KR101807808B1 - Method for Preparimg AuPt Nanocrystals with Electrocatalytic Activity - Google Patents

Abstract

The present invention relates to a method for producing gold-platinum alloy nanocrystals having enhanced catalytic activity without containing a surfactant by injecting a gold precursor and a platinum bimetallic precursor into a silica (SiO ₂ ) nano structure and annealing the same to remove silica .

Description

TECHNICAL FIELD The present invention relates to a method for preparing a gold-platinum alloy nanocrystal having catalytic activity,

The present invention relates to a method for producing gold-platinum alloy nanocrystals, and more particularly, to a method for producing gold-platinum alloy nanocrystals, which comprises the steps of injecting a gold precursor and a platinum 2 precursor into a silica (SiO ₂ ) precursor, To a process for producing the same.

Platinum-based alloy nanocrystals are the most efficient electrochemical catalytic materials in fuel cells. It is used to oxidize small fuel molecules such as hydrogen, methanol, and formic acid in the anode and oxygen reduction reaction in the anode. Most studies have focused on the use of nanocrystals containing platinum in hydrogen-exchanged membrane fuel cells (PEMFCs) and are increasingly interested in using suitable catalysts for formic acid oxidation, an essential element of commercial direct formic acid fuel cells (DFAFC) .

In particular, gold-platinum alloy nanocrystals are one of the more interesting materials as efficient catalysts for the oxidation of formic acid, because they facilitate the direct oxidation reaction and reduce the poisoning of the catalyst. Recent studies can control the activity and durability of gold-platinum catalysts by controlling the composition and morphology of the gold-platinum catalysts and the nature of the support and interface.

Many methods of forming gold-platinum alloy nanocrystals have been proposed by prior researchers, including the simultaneous reduction in the presence of organic surfactants with the mixing of precursors. However, because of this method, gold / platinum alloys do not mix well, so nanocrystals are formed by high energy, such as complex processes using high temperatures and strong reducing agents. At this time, the removal of the surfactant of the support-based catalyst is a necessary process for activating the catalyst surface. When the surfactant is removed, the nanocrystals have a problem that sintering or deformation frequently occurs, thereby reducing catalytic activity.

Therefore, it is required to develop a method for producing gold-platinum alloy nanocrystals that have high formic acid oxidation reactivity but do not contain a surfactant.

It is an object of the present invention to provide a method for producing a gold-platinum alloy nanocrystal which is high in formic acid oxidation reactivity but does not contain a surfactant.

It is still another object of the present invention to provide a method for producing hybrid nanoparticles (AuPt / Fe ₃ O ₄ ) of gold-platinum alloy nanocrystals or gold-platinum and iron oxide.

It is another object of the present invention to provide hybrid nanoparticles of gold-platinum alloy nanocrystals, gold-platinum alloys and iron oxides produced by the above-described method, or an electrochemical catalyst containing them.

In order to achieve the above object, the present inventors have discovered that a gold precursor forms a gold nanocrystal in a reverse-microemulsion solution and then a mononuclear layer is formed continuously on the surface by a platinum ²⁺ precursor, The present inventors have developed a method for producing gold-platinum alloy nanocrystals that are thermally converted and reduced through a state conversion process.

One example of the present invention is a method of preparing a first nanoparticle (Au / Pt ^{2 +} ) having a structure containing gold and platinum oxide in a silica nanosphere by mixing an emulsion containing a gold precursor and a platinum oxide precursor with a silica precursor, preparing a @SiO _2); Annealing the first nanoparticles to produce second nanoparticles (AuPt @ SiO ₂ ) comprising gold-platinum alloy crystals; And removing the silica from the second nanoparticles. The present invention also relates to a method for producing a gold-platinum alloy nanocrystal (AuPt).

Another example of the present invention relates to a method for preparing a silica nanoparticle by mixing an emulsion including a gold precursor and a platinum oxide precursor, a silica precursor, and iron oxide nanoparticles, 1 mixed nanoparticles ([Au / Pt ²⁺ / Fe ₃ O ₄ ] @SiO ₂ ); Annealing the first hybrid nanoparticles to prepare second hybrid nanoparticles (AuPt / Fe ₃ O ₄ ) @SiO ₂ containing iron oxide nanoparticles and gold-platinum alloy crystals; And a step of removing silica from the second hybrid nanoparticles, wherein the mixed nanoparticles (hereinafter referred to as the gold-platinum / iron oxide hybrid nanoparticles or the iron oxide Hybrid nano-particles).

The gold-platinum alloy nanocrystals or gold-platinum / iron oxide hybrid nanoparticles prepared by the production method of the present invention can be uniformly dispersed and fixed on a support in the form of a surfactant-free form and compared with the conventional platinum / The activity of the formic acid oxidation reaction is more excellent.

Hereinafter, the present invention will be described in more detail.

The first nanoparticle ((Au / Pt ^{2 +} ) @ SiO ₂ ) Manufacturing steps

The method of the present invention comprises mixing a silica precursor with an emulsion containing a gold precursor and a platinum oxide precursor to prepare a first nanoparticle ((Au / Pt ^{2 +} ) having a structure containing gold and platinum oxide in the interior of the silica nanosphere, ≪ _{RTI ID} = 0.0 &_gt; @SiO2. ≪ / _RTI >

In the first nanoparticle ((Au / Pt ^{2 +} ) @SiO ₂ ), the gold and platinum oxide may be composed of a structure in which a gold monocrystal layer of gold nanocrystalline core and platinum oxide surrounds the gold nanocrystal core .

