JP2015105420A - Method for preparing metal nanoparticle, and metal nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new heterogeneous composite metal nanoparticle having excellent catalytic activity, and to provide a method for preparing the heterogeneous composite metal nanoparticle.SOLUTION: The method for preparing the heterogeneous composite metal nanoparticle comprises the steps of: forming a micell which comprises a metal polymer complex of an amphiphilic polymer, that has a hydrophilic part and a hydrophobic part having a multidentate ligand to be bonded coordinately to a metal atom, with a first metal ion and which has the hydrophobic part on the inside thereof; reducing the first metal ion on the inside of the micell to form a first metal nanoparticle; introducing a second metal ion different from the first metal ion into the inside of the micell and reducing the introduced second metal ion to prepare the heterogeneous composite metal nanoparticle. The heterogeneous composite metal nanoparticle comprises two metals selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt and zinc.

Description

  The present invention relates to a method for preparing metal nanoparticles and metal nanoparticles.

  It is known that metal nanoparticles have optical characteristics, catalytic activity, and the like that are different from bulk materials due to their limited space size and surface effects. Therefore, metal nanoparticles are applied to various fields such as electronics and medicine. Conventionally, methods for preparing the metal nanoparticles have been extensively studied.

  For example, Non-Patent Document 1 discloses forming a micelle made of a metal polymer complex of an amphiphilic polymer having a polydentate ligand and a platinum ion, and reacting in the micelle. It is disclosed that platinum nanoparticles were synthesized by reducing platinum ions as a field. Further, Non-Patent Document 1 discloses that the catalytic activity of platinum nanoparticles is increased by further adding platinum ions and a reducing agent to a micelle solution containing platinum nanoparticles and reducing the solution.

Akane Takagi, et al. , POLYMER Preprints, Japan vol. 62, No. 1, p. 1627 (2013)

  An object of the present invention is to provide a novel dissimilar composite metal nanoparticle excellent in catalytic activity, replacing the platinum nanoparticle prepared by the above method, and a method for preparing the dissimilar composite metal nanoparticle.

  The present inventors can prepare different types of composite metal nanoparticles by preparing metal nanoparticles using a predetermined metal and using the inside of micelles as a reaction field. It has been found that the catalyst activity is excellent, and the present invention has been completed. More specifically, the present invention provides the following.

(1) A method for preparing heterogeneous composite metal nanoparticles,
A hydrophobic part comprising a metal polymer complex of an amphiphilic polymer having a hydrophobic part and a hydrophilic part having a polydentate ligand coordinated to a metal atom, and a first metal ion, Forming a micelle to perform,
Reducing the ions of the first metal inside the micelles to form nanoparticles of the first metal;
Preparing the heterogeneous composite metal nanoparticles by introducing ions of a second metal different from the first metal into the micelles and then reducing the ions;
A method for preparing heterogeneous composite metal nanoparticles, wherein the first metal and the second metal are elements selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc.

  (2) The method for preparing heterogeneous composite metal nanoparticles according to (1), wherein the first metal is platinum or gold, and the second metal is silver.

  (3) Dissimilar composite metal nanoparticles prepared by the method according to (1) or (2).

  (4) Dissimilar composite metal nanoparticles composed of two kinds of metals selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc.

  ADVANTAGE OF THE INVENTION According to this invention, the preparation method of the novel metal nanoparticle excellent in catalyst activity and a metal nanoparticle can be provided.

It is a figure which shows the photograph of the platinum nanoparticle produced | generated by reduce | restoring the platinum ion inside the micelle prepared by the method which concerns on one Example of this invention. It is a figure which shows the UV spectrum of the micelle solution after introduce | transducing a silver ion into the inside of the micelle which has the platinum nanoparticle inside prepared by the method which concerns on one Example of this invention. It is a figure which shows the photograph of the dissimilar composite metal nanoparticle after introduce | transducing a silver ion into the inside of the micelle which has the platinum nanoparticle inside prepared by the method which concerns on one Example of this invention. It is a figure which shows the UV spectrum of the micelle solution after adding a reducing agent to the micelle solution which has the gold ion inside prepared by the method which concerns on one Example of this invention. It is a figure which shows the catalytic activity of the dissimilar composite metal nanoparticle prepared by the method based on one Example of this invention. It is a figure which shows the catalytic activity of the platinum nanoparticle prepared by the method based on one Example of this invention.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. .

<Method for preparing heterogeneous composite metal nanoparticles>
The method for preparing a heterogeneous composite metal nanoparticle according to the present invention comprises an amphiphilic polymer having a hydrophobic portion and a hydrophilic portion having a multidentate ligand coordinated to a metal atom, and an ion of a first metal. A step of forming a micelle made of a metal polymer complex and having a hydrophobic portion inside, a step of reducing a first metal ion inside the micelle to form a first metal nanoparticle, And a step of preparing heterogeneous composite metal nanoparticles by introducing ions of a second metal different from the first metal into the interior and then reducing the ions. According to the preparation method, the first metal and the second metal are heterogeneous composite metal nanoparticles that are elements selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc. Can be prepared. Hereafter, each process of the preparation method of the different composite metal nanoparticles of this invention is demonstrated in detail.

