0097] (20) A noble metal electrode material, characterized in that
the noble metal electrode material includes the single crystalline
noble metal ultrathin-film determinate-form nanoparticle of any one
of items (1) through (7), to be used as an electrode designing
material for cell or electrolysis.
[0098] (21) A noble metal sensor material, characterized in that
the noble metal sensor material includes the single crystalline
noble metal ultrathin-film determinate-form nanoparticle of any one
of items (1) through (7), to be used as a sensor designing
material.
[0099] According to the present invention as described above, it
becomes possible to provide single crystalline noble metal
ultrathin-film nanoparticles each satisfactorily controlled to be
in a thin-film shape of disk, rod, plate, or sheet with a thickness
of 2 to 5 nm. Further, the particles can be readily controlled in
form, size, and the like and carried on a carrier substrate surface
with arbitrary forms, sizes, and arrangements in a controlled
manner, by varying a concentration of a starting noble metal salt,
such as kinds and mixing ratio of one kind or two kinds of
surfactants, a concentration of chloroplatinic acid, and the
like.
[0100] Particles intended by the present invention are single
crystalline noble metal ultrathin-film nanoparticles each having a
thickness of 2 to 5 nm and exhibiting an ultrathin-film shape
selected from disk, rod, plate, and sheet shapes, and can be grown
with a controlled arrangement thereof, by steps of: immobilizing
micelles onto a carrier substrate such as made of graphite; and
conducting a reductive reaction within the immobilized micelles to
produce single crystalline noble metal particles such as
thinfilm-like platinum particles on the substrate having the formed
micelles thereon.
[0101] Examples of surfactants usable for forming micelles in the
present invention concretely include one kind or two kinds of
nonionic or ionic surfactants selected from a group consisting of:
polyoxyethylene alkyl ether such as nonaethyleneglycol
monohexadecyl ether; polyoxyethylene fatty acid esters; organic
sulfates such as dodecyl sodium sulfate, dodecyl sodium
benzenesulfonate; alkyl ammonium salts such as hexadecyltrimethyl
ammonium bromide; amine oxides such as dodecyldimethyl amine oxide;
polyoxyethylene sorbitan ester such as polyoxyethylene sorbitan
monostearate; polyoxyethylene alkylphenyl ether; and
polyoxyethylene polyoxypropylene block polymer.
[0102] In case of selecting polyoxyethylene alkyl ethers, larger
polymerization degrees of polyoxyethylene chains tend to lead to
increased thicknesses of thinfilm-like platinum particles to be
produced, so that the target of polymerization degree is 40 or
more. Concerning a mixing ratio of two kinds of surfactant
materials in case of a nonionic surfactant based mixture system
such as polyoxyethylene sorbitan ester with polyoxyethylene alkyl
ether, massive platinum particles are caused by mixing ratios of
50% or less of polyoxyethylene sorbitan ester, so that such mixing
ratios are unsuitable for preparation of single crystalline
thinfilm-like platinum particles.
[0103] On the other hand, when the ratio of polyoxyethylene
sorbitan ester is 60% or more, larger ratios lead to larger
thicknesses of thinfilm-like platinum particles to be produced.
[0104] Further, in case of adoption of alkylamine oxide, the
protonation degree of alkylamine oxide is preferably 0.3 or less.
Protonation degrees of alkylamine oxide exceeding 0.3 lead to
massive platinum particles on a substrate, thereby making it
difficult to produce thin particles.
[0105] To be added into the water solution of the above selected,
mixed, and adjusted surfactant, is one kind of platinum complex
compound selected from a group consisting of platinum complex
compounds such as hexachloro platinate. Desirable concentration
ranges of the platinum complex compound is 1 mM to 10 mM. Adjusting
a concentration of a platinum complex compound enables to control a
thickness and a surface coating ratio of thinfilm-like platinum
particles to be produced. Note that the platinum solution may be
added after formation of micelles.
[0106] The concentration of the surfactant is preferably near a
critical micelle concentration (CMC), and desirably in a range of
0.1 mM to 10 mM. Immersing a graphite substrate in the reaction
solution spontaneously forms semicylindrical micelles at a
graphite/solution interface. The micelles form complexes with the
platinum complex compound, and act as templates for growth of
thinfilm-like platinum particles ("A" in FIG. 1).
[0107] Added into the mixed water solution of the surfactant and
platinum salt is a reducing agent such as hydrazine so as to reduce
the platinum salt, thereby growing thinfilm-like platinum particles
within the micelles immobilized to the graphite substrate ("B" in
FIG. 1). This produces platinum thinfilm-like nanoparticles ("C" in
FIG. 1) characterized in that the nanoparticles are single
crystalline thinfilm-like particles (thickness: about 2 to 5 nm)
which are each extremely thin and has a frame of platinum (Pt) as a
noble metal element, and which are each a single crystal body. In
the present invention, there is adopted a reducing agent having a
higher production efficiency of metal clusters (nuclei for growth
of nanoparticles). Desirably, hydrazine as a chemical reducing
agent is used.
[0108] As described above, the production method is capable of
producing noble metal thinfilm-like particles including a group
consisting of gold (Au), silver (Ag), palladium (Pd), rhodium (Rh),
iridium (Ir), and ruthenium (Ru), in addition to platinum (Pt).
[0109] One kind or two kinds of surfactants are added into a water
solution containing, at a predetermined concentration, one or more
kinds of metal salts or metal complex compounds selected from a
group consisting of noble metal salts such as nitrate, chloride,
metal chloride acid, or noble metal complex compounds of gold (Au),
silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir), or
ruthenium (Ru).