The emulsion used in the first nanoparticle preparation step may be prepared by mixing a gold precursor and a platinum oxide precursor into an organic solvent, a surfactant, and a basic solution. The gold precursor, the platinum oxide precursor, and the silica (SiO ₂ ) precursor may be added to the emulsion solution, followed by stirring. The emulsion may be in the form of a reverse-microemulsion (or reverse-microemulsion) and the reverse-microemulsion solution is a solution in the form of an oil-in-water emulsion. The reverse microemulsion, which is mainly composed of an organic solvent, makes a gold-platinum precursor in the form of an aqueous solution, and a surfactant (for example, IGEPAL-co 520) used to form an emulsion- It can serve as a space for securing the space and a framework in which silica can be formed into a spherical shape

The organic solvent used for the emulsion is not limited, but may preferably include at least one selected from the group consisting of cyclohexane and hexane.

The basic solution is added to the emulsion is preferably from a solution containing at least one selected from the group consisting of ammonia (NH ₄ OH), sodium hydroxide (NaOH), and potassium hydroxide (KOH). A simple substance layer of gold nanocrystals and platinum oxide can be formed by the basic solution (Example 3).

The surfactant added to the emulsion may be an amphipathic polymer, and preferably a surfactant containing PEG (polyethylene glycol) may be used. More preferably, it may be at least one selected from the group consisting of polyoxyethylene nonylphenyl ether (IGEPAL CO-520® having a hydrophilic functional group at 50 mol%), NP-5 and Brji 35. The surfactant may be contained in an amount of 4.5 to 7.0% by volume based on the volume of the organic solvent.

The first gold precursor used in the nanoparticle manufacturing step tetrachloride geumso hydroxyl (HAuCl4) trichloride Keumsan (AuCl _3), and sodium tetrachloride Keumsan be that more than one selected from the group consisting of (NaAuCl _4), preferably a tetrachloride geumso Acid can be used. The gold precursor may be included in an amount of 50 to 83 parts by weight, preferably 56 to 83 parts by weight, based on the final total of the gold-platinum alloy nanocrystals.

The platinum divalent precursor may be at least one selected from the group consisting of sodium platinate (Na ₂ PtCl ₄ ) and potassium platinate (K ₂ PtCl ₄ ), preferably sodium platinate. The platinum divalent precursor may be included in an amount of 10 to 50 parts by weight, preferably 17 to 44 parts by weight, based on the total amount of the gold-platinum alloy nanocrystals.

Also, the silica precursor may be selected from the group consisting of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrabutyl orthosilicate (TBOS), and tetrapropyl orthosilicate , And tetraethoxysilane may be preferably used. The silica precursor may be contained in an amount of 0.5 to 0.9% by volume when the volume of the reverse emulsion solution is 100%.

Preferably, cyclohexane, polyoxyethylene nonylphenyl ether and an emulsion solution containing a gold precursor, a platinum oxide precursor and a silica precursor in an ammonia solution can be used in the above production process.

The first nanoparticle ((Au / Pt ^{2 +} ) @SiO ₂ ) produced by the above-described method is characterized in that a mono-layer of platinum oxide surrounds the gold nanocrystalline core to form gold / platinum nanocrystals, Gold / platinum oxide nanocrystals may be included. In particular, the gold / platinum oxide nanocrystals may be concentrated at the center of the silica nanosphere rather than near the shell, preferably gold and platinum may be present in a molar ratio of 1: 1 to 4: 1, more preferably 1: 1 have.

The gold / platinum oxynitride nanocrystals are formed by the formation of gold nanoparticles, which are formed by the formation of gold nanocrystals and the partially oxidized surfaces. This is similar to the deposition-precipitation (DP) process, which is the phenomenon that noble metal ions attach to large support materials in a basic solution.

The second nanoparticles (AuPt @ SiO ₂ ) Manufacturing steps

The manufacturing method of the present invention may include a step of annealing the first nanoparticles to prepare second nanoparticles (AuPt @ SiO ₂ ) containing gold-platinum alloy crystals in the silica nanosphere .

The annealing process is a series of operations in which the metal is slowly heated to a room temperature. In the present invention, the gold and platinum are thermally reduced through the annealing process and converted into alloyed metal nanocrystals. Also, the heating of the annealing process causes the surfactant to decompose.

The final temperature of the annealing may be 100 to 600 占 폚, preferably 100 to 500 占 폚, and more preferably 450 to 550 占 폚. Especially, when the final temperature is 500 ° C, the catalyst activity is most excellent.

The annealing may be performed in a reducing gas or air. Preferably, the reducing gas is at least one gas selected from the group consisting of argon (Ar), neon (Ne) and helium (He) , Preferably argon and 4% hydrogen gas may be used. The nanoparticles of the present invention are annealed in the air. The reduction of the platinum oxide adsorbed on the surface of the gold nanocrystalline core may be caused by the presence of a surfactant in the silica nanoparticles, especially PEG The surfactant may be provided by acting as a reducing agent to provide electrons. Since the surfactant is decomposed due to the heating process for the annealing process, clean nanocrystals containing no surfactant on the surface of silica can be obtained.

In particular, in air annealing, extra platinum nanocrystals formed in the silica shell are suppressed as compared with annealing in a reducing gas environment, so that only gold-platinum alloy nanocrystals can be synthesized singly.

The step of removing the silica of the second nanoparticle

The manufacturing method of the present invention may include removing silica from the second nanoparticles.

In the second nanoparticle, the gold-platinum alloy nanocrystals may be separated from the silica, and preferably the surfactant is removed by heat treatment in the annealing process. The method of removing silica includes all the conventional methods used in the art, preferably by a treatment with an acid solution or a treatment with a basic solution, more preferably by hydrofluoric acid (HF) or It can be removed by treatment with sodium hydroxide.

Particularly, after mixing the second nanoparticles with the carbon support, the silica is removed to prepare a nanocomposite in which gold-platinum alloy nanocrystals (AuPt / C) are supported on a carbon support. The nanoparticles of the present invention can be used as a surfactant So that the surface is clean and can be deposited on the carbon support in a well dispersed form by the electrostatic attraction between the nanoparticles and the support.