[Micelle formation process]
The micelle formation step consists of a metal polymer complex of an amphiphilic polymer having a hydrophobic part and a hydrophilic part having a polydentate ligand coordinated to a metal atom, and a first metal ion. This is a step of forming micelles with the hydrophobic part inside. In this step, ions of the first metal are trapped at the polydentate ligand site in the amphiphilic polymer to form a metal polymer complex, and a micelle composed of the metal polymer complex is formed.

  The amphiphilic polymer used in the present invention has a hydrophobic portion and a hydrophilic portion having a multidentate ligand coordinated to a metal atom. More specifically, the amphiphilic polymer is prepared using at least a monomer (A) having a multidentate ligand coordinated to a metal atom and a hydrophilic monomer (B). It is. For example, when the monomer (A) and the monomer (B) have a polymerizable functional group for copolymerization, the amphiphilic polymer is obtained by block copolymerization of the monomer (A) and the monomer (B). The monomer (A), the monomer (B), and other monomers may be block copolymerized. In addition, even if the amphiphilic polymer is a case where the monomer (A) does not have a polymerizable functional group, after synthesizing the macro chain transfer agent in which the chain transfer agent is introduced into the monomer (A). It can also be prepared by copolymerizing the macro chain transfer agent and the monomer (B) having a polymerizable functional group, even if the monomer (B) does not have a polymerizable functional group. It can also be prepared by synthesizing a macro chain transfer agent in which a chain transfer agent is introduced into the monomer (B) and then copolymerizing the macro chain transfer agent and the monomer (A).

  When the monomer (A) has a polymerizable functional group in its structure, the polymerizable functional group is not particularly limited, and examples thereof include a vinyl group, an allyl group, a styryl group, a methacryloyl group, and an acryloyl group. . The monomer (A) may be copolymerized with the monomer (B) described later via these polymerizable functional groups.

  The monomer (A) is a hydrophobic monomer having a multidentate ligand coordinated to a metal atom. When the ligand is a polydentate ligand, a stable complex can be formed by a chelate effect. The polydentate ligand is not particularly limited. For example, bidentate ligands such as dipicolylamine (DPA), bipyridine, Schiff base, phenanthroline, orthobenzoquinone derivative, nucleobase, terpyridine, diethylenetriamine, Schiff base, tria Tridentate ligands such as zacycloalkane and tetrakis (2'-aminoethyl) -1,2-diaminopropane, porphyrin and derivatives thereof, phthalocyanine and derivatives thereof, tetradentate ligands such as tetraazacycloalkane, aminoalkyl -Tetraazacycloalkane etc. are mentioned. Tridentate ligands such as tri (aminoalkyl) triazacycloalkane, 1,14-diamino-3,6,9,12-tetraazatetradecane, tri (aminoalkyl) triazacycloalkane, 1,14-diamino And hexadentate ligands such as -3,6,9,12-tetraazatetradecane. Among these, dipicolylamine, bipyridine, and phenanthroline are preferable in that they have high strength to release radicals described later. Further, dipicolylamine, bipyridine, and phenanthroline tend to form a complex with the first metal ion (particularly, platinum ion and gold ion).

  The monomer (B) is a hydrophilic monomer. In addition, when the monomer (B) has a polymerizable functional group in its structure, the polymerizable functional group is not particularly limited, and examples thereof include a vinyl group, an allyl group, a styryl group, a methacryloyl group, An acryloyl group etc. are mentioned. The monomer (B) may be polymerized with the monomer (A) through such a polymerizable group.

  Specifically, the monomer (B) includes hydroxyalkyl (meth) acrylic acid, aminostyrene, hydroxystyrene, vinyl acetate, glycidyl (meth) acrylate, (meth) acrylamide, 2-hydroxyethyl (meth) acrylate and the like ( (Meta) acrylate, (alkyl) aminoalkyl (meth) acrylate, alkylene glycol mono (meth) acrylate, polyalkylene glycol mono (meth) acrylate, polyalkylene oxide modified (meth) acrylate, N, N-dimethylacrylamide, etc. ) N-vinyl lactams such as acrylamides, N-vinyl-2-pyrrolidone, N-vinylamides such as N-vinylformamide, polyethylene glycol monoalkyl such as polyethylene glycol monomethyl ether Ether and the like. The monomer (B) is methacrylic acid (MAA), polyethylene glycol (meth) acrylate having a methoxy group, carboxyl group, amino group, azide group, or propargyl group at the end, polyethylene glycol monomethyl ether, 2-hydroxyethyl methacrylate. (HEMA), N-vinyl-2-pyrrolidone (NVP), and at least one selected from the group consisting of N, N-dimethylacrylamide (DMAA), the amphiphilic polymer is a polar solvent, In particular, it exhibits superior dispersibility in a solvent containing water.

  The amphiphilic polymer may have other monomers in addition to the monomer (A) and the monomer (B). Examples of other monomers include (meth) acrylamide, methylol (meth) acrylamide, methoxymethyl (meth) acrylamide, ethoxymethyl (meth) acrylamide, propoxymethyl (meth) acrylamide, butoxymethoxymethyl (meth) acrylamide, N- Methylol (meth) acrylamide, N-hydroxymethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylamide, 2-hydroxypropyl (meth) acrylamide, 2-hydroxybutyl (meth) acrylamide, (meth) acrylic acid, fumaric acid , Maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, citraconic acid, citraconic anhydride, crotonic acid, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth ) Acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-phenoxy-2- Hydroxypropyl (meth) acrylate, 2- (meth) acryloyloxy-2-hydroxypropyl phthalate, glycerin mono (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, dimethylamino (meth) acrylate, glycidyl (meth) acrylate, etc. Can be mentioned. These monomers may be used alone or in combination of two or more.