[0110] Usable surfactants are one kind or two kinds of nonionic or
ionic surfactants selected from a group consisting of:
polyoxyethylene alkyl ether such as nonaethyleneglycol
monohexadecyl ether; polyoxyethylene fatty acid esters; organic
sulfates such as dodecyl sodium sulfate, dodecyl sodium
benzenesulfonate; alkyl ammonium salts such as hexadecyltrimethyl
ammonium bromide; amine oxides such as dodecyldimethyl amine oxide;
polyoxyethylene sorbitan ester such as polyoxyethylene sorbitan
monostearate; polyoxyethylene alkylphenyl ether; and
polyoxyethylene polyoxypropylene block polymer; and such
surfactants are added into the above solution to prepare a micelle
forming solution.
[0111] Immersed or dispersed into the micelle forming solution is
an arbitrary carrier such as graphite, followed by still standing,
to cause micelles such as in semicylindrical shapes to be arranged
and formed on the carrier substrate surface in a self-sustained
manner.
[0112] Next, there is added a reducing agent water solution such as
hydrazine into the starting reaction solution to cause a reductive
reaction on the graphite substrate, thereby producing extremely
thinfilm-like particles (thickness: 2 to 5 nm) each in a shape of
disk, rod, plate, or sheet and each having a frame made of noble
metal, i.e., a frame constituted of a structure mixedly including
one or more kinds of noble metal elements selected from a group
consisting of Au, Ag, Pd, Rh, Ir, and Ru at an arbitrary ratio.
Note that although the noble metal salt solution has been added in
the step of preparation of the micelle forming solution, the noble
metal salt solution may be added after formation of micelles.
EFFECT OF THE INVENTION
[0113] Unlike the conventional noble metal particles, the present
invention provides the noble metal nanoparticles with only an
extremely small amount of platinum source by virtue of the
above-mentioned unique synthesis process, and the present invention
can provide composites each including a carrier substrate and
single crystalline ultrathin-film nanoparticles of noble metal
represented by platinum and carried on the carrier substrate, in a
manner that the nanoparticles exhibit unique and novel
ultrathin-film shapes having controlled forms, sizes, and
arrangements and are controlled to have thicknesses in "nm" ranges
with an extremely fine precision. Even without separation of the
noble metal nanoparticles from the composites, such composites can
be each directly and exemplarily utilized in themselves as: a fuel
cell-oriented catalyst configured to react hydrogen with oxygen and
to extract electrical energy; a catalyst such as utilized in
vehicular exhaust gas purification, petrochemical industry,
synthesis gas production, production of medicine and fat and oil,
and the like; and an ultra fine sensor material, electrode
material, and the like; so that the composites are expected to
remarkably contribute to development of the industry.
BEST MODE FOR CARRYING OUT THE INVENTION
[0114] The invention in the present application possesses the above
features, and the present invention will be concretely described
based on embodiments and the accompanying drawings. However, these
embodiments merely disclose one aspect of the present invention,
and are never intended to limit the present invention. Namely, the
present invention resides in a production method of single
crystalline thinfilm-like platinum particles characterized in that
the single crystalline thinfilm-like platinum particles are grown
within micelles immobilized on a carrier substrate such as made of
graphite as noted above.
[0115] The production method of the present invention can also be
applied to noble metals (Au, Ag, Pd, Rh, Ir, and Ru) in addition to
platinum, thereby allowing diversified thinfilm-like noble metal
particles. As the substrate for immobilizing micelles thereon, it
is possible to use substrates comprising inorganic substances such
as mica, silica, and the like, in addition to graphite.
[0116] Further, the production method has its essential feature to
reduce a metal salt within micelles immobilized on a graphite
substrate to thereby induce thinfilm-like noble metal particles of
particular dimensions and in shapes of disk, rod, plate, or sheet,
in a manner to control forms, sizes, and arrangements of the
thinfilm-like noble metal particles produced on the substrate.
Concretely, these characteristics can be varied by kinds,
combinations, concentrations, and the like of surfactants,
including forms thereof. Thus, the embodiments to be described
hereinafter exhibit mere examples of such configurations of
surfactants, and the present invention is not limited to such
embodiments.
[0117] The platinum thinfilm-like particles in sheet-like shapes
obtained by the present invention are analogous to platinum
thinfilm-like particles in sheet-like shapes described in the
previously mentioned prior reference (non-patent reference 27), in
terms of shape. However, the platinum thinfilm-like particles in
sheet-like shapes obtained by such a report are not proven nor
mentioned to be single crystalline.
[0118] Contrary, in the present invention as apparent from an
electron photomicrograph (FIG. 3) of Example 1 to be described
hereinafter, even those platinum thinfilm-like particles in
sheet-like shapes which each have one side of 50 nm or more have
been proven to be single crystals, respectively, based on lattice
patterns thereof, and are basically and remarkably different from
the conventional. Further, there has also been confirmed formation
of a platinum thinfilm-like particle domain having one side of
1,000 nm or more, by an atomic force photomicrograph. Also, the
production method of the platinum thinfilm-like particles of the
present invention is perfectly different from the prior
reference.