Preferably, the carbon support is not limited, but at least one selected from the group consisting of carbon black, graphene and reduced graphene oxide (RGO) can be used, and the nanostructures produced by the above method can be used as gold- Lt; / RTI >

Another example of the present invention is a method for preparing a composite nanoparticle (AuPt / Fe (II)) containing iron oxide nanoparticles and gold-platinum alloy nanoparticles (AuPt), further comprising iron oxide together with a gold precursor, ₃ O ₄ ).

Preferably, the method comprises mixing an emulsion comprising a gold precursor and a platinum oxide precursor, a silica precursor, and iron oxide nanoparticles to form a silica nanosphere having a structure containing iron oxide nanoparticles, gold and platinum oxide 1 mixed nanoparticles ([Au / Pt ²⁺ / Fe ₃ O ₄ ] @SiO ₂ ); Annealing the first hybrid nanoparticles to prepare second hybrid nanoparticles (AuPt / Fe ₃ O ₄ ) @SiO ₂ containing iron oxide nanoparticles and gold-platinum alloy crystals; And a step of removing silica from the second hybrid nanoparticles, wherein the mixed nanoparticles are composed of iron oxide nanoparticles and gold nanoparticles of gold-platinum alloy (AuPt).

The first iron oxide nanoparticles ([(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @ SiO ₂ include the gold / platinum nanocrystals and iron oxide adhered to the silica nanorods, The platinum oxide nanocrystals may comprise a gold nanocrystalline core and a mono-layer of platinum oxide surrounding the gold nanocrystalline core. Preferably, the gold / platinum oxide nanocrystals may be attached in a dispersed form on the iron oxide surface.

The iron oxide hybrid nanoparticles prepared by the above method have a heterojunction structure in which a metal catalyst without a surfactant is fixed on a metal oxide support.

In the step of removing the silica, the mixed nanoparticles and the carbon support may be mixed and then the silica may be removed to obtain the hybrid nanoparticles carried on the carbon support. Preferably, the carbon support is carbon black, And reduced graphene oxide (RGO). Preferably, gold-platinum / iron oxide / reduced grapheme oxide (RGO) nanostructures can be prepared by the above-described preparation method.

The gold-platinum / iron oxide / RGO nanocomposite may be prepared by further comprising GO in the step of removing silica from the second nanoparticles. Preferably, the gold-platinum / iron oxide / RGO nanocomposite includes hydrofluoric acid and GO To prepare a gold-platinum / iron oxide / GO nanocomposite; And reacting the gold-platinum / iron oxide / GO nanocomposite with a hydrazine (NH2NH2) solution to produce a gold-platinum / iron oxide / RGO nanocomposite.

The gold-platinum / iron oxide / RGO nanocomposite has a much better electrochemically active surface area (ECSA) than gold-platinum / iron oxide (Example 8.1) This is due to the increased conductivity. In addition, AuPt / Fe ₃ O ₄ can be loaded on the support in the form of well-dispersed nanoparticles rising at a number of functional sites due to coordination with graphene oxide (GO) functional groups.

The details of the nanocrystal production method can be applied to a hybrid nanoparticle of gold-platinum alloy and iron oxide or a method of manufacturing a nanocomposite containing the same.

Another example of the present invention is a mixed nanoparticle of a gold-platinum alloy nanocrystal or a gold-platinum alloy and iron oxide produced by the above production method; And electrochemical catalysts comprising them.

The nanocrystalline or iron oxide hybrid nanoparticles according to the present invention include nanocrystals in which gold and platinum are alloyed with a surfactant or the like by decomposition of the surfactant by an annealing step in the above manufacturing method and do not contain a surface active agent. The nanocrystal or iron oxide hybrid nanoparticles according to the present invention have much better electrochemical catalytic activity than the conventional Pt / C catalyst (Example 8).

The details of the above production method can be applied to nanocrystals or hybrid nanoparticles or electrochemical catalysts containing them.

According to the production method of the present invention, it is possible to produce gold-platinum alloy nanocrystals having superior electrochemical catalytic activity as compared with the conventional platinum catalysts, which does not require the step of removing the surfactant, Gold-platinum alloy nanocrystals can be produced without fear of sintering or deformation resulting in reduced catalytic activity.

When the gold-platinum alloy nanocrystals according to the present invention are used as a catalyst, the surface of the gold-platinum alloy nanocrystal is exposed without containing a surfactant, so that the reactants can be easily accessed and have excellent electrochemical catalytic activity.

The gold-platinum alloy nanocrystals of the present invention can be supported on a carbon support to improve the stability of the catalyst to an acid due to the triple junction of the catalyst-metal oxide-carbon support and improve the catalytic properties.