  According to the amphiphilic polymer prepared using at least the monomer (A) and the monomer (B), a metal polymer complex in which a large amount of metal atoms are stably coordinated can be formed.

  The mass average molecular weight (measured by GPC using polystyrene as a standard substance) of the amphiphilic polymer is preferably 5,000 to 5,000,000, and preferably 10,000 to 1,000,000. More preferred. If it is the said range, the outstanding dispersibility can be shown.

  The proportion of the monomer (A) in the amphiphilic polymer is not particularly limited, but is preferably 10 to 90 mol%, more preferably 20 to 60 mol%. If it is the said range, sufficient quantity of a metal atom can be coordinated. The proportion of the monomer (B) in the amphiphilic polymer is not particularly limited, but is preferably 10 to 90 mol%, more preferably 20 to 60 mol%.

  The molar ratio of the monomer (A) and the monomer (B) in the amphiphilic polymer is not particularly limited, but is preferably 1:99 to 99: 1, more preferably 10:90 to 90:10. When the ratio of the monomer (A) is high, excellent dispersibility is shown in a nonpolar solvent, and when the ratio of the monomer (B) is high, excellent dispersibility is shown in a polar solvent such as water. The molar ratio of monomer (A) / monomer (B) in the amphiphilic polymer may be adjusted depending on the type of the metal ion-containing solution.

  The polymerization method of the amphiphilic polymer is not particularly limited, and a conventionally known method can be used. Living radical polymerization methods such as addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are preferable. . According to the living radical polymerization method, the molecular weight and molecular weight distribution of the amphiphilic polymer to be synthesized can be controlled. Below, the synthesis method of an amphiphilic polymer is illustrated.

  First, the case of RAFT will be described. The monomer (B), the chain transfer agent, and the polymerization initiator are dissolved in a predetermined solvent, and after the oxygen in the reaction vessel containing dissolved oxygen is completely removed, the polymerization initiator is at or above the temperature at which it is cleaved. In addition, a macro chain transfer agent in which a chain transfer agent is introduced at the terminal of a polymer obtained by polymerizing the monomer (B) (hereinafter referred to as B block) is synthesized by heating at a temperature of 100 ° C. or lower for 24 to 48 hours. To do. Next, the macro chain transfer agent and the monomer (A) are dissolved in a predetermined solvent and heated at a temperature not lower than the temperature at which the polymerization initiator is cleaved and not higher than 100 ° C. for 24 to 300 hours. Thus, an amphiphilic polymer in which the B block and a polymer obtained by polymerizing the monomer (A) (hereinafter referred to as A block) are coupled in series can be synthesized. In addition, when the monomer (B) is, for example, a monomer having a polyalkylene oxide chain, after synthesizing a macro chain transfer agent in which a chain transfer agent is introduced into the monomer (B), this macro chain transfer agent, The monomer (A) was dissolved in a predetermined solvent and heated in the same manner as described above, whereby the monomer (B) and a polymer obtained by polymerizing the monomer (A) (hereinafter referred to as A block) were connected in series. Amphiphilic polymers can be synthesized.

  The chain transfer agent used for RAFT is not particularly limited. For example, butylbenzyl trithiocarbonate, cumyl dithiobenzoate (CDB), 4-cyanopentanoic acid dithiobenzoate, acetic acid dithiobenzoate, butanoic acid dithiobenzoate, 4- And toluic acid dithiobenzoate.

  The polymerization initiator is not particularly limited. For example, 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis (2-methylbutyronitrile), diisopropyl peroxycarbonate, t-butylperoxy -2-Ethylhexanoate, t-butylperoxypivalate, t-butylperoxydiisobutyrate, benzoyl peroxide, lauroyl peroxide, ammonium persulfate, potassium persulfate, and the like can be used. The suitable usage-amount of a polymerization initiator is 0.001-1 mass% with respect to a monomer, and 1-33 mass% with respect to a chain transfer agent.

  Next, the case using ATRP will be described. First, a monomer (B), a halogenated alkyl agent, and a catalyst are dissolved in a predetermined solvent and reacted to synthesize a macrohalogenated alkyl agent having a halogenated alkyl agent introduced at the end of the B block. . Next, the macrohalogenated alkyl initiator and the monomer (A) are dissolved in a predetermined solvent, a catalyst is added, and the mixture is heated at a temperature of room temperature or higher and 100 ° C. or lower for 6 to 50 hours. By doing so, the amphiphilic polymer (block amphiphilic polymer) used in the present invention in which the B block and the A block are connected in series can be synthesized.

  The halogenated alkyl initiator used for ATRP is not particularly limited, and examples thereof include 2-bromoisobutyryl bromide, 2-chloroisobutyryl chloride, bromoacetyl bromide, bromoacetyl chloride, and benzyl bromide.

  As the catalyst, for example, a transition metal complex such as monovalent copper or divalent ruthenium can be used.

  The solvent used for the polymerization reaction is not particularly limited. For example, water, methanol, ethanol, propanol, t-butanol, benzene, toluene, N, N-dimethylformamide, tetrahydrofuran, chloroform, 1,4-dioxane, dimethyl Examples thereof include sulfoxide and a mixed solution thereof.