[0119] While the prior reference utilizes spaces between graphite
layers, the present invention utilizes micelles immobilized on a
graphite substrate as reaction fields, respectively. Further, based
on the difference of the reaction manner, although it is difficult
in the prior reference to collect platinum thinfilm-like particles
produced between graphite layers, it is possible in the present
invention to readily collect the platinum thinfilm-like particles
such as by ultrasonic irradiation because the platinum
thinfilm-like particles are produced at the graphite substrate
surface.
[0120] Further, since platinum thinfilm-like particles are produced
at a solid surface, it is possible to carry the platinum particles
on the solid surface at an extremely small thickness in a
nano-order, and to carry the particles at an arbitrary coating
ratio between smaller and larger values. This allows expensive
noble metals such as platinum to be effectively utilized.
[0121] The present invention as described above is configured to
immerse a substrate into a liquid phase containing noble metal ions
in the presence of a surfactant(s) to fix surfactant micelles onto
the substrate in a manner to grow thinfilm-like noble metal
crystals by virtue of a reductive reaction within the micelles
restricted by the substrate, such that the produced thinfilm-like
noble metal particles are formed not only into mere nanoparticles
but also into shapes of disk, rod, plate, or sheet. This is the
essential point of the present invention.
[0122] Against the present invention, also the patent-related
reference (patent-related reference 7) describes that noble metal
nanoparticles are deposited in a solution by virtue of an action of
a reducing agent, from a liquid phase containing noble metal ions
in the presence of a surfactant. However, the configurations of the
noble metal nanoparticles obtained by such a report are bulky and
massive particles, and are never proven nor mentioned to be single
crystalline. To the contrary, the present invention provides
thinfilm-like noble metal nanoparticles which are not simple
nanoparticles but are arbitrarily controllably formed into
particles in shapes of disk, rod, or sheet with thicknesses of 2 to
5 nm as apparent from electron photomicrographs in Examples 1, 7,
and 8, which is the fundamental and decisive difference of the
present invention. As compared to simple particle forms, the
extremely thinfilm-like forms exhibit such functions and effects
that surface energies at peripheral portions of the thinfilm-like
noble metal nanoparticles are increased, so that the thinfilm-like
noble metal nanoparticles can be resultingly expected as catalyst
materials having higher catalytic abilities.
[0123] Moreover, the present invention is configured to cause
nanoparticles to be deposited on a substrate in a self-creating
manner, thereby advantageously and extremely decreasing the usage
amount of platinum to be required for carrying noble metal
nanoparticles on a substrate, as compared with the patent-related
reference 7. Additionally, the present invention is characterized
in that nanoparticles can be not only deposited on a substrate in a
self-creating manner but also simultaneously controlled in
arrangement of nanoparticles themselves on the substrate. This
leads to a remarkable difference from the patent-related reference
7 which is configured to simply reduce and deposit nanoparticles
from interior of a solution onto a substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0124] FIG. 1 is a schematic view of a production process of
thinfilm-like platinum particles (platinum nano-sheets) to be
produced in Tween60 rod-like micelles as reaction fields at a
graphite/solution interface.
[0125] FIG. 2 is a view of images observed within a liquid by an
atomic force microscope (AFM) of forms of rod-like micelles formed
at a graphite/solution interface, in cases of (a) without addition
of a platinum chloride salt, and (b) with addition of a platinum
chloride salt.
[0126] FIG. 3 is a view of (a) an AFM image and (b) a
high-resolution transmission electron microscope (TEM) image of
sheet-like thinfilm-shaped platinum particles produced in Tween60
rod-like micelles as reaction fields at a graphite/solution
interface.
[0127] FIG. 4 is a view of (b) an image of forms of Tween60
rod-like micelles formed at a graphite/solution interface, observed
within a liquid by an atomic force microscope (AFM), (a) an AFM
image of thinfilm-like platinum particles produced in the rod-like
micelles as reaction fields, and (c) a major axis direction (arrow)
of rod-like micelles and an orientation of thinfilm-like platinum
particles.
[0128] FIG. 5 is a view of AFM images of thinfilm-like platinum
particles produced in Tween60/C.sub.12EO.sub.9 mixed rod-like
micelles as reaction fields at a graphite/solution interface.
[0129] FIG. 6 is a view of phase images by AFM observation of (a)
thinfilm-like palladium particles (black portions) and (b)
thinfilm-like gold particles (white portions) produced in Tween60
rod-like micelles as reaction fields at a graphite/solution
interface.
[0130] FIG. 7 is a view of an AFM image and a transmission electron
microscope (TEM) image of rod-like platinum particles produced in
rod-like micelles by dodecyldimethyl amine oxide (protonation
degree .alpha.=0.2) as reaction fields at a graphite/solution
interface.
[0131] FIG. 8 is a graph of protonation degree (a) dependency of
sizes of rod-like platinum particles produced in rod-like micelles
by dodecyldimethyl amine oxide as reaction fields at a
graphite/solution interface.
[0132] FIG. 9 is a schematic view of a synthetic method of
disk-like platinum nanoparticles produced on a substrate and in
nanofiber-like micelles of hexadecyltrimethyl ammonium hydroxide as
reaction fields at a graphite/solution interface.
[0133] FIG. 10 is a view of an AFM image and a transmission
electron microscope (TEM) image of disk-like platinum nanoparticles
produced on a substrate and in nanofiber-like micelles of
hexadecyltrimethyl ammonium hydroxide as reaction fields at a
graphite/solution interface.