FIG. 1 schematically shows a method of synthesizing a gold-platinum alloy nanocrystal and a gold-platinum / carbon nano structure according to the manufacturing method of the present invention.
FIG. 2 schematically shows a method of synthesizing gold-platinum / iron oxide nanoparticles and gold-platinum / iron oxide / RGO nanostructures according to the manufacturing method of the present invention.
FIG. 3 is a transmission electron microscope image of (Au / Pt ^{2 +} ) @ SiO ₂ nanosphere, (b) an energy dispersive X-ray atom map of Au (red) and Pt (blue) / Pt ^{2 +} ) @ SiO ₂ Nanocrystalline Ar + 4% H2 gas stream at various temperatures before and after annealing.
4 shows (a) a high-resolution transmission electron microscope image of Au / Pt ^{2 +} nanoparticles, (b) an energy dispersive X-ray atom line profile of a scanning tunneling electron microscope, and (c) a photoelectron spectroscopy spectrum.
FIG. 5 is a transmission electron microscope and energy dispersive element map image of (a) Au @ SiO ₂ and (b) SiO ₂ / Pt ^{2 +} nanospheres formed without Na ₂ PtCl ₄ or HAuCl ₄ .
6 shows the results of the reaction between HAuCl ₄ and Na ₂ PtCl ₄ in the reverse microemulsion solution by adding (a) ammonia (NH ₄ OH), (b) sodium hydroxide solution (NaOH solution) Transmission electron microscope images, energy dispersive X-ray maps of Au (red) and Pt (green), and energy spectral analysis results.
FIG. 7 shows (a) transmission electron microscopy of (Au / Pt ^{2 +} ) @ SiO ₂ nanospheres of nanocrystals obtained from particles annealed at 100 ° C in a reducing gas environment, (b) energy dispersive X- And (c) X-ray photoelectron spectroscopy.
FIG. 8 shows (a) transmission electron microscope image of (Au / Pt ^{2 +} ) @ SiO ₂ reductively annealed at 500 ° C, (b) energy dispersive X-ray atom line profile of a scanning tunneling electron microscope, Microscope image (illustration) and (c) photoelectron spectroscopy.
Figure 9 ^{(a) (Au / Pt 2} +) @SiO the annealing of ₂ nm at various temperatures of the air before and after annealing of the rectangle and the X-ray diffraction pattern, the air at 200 ° C of the nano-sphere (Au / Pt ^{2 +)} shows the (b) transmission electron microscope (c) of the scanning tunneling electron microscope energy dispersive X-ray line profile atom and (d) X-ray photoelectron spectroscopy spectra of nanocrystals obtained from AuPt @SiO _2.
Fig. 10 shows the results of forward scanning of mass surface area obtained from a 0.5 M formic acid + 0.5 M sulfuric acid solution saturated with N ₂ at a scanning speed of 50 mV s < ^-1 > of the used Pt / C in the AuPt / C series.
11 shows (a) an X-ray diffraction pattern of a mixture powder of Na ₂ PtCl ₄ , NH ₄ OH and IGEPAL® (b) Na ₂ PtCl ₄ and NH ₄ OH reacted in air at 200 ° C. (c) X-ray diffraction pattern and X-ray photoelectron spectroscopic analysis of nanocrystals obtained by annealing Au / Pt ^{2 +} made in microemulsion solution stabilized with IGEPAL® without TEOS at 200 ° C in air.
Figure 12 shows the change of surfactant with heating temperature in (Au / Pt ^{2 +} ) @ SiP ² nanoparticles.
13 is a transmission electron microscope image of (a) Sf-AuPt nanocrystals obtained from (Au / Pt ^{2 +} ) @ SiO ₂ annealed at 500 ° C in air, (b) X-ray component line profile and (c) X-ray photoelectron spectroscopy spectra.
FIG. 14 shows a transmission electron microscope image of a (Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] SiO ₂ nanoparticles and a high-resolution transmission electron microscope image of the (AuPt / Fe ₃ O ₄ ) @SiO transmission electron microscope image of the _second nanoparticles, (c) (AuPt / Fe 3 O 4) @SiO obtained from AuPt ₂ / Fe ₃ O ₄ nanoparticles transmission electron microscope images, and (d) AuPt / Fe ₃ O of ₄ shows an energy dispersive X-ray line profile of a scanning tunneling electron microscope.
FIG. 15 shows a transmission electron microscope image of an AuPt / Fe ₃ O ₄ / RGO nanocomposite.
16 shows a transmission electron microscope image of an AuPt / Fe ₃ O ₄ / RGO nanocomposite.
17 is a cyclic voltammetry method using AuPt / Fe ₃ O ₄ and AuPt / Fe ₃ O ₄ / RGO. (A) 0.1 MH ₂ SO ₄ solution, (b) 0.5 M formic acid + 0.5 MH ₂ SO ₄ solution, _{2 < /} RTI > saturation with a scanning rate of 50 mV s < ^-1 >.

Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

Example 1. (Au / Pt ^{2 +} ) @ SiO ₂  Nanoparticle synthesis

1.1 Synthesis of (Au / Pt ^{2 +} ) @ SiO ₂ nanoparticles

(Au / Pt ^{2 +} ) @ SiO ₂ nanoparticles were synthesized using a reverse microemulsion technique. 34 mL of cyclohexane was added to a round bottom flask, and IGEPLA CO-520® (2.0 mL) was dispersed using ultrasonic waves. Then, 62.5 uL of 16 mg mL- ¹ hydrochloric acid (HAuCl ₄ ) was slowly added dropwise to the mixed solution and mixed to make a clear solution. Then, 62.5 uL of sodium tetraplatinate (Na ₂ PtCl ₄ ) at a concentration of 16 mg mL ^-1 and 0.2 mL of a 30% ammonia solution (NH ₄ OH) were added. Finally, 0.3 mL TEOS was added and reacted for 15 hours. Methanol (MeOH) was added to the reaction solution, and yellow (Au / Pt ^{2 +} ) @ SiO ₂ nanoparticle precipitate was formed. After coagulation by centrifugation of the methanol layer, the resultant was redispersed in ethanol (EtOH) . The separated material is a form in which a monolayer of Pt ^{2 +} is enclosed on the surface of gold (Au) nanoparticles. A gold (platinum) alloy nanocrystal core of 3.4 (± 0.3) nm and a 24 nm thick round silica The solid particles consisting of nanoshells were separated.

1.2 Observation of (Au / Pt ^{2 +} ) @ SiO ₂ nanoparticles

The separated nanoparticles were observed by transmission electron microscopy (TEM) and scanning tunneling electron microscopy (STEM), and analyzed by X-ray diffraction (XRD) Are shown in Figs. 3A to 3D in order.

3A and 3B, elemental map analysis using TEM or STEM showed that gold and platinum were concentrated in the center of nanoparticles, and gold and platinum were distributed in the same mole ratio. Based on the EDS data, the elemental ratios of gold and platinum were 56:44 and 61:39, respectively, before and after removal of silica, confirming that platinum was distributed near the core nanoparticles rather than the silica water-ray.