  By selecting the molar ratio of monomer (A) / monomer (B) in the amphiphilic polymer and the type of the metal ion-containing solution as appropriate, the amphiphilic polymer forms micelles in the metal ion-containing solution. Become distributed.

  The metal polymer complex of the present invention can be made into micelles, for example, by dissolving the metal polymer complex of the present invention in a predetermined solvent and dialyzing it using a dialysis membrane. The predetermined solvent is selected so as to form micelles with the hydrophobic portion inside. Although it does not specifically limit as such a predetermined solvent, For example, organic solvents, such as ethanol, acetone, N, N- dimethylformamide, benzene, N, N- dimethylacetamide, are suitable. As the dialysis membrane, it is preferable to use a regenerated cellulose membrane having a molecular weight cut-off of 5,000 to 30,000. In order to obtain micelles (monodispersed micelles) with a uniform particle size, it is preferable to filter with a filter or the like after the dialysis.

[First Metal Nanoparticle Formation Step]
The first metal nanoparticle forming step is a step of reducing first metal ions inside the micelle to form first metal nanoparticles.

  Since the first metal ion is reduced inside the micelle, stable and selective uptake of the metal ion and separation of the reduction reaction are possible, and as a result, the particle size of the nanoparticles becomes closer to a uniform size. .

  Although the reduction | restoration of the 1st metal ion inside a micelle is not specifically limited, For example, it adds by adding a reducing agent to a micelle. The reducing agent is not particularly limited, and examples thereof include sodium borohydride, diisobutylaluminum hydride, lithium aluminum hydride, oxalic acid, formic acid, hydrazine and the like. Of these, sodium borohydride is preferable. The addition amount of the reducing agent is not particularly limited, but can be appropriately selected in order to produce appropriate nanoparticles.

[Preparation process of heterogeneous composite metal nanoparticles]
The step of preparing the heterogeneous composite metal nanoparticles is a step of preparing the heterogeneous composite metal nanoparticles by introducing ions of a second metal different from the first metal into the micelle and then reducing the ions. is there. Reduction of the second metal ion occurs without introducing a reducing agent by introducing the second metal ion into the micelle. As a result, heterogeneous composite metal nanoparticles can be prepared. Hereinafter, the action of reducing the second metal ions without adding a reducing agent will be described.

  It is considered that radicals are generated from a polydentate ligand coordinated to a metal atom or a solvent in the micelle inside the micelle made of the metal polymer complex. Furthermore, it is considered that the first metal nanoparticles have a capability as a radical scavenger. As a result, the first metal nanoparticles scavenge the generated radicals, and the radicals are locally accumulated on the first metal nanoparticles, whereby the second metal introduced into the micelles. It is estimated that ion reduction occurs. Thus, since the reduction | restoration of the ion of a 2nd metal is performed spontaneously within a micelle, a reducing agent is not required. The heterogeneous composite metal nanoparticles are prepared by reduction of the second metal ions. The heterogeneous composite metal nanoparticles prepared in this way are excellent in catalytic activity. The reason is considered that the prepared heterogeneous composite metal nanoparticles have a core / shell structure or an alloy structure, and some interaction occurs between the first metal and the second metal. .

  Although the temperature at the time of reduction | restoration of a 2nd metal is not specifically limited, 30 degreeC or more is preferable and 50 degreeC or more is more preferable at the point that the activity of the dissimilar composite metal nanoparticle after reduction | restoration becomes higher.

  The first metal and the second metal of the present invention are not particularly limited as long as they are elements selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc. As described above, these metal nanoparticles are considered to have a capability as a radical scavenger, so it is assumed that these metals act as the first metal. Of these, the first metal is preferably platinum or gold, and most preferably platinum. In addition, as described above, the reduction of the second metal ion in the autoreduction environment formed by the radical generating species generated from the polydentate ligand such as DPA (dipicolylamine) and the first metal nanoparticles. Therefore, dissimilar composite metal nanoparticles are formed. The second metal is preferably silver, palladium or rhodium, and most preferably silver. Also, the first metal and the second metal are different.

<Different composite metal nanoparticles>
The present invention includes heterogeneous composite metal nanoparticles composed of two kinds of metals selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc.

  The heterogeneous composite metal nanoparticles of the present invention are excellent in catalytic activity. The reason is presumed that some kind of interaction occurs between the first metal and the second metal.

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

<Synthesis of Monomer (A)>
[Synthesis of Monomer (A) Having Dipicolylamine (DPA) as Multidentate Ligand]
Under normal temperature and argon atmosphere, 2- (chloromethyl) pyridine hydrochloride (10.0 g, 61.0 mmol, 2.90 equivalents relative to 3-amino-1-propanol), TBAB (tetrabutylammonium bromide) (322 mg) , 1 mmol), potassium carbonate (28.1 g, 203 mmol, 9.67 equivalents to 3-amino-1-propanol) was dissolved in dehydrated acetonitrile. Thereafter, 3-amino-1-propanol (1.6 mL, 21.0 mmol) was added at 95 ° C. under reflux, and the mixture was stirred for 4 days. After stirring, the progress of the reaction was confirmed with a TLC plate (developing solvent: ethyl acetate / methanol = 9/1), followed by filtration through celite. After concentration, separation and purification by column chromatography (developing solvent: ethyl acetate / hexane = 1/9) was performed. It was confirmed by structural analysis by ¹ H-NMR that the obtained product was a compound represented by the formula (1) (DPA-OH) (4.67 g, yield: 89.3%).

