JP2004183009A - Method of producing metal fine particle - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は触媒、光学材料、電子材料、感圧材料などに用いられるナノサイズ金属微粒子の製造方法に関する。
【０００２】
【従来の技術】
数十ｎｍ以下の粒径を有する貴金属の微粒子は、バルク金属には見られない微粒子に特有の性質を活かして、化学的に安定な着色剤、カラーフィルター、導電性ペースト、化学反応の触媒、透明導電膜等、その応用を拡大している。従来のリソグラフィー技術に基づいたＬＳＩの高集積化の限界を打破する目的で研究が進められている単一電子デバイスにおいては、その一構成要素である量子ドットとして金属微粒子の利用も検討されている。
【０００３】
このような金属微粒子を製造する方法として、気相法と液相法がある。気相法にはガス中蒸発法、スパッタリング法等があり、例えばガス中蒸発法では、不活性ガスを導入した真空容器内で金属を蒸発させ、有機溶剤で被覆した状態の金属微粒子が得られる。高濃度の金属微粒子分散液を製造可能である利点を有するが、金属微粒子の粒径分布を制御することは困難である。また、特別な装置を必要とするためコスト面の問題もある。
【０００４】
一方、液相法は、金属イオン含有溶液に紫外光を照射あるいは還元剤を加えて金属イオンを還元することによって金属微粒子を得る方法である。なかでも還元剤を用いる方法は、特別な装置を必要とすることなく、比較的容易に粒径分布の狭い金属微粒子を製造することが可能であるといった特徴がある。このような手法として具体的には、保護ポリマーの存在下、金属塩を溶液中で還元してコロイド溶液を得る手法が古くから用いられており、これを応用した技術として、溶媒中に金属塩とアミンを溶解した溶液を還元することにより得られた溶液に、チオールまたはチオール溶液を添加することにより得られる表面がチオールで保護された金属超微粒子を作製する手法が開示されている。（特許文献１参照）
【０００５】
更にこれら手法の他に、金属微粒子の製造方法としては、脂肪酸と水酸化ナトリウムを反応させ鹸化後、硝酸銀と反応させることにより脂肪酸塩銀を作製し、窒素存在下２５０℃で該金属塩を熱分解させることにより銀超微粒子を作製する技術も提案されている。（非特許文献１参照）
【０００６】
【非特許文献１】
長澤浩、他５名、「金属錯体の固相熱分解法による銀超微粒子の合成と評価」、超微粒子とクラスター懇談会 第２回研究会公演予稿集、１９９８年４月２２日、Ｐ４５−４８
【特許文献１】
特開平１０−１９５５０５号公報
【０００７】
【発明が解決しようとする課題】
しかし、液相法においても、一般的に粒径分布の狭い金属微粒子を得ることは非常に厳密な条件を必要とし、より厳密に制御された平均粒径及び粒径分布を有する金属微粒子を得ることは困難であるという問題があった。更に、副生成物が多く、安定な銀コロイドが作製できないといった問題も有するものであった。また、熱分解を行う方法においては、不活性ガスの存在下で熱分解を行うことが必要であるために大掛かりな装置を必要とし、また高温条件下で製造を行なう必要がある。本発明はこのような問題点に注目し、安定な金属微粒子を容易に製造することのできる金属微粒子の製造方法を提供することを目的とするものである。
【０００８】
【課題を解決するための手段】
すなわち本願請求項１記載の発明は、金属微粒子の製造方法において、（１）少なくともカルボキシル基、ニトリル基、アミノ基のいずれか１つの官能基を有する芳香族化合物もしくは炭化水素化合物から選ばれてなる相間移動剤の存在下、金属塩水溶液と水と相溶しない有機溶媒を攪拌混合し、有機溶媒に金属イオンを相間移動させる工程、（２）ニトリル化合物もしくはアミン化合物から選ばれてなる保護剤の存在下、金属イオンを含有する有機溶媒と還元剤を攪拌混合し、金属微粒子コロイド溶液を作製する工程、（３）溶媒を除去し、表面保護されたを金属微粒子を得る工程、を含むことを特徴とする。
【０００９】