The XRD of FIG. 3c shows a correlation with the gold phase of a face-centered cubic (fcc) structure with a broad diffraction peak, indicating that AuCl ₄ is reduced to gold crystals of very small crystals. It appears to be produced by IGEPLA, a surfactant with PEG

1.3 Identification of Core Structure in Nanoparticles

In order to confirm the structure of the core in the nanoparticles, the center of the nanoparticles was extracted from silica and subjected to line-prolfiling analysis using high-resolution TEM and energy dispersive x-ray. And 4b. As a result, it was confirmed that the core nanocrystals consisted of platinum-rich amorphous platinum-rich shells in the gold nanocrystal core. The thickness of the outer shell was about 0.34 nm, which was similar to the platinum atomic diameter and was surrounded by a mono-layer.

Further, X-ray photoelectron spectroscopy (XPS) analysis was carried out to confirm that gold in the core region is 0-valence and +3-valence, and platinum surrounding the periphery thereof is mostly ²⁺ in oxidation state.

By the present method through which (Au / Pt ^{2 +)} @SiO when the _two are formed, Au / Pt ²⁺ nanocrystals within the silica is partially oxidized gold nanocrystal core and a +2 valence that it surrounds a section jacheung platinum . ≪ / RTI >

Example  2. Synthesis of nanoparticles with or without gold or platinum

The preparation of nanoparticles (Au / Pt ^{2 +} ) @ SiO ₂ was carried out in the same manner as in Example 1.1 except that Na ₂ PtCl ₄ or HAuCl ₄ was excluded to compare the necessity of Pt and Au.

The prepared control nanoparticles were observed using transmission electron microscopy (TEM) and energy dispersive X-ray.

Na ₂ PtCl showed an Au @ SiO ₂ nanoparticles containing only gold sole component made without adding ₄ to the Figures 5a, the SiO ^₂ / Pt ₂ ⁺ nanoparticles containing only one platinum only component prepared without putting the HAuCl ₄ 5b. As shown in FIGS. 5A and 5B, it was confirmed that the gold nanocrystals reduced in the nanoparticles form a core or platinum spreads in the first half of the silica.

Example  3. Synthesis of nanoparticles with and without basic solution

The nanoparticles (Au / Pt ^{2 +} ) @SiO ₂ were produced in the same manner as in Example 1.1, except that they contained ammonia solution or sodium hydroxide solution and no basic solution, The need for solution was compared.

The prepared nanoparticles were subjected to energy dispersive X-ray mapping and energy spectral analysis, and the results are shown in FIG.

6A and 6B). In the case of not containing a basic solution (FIG. 6C), it was confirmed that Au / Pr ²⁺ nanocrystals were formed on the surface of platinum ²⁺ It was confirmed that the Au / Pt ^{2 +} nanocrystals were formed on the partially oxidized surface while the gold nanocrystals were formed and the poorly soluble Pt ^{2 +} hydrates or oxides were attached to the partially oxidized surface.

Example  4. AuPt @ SiO ₂  Nanoparticle manufacturing

4.1 Ar + 4% H ₂ gas annealing under

(Au / Pt ^{2 +} ) @ SiO ₂ nanoparticle powder prepared using IGEPLA ® as a surfactant in Example 1 was heated in a tube furnace at a heating rate of 5 min ^-1 for 5 hours with Ar + 4% H ₂ Lt; RTI ID = 0.0 > 100 C, < / RTI >

The annealed product was analyzed using transmission electron microscopy (TEM), energy dispersive X-ray line profile and X-ray photoelectron spectroscopy (XPS).

The results of Au / Pt ^{2 +} analysis of the core after annealing at 100 ° C are shown in FIGS. 7a to 7c. It is confirmed that the core is an alloyed metal nanocrystal having a core of rich gold and a shell of rich platinum Respectively. The result of analysis after annealing at 200 ° C is shown in FIG. 3c. Platinum signal is strong and platinum nanocrystal is formed in the silica shell. When 500 annealing is performed, gold-platinum alloy and platinum nanocrystal And it was confirmed that the surfactant was removed due to the heating (Figs. 8A to 8C)

4.2 Annealing Effect in Air

(Au / Pt ^{2 +} ) @ SiO ₂ nanoparticles prepared using IGEPLAL® as a surfactant in Example 1 were annealed in air at temperatures of 100, 200, 300, 400, 500.

The results of the analysis using the transmission electron microscope as a result of annealing are shown in FIG. Particularly, it was confirmed that the metal-phase diffraction signal at the face-centered cubic plane greatly increased at 200 nm. This means that the crystalline surface of the reduced metal at 200 is grown. In the TEM, HRTEM and XPS analyzes, it was confirmed that the gold and platinum precursors were reduced in air at a temperature of 200, and the gold / platinum nanocrystals changed to gold-platinum alloy nanocrystals. 0.3 nm). The surfactant was also removed by heating (Fig. 9).

In particular, when annealed in the air, formation of extra platinum nanocrystals in the silica shell was suppressed as compared with annealing in a reducing gas environment, and it was confirmed that only gold-platinum alloy nanocrystals could be synthesized singly.

4.3 Effect of air annealing with and without surfactant

Assuming that the surfactant in the silica nanospheres enabled air annealing, when the nanoparticles of Example 1 were composed of Na2PtCl4, ammonia and a surfactant (IGEPAL), only Na2PtCl4 and ammonia When present, and in the microemulsion stabilized by IGEPAL®, the gold / platinum oxide nanocrystals without TEOS were heated to 200 ° C in air. The Na2PtCl4 and ammonia were mixed in an aqueous solution and dried to prepare a powder, followed by annealing in air.

