JP4958109B2 - Sheet-like platinum nanoparticles having nanoholes and method for producing the same - Google Patents

Description

  The present invention relates to a catalyst for various chemical reactions in industrial and environmental fields, such as a catalyst for a fuel cell, a catalyst for exhaust gas treatment of automobiles utilizing the chemical, electrochemical and magnetic properties of metallic platinum, and various types of electrodes for electrolysis. Electrodes for electrochemical reaction, or sheet metal nanoparticles having nanoholes, mainly composed of platinum used as basic materials or functional elements for photonics, electronics, information technology such as temperature, pressure, gas sensor elements, and the production thereof Regarding the method.

    Various electrocatalysts and gas diffusion electrodes for energy conversion and substance conversion are generally used after introducing a metal component into a conductive support such as carbon using an aqueous solution or colloidal dispersion of a metal salt, followed by firing, hydrogen reduction, etc. It is prepared using a method (Non-patent Document 1) for preparing by performing the above-mentioned treatment or a vapor phase method such as CVD. That is, the electrode catalyst is prepared in the form of composite particles in which metal particles are supported on the surface of a solid support, and its activity is not only the metal species but also the size of the supported metal fine particles, the type of crystal plane, the type of support. The control of the shape and size of the fine particles is particularly important.

  For this reason, as a method for preparing the noble metal catalyst and the noble metal electrode catalyst, in addition to devising the above general methods in various ways, a method for producing a noble metal colloid by liquid phase reduction in the presence of a protective agent such as polyvinylpyrrolidone ( Non-patent document 2) has also been developed.

Recently, platinum nanowires have been obtained by photoreduction using mesoporous silica as a template, reduction using H ₂ gas and electrodeposition (Non-Patent Documents 3 and 4). Nanowires having a diameter and length corresponding to the pore diameter have been synthesized (Non-patent Document 5). Also, porous platinum particles with pores with a diameter of about 3 nm corresponding to the thickness of the silica wall, with platinum wires connected in a three-dimensional network by hydrogen reduction using mesoporous silica with a three-dimensional pore structure as a template. (Non-Patent Document 6), but there is no mention of loading on carbon.

  On the other hand, the present inventors have developed a technique for reducing chloroplatinic acid using a liquid crystal composed of two kinds of surfactants as a template, and an outer diameter of 6 to 7 nm and an inner diameter of 3 to 4 nm depending on the kind of the reducing agent and the platinum salt. Noble metal nanotubes such as platinum and palladium, sponge-like noble metal nanoparticles, and sponge-like noble metal nanoparticle-supported carbon were produced (Patent Document 1, Patent Document 2, Patent Document 3).

  However, the noble metal nanostructures disclosed in the above documents are bulk ultrafine powder and sponge-like platinum-supporting carbon that are independently generated, and there is no mention of sheet-like platinum nanoparticles having nanoholes.

Hiroo Tominaga et al., Chemical Review “Catalyst Design”, The Chemical Society of Japan, 1982, p.50-63 N. Toshima and 1 other person, Bull. Chem. Soc. Jpn., 65, 400 (1992) M. Sasaki and 6 others, Microporous Mesoporous Mater., 21, 597 (1998). Z. Liu and 7 others, Angew. Chem. Int. Ed., 39, 3107 (2000). K-. B. Lee and two others, Adv. Mater., 13, 7, 517 (2001). H. J. Shin and three others J. Am. Chem. Soc., 123, 1246-1247 (2001). Tsuyoshi Kijima, Japanese Patent No. 3842177 Takeshi Kijima et al., Japanese Patent Laid-Open No. 2006-045582 Takeshi Kijima and 1 other, JP-A-2006-228450

  As described above, the prior art relating to platinum includes spherical or amorphous ultrafine particles, nanometer-sized wires, granular or membrane-like porous bodies having honeycomb- or three-dimensional network pores, and the present invention. It remains to provide nanotubes by the hand of the person. On the other hand, it is desired to create platinum nanoparticles with new pore shapes, new sizes, and new physical properties different from these, and realize unprecedented performance as catalysts and electrodes. . Further, as an electrode for a fuel cell, it is strongly desired to reduce the cathode overvoltage resulting from the low oxygen reduction activity.