[0134] FIG. 11 is a view of (a) an AFM image of nanofiber-like
micelles of hexadecyltrimethyl ammonium hydroxide at a
graphite/solution interface, and (b) a transmission electron
microscope (TEM) image of disk-like gold nanoparticles produced on
a substrate and in the micelles as reaction fields.
[0135] FIG. 12 is a schematic view of a synthesis process of thin
plate-like platinum particles (platinum nano-sheets) produced in
Tween60 rod-like micelles as reaction fields at a graphite/solution
interface.
[0136] The present invention will be more concretely described
based on the drawings and embodiments.
[0137] FIG. 1 is a conceptual explanatory view of a process for
forming thin platinum nanoparticles or nano-sheets according to the
present invention as previously described in detail exemplarily
based on platinum.
[0138] FIG. 2 is a view of images observed within a liquid by an
atomic force microscope (AFM) of forms of rod-like micelles formed
at a graphite/solution interface. In this figure, white striped
domains are Tween60 rod-like micelles in cases of (a) without
addition of a platinum chloride salt and (b) with addition of a
platinum chloride salt, and it is recognized that forms of rod-like
micelles are changed based on interactions between the platinum
chloride salt and rod-like micelles.
[0139] FIG. 3 is a view of (a) an AFM image and (b) a
high-resolution transmission electron microscope (TEM) image of
thinfilm-like platinum particles produced in Tween60 rod-like
micelle as reaction fields at a graphite/solution interface. From
the AFM image, it was recognized that the thinfilm-like platinum
particles had thicknesses of 2 to 5 nm, and surfaces thereof had a
root-mean-square plane roughness of 0.15 nm. There was observed a
lattice fringe with an interval of 0.23 nm (Pt(111) interlayer
spacing) and a Fourier image thereof from the TEM image, so that
the thinfilm-like platinum particles were each recognized to be
constituted of a single piece of single crystal body as a whole of
the particle.
[0140] FIG. 4 shows (b) an AFM image of Tween60 rod-like micelles
at a graphite/solution interface, and (a) an AFM image of
thinfilm-like platinum particles (platinum nano-sheets) produced in
the rod-like micelles as reaction fields. The AFM images exemplify
that thinfilm-like platinum particles having thicknesses of 2 to 5
nm are produced on a substrate. Then, since platinum nano-sheets
have characteristics to grow in major axis directions of rod-like
micelles, it is observed that also the produced thinfilm-like
platinum particles are oriented in directions different from one
another by 60 degrees similarly to orientations of the rod-like
micelles acting as reaction fields.
[0141] FIG. 5 is a view of AFM images of thinfilm-like platinum
particles produced in Tween60/C.sub.12EO.sub.9 mixed rod-like
micelles as reaction fields at a graphite/solution interface, and
production of platinum thinfilm-like particles was recognized at
mole fractions .gamma. of 0.7 or more of Tween60. It was confirmed
that thicknesses of platinum thinfilm-like particles depend on
.gamma. (i.e., 0.5 to 1 nm by .gamma. of 0.7, and 2 to 4 nm by
.gamma. of 0.8, and 2 to 5 nm by .gamma. of 1). Meanwhile, it was
impossible to confirm production of platinum
thinfilm-like-nanoparticles by .gamma. of 0.5 or less, and striped
domains representing rod-like micelles were merely observed.
[0142] FIG. 6 shows phase images by AFM observation of (a)
thinfilm-like palladium particles (black portions) and (b)
thinfilm-like gold particles (white portions) produced in Tween60
rod-like micelles as reaction fields at a graphite/solution
interface.
[0143] FIG. 7 shows (a) an AFM image of rod-like micelles
(protonation degree .alpha.=0.2) of dodecyldimethyl amine oxide at
a graphite/solution interface, (b) an AFM image of rod-like
platinum nanoparticles produced on a substrate and in the micelles
as reaction fields, and (c) a transmission electron microscope
(TEM) image of the particles. The AFM images show that the platinum
particles are rod-like shapes (or necklace-like shapes) having
thicknesses of about 3 to 4 nm and diameters of about 10 nm, and
are produced on the substrate.
[0144] Further, identically to orientations (black arrows) of
rod-like micelles, the produced rod-like platinum particles are
observed to be also oriented (black arrows) in directions different
from one another by 60 degrees. At this time, sizes and forms of
platinum particles produced on the substrate were found to be
controllable by a protonation degree .alpha. of rod-like micelles
(FIG. 8). Namely, it is shown that sizes and the like of particles
depend on the protonation degree .alpha., according to FIG. 8.
[0145] Here, the protonation degree .alpha. is defined as
.alpha.=[cation type amine oxide surfactant]/[cation type amine
oxide surfactant+nonionic type amine oxide surfactant]. .delta.
represents a thickness of a platinum particle, and D represents a
diameter thereof. It was proven that platinum nanoparticles are
produced only when a protonation degree is 0.3 or less.
[0146] FIG. 9 schematically shows a synthetic method of disk-like
platinum nanoparticles produced on a substrate and in
nanofiber-like micelles of hexadecyltrimethyl ammonium hydroxide as
reaction fields at a graphite/solution interface.
[0147] FIG. 10 shows (a) an AFM image and (b) a transmission
electron microscope (TEM) image of disk-like platinum nanoparticles
produced on a substrate and in nanofiber-like micelles of
hexadecyltrimethyl ammonium hydroxide as reaction fields at a
graphite/solution interface. Based on the AFM image and TEM image
of this figure, it is shown that disk-like platinum nanoparticles
having thicknesses of about 3 nm are produced in a highly dispersed
state on the substrate.