請求項２記載の発明は、請求項１記載の金属微粒子の製造方法にあって、前記金属微粒子が銀微粒子である。
【００１０】
請求項３記載の発明は、請求項２記載の金属微粒子の製造方法にあって、前記相間移動剤が安息香酸である。
【００１１】
請求項４記載の発明は、請求項１乃至３のいずれかに記載の金属微粒子の製造方法にあって、前記還元剤が水素化ホウ素ナトリウムである。
【００１２】
請求項５記載の発明は、請求項１乃至４のいずれかに記載の金属微粒子の製造方法にあって、前記保護剤がアミン化合物である。
【００１３】
【発明の実施の形態】
以下、本発明の金属微粒子の製造方法について詳細に説明する。
本発明の製造方法は、（１）少なくともカルボキシル基、ニトリル基、アミノ基のいずれか１つの官能基を有する芳香族化合物もしくは炭化水素化合物から選ばれてなる相間移動剤の存在下、金属塩水溶液と水と相溶しない有機溶媒を攪拌混合し、有機溶媒に金属イオンを相間移動させる工程、（２）ニトリル化合物もしくはアミン化合物から選ばれてなる保護剤の存在下、前記有機溶媒と還元剤を攪拌混合し、金属微粒子コロイド溶液を作製する工程、（３）溶媒を除去し、表面保護されたを金属微粒子を得る工程、を含むことを特徴とする。
【００１４】
本発明の対象となる金属微粒子としては、金、銀、銅、白金、パラジウム、ロジウム、ルテニウム、イリジウム、鉄、ニッケル等が挙げられる。金属塩としては、塩化金酸、塩化第一金、塩化第二金、硝酸銀、亜硝酸銀、塩化銀、硫酸銅、硝酸銅、塩化第一白金、塩化第一白金アンモニウム、塩化パラジウム、四塩化パラジウムアンモニウム、六塩化パラジウムアンモニウム、酢酸パラジウム、硝酸パラジウム、三塩化ロジウム、六塩化ロジウムアンモニウム、六塩化ロジウムカリウム、塩化ヘキサミンロジウム、酢酸ロジウム、ニトロソ硝酸ルテニウム、塩化ルテニウム、塩化ルテニウムアンモニウム、塩化ルテニウムカリウム、塩化ルテニウムナトリウム、酢酸ルテニウム、三塩化イリジウム、四塩化イリジウム、六塩化イリジウムアンモニウム、六塩化イリジウム三カリウム、酢酸イリジウム等が挙げられる。前記金属塩の水溶液は濃度０．１ｍＭ以上に調整されてなることが望ましい。
【００１５】
まず（１）特定の相間移動剤の存在下、前記金属塩水溶液と水と相溶しない有機溶媒を攪拌混合する。
相間移動剤とは、金属イオンに配位して、有機相に金属イオンを移動させるものであって、具体的には、カルボキシル基、ニトリル基、アミノ基のいずれか１つの官能基を有する芳香族化合物もしくは炭化水素化合物から選ばれてなる物質であって、炭素数６以上のものが好ましく用いられる。具体的には、オクチルアミン、ドデカンニトリル、ドデカン酸、安息香酸などが挙げられる。なかでも本発明者らは知見するところによれば、金属が銀である場合、安息香酸が好ましい。これらは単独に限らず、２種以上を併用して用いることができる。また相間移動剤は後工程において、保護剤としての役割も担うと考えられる。
【００１６】
有機溶媒は特に限定されず、ノルマルヘキサン、シクロヘキサン、ノルマルペンタン、ノルマルヘプタン、トルエン、メチルイソブチルケトン、キシレン、ベンゼン、クロロホルム、四塩化炭素、メチルエチルケトン、酢酸エチル、酢酸ブチル、酢酸イソブチル、エチルベンゼン等が挙げられる。
【００１７】
相間移動剤は、溶液に直接添加してもよいし、あらかじめ有機溶媒に溶解させていても良い。溶液中の相間移動剤の濃度は、金属種にもよるが金属イオンに対して２〜１００倍モル程度であることが望ましい。また相間移動時間としては、用いられる金属ならびに相間移動剤などによって異なるが、例えば金属が銀である場合、オクチルアミン、ドデカンニトリル、ドデカン酸などは２４時間以上であることが好ましいが、安息香酸の場合は数時間程度でもかまわない。
【００１８】
続いて、（２）特定の保護剤の存在下、前記金属イオンを含有する有機溶媒と還元剤を攪拌混合し、金属微粒子コロイド溶液を作製する。