  The present invention is intended to solve the above-mentioned problems, and provides a sheet-shaped platinum nanoparticle having a novel pore shape and a novel size that can be used as a catalyst or an electrode, and a method for producing the same. The task is to do.

  The inventors have introduced various conventional research reports on the nanotubes listed above and enumerated the prior art while keeping in mind the prior art. Has been investigating the types of metal sources and reducing agents used and the reaction conditions in order to create platinum nanoparticles with different novel pore shapes and new sizes. , One kind of polyoxyethylene sorbitan unsaturated fatty acid ester such as polyoxyethylene sorbitan monooleate, which is a nonionic surfactant in which a polyethylene oxide chain having a relatively large size is a hydrophilic part and these are linked by an ester bond, or A total of two types of nonionic surfactants combined with other nonionic surfactants were mixed with water. A monocrystalline sheet having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm having a platinum skeleton by a reaction in which an alkali metal chloroplatinate added in advance to the molecular structure is reduced with an aqueous reducing agent solution such as borohydride. Then, hexagons or circles having a diameter of 1 to 3.5 nm, or elliptical or rectangular concave nanoholes having a width of 1 to 3.5 nm and a length of 5 to 10 nm are arranged at substantially equal intervals of 4 to 5 nm or 1 to 4 nm. It was investigated that sheet-like platinum nanoparticles characterized by having a structure arranged at unequal intervals grow.

  That is, the first invention is (1) a single crystalline sheet-like particle having a skeleton composed of platinum (Pt) as a noble metal element and having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm. Hexagonal or circular shape of 1 to 3.5 nm, or elliptical or rectangular concave nanoholes having a width of 1 to 3.5 nm and a length of 3.5 to 10 nm are arranged at approximately equal intervals of 4 to 5 nm or irregularities of 1 to 5 nm. It is a sheet-like platinum nanoparticle characterized by having the structure arranged at equal intervals.

It can be said that the metal nanoparticles described in (2) to (3) below are derived from platinum nanoparticles described in (1) as a basic structure.
That is, the second invention is (2) platinum (Pt) which is a noble metal element and gold (Au), silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir), which are noble metal elements, A single crystalline sheet-like particle having a skeleton composed of a structure in which one or more elements selected from the group consisting of ruthenium (Ru) are mixed in an arbitrary ratio and having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm. A hexagonal or circular shape having a diameter of 1 to 3.5 nm, or an elliptical or rectangular concave nanohole having a width of 1 to 3.5 nm and a length of 3.5 to 10 nm, or approximately equal intervals of 4 to 5 nm or 1 It is a sheet-like noble metal nanoparticle having a structure arranged at unequal intervals of ˜5 nm.

  The third aspect of the present invention is that (3) the skeleton is formed by a structure in which platinum (Pt), which is a noble metal element, and one or more elements selected from a group of base metal elements such as nickel (Ni) are mixed at an arbitrary ratio. 1. A single crystalline sheet-like particle having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm, which is a hexagon or a circle having a diameter of 1 to 3.5 nm, or a width of 1 to 3.5 nm and a length of 3. 5. A sheet-like noble metal nanoparticle having a structure in which 5 to 10 nm elliptical or rectangular concave nanoholes are arranged at substantially equal intervals of 4 to 5 nm or unequal intervals of 1 to 5 nm.

The fourth to sixth inventions present the method for producing rare earth oxides of the first to third inventions.
That is, the fourth invention is (4) one kind of platinum complex compound selected from the group consisting of platinum complex compounds such as hexachloroplatinate, and polyoxyethylene sorbitan unsaturated fatty acid ester such as polyoxyethylene sorbitan monooleate. One nonionic surfactant selected from the group consisting of, or one nonionic surfactant selected from the group consisting of polyoxyethylene sorbitan unsaturated fatty acid esters such as polyoxyethylene sorbitan monooleate and nona Preparing a reaction mixture consisting of two surfactants in combination with one nonionic surfactant selected from the group consisting of polyoxyethylene alkyl ethers such as ethylene glycol monohexadecyl ether, and water; Reducing agent water such as sodium borohydride is added to the reaction mixture. By reacting with the addition of liquid, a method for producing a sheet-like platinum nanoparticles, characterized by producing a sheet-like platinum nanoparticles of the first aspect of the present invention.