[0148] FIG. 11 shows (a) an AFM image of nanofiber-like micelles of
hexadecyltrimethyl ammonium hydroxide at a graphite/solution
interface, and (b) a transmission electron microscope (TEM) image
of disk-like gold nanoparticles produced on a substrate and in the
micelles as reaction fields. Based on the AFM image and TEM image,
it is shown that disk-like gold nanoparticles having thicknesses of
about 1 to 3 nm are produced in a highly dispersed state on the
substrate.
[0149] As described later, FIG. 12 schematically shows a synthesis
process of thin plate-like platinum particles (platinum
nano-sheets) produced in Tween60 rod-like micelles as reaction
fields at a graphite/solution interface.
[0150] Note that although the present invention will be concretely
disclosed based on Examples, the present invention is not limited
thereto.
EXAMPLE 1
[0151] Added into a weighing bottle was 10 mL of a weighed water
solution (0.5 mM) of polyoxyethylene (20) sorbitan monostearate
(Tween60: product name sold by Atlas Powder Company in U.S.).
Immersed into this solution was a highly oriented graphite
substrate (HOPG), thereby causing semicylindrical rod-like micelles
to be spontaneously formed at a graphite/solution interface.
[0152] Next, 1 mL of hexachloro platinate water solution (0.1 M)
was added, thereby establishing a reaction solution. At this time,
rod-like micelles adsorbed on the graphite substrate surface
cooperated with platinum complex compounds to form composites which
acted as templates for growth of thinfilm-like platinum particles.
FIG. 2 shows images observed within a liquid by an atomic force
microscope (AFM) of shapes of rod-like micelles formed at a
graphite/solution interface.
[0153] Subsequently, 1.5 molar equivalent of hydrazine relative to
chloroplatinic acid was added to the reaction solution held at
25.degree. C. to conduct chemical reduction of the platinum
chloride salt, and the solution was left stand still as it was for
48 hours. In this way, thinfilm-like platinum particles were grown
within rod-like micelles immobilized on the graphite substrate. At
this time, since massive platinum particles (bulk particles)
produced in the solution were to be possibly deposited on the
graphite substrate surface, the reaction was conducted by fixingly
directing the graphite substrate downwardly so as to prevent
deposition of bulk particles.
[0154] This is because, in addition to platinum particles to be
controlledly formed within micelles as reaction fields on the
carrier substrate, part of the platinum salt contained in the
solution is to be possibly and directly reduced by the action of
hydrazine and deposited as bulky and massive platinum particles
which precipitate onto the carrier substrate and are thus deposited
thereon. To avoid it, the graphite substrate was downwardly
oriented and fixed.
[0155] The reductive reaction to be conducted in micelles as
reaction fields is distinguished from deposition of massive
particles in that the former resides in reduction within micelles
downwardly oriented and formed in a self-creating manner on the
downwardly oriented substrate so as to avoid deposition of massive
particles due to precipitation. At the time when deposition and
precipitation of platinum particles by hydrazine were completed
after lapse of several days, the graphite substrate was taken out
of the solution, followed by drying, thereby enabling obtainment of
thinfilm-like platinum particles on the graphite substrate surface
(FIG. 12).
[0156] The sheet-like thinfilm platinum particles thus formed on
the graphite substrate surface exhibited an AFM image as shown in
FIG. 3(a). Spherical domains originated from thinfilm-like platinum
particles were observed, and it was shown that the thinfilm-like
platinum particles had thicknesses of 2 to 5 nm based on a
cross-sectional view of the thinfilm-like platinum particles
obtained as the AFM image. It was further confirmed that surfaces
of the thinfilm-like platinum particles had a root-mean-square
plane roughness of 0.15 nm, thereby enabling confirmation that the
surfaces were flat and smooth at an atomic level. According to
observation (FIG. 3(b)) by a transmission electron microscope,
there was observed a lattice fringe with an interval of 0.23 nm
(Pt(111) interlayer spacing) and a Fourier image thereof, so that
the thinfilm-like platinum particles were each recognized to be
constituted of a single piece of single crystal body as a whole of
the particle. This allowed for recognition of obtainment of single
crystalline platinum thinfilm-like particles according to the
present invention.
EXAMPLE 2
Concentration Effect of Chloroplatinic Acid Water Solution on
Production of Platinum Thinfilm-Like Particle in Sheet-Like
Shape
[0157] Semicylindrical rod-like micelles were spontaneously formed
at graphite/solution interfaces, by the same procedures and under
the same conditions as Example 1, respectively. Next, added into
the water solutions including precursory rod-like micelles at the
graphite substrate surfaces, were chloroplatinic acid water
solutions so as to attain their concentrations of 0.02 mM, 0.1 mM,
1 mM, and 10 mM, respectively.
[0158] Next, 2 molar equivalent of hydrazine relative to
chloroplatinic acid was added into each reaction solution held at
25.degree. C., followed by reaction for 24 hours as it was. In this
way, thinfilm-like platinum particles were grown within rod-like
micelles immobilized on the graphite substrates, respectively. At
this time, the graphite substrates were downwardly oriented and
fixed, to avoid deposition of massive platinum particles produced
in the solutions onto the graphite substrate surfaces,
respectively. After precipitation of massive platinum particles
produced in the solutions, the graphite substrates were taken out
of the solutions, followed by drying, to obtain thinfilm-like
platinum particles on the graphite substrate surfaces,
respectively.