前記保護剤は、有機溶媒中で金属微粒子の凝集による二次粒子の生成を妨げ、金属微粒子を安定化するものであって、ニトリル化合物あるいはアミン化合物が好適に用いられる。具体的には、ニトリル化合物としてはデカンニトリル、ドデカンニトリルなどがある。アミン化合物としては、第１アミン類、第２アミン類、第３アミン類、ジアミン類、ポリアミン類、環式アミン類があげられ、なかでもプロピルアミン、ブチルアミン、ペンチルアミン、ヘキシルアミン、ペプチルアミン、オクチルアミン、ノニルアミン、デシルアミン、ウンデシルアミン、ドデシルアミン、トリデシルアミン、テトラデシルアミン、ペンタデシルアミン、ヘキサデシルアミン等のアルキルアミンが好適に用いられる。これら保護剤は金属イオンに対して０．１〜１０倍モル程度の量を滴下することによって添加する。これらは単独または２種以上を併用して用いることができる。
【００１９】
還元剤は通常使用されるもので特に限定されず、水素化ホウ素ナトリウム、水素化ホウ素カリウムなどの水素化ホウ素金属塩、水素化アルミニウムリチウム、水素化アルミニウムカリウム、水素化アルミニウムセシウム、水素化アルミニウムベリリウム、水素化アルミニウムマグネシウム、水素化アルミニウムカルシウム等の水素化アルミニウム塩、ヒドラジン化合物、クエン酸及びその塩、コハク酸及びその塩、アスコルビン酸及びその塩等がある。還元剤の添加方法としては、直接溶液中に還元剤を添加する方法、または予め還元剤を溶解させた溶液を添加する方法のどちらでもよいが、前記各種還元剤を水あるいはエタノール、プロパノール等のアルコールに溶解した状態で、前記金属イオンを含む有機溶媒に添加することが好ましい。
【００２０】
前記混合物全体を、攪拌子等を用いて１時間以上混合攪拌した後静置することによって、各金属微粒子に特有の色に着色した有機相を得る。この金属微粒子コロイド溶液は、例えば金微粒子の場合、５２０ｎｍ付近に、銀微粒子の場合、４２０ｎｍ付近に特有の吸収を示し、それによって各金属微粒子の生成が確認される。
【００２１】
そして（３）溶媒を除去し、表面保護されたを金属微粒子を得る。
前記有機相のみを分離し、乾燥させることにより、保護剤によって表面保護された金属微粒子を得る。尚、有機相に貧溶媒（溶質に対して溶解度の小さい溶媒）を加えることで迅速に金属微粒子を沈殿せしめることができる。有機相のみを分離するには、分液ロートを用いる方法、有機相のみを吸引する方法、あるいは単純にデカンテーションによってもよい。この沈殿物を洗浄し、不純物を除去することにより、高濃度の金属微粒子を得ることができる。
また、得られた金属微粒子を別の有機溶媒に再分散させることにより、制御された平均粒径及び粒径分布を有する金属微粒子を得ることもできる。ここで再分散させる有機溶媒としては、例えばトルエン、イソオクタン、キシレン、ヘキサン、ジエチルベンゼン、テルピネオール、ヘキサデカン、あるいはシクロヘキサンが好ましい。
【００２２】
【実施例】
以下、本発明の金属微粒子の製造方法について、実施例を示しさらに詳細に説明する。
硝酸銀水溶液（３．０×１０−２ｍｏｌ／ｌ）４ｍｌに、表１の相間移動剤を溶解させたトルエン溶液（５．０×１０−２ｍｏｌ／ｌ）６４ｍｌを加えて、室温雰囲気下で１０分間攪拌した後静置し、金属イオンの相間移動速度について評価した。尚、評価は静置してから５時間、２４時間後の溶液に還元剤を滴下して銀微粒子が生成を観察することにより判断した。表１に結果を示す。
【００２３】
【表１】
結果、カルボキシル基、ニトリル基、アミノ基を官能基として有さない化合物を相間移動剤として使用した試料では、２４時間経過後も有機相に銀イオンの存在が確認されなかった。また安息香酸を相間移動剤として使用した場合は、銀イオンの相間移動速度が早いことが判明した。
【００２５】
次に、硝酸銀水溶液（３．０×１０−２ｍｏｌ／ｌ）４ｍｌに、相間移動剤を溶解させたトルエン溶液（５．０×１０−２ｍｏｌ／ｌ）６４ｍｌを加えて、室温雰囲気下で１０分間攪拌した後、２４時間静置した。続いて、保護剤を０．１０ｇ加えて１０分間攪拌した後、水酸化ホウ素ナトリウム水溶液（０．４ｍｏｌ／ｌ）を加え、３時間以上攪拌した。相間移動剤、保護剤は表２に示す組合せで使用し、得られた有機相の着色の有無を観測して銀微粒子コロイド生成状況を評価した。尚、銀微粒子コロイド溶液は茶黄色を呈することが知られており、結果を表２に併記する。