The compound represented by the formula (1) (2.70 g, 10.5 mmol) is dissolved in 5 mL of dehydrated THF (tetrahydrofuran) at room temperature under an argon atmosphere, and TEA (triethylamine) (2.0 mL, 14.3 mmol, formula) 1.37 equivalents) was added to the compound represented by (1). Thereafter, acrylic chloride (1.1 mL, 13.5 mmol, 1.28 equivalents relative to the compound represented by formula (1)) was added dropwise in an ice bath, and the mixture was stirred for 1 day. After stirring, the mixture was filtered through celite, concentrated, dissolved in diethyl ether, and filtered through celite. Thereafter, the solution was concentrated, dissolved in ethyl acetate, and washed with sodium bicarbonate and brine. The obtained organic layer was dehydrated with magnesium sulfate, concentrated, and then separated and purified by a column (developing solvent: ethyl acetate / methanol = 9/1). It was confirmed by structural analysis by ¹ H-NMR that the obtained product was a DPA monomer represented by the formula (2) (1.52 g, yield: 46.5%). The reaction scheme is shown below.

<Synthesis of Monomer (B) -Macro-RAFT Agent>
[Synthesis of RAFT agent]
1-butanethiol (6.0 mL, 55.9 mmol, 1.20 equivalents relative to the compound represented by formula (3)) was dissolved in dehydrated THF at room temperature under an argon atmosphere. Thereafter, DBU (diazabicycloundecene) (8.3 mL, 55.5 mmol, 1.19 equivalent to the compound represented by the formula (3)) was added, and carbon disulfide (3. 3 mL, 55.8 mmol, 1.20 equivalents to the compound represented by formula (3)) was added dropwise, and the mixture was stirred at room temperature for 30 minutes. Thereafter, 4-bromobenzoic acid (formula (3)) (10.0 g, 46.5 mmol) dissolved in dehydrated THF (tetrahydrofuran) was added dropwise and stirred overnight. After stirring, the mixture was filtered through Celite, concentrated, dissolved in IPE (isopropyl ether), and washed with 1N hydrochloric acid. The obtained organic layer was dehydrated with magnesium sulfate and lyophilized. It was confirmed by structural analysis by ¹ H-NMR that the obtained product was a RAFT agent (CTA) represented by the formula (4) (9.23 g, yield: 66.1%). The reaction scheme is shown below.

[Synthesis of PEG-Macro-RAFT Agent]
Poly (ethylene glycol) methyl ether (formula (5)) (10.0 g, 2.00 mmol) was dissolved in dehydrated THF at room temperature under an argon atmosphere. Thereafter, TEA (0.9 mL, 6.46 mmol, 3.23 equivalents relative to the compound represented by formula (5)) was added, and methanesulfonyl chloride (0.5 mL, 6.45 mmol, formula) was added in an ice bath. (3.23 equivalents) of the compound represented by (5)) was added dropwise and stirred for 3 hours. After stirring, the mixture was filtered through celite, concentrated, reprecipitated with IPE (isopropyl ether), and lyophilized. It was confirmed by structural analysis by ¹ H-NMR that the obtained product was PEG-OMs represented by the formula (6) (10.4 g, yield: 99.9%).

PEG-OMs (5.00 g, 0.99 mmol) represented by the formula (6) was dissolved in 100 mL of an ammonium solution and stirred at room temperature for 3 days. After stirring, the mixture was concentrated, reprecipitated with IPE, and lyophilized. It was confirmed by structural analysis by ¹ H-NMR that the obtained product was PEG-NH ₂ represented by formula (7) (4.88 g, yield: 99.9%). The reaction scheme is shown below.

Under normal temperature and argon atmosphere, the RAFT agent represented by formula (4) (1.496 g, 4.98 mmol, 4.73 equivalents to the compound represented by formula (7)) is dissolved in about 100 mL of toluene. , DCC (dicyclohexylcarbodiimide) (1.042 g, 5.05 mmol, 4.80 equivalents to the compound represented by formula (7)) was added, and the mixture was stirred for 10 minutes. After stirring, PEG-NH ₂ (formula (7)) (4.88 g, 1.05 mmol) and DMAP (dimethylaminopyridine) (0.017 g, 0.115 mmol, based on the compound represented by formula (7) 10.9 mol%) was added, and the mixture was stirred at 90 ° C. under reflux for 2 days. Thereafter, the mixture was filtered through celite, concentrated, reprecipitated by IPE, and lyophilized. It was confirmed by structure analysis by ¹ H-NMR that the obtained product was a PEG-macro-RAFT agent represented by the formula (8) (4.20 g, yield: 81.1%). The reaction scheme is shown below.

<Synthesis of amphiphilic polymer>
[Synthesis of PEG-b-DPA]
DPA monomer represented by formula (2) (3026 mg, 9.72 mmol, 100 equivalents relative to the compound represented by formula (8)), PEG-macro-RAFT agent represented by formula (8) (478. 6 mg, 0.0972 mmol), AIBN (azobisisobutyronitrile) (4.79 mg, 0.0292 mmol, 0.3 equivalent to the compound represented by formula (8)) in DMF (dimethylformamide) 9. Dissolved in 72 mL (monomer concentration 1M). Freeze deaeration and argon substitution were performed, and the mixture was stirred at 70 ° C. for 348 hours. After the reaction, reprecipitation was performed with diethyl ether, and the product was obtained by lyophilization. ^{From the} structural analysis by ¹ H-NMR, the synthesis of PEG-b-DPA ₅₆ (formula (9)) having 56 DPA monomer units was confirmed (2.12 g, yield: 60.5%). The reaction scheme is shown below.