  The fifth invention provides (5) one kind of platinum complex compound selected from the group consisting of platinum complex compounds such as hexachloroplatinate, gold (Au), silver (Ag), palladium (Pd), rhodium ( Rh), iridium (Ir), ruthenium (Ru) nitrates, chlorides, metal chlorides and the like, one or more noble metal salts or noble metal complex compounds, polyoxyethylene such as polyoxyethylene sorbitan monooleate One type of nonionic surfactant selected from the group consisting of sorbitan unsaturated fatty acid esters, or one type of nonionic selected from the group consisting of polyoxyethylene sorbitan unsaturated fatty acid esters such as polyoxyethylene sorbitan monooleate Surfactant and polyoxyethylene amines such as nonaethylene glycol monohexadecyl ether Prepare a reaction mixture consisting of two types of surfactants combined with one kind of nonionic surfactant selected from the group consisting of kill ethers, and water, and then reduce the reaction mixture to sodium borohydride or the like. A sheet-like noble metal nanoparticle according to the second aspect of the present invention is produced by adding and reacting an aqueous agent solution.

  The sixth invention is a group consisting of (6) one type of platinum complex compound selected from the group consisting of platinum complex compounds such as hexachloroplatinate, and nitrates, chlorides, etc. of base metal elements such as nickel (Ni) One or more base metal salts selected from the group consisting of one nonionic surfactant selected from the group consisting of polyoxyethylene sorbitan unsaturated fatty acid esters such as polyoxyethylene sorbitan monooleate, or polyoxyethylene sorbitan monooleate One non-ionic surfactant selected from the group consisting of polyoxyethylene sorbitan unsaturated fatty acid esters and one type selected from the group consisting of polyoxyethylene alkyl ethers such as nonaethylene glycol monohexadecyl ether Two types of surfactants, including nonionic surfactants, and water The sheet-like noble metal nanoparticles of the third invention are manufactured by adding a reducing agent aqueous solution such as sodium borohydride to the reaction mixture and reacting with the reaction mixture. This is a method for producing noble metal nanoparticles.

Further, the inventions of the use of the noble metal nanoparticles of the first to third inventions such as the following (7) to (8) are presented.
That is, (7) A functional material comprising any one kind or two or more kinds of noble metal nanoparticles described in the above (1) to (3) and used for applications based on their physical properties.
(8) The functional material as described in (7) above, which is used and used exclusively as a catalyst for fuel cells, automobile exhaust gas, and the like.
(9) The functional material according to (7), wherein the functional material is used and used exclusively as an electrode for electrolysis or the like.
(10) The above-mentioned (7), characterized in that its use is provided and used exclusively as a sensor for detecting or measuring temperature, pressure, humidity, condensation, flow rate, wind speed, light, gas, oxygen concentration, or displacement. Functional materials.

In the present invention, since the noble metal nanoparticles have the composition and structure as described above, the following effects can be expected.
1) When platinum or sheet-shaped platinum nanoparticles containing platinum as a main component and used as a fuel cell catalyst for extracting electric energy by reacting hydrogen with oxygen, nano-based nano-holes based on a fine single crystalline skeleton It can be expected that the structural effect acts synergistically, and a catalytic effect much higher than that of the conventional material can be exhibited, and the required amount of catalyst can be greatly reduced.
2) When this is used as a catalyst in automobile exhaust gas purification, petrochemistry, synthesis gas production, pharmaceutical / oil production, etc., the catalyst efficiency is dramatically increased for the same reason as the previous section, further improving the environment and saving energy in the production process. Such remarkable effects are expected.
3) When this is used as an electrode for electrolysis or the like, it is expected to bring about a dramatic increase in reaction efficiency due to a significant increase in the electrode surface area compared to conventional materials.
4) When this is used as a sensor for detecting or measuring temperature, pressure, humidity, condensation, flow rate, wind speed, light, gas, oxygen concentration, or displacement, the detection accuracy and sensitivity are greatly improved, and the element is miniaturized.・ High performance is realized.