【００２６】
【表２】
結果、アミン化合物、ニトリル化合物以外の化合物を保護剤として使用した試料では銀微粒子コロイドの生成がみられなかった。また保護剤としてニトリル化合物を使用した場合、銀微粒子コロイドは生成されるものの、有機相と水相の相間や壁面に副生成物が観察されることがあった。
【００２８】
次に、上記コロイド溶液の有機相を分離し、エタノールを加えた後、吸引濾過により褐色の沈殿物を得た。この沈殿物をトルエンに再分散して、紫外可視吸収スペクトルを測定したところ、図１に示すように銀微粒子に起因すると考えられる波長４３３．５ｎｍに極大値が見られた。また透過型電子顕微鏡により、図２に示すように粒子径２〜１０ｎｍの大きさの銀微粒子が観測された。これらの結果より、銀微粒子が合成できたことが確認できた。
【００２９】
【発明の効果】
以上説明したように、本願請求項記載の発明は、金属微粒子の製造方法において、（１）少なくともカルボキシル基、ニトリル基、アミノ基のいずれか１つの官能基を有する芳香族化合物もしくは炭化水素化合物から選ばれてなる相間移動剤の存在下、金属塩水溶液と水と相溶しない有機溶媒を攪拌混合し、有機溶媒に金属イオンを相間移動させる工程、（２）ニトリル化合物もしくはアミン化合物から選ばれてなる保護剤の存在下、金属イオンを含有する有機溶媒と還元剤を攪拌混合し、金属微粒子コロイド溶液を作製する工程、（３）溶媒を除去し、表面保護されたを金属微粒子を得る工程、を含むことを特徴とする金属微粒子の製造方法であって、簡易に安定な金属微粒子を製造することができる。また金属が銀の場合、特定の相間移動剤を用いることで、金属イオンの相間移動速度が速くなり、生産性が高まることを知見した。更に特定の保護剤を用いることにより、副生成物が少なく、より安定な金属微粒子が得られることが判った。
【図面の簡単な説明】
【図１】実施例により得られた沈殿物をトルエンに再分散させた物質の紫外可視吸収スペクトル（ＵＶ−ＶＩＳ）である。
【図２】実施例により得られた沈殿物をトルエンに再分散させた物質の透過型電子顕微鏡（ＴＥＭ）像である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing nano-sized metal fine particles used for a catalyst, an optical material, an electronic material, a pressure-sensitive material, and the like.
[0002]
[Prior art]
Noble metal particles having a particle size of several tens of nanometers or less make use of the unique properties of fine particles not found in bulk metals, and use chemically stable coloring agents, color filters, conductive pastes, catalysts for chemical reactions, Its applications, such as transparent conductive films, are expanding. In single-electron devices, which are being studied for breaking the limits of high integration of LSIs based on conventional lithography technology, the use of metal fine particles as quantum dots, which is one of the components, is also being studied. .