The above results were confirmed by XRD analysis. When IGEPAL® was included, it was reduced to annealing with or without silica (FIG. 10 and FIG. 11C), but it was not observed that Pt ^{2 +} was reduced without IGEPAL® (Fig. 11B)

4.4 Confirmation of Surfactant Removal

Performed (Ag / Pt2 +) @ SiO 2 nano thermogravimetric analysis to confirm that the temperature interval where the surfactant is removed from the particles (TGA) and the results are shown in Figure 12, in order.

12A, it can be seen that the surfactant was rapidly removed when the heating temperature was 500 ° C., and that the surfactant was removed from the (Au / Pt ^{2 +} ) SiO ₂ nanoparticles through the weight change according to FIG. Respectively.

Example  5. Manufacture of gold-platinum alloy nanocrystals

In order to separate the AuPt nanocrystals from the SiO ₂ nanoparticles, the nanoparticles annealed at 500 in air in Example 4.2 were soaked in 5% hydrofluoric acid (HA) in a polypropylene vial and stirred at room temperature for 1 hour. Thereafter, centrifugal separation was performed to obtain gold-platinum alloy nanocrystals, which were then dispersed in water and centrifuged repeatedly to remove impurities.

The obtained gold-platinum alloy nanocrystals were analyzed by a transmission electron microscope, an energy dispersive X-ray line profile of a scanning tunneling electron microscope, and X-ray photoelectron spectroscopy. The results are shown in FIG. It was confirmed that gold and platinum were diffused at high temperature and alloyed randomly.

Example  6. AuPt / C Nanostructured Fabrication

(Au / Pt) SiO ₂ , conductive carbon black (Vulcan XC-72) 0.5 mg mL-1 annealed in air at 500 ° C. in Example 4.2 and Water 5 mg mL-1 was mixed for 1 hour. The mixed powder was recovered by centrifugation, and 1 mL of a 5% hydrofluoric acid solution was put into a polypropylene vial to remove SiO ₂ , and the prepared mixed powder was added and mixed at room temperature for 1 hour. The resulting AuPt / C nanocomposites can be obtained by centrifugation, and the impurities can be removed by agglomeration using two redispersions and centrifugation in water.

The amount of gold in the (Au / Pt ^{2 +} ) SiO ₂ and AuPt / C nanostructures annealed at 500 in air using ICP-AES was measured to be 0.17 and 0.11 mg, respectively, And that about 35% of the AuPt nanocrystals are lost in the process. At this time, the weight ratio of AuPt and carbon of the nanocompatible was 7.5: 92.52.

Example  7. [(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @ SiO ₂ Nanoparticle

7.1 [(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @SiO ₂ nanoparticle synthesis

[(Au / Pt ²⁺ ) / Fe ₃ O ₄ ] @SiO ₂ nanoparticles were synthesized by reverse microemulsion technique. 4 mg of Fe ₃ O ₄ nanoparticles were placed in a microemulsion solution in which 4.0 mL of IGEPAL CO-520® was dispersed in 20 mL of cyclohexane nucleic acid. The Fe ₃ O ₄ nanoparticles were used as the Fe ₃ O ₄ nanocrystals surface enclosed by oleic acid (oleic acid) in the average 6 nm. 16 mg mL-1 0.05 mL of sodium hydrogen tetrachloride, 0.05 mL of 16 mg mL-1 sodium tetrapretinate and 0.2 mL of 28-30% ammonia solution are added sequentially to a microemulsion solution containing Fe ₃ O ₄ nanoparticles Respectively. Finally, 0.3 mL TEOS was added and stirred for 15 hours. The resulting [(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @ SiO ₂ nanospheres were obtained by centrifugation, redispersed in ethanol and centrifuged to remove impurities.

7.2 [(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @SiO ₂ nanoparticle observation

The separated nanoparticles were observed using a transmission electron microscope and a high-resolution transmission electron microscope, and the results are shown in FIG. 14A.

The nanoparticles form the [@ (Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @SiO ₂ nanospheres in the core @ shell, which is composed of 6.2 (± 0.5) nm Fe ₃ O ₄ nanocrystals and several 1.6 ) nm of Au / Pt < ^{2 + & gt ;} , which is a mixed core surrounded by nanocrystals of Au / Pt < ^{2 + &} gt ;.

7.3 [(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @SiO ₂ nanoparticle annealing

The nanoparticles prepared in Example 7.1 were annealed in air at 500 in the same manner as in Example 4.2, and the result was observed using a transmission electron microscope (Fig. 14B). In the figure, it can be seen that the hybrid core surrounded by Au / Pt ^{2 +} nanocrystals is supported by the silica nanoclust.

7.4 Synthesis of AuPt / Fe ₃ O ₄ Nanostructures

[(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @ SiO ₂ nanoparticle powder prepared in Example 7.1 was heated at a rate of 5 ° C. min -1 and annealed in a box furnace at 500 ° C. for 5 hours to obtain a limited space It was changed to AuPt / Fe ₃ O ₄ in silica. The resultant (AuPt / Fe ₃ O ₄ ) @SiO ₂ nanosphere powder was mixed with 3M NaOH at a concentration of 5 mg mL-1 and stirred at 40 ° C for 1 hour to remove the silica shell from the AuPt / Fe ₃ give a O _4. AuPt / Fe ₃ O ₄ nano-structure body is then agglomerated with a centrifugal separation by re-dispersion and repeating the obtaining the water to remove impurities.

The separated nanocrystals were observed using an energy dispersive X-ray line profile of a transmission electron microscope and a scanning tunneling electron microscope, and the results are shown in FIGS. 14C and 14D. It was confirmed that AuPt / Fe ₃ O ₄ nanocrystals have a heterojunction structure in which a metal catalyst without a surfactant is fixed on a metal oxide support.

7.4 Synthesis of AuPt / Fe ₃ O ₄ / RGO nanostructures

20 mg of (AuPt / Fe ₃ O ₄ ) @ SiO ₂ powder of Example 7.1 was added to a well-dispersed aqueous solution of 2 mL of graphene oxide (1 mg mL-1) and stirred for 1 hour. To remove the silica of (AuPt / Fe ₃ O ₄ ) @ SiO ₂ , ₂ mL of 6M NaOH solution was added and stirred at 40 ° C for 1 hour. As a result, AuPt / Fe ₃ O ₄ / GO solids were obtained by centrifugation.