[0159] In cases of the 0.1 mM and 1 mM concentrations of
chloroplatinic acid water solutions, platinum particles were
obtained at the graphite substrate surfaces, and confirmed to be
platinum thinfilm-like particles having thicknesses of about 2 to 5
nm from cross-sectional views of the thinfilm-like platinum
particles obtained from AFM images, respectively. On the other
hand, in case of the 10 mM concentration of chloroplatinic acid
water solution, there was confirmed, by an AFM image, production of
platinum thinfilm-like particles each having a three-dimensionally
stacked structure of a thickness of 10 nm or more based on a
structure including stacked platinum thinfilm-like particles each
having a thickness of about 4 nm. In turn, there was not confirmed
production of platinum thinfilm-like particles, in case of the 0.02
mM concentration of chloroplatinic acid water solution.
EXAMPLE 3
Production of Platinum Thinfilm-Like Particle in Sheet-Like Shape
by Two-Kind Mixed Surfactant System
[0160] Semicylindrical rod-like micelles were spontaneously formed
at graphite/solution interfaces, by the same procedures and under
the same conditions as Example 1, respectively, by each adopting a
two-kind mixed system of Tween60 and nonaethyleneglycol
monohexadecyl ether (C.sub.12EO.sub.9: product name: Nikkol BL-9EX
by Wako, Japan) as surfactants, instead of Tween60 only. The whole
concentrations of surfactants were fixed at 0.5 mM, and the mole
fractions (.gamma.) of Tween60 in the two-kind mixed systems were
varied, respectively.
[0161] Next, 1.5 molar equivalent of hydrazine relative to
chloroplatinic acid was added into each reaction solution held at
25.degree. C., followed by reaction for 24 hours as it was. In this
way, thinfilm-like platinum particles were grown within rod-like
micelles immobilized on the graphite substrates, respectively. At
this time, the graphite substrates were downwardly oriented and
fixed, to avoid deposition of massive platinum particles produced
in the solutions onto the graphite substrate surfaces,
respectively. After precipitation of massive platinum particles
produced in the solutions, the graphite substrates were taken out
of the solutions, followed by drying, to obtain thinfilm-like
platinum particles on the graphite substrate surfaces,
respectively.
[0162] According to AFM observation, production of platinum
thinfilm-like particles were confirmed by .gamma. of 0.7 or more
(FIG. 5). From cross-sectional views of thinfilm-like platinum
particles obtained as AFM images, thicknesses of platinum
thinfilm-like particles were confirmed to depend on .gamma. (1 to 2
nm when .gamma.=0.7; 2 to 4 nm when .gamma.=0.8; and 2 to 5 nm when
.gamma.=1). On the other hand, production of platinum thinfilm-like
particles was not confirmed when .gamma. was 0.5 or less.
EXAMPLE 4
Effect of Polyoxyethylene Chain Lengths of Polyoxyethylene Alkyl
Ethers on Production of Platinum Thinfilm-Like Particle in
Sheet-Like Shape
[0163] Semicylindrical rod-like micelles were spontaneously formed
at graphite/solution interfaces, by the same procedures and under
the same conditions as Example 1, by adopting Polyoxyethylene
DodecylEther (C.sub.12EO.sub.23: product name: Brij 35, by KANTO
CHEMICAL CO., INC.), Polyoxyethylene 40 Stearate
(C.sub.18EO.sub.40: product name Myrh52 by SIGMA Inc., U.S.), and
Polyoxyethylene 100 Stearate (C.sub.18EO.sub.100: product name
Myrh59 by SIGMA Inc., U.S.), instead of the surfactant Tween60,
respectively. Concentrations of the surfactants were each fixed at
1 mM.
[0164] Next, 1.5 molar equivalent of hydrazine relative to
chloroplatinic acid was added into each reaction solution held at
25.degree. C., followed by reaction for 24 hours as it was. In this
way, thinfilm-like platinum particles were grown within rod-like
micelles immobilized on the graphite substrates, respectively. At
this time, the graphite substrates were downwardly oriented and
fixed, to avoid deposition of massive platinum particles produced
in the solutions onto the graphite substrate surfaces,
respectively. After precipitation of massive platinum particles
produced in the solutions, the graphite substrates were taken out
of the solutions, followed by drying, to obtain thinfilm-like
platinum particles on the graphite substrate surfaces,
respectively.
[0165] Obtained particles were subjected to AFM observation,
thereby confirming production of platinum thinfilm-like particles
in case of C.sub.18EO.sub.40. From a cross-sectional view obtained
as an AFM image of he thinfilm-like platinum particles, the
platinum thinfilm-like particles were each about 5 to 25 nm in
thickness. However, in case of C.sub.18EO.sub.100, particles were
confirmed to be each increased to several hundreds nanometers in
thickness. On the other hand, production of platinum thinfilm-like
particles was not confirmed, in case of adoption of
C.sub.12EO.sub.23. In this way, it was confirmed that thicknesses
of platinum thinfilm-like particles increased as polyoxyethylene
chain lengths of used polyoxyethylene alkyl ethers were
increased.
EXAMPLE 5
Application of Present Invention to Production of Other Noble Metal
Particle: Production of Palladium Thinfilm-Like Particle
[0166] Semicylindrical rod-like micelles were spontaneously formed
at a graphite/solution interface, by the same procedure and under
the same condition as Example 1, by adopting disodium palladium
chloride, instead of hexachloro platinate.