The invention of this application has the above-described features, and will be specifically described below with reference to the accompanying drawings. However, these examples merely disclose one aspect of the present invention, and are not intended to limit the present invention. That is, the aim of the present invention is to provide single crystalline sheet-like metal nanoparticles having nanoholes organized with platinum or two or more metal elements mainly composed of platinum as main components. Is as described above. The contained components and structure are one or more noble metal elements including platinum, or sponge-like nanoparticles of a specific size composed of a skeleton having platinum as a main component and a base metal element as a minor component. As for the subcomponent itself, various combinations in composition are allowed.
In addition, the main point of the production method is a kind of nonionic surfactant in which a bent unsaturated alkyl group is a hydrophobic part and a relatively large polyethylene oxide chain is a hydrophilic part and these are linked by an ester bond, or A platinum complex salt or platinum complex salt as a main component is a structure obtained by mixing a total of two types of nonionic surfactants with one kind of nonionic surfactant and an aqueous solution of metal salt under appropriate conditions. By reducing two or more kinds of metal salts, sheet-like nanoparticles with specific dimensions having nanoholes are derived. The optimum temperature and mixing conditions for constructing the template are also targeted and the surface activity used. It varies depending on the characteristics of the agent. On the other hand, an Example shows only the example of the aspect with respect to this invention to the last, The metal seed | species and manufacturing method which comprise this invention should not be limited by this Example.

  1 (A) to (D) and FIGS. 2 (A) to (C) are photographs taken by a transmission electron microscope of sheet-like platinum nanoparticles having nanoholes of the present invention. It is observed that the metal structure is monocrystalline and has a structure in which hexagonal, circular, elliptical, or rectangular concave nanoholes are arranged at approximately equal or unequal intervals.

An aqueous solution containing chloroplatinic acid (H ₂ PtCl ₆ ) weighed in a test tube and twice its molar amount of sodium hydroxide was heated to 60 ° C. Next, polyoxyethylene (20) sorbitan monooleate (Tween 80; US Atlas)
Powder product name) was added, shaken in a 60 ° C. hot water bath for 10 minutes, and then cooled to 15 ° C.
Let stand at 15 ° C. for another 20 minutes, and charge molar ratio Na ₂ PtCl ₆ :
A mixture of Tween 80: H ₂ 0 = 1: 1: 60 was prepared. Next, a solution consisting of sodium chloroplatinate 5 times molar amount of sodium borohydride and 20 times molar amount of water was added to this mixture kept at the same temperature and allowed to react for 24 hours. The precipitated fine solid phase was centrifuged, washed with water, then with ethanol, and dried to obtain a black powder.
Preparation molar ratio Na ₂ PtCl ₆ prepared in the same procedure using chloroplatinic acid H ₂ PtCl ₆ as a metal source:
The reaction precursor of Tween 80: H ₂ 0 = 1: 1: 60 (x = 1.0) is a liquid crystal giving an X-ray diffraction peak of d = 7.65 nm, and has a regular hexagonal structure of a = 8.83 nm. [FIG. 3A].
By observation with a transmission electron microscope, a powder sample obtained by adding the above-mentioned sodium borohydride aqueous solution to the liquid crystal having this regular structure has a single product with a main product of 2 to 25 nm in thickness and an outer diameter of 30 to 600 nm. A crystalline sheet, hexagonal or circular with a diameter of 1 to 3.5 nm, or elliptical or rectangular concave nanoholes with a width of 1 to 3.5 nm and a length of 3.5 to 10 nm, with unequal intervals of 1 to 5 nm. It was confirmed that the platinum nanoparticles had an arrayed structure [FIGS. 1 (A) to (C)]. The sheet form can be confirmed from (A). In (B) in which a part of (A) is enlarged, a white spot-like portion shows a concave nanohole in which the sheet surface is depressed and the electron density is lowered. The lower figure of (B) is a histogram showing the distribution of the size of nanoholes. It can be seen that the diameter is distributed in the range of 1 nm to 3.2 nm, and the average size is 1.8 nm. Furthermore, from (C), which is an enlarged image of (B), each sheet-like particle has a continuous width of 0.22 nm (corresponding to the spacing of the <111> plane of the platinum crystal) along the arrow direction over a wide range. Lattice fringes are observed, indicating that the sheet is a single crystal and that the <111> plane of the platinum crystal faces this direction. Thus, it was confirmed that single crystalline sheet-like platinum nanoparticles having nanoholes according to the present invention were obtained.
This nanohole is formed by masking agent by adsorbing oleic acid molecules produced by hydrolysis of Tween80 as bundled clusters on Pt sites on (110) plane of platinum nanosheets formed in the gap between cylindrical micelles of hexagonal liquid crystal. It is estimated that this is because the non-masked portion continued to grow and thicken. When such mask crystallization proceeds sequentially, the size and distribution of holes may be nonuniform as shown in FIG.
Moreover, when the product and carbon powder were mixed and CV measurement was performed, it turned out that a high catalytic activity is shown with respect to oxygen reduction reaction.