  When the spectrum of DPA-OH-Pt was confirmed, a peak derived from DPA and a peak derived from DPA-Pt could be observed in a 0.5 equivalent spectrum. In addition, no peak derived from DPA was observed in the 1.0 equivalent spectrum, and a peak derived from DPA-Pt was observed. A peak derived from DPA-Pt was also observed in the 2.0 equivalent spectrum. It is considered that the Pt coordinated to the amine of the pyridine ring changed the electronic state of the pyridine ring, and the proton peak shifted to the low magnetic field side. It was confirmed that the Pt complexation rate of PEG-b-DPA-Pt can be determined by this peak shift.

<Synthesis of PEG-b-DPA-Pt>
In a solution of PEG-b-DPA (48.85 mg, 2.18 μmol) represented by the formula (9) dissolved in 5 mL of methanol, Pt (DMSO) ₂ Cl ₂ (69.08 mg, 0.164 mmol, in DPA unit). Solution of 1.337 equivalents) in 5 mL of methanol was added dropwise and stirred for 1 day. Thereafter, purification by dialysis (MWCO: 3500) was performed, followed by lyophilization. It was confirmed from the peak shift of ¹ H-NMR that the obtained product was PEG-b-DPA-Pt represented by the formula (10) (82.9 mg, yield: 92.9%). The platinum complexation of PEG-b-DPA is a quantitative peak shift to the low magnetic field side of ¹ H-NMR showing the change in the electronic state of the pyridine ring due to the coordination of Pt to the amine of the pyridine ring of DPA. Confirmed by The reaction scheme is shown below.

<Micelleization of PEG-b-DPA>
50 mg of PEG-b-DPA (formula (9)) was dissolved in 5 mL of dimethyl sulfoxide, and dialyzed against Milli-Q water using a dialysis membrane (MWCO: 3500). Three days later, the recovered solution was adjusted to 1 mg / mL and used as a mother liquor. Prepare 4 mL of each concentration of 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01, 0.001, 0.0001, 0.00001 mg / mL from the mother liquor. It was left for 3 days.

<Micelleization of PEG-b-DPA-Pt>
50 mg of PEG-b-DPA-Pt (formula (10)) was dissolved in 5 ml of dimethyl sulfoxide, and dialyzed against PBS using a dialysis membrane (MWCO: 3500). Three days later, the recovered solution was adjusted to 1 mg / mL and used as a mother liquor. Prepare 4 mL of each concentration of 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01, 0.001, 0.0001, 0.00001 mg / mL from the mother liquor. It was left for 3 days.

<Physical properties evaluation of PEG-b-DPA, PEG-b-DPA-Pt>
[Evaluation of critical micelle concentration]
Using the micelle solution of PEG-b-DPA (Formula (9)) and PEG-b-DPA-Pt (Formula (10)) obtained above, the respective critical micelle concentration was measured by the pyrene fluorescent probe method. When (cmc) was calculated | required, cmc of PEG-b-DPA was computed with 0.02597 mg / mL. Moreover, cmc of PEG-b-DPA-Pt was calculated to be 0.2277 mg / mL. Since the association behavior of PEG-b-DPA-Pt was observed in PBS, it is considered that the charge repulsion was relaxed by ion addition to form an aggregate. However, when compared with uncomplexed PEG-b-DPA, the cmc of PEG-b-DPA-Pt after complexation was confirmed to be about 10 times. This is considered to be due to a change in the hydrophilic / hydrophobic balance due to the Pt complexation, and it is considered that only the charge repulsion does not affect the association behavior.

[Evaluation by dynamic light scattering photometer]
3 mL of the mother liquid (1.0 mg / mL) of PEG-b-DPA obtained above was taken, filtered with a 0.22 μm filter, and then a dynamic light scattering photometer (DLS (Dynamic Light Scattering) -7000 (Otsuka Electronics ( Lower part), Osaka, Japan)), and the measurement was performed with an Ar laser (488 nm). The same operation was performed for PEG-b-DPA-Pt. As a result, it was confirmed that the particle sizes of the micelles in PEG-b-DPA and PEG-b-DPA-Pt were 80.8 nm and 87.1 nm, respectively. Moreover, the polydispersity index (PD) of the micelle in PEG-b-DPA and PEG-b-DPA-Pt is 0.06936 and 0.08488, respectively, and the micelle polydispersity index is 0. The value was less than 1. This confirmed that each micelle was very monodispersed.

<Preparation of Pt nanoparticles>
The PEG-b-DPA-Pt micelle solution (2 mg / mL) obtained above was diluted with 150 mM PBS to prepare 6 mL of PEG-b-DPA-Pt (0.3533 mg / mL) micelle solution. . NaBH ₄ (12.71 mg, 100 equivalents with respect to the DPA unit) was directly added to the prepared micelle solution, and the mixture was stirred at room temperature for 1 day.

  The micelle solution was changed from yellow to brown within 1 hour after adding the reducing agent. As the amount of reducing agent added increased, the solution turned darker brown, suggesting reduction of Pt ions. Since the solution was a brown dispersion solution even after the lapse of a predetermined time, Pt particles were generated in the micelle core part, and it is considered that the block amphiphilic polymer plays a role as a dispersant.