[0167] Next, 1.5 molar equivalent of hydrazine relative to
chloroplatinic acid was added into the reaction solution held at
25.degree. C., followed by reaction for 24 hours as it was. In this
way, thinfilm-like palladium particles were grown within rod-like
micelles immobilized on the graphite substrate. At this time, the
graphite substrate was downwardly oriented and fixed, to avoid
deposition of massive palladium particles produced in the solution
onto the graphite substrate surface. After precipitation of massive
palladium particles produced in the solution, the graphite
substrate was taken out of the solution, followed by drying, to
obtain thinfilm-like palladium particles on the graphite substrate
surface.
[0168] FIG. 6(a) shows an AFM image of thinfilm-like palladium
particles produced on the graphite substrate surface. The domains
visible in black are thinfilm-like palladium particles,
respectively, and the thinfilm-like palladium particles were
confirmed to each have a thickness of about 5 nm from a
cross-sectional view of the thinfilm-like palladium particles
obtained as the AFM image.
EXAMPLE 6
Application of Present Invention to Production of Other Noble Metal
Particle: Production of Gold Thinfilm-Like Particle
[0169] Semicylindrical rod-like micelles were spontaneously formed
at a graphite/solution interface, by the same procedure and under
the same condition as Example 1, by adopting tetrachloro aurate,
instead of hexachloro platinate.
[0170] Next, 1.5 molar equivalent of hydrazine relative to
chloroauric acid was added into the reaction solution held at
25.degree. C., followed by reaction for 24 hours as it was. In this
way, thinfilm-like gold particles were grown within rod-like
micelles immobilized on the graphite substrate. At this time, the
graphite substrate was downwardly oriented and fixed, to avoid
deposition of massive gold particles produced in the solution onto
the graphite substrate surface. After precipitation of massive gold
particles produced in the solution, the graphite substrate was
taken out of the solution, followed by drying, to obtain
thinfilm-like gold particles on the graphite substrate surface.
[0171] FIG. 6(b) shows an AFM image of thinfilm-like gold particles
produced on the graphite substrate surface. The domains visible in
white are thinfilm-like gold particles, respectively, and the
thinfilm-like gold particles were confirmed to each have a
thickness of 2 to 5 nm from a cross-sectional view of the
thinfilm-like gold particles obtained as the AFM image. Only, gold
spherical particles grown in massive forms were also observed, in
addition to thinfilm-like gold particles.
EXAMPLE 7
Production of Thinfilm-Like Platinum Particle Having Rod-Like
Shape
[0172] Semicylindrical rod-like micelles were spontaneously formed
at a graphite/solution interface, by the same procedure and under
the same condition as Example 1, by adopting dodecyldimethyl amine
oxide (Fulka Corp.), instead of the surfactant Tween60. The
concentration of the surfactant was fixed at 10 mM.
[0173] Next, 0.1 molar equivalent (1 mM) of chloroplatinic acid
relative to dodecyldimethyl amine oxide was added into the reaction
solution held at 25.degree. C., to form composites of rod-like
micelles and platinum ions. Subsequently, hydrazine (10 mM) was
added into the reaction solution held at 25.degree. C., followed by
reaction for 24 hours as it was. In this way, thinfilm-like
platinum particles having rod-like shapes were grown within
rod-like micelles immobilized on the graphite substrate. At this
time, the graphite substrate was downwardly oriented and fixed, to
avoid deposition of massive platinum particles produced in the
solution onto the graphite substrate surface. After precipitation
of massive platinum particles produced in the solution, the
graphite substrate was taken out of the solution, followed by
drying, to obtain thinfilm-like platinum particles having rod-like
shapes (or necklace-like shapes) on the graphite substrate surface
(see FIG. 7(b)).
[0174] From an AFM image, rod-like platinum particles having
thicknesses of about 2 to 4 nm and diameters of about 10 nm were
seen to be produced on the substrate. It was observed that also the
produced thinfilm-like platinum particles were oriented in
directions different from one another by 60 degrees (arrows in FIG.
7(b)) similarly to orientations of the rod-like micelles (arrows in
FIG. 7(a)). At this time, sizes of platinum particles produced on
the substrate were found to be controllable by the protonation
degree (FIG. 8).
EXAMPLE 8
Production of Thinfilm-Like Platinum Particle Having Disk-Like
Shape
[0175] Fibrous micelles were spontaneously formed at a
graphite/solution interface, by a procedure and under a condition
similar to those in Example 1, by adopting cethyltrimethyl ammonium
hydroxide (TOKYO CHEMICAL INDUSTRY Co., Ltd.), instead of the
surfactant Tween60. The concentration of the surfactant was fixed
at 10 mM. Next, 1.2 molar equivalent (12 mM) of chloroplatinic acid
relative to cethyltrimethyl ammonium hydroxide was added into the
reaction solution held at 25.degree. C. This produced precipitation
of white solid crystal comprising composites of chloroplatinic acid
and the surfactant (FIG. 9(a)). In this solution, platinum ions
caused from the white solid crystal were present.
[0176] Subsequently, immersed into this reaction solution was a
graphite (HOPG) substrate, thereby causing fibrous micelles
complexed with platinum ions to be spontaneously formed on the
graphite substrate surface (FIG. 9(a)). Next, the graphite
substrate carrying fibrous micelles thereon was immersed into pure
water (FIG. 9(b)). The fibrous micelles were stable even within
water. Hydrazine (10 mM) was added into this reaction solution held
at 25.degree. C., followed by reaction for 24 hours as it was (FIG.