Nonaethylene glycol monodecyl ether (C1 ₂ EO ₉ ) was added dropwise to an aqueous solution containing chloroplatinic acid (H ₂ PtCl ₆ ) weighed in a test tube and twice its molar amount of sodium hydroxide, and the temperature was raised to 60 ° C. Warm up. Next, polyoxyethylene (20) sorbitan monooleate (Tween 80; US Atlas)
Powder product name) was added, shaken in a 60 ° C. hot water bath for 10 minutes, and then cooled to 15 ° C.
The mixture was further allowed to stand at 15 ° C. for 20 minutes to prepare a mixture having a feed molar ratio of Na ₂ PtCl ₆ : C1 ₂ EO ₉ : Tween 80: H ₂ 0 = 1: 1: 1: 60. Next, to this mixture kept at the same temperature, a solution consisting of 5 times molar amount of sodium chloroplatinate and 20 times molar amount of water was added and allowed to react for 24 hours. The precipitated fine solid phase was centrifuged, washed with water, then washed with ethanol, and dried to obtain a black powder.
Reaction of charge molar ratio Na ₂ PtCl ₆ : C1 ₂ EO ₉ : Tween 80: H ₂ 0 = 1: 1: 1: 60 (x = 1.0) prepared in the same procedure using chloroplatinic acid H ₂ PtCl ₆ as a metal source The precursor gave a clear X-ray diffraction peak of d = 6.32 nm, and was confirmed to be a highly ordered hexagonal structure of a = 7.3 nm [FIG. 3 (B)].
A powder sample obtained by adding the above-mentioned aqueous sodium borohydride solution to the liquid crystal having this regular structure by observation with a transmission electron microscope has a diameter similar to that in Example 1 by observation with a transmission electron microscope. Hexagonal or circular shape of 1 to 3.5 nm, or elliptical or rectangular concave nanoholes having a width of 1 to 3.5 nm and a length of 3.5 to 10 nm are arranged in a hexagonal shape at substantially equal intervals of 4 to 5 nm. In addition, it was confirmed that sheet-like platinum nanoparticles with an outer diameter of more than 300 nm having a structure arranged at unequal intervals of 1 to 5 nm were generated [FIGS. 2 (A) to (C)]. In addition, continuous lattice stripes having a width of 0.2 nm were observed along the arrow direction of (A), and it was confirmed that the entire particle was composed of one single crystal.

The observation figure by the transmission electron microscope of the platinum nanoparticle of this invention. (A) is the observation figure by the transmission electron microscope of the platinum nanoparticle obtained in Example 1. FIG. (B) is the transmission electron microscope of the platinum nanoparticle similarly obtained in Example 1, and the image which expanded a part of (A). The lower figure in (B) is a histogram showing the distribution of nanohole sizes. (C) is the high resolution transmission electron microscope of the platinum nanoparticle similarly obtained in Example 1, and is an enlarged image of (B). (D) is a Fourier pattern of lattice fringes appearing in the image (C), and a pair of bright spots facing each other indicates that the lattice is oriented in a certain direction. The observation figure by the transmission electron microscope of the platinum nanoparticle of this invention. (A) is the observation figure by the high-resolution transmission electron microscope of the platinum nanoparticle obtained in Example 2. FIG. (C) is the observation figure by the high-resolution transmission electron microscope of the platinum nanoparticle obtained in Example 2, and is an enlarged image of (A). (B) is the Fourier pattern of the lattice fringes that appeared in the image (A). (A) is an X-ray diffraction pattern of a liquid crystal mixture containing a reaction precursor having a charged molar ratio of H ₂ PtCl ₆ : Tween 80: H20 = 1: 1: 60 (x = 1.0) described in Example 1. (B) is a liquid crystal mixture containing a reaction precursor described in Example 2 and having a charged molar ratio of Na ₂ PtCl ₆ : C1 ₂ EO ₉ : Tween 80: H ₂ 0 = 1: 1: 1: 60 (x = 1.0). X-ray diffraction pattern.