[Evaluation by dynamic light scattering photometer]
After stirring for 1 day after the addition of NaBH ₄ , DLS measurement and TEM observation were performed. According to the DLS measurement, the particle size of the micelle was 87.7 nm, and the polydispersity index (PD) was 0.1144. The micelle solution before reduction had a particle size of 87.1 nm and a polydispersity index (PD) of 0.08488. Thus, no significant changes were observed in the micelle particle size and polydispersity index. This indicates that the micelles maintain monodispersity before and after the reduction, suggesting that the reduction occurred using the core as a reaction field without the micelles collapsing.

[TEM observation]
When TEM observation was performed on the micelle after stirring, a black spot of 1-2 nm was observed in a faint black mass of 37.5-50 nm. Transmission electron microscope (TEM) obtains image contrast based on the density of electrons that have passed through the sample, so it is possible to observe metals that are difficult to transmit electron beams in areas where the image contrast is high, and organic substances that are easily transmitted through electron beams in thin areas. Is done. That is, the black spots observed by TEM are considered to be Pt nanoparticles.

  From this result, it was observed that the PEG-b-DPA-Pt aggregates maintained a certain shape in the micelle solution, and Pt nanoparticles having a very uniform size of 1-2 nm were observed, and the micelle shape was maintained. It is considered that Pt nanoparticles were generated in the core part. An image of this micelle observed using STEM is shown in FIG. From FIG. 1, it was confirmed that 1-2 nm Pt nanoparticles were generated in 66 nm micelles.

From the above results, it was confirmed that Pt nanoparticles were synthesized by adding 100 equivalents to the DPA unit of NaBH ₄ . Hereinafter, PEG-b-DPA-Pt after the first reduction by adding a reducing agent is referred to as “1 ^st reduced PEG-b-DPA-Pt”.

<Evaluation of catalytic activity of Pt nanoparticles>
1 ^st reduced PEG-b-DPA-Pt solution (0.7377 mg / mL) 0.5677 mL, 4-nitrophenol aqueous solution (2 mM) 0.037 mL, Milli-Q1.321 mL were added to prepare a solution. 926 mL. After quickly adding 0.074 mL of NaBH ₄ aqueous solution prepared to 29.7 mM and shaking well, UV-vis spectrum measurement was started immediately. As a result, a decrease in peak at 400 nm, which is the absorption wavelength of 4-nitrophenol, was confirmed. This is considered to be due to the change of 4-nitrophenol to 4-aminophenol. Since 4-nitrophenol changes to 4-aminophenol only in the presence of a catalyst, it was suggested that 1 ^st reduced PEG-b-DPA-Pt contributed to the progress of this reaction as a catalyst.

<Preparation of heterogeneous composite metal nanoparticles>
The solutions of Examples 1 and 2 were prepared in an optical cell with the compositions shown in Table 1 below, and allowed to stand at each temperature. UV-vis spectrum measurement was performed at regular time intervals, and after confirming the completion of the reaction, DLS measurement and TEM observation were performed.

[UV-vis spectrum measurement]
In the solutions of Examples 1 and 2, peaks derived from surface plasmon resonance of the metal nanoparticles were observed with time. However, since the baseline rise derived from 1 ^st reduced PEG-b-DPA-Pt is observed and it is difficult to observe the peak top wavelength derived from the metal nanoparticles, the blank is replaced with 1 ^st reduced PEG-b-DPA-Pt. The UV-vis spectrum was measured for each solution. The result is shown in FIG. From FIG. 2, it was confirmed that the peak top wavelengths of the respective solutions were Example 1: 408 nm and Example 2: 410 nm. Also from the peak top wavelength, it was confirmed that Ag ions were reduced and Ag nanoparticles were generated. Thus, it is considered that the reason for the reduction of Ag ions is that Pt nanoparticles are a catalyst for radical transfer. In general, Pt nanoparticles have a capability as a radical scavenger, and it is known to scavenge the radical of 2,2-diphenyl-1-picrylhydrazyl (DPPH), which is famous as a stable radical. . In other words, the radicals generated from DPA or the radicals generated from the solvent are scavenged by Pt nanoparticles, and the radicals are locally accumulated on the Pt nanoparticles, so that the reduction of Ag ions may have occurred. It is done.

  Each solution was compared for each reaction condition. First, comparison was made between 30 ° C. (Example 1) and 50 ° C. (Example 2). As a result, it was confirmed that the reduction rate of metal ions was faster at 50 ° C. This is presumably because the activation energy of DPA was reduced by applying heat and the reduction of metal ions was promoted. In addition, it is considered that the number of associations increased by applying heat, the DPA concentration in the micelle reaction field increased, and it was easily reduced.

[Evaluation by dynamic light scattering photometer]
Table 2 shows the measurement results by DLS. In any of the solutions, there was no significant change in the micelle particle size and polydispersity index before and after the addition of metal ions. This indicates that the micelle maintains monodispersity before and after the reduction, suggesting that the reduction occurred using the core as a reaction field without the micelle collapsing.

[TEM observation]
The TEM observation result of each micelle is shown in FIG. In FIG. 3, in Examples 1 and 2, a 40 nm PEG-b-DPA-Pt micelle and a 1-2 nm black spot were observed. This 1-2 nm black spot is considered to be a composite metal of Pt nanoparticles and Ag nanoparticles.