[0003]
Methods for producing such metal fine particles include a gas phase method and a liquid phase method. The vapor phase method includes a gas evaporation method, a sputtering method, and the like. For example, in the gas evaporation method, metal is evaporated in a vacuum vessel into which an inert gas is introduced, and metal fine particles coated with an organic solvent are obtained. . Although it has the advantage of being able to produce a metal particle dispersion having a high concentration, it is difficult to control the particle size distribution of the metal particles. In addition, there is a problem in terms of cost because a special device is required.
[0004]
On the other hand, the liquid phase method is a method of obtaining metal fine particles by irradiating a metal ion-containing solution with ultraviolet light or adding a reducing agent to reduce metal ions. Among them, the method using a reducing agent has a feature that metal fine particles having a narrow particle size distribution can be produced relatively easily without requiring a special apparatus. As such a technique, specifically, a technique of obtaining a colloid solution by reducing a metal salt in a solution in the presence of a protective polymer has been used for a long time. Discloses a method for producing ultrafine metal particles whose surface is protected by thiol by adding a thiol or a thiol solution to a solution obtained by reducing a solution obtained by dissolving an amine and an amine. (See Patent Document 1)
[0005]
In addition to these methods, as a method for producing metal fine particles, a fatty acid is reacted with sodium hydroxide, saponified, and then reacted with silver nitrate to produce silver salt of a fatty acid, and the metal salt is heated at 250 ° C. in the presence of nitrogen. A technique for producing ultrafine silver particles by decomposition is also proposed. (See Non-Patent Document 1)
[0006]
[Non-patent document 1]
Hiroshi Nagasawa and 5 others, "Synthesis and evaluation of silver ultrafine particles by solid-phase pyrolysis of metal complex", Ultrafine Particles and Cluster Roundtable, 2nd Workshop, April 22, 1998, P45- 48
[Patent Document 1]
JP 10-195505 A
[Problems to be solved by the invention]
However, even in the liquid phase method, it is generally necessary to obtain very fine metal fine particles having a narrow particle size distribution, and to obtain metal fine particles having a more strictly controlled average particle size and particle size distribution. There was a problem that it was difficult. Further, there is a problem that many by-products cannot be produced and a stable silver colloid cannot be produced. Further, in the method of performing thermal decomposition, it is necessary to perform thermal decomposition in the presence of an inert gas, so a large-scale apparatus is required, and production must be performed under high temperature conditions. An object of the present invention is to pay attention to such a problem and to provide a method for producing fine metal particles that can easily produce stable fine metal particles.
[0008]
[Means for Solving the Problems]
That is, the invention according to claim 1 of the present application is the method for producing metal fine particles, wherein (1) an aromatic compound or a hydrocarbon compound having at least one functional group of a carboxyl group, a nitrile group, and an amino group. A step of stirring and mixing an aqueous metal salt solution and an organic solvent incompatible with water in the presence of a phase transfer agent to phase-transfer metal ions to the organic solvent; (2) a step of preparing a protective agent selected from a nitrile compound or an amine compound; A step of preparing a metal fine particle colloid solution by stirring and mixing an organic solvent containing a metal ion and a reducing agent in the presence thereof, and (3) a step of removing the solvent to obtain surface-protected metal fine particles. Features.
[0009]
According to a second aspect of the present invention, in the method for producing metal fine particles according to the first aspect, the metal fine particles are silver fine particles.
[0010]
The invention according to claim 3 is the method for producing metal fine particles according to claim 2, wherein the phase transfer agent is benzoic acid.
[0011]
The invention according to claim 4 is the method for producing metal fine particles according to any one of claims 1 to 3, wherein the reducing agent is sodium borohydride.
[0012]
The invention according to claim 5 is the method for producing metal fine particles according to any one of claims 1 to 4, wherein the protective agent is an amine compound.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the method for producing metal fine particles of the present invention will be described in detail.
The production method of the present invention comprises: (1) an aqueous metal salt solution in the presence of a phase transfer agent selected from an aromatic compound or a hydrocarbon compound having at least one functional group of a carboxyl group, a nitrile group, and an amino group And mixing an organic solvent that is incompatible with water with water to phase-transfer the metal ion into the organic solvent. (2) The organic solvent and the reducing agent are mixed in the presence of a protective agent selected from a nitrile compound or an amine compound. It is characterized by comprising a step of stirring and mixing to prepare a metal fine particle colloid solution, and (3) a step of removing a solvent to obtain surface-protected metal fine particles.