Claims (6)

  The skeleton is composed of platinum (Pt), a noble metal element, and is a single crystalline sheet-like particle having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm, and having a diameter of 1 to 3.5 nm, Alternatively, the present invention has a structure in which elliptical or rectangular concave nanoholes having a width of 1 to 3.5 nm and a length of 3.5 to 10 nm are arranged at substantially equal intervals of 4 to 5 nm or unequal intervals of 1 to 5 nm. Sheet-like platinum nanoparticles.   It is selected from the group consisting of platinum (Pt) as a noble metal element and gold (Au), silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir), and ruthenium (Ru) as noble metal elements. A single crystalline sheet-like particle having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm, wherein the skeleton is constituted by a structure in which one or more elements are mixed in an arbitrary ratio. A structure in which hexagonal or circular, or elliptical or rectangular concave nanoholes having a width of 1 to 3.5 nm and a length of 3.5 to 10 nm are arranged at substantially equal intervals of 4 to 5 nm or unequal intervals of 1 to 5 nm. A sheet-like noble metal nanoparticle characterized by comprising:   A single crystal having a skeleton composed of a structure in which platinum (Pt), which is a noble metal element, and one or more elements selected from base metal elements are mixed in an arbitrary ratio and having a thickness of 2 to 25 nm and an outer diameter of 30 to 600 nm A sheet-like particle having a hexagonal or circular shape with a diameter of 1 to 3.5 nm, or an elliptical or rectangular concave nanohole with a width of 1 to 3.5 nm and a length of 3.5 to 10 nm. A sheet-like noble metal nanoparticle having a structure arranged at substantially equal intervals or at unequal intervals of 1 to 5 nm.   Nonionic surfactant made of platinum complex compound, polyoxyethylene sorbitan unsaturated fatty acid ester, or nonionic surfactant made of polyoxyethylene sorbitan unsaturated fatty acid ester and polyoxyethylene alkyl ethers The sheet-like platinum nanoparticles according to claim 1 are prepared by preparing a reaction mixture composed of two surfactants in combination with the agent and water, and then adding a reducing agent aqueous solution to the reaction mixture for reaction. A method for producing sheet-like platinum nanoparticles, characterized by comprising:   A platinum complex compound and a noble metal salt of one or more elements selected from the group consisting of gold (Au), silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir), and ruthenium (Ru), or Nonionic surfactant made of noble metal complex compound, polyoxyethylene sorbitan unsaturated fatty acid ester, or nonionic surfactant made of polyoxyethylene sorbitan unsaturated fatty acid ester and polyoxyethylene alkyl ethers The sheet-like noble metal nanoparticles according to claim 2 are prepared by preparing a reaction mixture comprising two types of surfactants in combination with the agent and water, and then reacting the reaction mixture by adding an aqueous reducing agent solution. A method for producing noble metal nanoparticles, characterized by comprising:   A platinum complex compound and a base metal salt of one or more elements selected from the group consisting of base metal elements, a nonionic surfactant made of polyoxyethylene sorbitan unsaturated fatty acid ester, or a polyoxyethylene sorbitan unsaturated fatty acid ester Prepare a reaction mixture consisting of two surfactants and water together with a nonionic surfactant and a nonionic surfactant consisting of polyoxyethylene alkyl ethers, and then add an aqueous reducing agent solution to the reaction mixture. A method for producing noble metal nanoparticles, comprising producing the sheet-like noble metal nanoparticles according to claim 3 by reacting them.