9(c)). In this way, there were reduced only the platinum salts
within fibrous micelles immobilized on the graphite substrate,
thereby causing thinfilm-like platinum particles having disk-like
shapes to be grown from an extremely small amount of platinum
source. The substrate was taken out of the solution and dried, to
obtain thinfilm-like platinum particles having disk-like shapes on
the graphite substrate surface. From an AFM image and a TEM image,
it was confirmed that disk-like platinum particles having
thicknesses of about 2 to 4 nm and diameters of about 3 to 10 nm
were produced on the substrate (FIG. 10(a), (b)). It is possible to
peel off the surface of the HOPG substrate to expose a clean
surface (FIG. 9(d)), followed by immersing it into the reaction
solution (FIG. 9(a)) and the same process as the above, thereby
allowing platinum particles to be produced on the graphite
substrate surface. Platinum ions are constantly supplied from the
white solid crystal, thereby allowing the mother reaction solution
to be used again and again insofar as the white solid crystal is
present.
EXAMPLE 9
Production of Thinfilm-Like Gold Particle Having Disk-Like
Shape
[0177] Fibrous micelles were spontaneously formed at a
graphite/solution interface, by a procedure and under a condition
similar to those in Example 8, by adopting cethyltrimethyl ammonium
hydroxide (TOKYO CHEMICAL INDUSTRY Co., Ltd.). The concentration of
the surfactant was fixed at 10 mM. Next, 1.2 molar equivalent (12
mM) of tetrachloroauric acid relative to cethyltrimethyl ammonium
hydroxide was added into the reaction solution held at 25.degree.
C. This produced precipitation of white solid crystal comprising
composites of chloroauric acid and the surfactant. In this
solution, gold ions caused from the white solid crystal were
present.
[0178] Subsequently, immersed into this reaction solution was a
graphite (HOPG) substrate, thereby causing fibrous micelles
complexed with gold ions to be spontaneously formed on the graphite
substrate surface (FIG. 11(a)). Next, the graphite substrate
carrying fibrous micelles thereon was immersed into pure water. The
fibrous micelles were stable even within water. Hydrazine (10 mM)
was added into this reaction solution held at 25.degree. C.,
followed by reaction for 24 hours as it was. In this way, there
were reduced only the gold salts within fibrous micelles
immobilized on the graphite substrate, thereby causing
thinfilm-like gold particles having disk-like shapes to be grown
from an extremely small amount of gold source. The substrate was
taken out of the solution and dried, to obtain thinfilm-like gold
particles having disk-like shapes on the graphite substrate
surface. From an AFM image and a TEM image, it was confirmed that
disk-like gold particles having thicknesses of about 1 to 3 nm and
diameters of about 3 to 5 nm were produced on the substrate (FIG.
11(b)).
INDUSTRIAL APPLICABILITY
[0179] As described above in detail, the present invention has
succeeded in obtaining single crystalline noble metal
ultrathin-film determinate-form nanoparticles exhibiting
ultrathin-film shapes of thicknesses of 2 to 5 nm and having
arbitrary contours selected from disk, rod, plate, and sheet
shapes, by virtue of a simple scheme to progress a reductive
reaction in micelles made of two kinds of surfactants as reaction
fields. The present invention has succeeded in obtaining ultrathin
films having predetermined and controlled contour shapes on
arbitrary substrates, without stacking particles one above the
other, i.e., in single layer states, respectively, by a perfectly
novel method. This means that expensive noble metals are enabled to
be thinly carried on carrier surfaces, respectively, thereby
exhibiting a remarkable significance. As compared with the
conventional catalytic metal carrying methods, the present
invention allows noble metal particles to be coated onto carrier
surfaces in an extremely thin and uniform manner without stacking
one above the other, with a carried amount which is only a few
percents to a few tenth percents of the conventional, so that the
present invention can be expected to be greatly utilized in
catalyst design using noble metal elements represented by expensive
platinum, and particularly in the field of fuel cell expected to
largely grow.
[0180] Further, contour shapes of ultrathin-film nanoparticles are
controllable to enable provision of ultrathin-film nanoparticles in
forms of extremely thin and single crystalline thinfilm-like
platinum particles having arbitrarily selected contours, in a
manner to enable deposition of nanoparticles in arbitrary shapes
suitable for carrier shapes to be used for deposition and coating,
so that the ultrathin-film nanoparticles are enabled to be coated
and designed with a better efficiency than the conventional
deposition and coating in indeterminate shapes, thereby allowing
the ultrathin-film nanoparticles to be greatly utilized in various
material designs. Namely, the ultrathin-film nanoparticles enable
expression of extremely significant activities not only in catalyst
design but also in electrode design and sensor design, so that the
ultrathin-film nanoparticles can be expected to naturally exhibit
material saving effects as well as high level qualities and
functions for material design in technical fields using extremely
expensive noble metal materials.
[0181] Rare and expensive noble metal elements tend to be further
increased in demand from now on, and in consideration thereof, it
is not overstating that the present invention has a remarkable
value and a significance at the highest level. Particularly, in
consideration of the importance of development of fuel cell, the
present invention has an extremely large significance in terms of
noble metal particles represented by platinum having unique
configurations and unique gaps. Thus, the present invention can be
expected to be remarkably utilized from now on in various technical
fields, in addition to catalyst and fuel cell fields.
* * * * *