[0014]
Examples of the metal fine particles targeted by the present invention include gold, silver, copper, platinum, palladium, rhodium, ruthenium, iridium, iron, nickel and the like. Metal salts include chloroauric acid, gold (II) chloride, gold (II) chloride, silver nitrate, silver nitrite, silver chloride, copper sulfate, copper nitrate, platinum (l) chloride, ammonium (l) platinum chloride, palladium chloride, palladium tetrachloride Ammonium, palladium ammonium chloride, palladium acetate, palladium nitrate, rhodium trichloride, rhodium ammonium chloride, rhodium potassium chloride, hexamine rhodium chloride, rhodium acetate, ruthenium nitrosonitrate, ruthenium chloride, ruthenium ammonium chloride, ruthenium potassium chloride, chloride Examples thereof include ruthenium sodium, ruthenium acetate, iridium trichloride, iridium tetrachloride, iridium ammonium hexachloride, tripotassium iridium hexachloride, and iridium acetate. The aqueous solution of the metal salt is desirably adjusted to a concentration of 0.1 mM or more.
[0015]
First, (1) in the presence of a specific phase transfer agent, the metal salt aqueous solution and an organic solvent incompatible with water are stirred and mixed.
The phase transfer agent is a substance which coordinates a metal ion and transfers the metal ion to an organic phase, and specifically, an aromatic compound having any one of a carboxyl group, a nitrile group and an amino group. A substance selected from group compounds or hydrocarbon compounds and having 6 or more carbon atoms is preferably used. Specific examples include octylamine, dodecanenitrile, dodecanoic acid, benzoic acid, and the like. Among them, the present inventors have found that when the metal is silver, benzoic acid is preferred. These can be used alone or in combination of two or more. Further, it is considered that the phase transfer agent also plays a role as a protective agent in a later step.
[0016]
The organic solvent is not particularly limited, and examples thereof include normal hexane, cyclohexane, normal pentane, normal heptane, toluene, methyl isobutyl ketone, xylene, benzene, chloroform, carbon tetrachloride, methyl ethyl ketone, ethyl acetate, butyl acetate, isobutyl acetate, and ethylbenzene. Can be
[0017]
The phase transfer agent may be added directly to the solution, or may be previously dissolved in an organic solvent. The concentration of the phase transfer agent in the solution depends on the metal species, but is preferably about 2 to 100 times the molar amount of the metal ion. Further, the phase transfer time varies depending on the metal used and the phase transfer agent, etc., for example, when the metal is silver, octylamine, dodecanenitrile, dodecanoic acid and the like are preferably 24 hours or more. In this case, it may be several hours.
[0018]
Subsequently, (2) the organic solvent containing the metal ion and the reducing agent are stirred and mixed in the presence of the specific protective agent to prepare a metal fine particle colloid solution.
The protective agent prevents secondary particles due to aggregation of metal fine particles in an organic solvent and stabilizes the metal fine particles, and a nitrile compound or an amine compound is preferably used. Specifically, examples of the nitrile compound include decannitrile and dodecanenitrile. Examples of the amine compound include primary amines, secondary amines, tertiary amines, diamines, polyamines, and cyclic amines, among which propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, and octyl. Alkylamines such as amine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine and hexadecylamine are preferably used. These protective agents are added by dropwise addition in an amount of about 0.1 to 10 times the mole of the metal ion. These can be used alone or in combination of two or more.
[0019]
The reducing agent is commonly used and is not particularly limited. Examples thereof include sodium borohydride, metal borohydride salts such as potassium borohydride, lithium aluminum hydride, potassium aluminum hydride, cesium aluminum hydride, and beryllium aluminum hydride. , Aluminum hydride salts such as aluminum magnesium hydride and calcium aluminum hydride, hydrazine compounds, citric acid and its salts, succinic acid and its salts, ascorbic acid and its salts, and the like. As a method of adding the reducing agent, either a method of directly adding the reducing agent to the solution or a method of adding a solution in which the reducing agent is dissolved in advance may be used, but the various reducing agents may be water or ethanol, propanol or the like. It is preferable to add the solution dissolved in alcohol to the organic solvent containing the metal ion.