<Preparation of metal nanoparticles using PEG-b-DPA>
According to the composition shown in Table 3 below, the solution of Test Example 1 was prepared in an optical cell and allowed to stand at each temperature. UV-vis spectrum measurement was performed at regular intervals.

  The UV-vis spectrum measurement result of Test Example 1 is shown in FIG. From FIG. 4, in the Au ion addition system (Test Example 1), a peak derived from plasmon resonance of the metal nanoparticles was observed. This is thought to be because Au ions were reduced by radicals generated from the tertiary amine of DPA to produce Au nanoparticles.

<Evaluation of catalytic activity of heterogeneous composite metal nanoparticles>
0.037 mL of 4-nitrophenol aqueous solution (2 mM), 0.838 mL of the solutions of Examples 1 and 2 (both 0.5 mg / mL) and Milli-Q 1.051 mL were added to the optical cell to make the total volume 1.926 mL. did. After quickly adding 0.074 mL of NaBH ₄ aqueous solution adjusted to 29.7 mM and shaking well, UV-vis spectrum measurement was started immediately.

[Catalyst activity evaluation]
FIG. 5 shows a graph representing the time-dependent change in absorbance at λ = 400 nm in logarithm based on the UV-vis spectrum measurement results. The reaction rate constant k was calculated from FIG. k is calculated using the following equation, and the results are shown in Table 4.

From Table 4, in Examples 1 and 2, the reaction rate constant was dramatically improved by a factor of 500 when compared with 1 ^st reduced PEG-b-DPA-Pt. As described above, it was confirmed that Examples 1 and 2 have extremely excellent catalytic activity as compared with 1 ^st reduced PEG-b-DPA-Pt. Further, when Example 1 (30 ° C. reduction) was compared with Example 2 (50 ° C. reduction), Example 2 had slightly higher catalytic activity. This is considered to be due to the formation of a metal crystal having a rigid phase structure.

<Production and catalytic activity evaluation of Pt nanoparticles by twice reduction>
NaBH ₄ 36.00 mg (100 equivalents to Pt) was added to 6 mL of PEG-b-DPA-Pt micelle solution (1 mg / mL), and the mixture was stirred for 1 day, and then dialyzed against PBS for 1 day. reduction). To the solution after dialysis, 33 mg of NaBH ₄ (100 equivalents relative to Pt) was added again and stirred for 1 day, followed by dialysis against PBS for 1 day (reduction twice). Evaluation of catalytic activity with 4-nitrophenol was performed using each solution of the 1-time reduction and the 2-time reduction. Solutions having compositions as shown in Table 5 below were prepared (Comparative Example 1 and Comparative Example 2), and evaluation was performed based on time-dependent UV-vis spectrum measurement results.

  The peak change at 400 nm of each sample of Comparative Examples 1 and 2 is shown in FIG. As shown in FIG. 6, the catalytic activity of the Pt nanoparticles produced by the reduction twice was slightly higher than that of the first reduction, but no significant difference was confirmed.

As shown above, Examples 1 and 2 (Pt / Ag nanoparticles) were confirmed to have extremely superior catalytic activity compared to 1 ^st reduced PEG-b-DPA-Pt (Pt nanoparticles). It was done. Further, Pt nanoparticles prepared by reducing Pt nanoparticles twice using a reducing agent (Comparative Example 2) were also reduced once (Comparative Example 1, ie, 1 ^st reduced PEG-b-DPA-). Since there was no significant difference in Pt) and catalytic activity, Examples 1 and 2 (Pt / Ag nanoparticles) were compared with Pt nanoparticles prepared by reduction twice (Comparative Example 2). It was shown that it has a very good catalytic activity. Here, it has been conventionally known that Pt nanoparticles have extremely higher catalytic activity than Ag nanoparticles (Kunio Esumi, et al., Langmuir, vol. 20, No. 1, p237-243 ( 2004)). If it does so, even if it combines the catalytic activity of Pt nanoparticle and Ag nanoparticle, it should be almost the same as the catalytic activity of the thing of only Pt nanoparticle. Nevertheless, as described above, Examples 1 and 2 (Pt / Ag nanoparticles) have very high activity compared to Pt nanoparticles. This is because the Pt / Ag nanoparticles prepared by the above method have a core / shell structure or an alloy structure composed of Pt and Ag, and some interaction works between Pt / Ag. This is presumably because of high catalytic activity.

Claims (4)

A method for preparing heterogeneous composite metal nanoparticles comprising:
A hydrophobic part comprising a metal polymer complex of an amphiphilic polymer having a hydrophobic part and a hydrophilic part having a polydentate ligand coordinated to a metal atom, and a first metal ion, Forming a micelle to perform,
Reducing the ions of the first metal inside the micelles to form nanoparticles of the first metal;
Preparing the heterogeneous composite metal nanoparticles by introducing ions of a second metal different from the first metal into the micelles and then reducing the ions;
A method for preparing heterogeneous composite metal nanoparticles, wherein the first metal and the second metal are elements selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc.   The method for preparing heterogeneous composite metal nanoparticles according to claim 1, wherein the first metal is platinum or gold, and the second metal is silver.   A heterogeneous composite metal nanoparticle prepared by the method according to claim 1 or 2.   A heterogeneous composite metal nanoparticle comprising two metals selected from the group consisting of platinum, gold, silver, copper, nickel, palladium, rhodium, cobalt, and zinc.