In addition, 20 mg of (AuPt / Fe ₃ O ₄ ) @ SiO ₂ powder was added to ₂ ml of GO having a concentration of 1 mg / ml dispersed in water, stirred for 1 hour, 2 ml of 6M NaOH solution was added and stirred at 40 ° C for 1 hour. The agitated solution was centrifuged to separate the GO from AuPt / Fe ₃ O _{4. The} solid was separated from the solution by centrifugation. The AuPt / Fe ₃ O ₄ / GO solid was obtained by removing impurities. The solid was dispersed in 2 ml of water and 20 mg of (AuPt / Fe ₃ O ₄ ) @ SiO ₂ powder was added and stirred for 1 hour to raise the AuPt / Fe ₃ O ₄ to GO. The above procedure was repeated to raise the AuPt / Fe ₃ O ₄ particles as much as possible in the GO.

In order to reduce GO, 0.02 mL of 0.642 x 10 ^-3 MN ₂ H ₄ H ₂ O was added to 2 mL of 1 mg mL-1 AuPt / Fe ₃ O ₄ / GO solution and stirred at 70 ° C for 24 hours Black solids formed a turbid solution. The AuPt / Fe ₃ O ₄ / RGO nanocomposites were obtained by centrifugation, and impurities were removed by re-dispersion in water and agglomeration using centrifugation.

The result was analyzed using TEM, and the results are shown in Fig. 15, it was confirmed that AuPt / Fe ₃ O ₄ nanocrystals were immobilized on the GO surface uniformly without aggregation.

The GO was reduced by reacting the AuPt / Fe ₃ O ₄ / GO nanocomposite with hydrazine (NH 2 NH 2) solution at 70 ° C for 24 h. Solids isolated from the reaction solution were analyzed using TEM, IR and XPS. The results are shown in FIG. 16 and FIG. 17, and it was confirmed that the GO was reduced in size, shape, oxidation, or immobilized AuPt nanocrystals without large change in RGO.

As measured by ICP-AES was confirmed _{(AuPt / Fe 3 O 4)} @SiO 2 and AuPt / Fe ₃ O ₄ / Au that the amount of the RGO are 0.15 and 0.06 mg This medicine for increasing the AuPt / Fe ₃ O ₄ to RGO Which means that a loss of 62% occurred. The ratio of AuPt, Fe ₃ O ₄ and RGO of AuPt / Fe ₃ O ₄ / RGO nanostructures was determined to be 6.5: 50.6: 42.9.

Example  8. Measurement of electrochemical catalytic performance of formic acid oxidation reaction

8.1 AuPt / C nanostructures

(Au / Pt ²⁺ ) @SiO ₂ nanoparticles were formed by varying the concentration of the Na ₂ PtCl ₄ solution in the manufacturing method of Example 1, and as a result, the Au: Pt ratio was adjusted to obtain a variety of Au56Pt44, Au63Pt37 and Au83Pt17 And an AuPt / C nanoconstructor was prepared in the same manner as in Example 6. The results are shown in Table 1. < tb >< TABLE >

The prepared nanocomposites were subjected to electrochemical measurements using a 660C (CH Instrument) potentiometer. Platinum wire and Ag / AgCl electrode (3 M potassium chloride) were used as a counter electrode and a reference electrode. Glassy carbon (GC) electrodes (CH Instruments, 3 mm diameter) were mechanically cleaned and used as working electrodes. The aqueous dispersion of the catalyst was ultrasonicated for 15 minutes and the dispersion was dropped on a glassy carbon rod and dried in air for 2 hours. After electrochemical measurement, the electrode was immersed in 5 uL of Nafion solution (0.05 wt%), . The voltage and current curves were obtained from an N 2 saturated sulfuric acid (H 2 SO 4) electrolyte solution and the surface of the electrode was cleaned several times during the current circulation process at -0.01 to 1.54 V before the voltage current measurement.

The forward inspection of the electrochemical formic oxidation of the Pt / C catalyst having the amorphous carbon spherical support as the support of the Au Pt / C series of platinum nanocrystals of size 2.1 (± 0.3) nm was normalized by the weight of the total metal species A current density is shown in Fig. The overall electrochemical activity of the AuPt / C series for the formic acid oxidation reaction was confirmed to be much higher than the Pt / C electrochemical catalytic activity. This means that the AuPt alloy system has increased electrochemical catalytic activity compared to the activity of the pure platinum catalyst of conventional electrochemical formic oxidation.

8.2 AuPt / Fe ₃ O ₄ nano-structure body and AuPt / Fe ₃ O ₄ / RGO nano-structure body

Subjected to Example 7.3 AuPt / Fe ₃ O ₄ nano-structure body and Example _{7.4 AuPt / Fe 3 O 4 /} RGO electrochemically measured in the same manner as the nano-structure body as in Example 6 of and the results are shown in Fig.

17, the electrochemical catalytic activity of Pt / C of 8.1 is remarkably superior to that of 8.1, and the AuPt / Fe ₃ O ₄ / RGO nanocompatibility is much higher than that of AuPt / Fe ₃ O ₄ system. Showed an electrochemically active surface area (ECSA), which shows that the electrical conductivity of the support is increased by the added RGO. This seems to be due to the increased electrical conductivity of the support by the added RGO.

8.2 Comparison of AuPt / C Nanostructures and AuPt / Fe ₃ O ₄ / RGO Nanostructures

The mass-specific activity of the AuPt / C of Example 8.1 versus the AuPt / Fe ₃ O ₄ / RGO catalyst of Example 8.2 for an electrochemical formic oxidation reaction is shown in Figure 1a . As a result, it was found that the two catalysts showed similar electrochemical activity although the starting potential and the signal position were slightly different in the formic acid oxidation reaction. The fact that the catalytic activity of AuPt deposited on Fe ₃ O ₄ / RGO was maintained demonstrates that it is effective to raise AuPt nanocrystals on a non-carbon support as a catalyst for the oxidation of formic acid.

AuPt / C and AuPt / Fe ₃ O ₄ of durability / RGO was measured by an electrochemical oxidation reaction of formic acid with a current time zone method (chronoamperometry). The results are shown in Figure 17b. Mass per surface area of the current density AuPt / Fe ₃ O ₄ / RGO is maintained higher than the AuPt / C catalyst and the current reduction was decreased more slowly than AuPt / Fe ₃ O ₄ / RGO is AuPt / C. This is that the electrochemical formic AuPt in oxidation / Fe ₃ O ₄ / RGO mean the increased durability compared to the AuPt / C, and AuPt / Fe ₃ O ₄ / RGO solid metal from triple nano constituent oxides effect .

Claims (24)

Mixing the gold precursor and the platinum oxide precursor with an organic solvent, a surfactant, and a basic solution to prepare an emulsion;
Mixing the emulsion and the silica precursor to prepare a first nanoparticle ((Au / Pt2 +) @ SiO2) having a structure containing gold and platinum oxide inside the silica nanosphere;
Annealing the first nanoparticles to produce second nanoparticles (AuPt @ SiO2) containing gold-platinum alloy crystals within the silica nanosphere; And
A method for producing gold-platinum alloy nanocrystals (AuPt) comprising removing silica from the second nanoparticles,
The annealing heat treatment decomposes the surfactant,
Wherein said gold-platinum alloy nanocrystals do not comprise a surfactant. The method according to claim 1, wherein the gold and platinum oxide in the first nanoparticle ((Au / Pt ^{2 +} ) @SiO ₂ ) have a structure in which a monolayer of gold nanocrystalline core and platinum oxide surrounds the gold nanocrystalline core ≪ / RTI > The method according to claim 1, wherein the step of removing the silica is carried out by a treatment with an acid solution or a treatment with a basic solution. The process according to claim 1, wherein the surfactant is contained in an amount of 4.5 to 7.0% by volume based on the volume of the organic solvent. 5. The method according to claim 4, wherein the surfactant is an amphipathic polymer. The method of claim 4, wherein the basic solution is a method for producing it in a solution containing at least one selected from the group consisting of ammonia (NH ₄ OH), sodium hydroxide (NaOH), and potassium hydroxide (KOH). The method of claim 1, wherein the emulsion is in the form of a reverse-microemulsion. The method of claim 1, wherein the gold precursor, the method of manufacturing is at least one selected from the group consisting of hydroxyl geumso tetrachloride (HAuCl4), Keumsan trichloride (AuCl _3), and sodium tetrachloride Keumsan (NaAuCl _4). The method according to claim 1, wherein the platinum oxide precursor is at least one selected from the group consisting of sodium platinate (Na ₂ PtCl ₄ ) and potassium platinate (K ₂ PtCl ₄ ). The method of claim 1, wherein the silica precursor is selected from the group consisting of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrabutyl orthosilicate (TBOS), and tetrapropyl orthosilicate Silicate, and tetrapropyl orthosilicate. The manufacturing method according to claim 1, wherein the annealing heat treatment is performed at a final temperature of 100 to 600 占 폚. The method according to claim 1, wherein the annealing heat treatment is performed in a reducing gas or air. 2. The method according to claim 1, wherein in the step of removing the silica, after the second nanoparticles and the carbon support are mixed, the silica is removed to obtain gold-platinum alloy nanocrystals supported on the carbon support. 14. The method of claim 13, wherein the carbon support is at least one selected from the group consisting of carbon black, graphene, and reduced graphene oxide (RGO). Mixing the gold precursor and the platinum oxide precursor with an organic solvent, a surfactant, and a basic solution to prepare an emulsion;
([Au / Pt2 + / Fe3O4] @ SiO2) having a structure containing iron oxide nanoparticles and gold and platinum oxide is mixed with the emulsion, the silica precursor, and the iron oxide nanoparticles to form the first hybrid nanoparticle Producing;
Annealing the first hybrid nanoparticles to produce second hybrid nanoparticles ((AuPt / Fe3O4) @ SiO2) containing iron oxide nanoparticles and gold-platinum alloy crystals in the silica nanosphere; And
(AuPt / Fe3O4) comprising nanocrystals of iron oxide nanoparticles and gold-platinum alloy (AuPt), comprising the step of removing silica from the second hybrid nanoparticles,
The annealing heat treatment decomposes the surfactant,
Wherein said gold-platinum alloy nanocrystals do not comprise a surfactant. The method of claim 15, wherein the gold and platinum oxide in the first hybrid nanoparticle ([(Au / Pt ^{2 +} ) / Fe ₃ O ₄ ] @SiO ₂ ) And a structure surrounding the gold nanocrystal core. 16. The method according to claim 15, wherein the step of removing the silica is carried out by a treatment with an acid solution or a treatment with a basic solution. 16. The method of claim 15, wherein the emulsion is in the form of a reverse-microemulsion. The method according to claim 15, wherein the annealing heat treatment is performed at a final temperature of 100 to 600 占 폚. 16. The method of claim 15, wherein the annealing heat treatment is performed in a reducing gas or air. 16. The method of claim 15, wherein in the step of removing the silica, and the second to remove the silica after mixing the hybrid nanoparticles and the carbon support, a hybrid nanoparticle _{(AuPt / Fe 3 O 4 /} C) supported on a carbon support ≪ / RTI > 22. The method of claim 21, wherein the carbon support is at least one selected from the group consisting of carbon black, graphene, and reduced graphene oxide (RGO). delete delete

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