[0020]
The whole mixture is mixed and stirred using a stirrer or the like for at least one hour and then allowed to stand to obtain an organic phase colored in a color unique to each metal fine particle. This colloidal solution of metal fine particles shows a specific absorption around 520 nm in the case of gold fine particles and around 420 nm in the case of silver fine particles, thereby confirming the generation of each metal fine particle.
[0021]
Then, (3) the solvent is removed to obtain metal fine particles whose surface is protected.
By separating and drying only the organic phase, metal fine particles whose surface is protected by a protective agent are obtained. In addition, by adding a poor solvent (a solvent having a low solubility to a solute) to the organic phase, metal fine particles can be precipitated quickly. To separate only the organic phase, a method using a separating funnel, a method of sucking only the organic phase, or simply decantation may be used. By washing this precipitate and removing impurities, high-concentration metal fine particles can be obtained.
Further, by re-dispersing the obtained metal fine particles in another organic solvent, it is also possible to obtain metal fine particles having a controlled average particle size and a controlled particle size distribution. Here, as the organic solvent to be redispersed, for example, toluene, isooctane, xylene, hexane, diethylbenzene, terpineol, hexadecane, or cyclohexane is preferable.
[0022]
【Example】
Hereinafter, the method for producing metal fine particles of the present invention will be described in more detail with reference to examples.
To 4 ml of an aqueous silver nitrate solution (3.0 × 10 −2 mol / l), 64 ml of a toluene solution (5.0 × 10 −2 mol / l) in which the phase transfer agent of Table 1 was dissolved was added, and the mixture was stirred at room temperature. After stirring for 10 minutes, the mixture was allowed to stand, and the phase transfer speed of metal ions was evaluated. The evaluation was made by observing the formation of fine silver particles by dropping a reducing agent into the solution 5 hours and 24 hours after standing. Table 1 shows the results.
[0023]
[Table 1]
As a result, in a sample using a compound having no carboxyl group, nitrile group or amino group as a functional group as a phase transfer agent, the presence of silver ions in the organic phase was not confirmed even after 24 hours. It was also found that when benzoic acid was used as a phase transfer agent, the phase transfer speed of silver ions was high.
[0025]
Next, 64 ml of a toluene solution (5.0 × 10 −2 mol / l) in which a phase transfer agent was dissolved was added to 4 ml of an aqueous silver nitrate solution (3.0 × 10 −2 mol / l), and the mixture was added at room temperature. After stirring for 10 minutes, the mixture was allowed to stand for 24 hours. Subsequently, 0.10 g of a protective agent was added, and the mixture was stirred for 10 minutes. Then, an aqueous sodium borohydride solution (0.4 mol / l) was added, and the mixture was stirred for 3 hours or more. The phase transfer agent and the protective agent were used in combinations shown in Table 2, and the presence or absence of coloring of the obtained organic phase was observed to evaluate the state of silver fine particle colloid formation. The silver fine particle colloid solution is known to exhibit a brown yellow color, and the results are also shown in Table 2.
[0026]
[Table 2]
As a result, in the sample using a compound other than the amine compound and the nitrile compound as the protective agent, no silver fine particle colloid was formed. When a nitrile compound is used as a protective agent, a silver fine particle colloid is generated, but by-products are sometimes observed between the organic phase and the aqueous phase or on the wall surface.
[0028]
Next, the organic phase of the colloid solution was separated, ethanol was added, and then a brown precipitate was obtained by suction filtration. This precipitate was re-dispersed in toluene and the ultraviolet-visible absorption spectrum was measured. As a result, as shown in FIG. 1, a maximum value was observed at a wavelength of 433.5 nm, which is considered to be caused by silver fine particles. Further, as shown in FIG. 2, silver fine particles having a particle size of 2 to 10 nm were observed by a transmission electron microscope. From these results, it was confirmed that silver fine particles could be synthesized.
[0029]
【The invention's effect】
As described above, the invention as claimed in the present application provides a method for producing metal fine particles, which comprises the steps of (1) using an aromatic compound or a hydrocarbon compound having at least one functional group of a carboxyl group, a nitrile group, and an amino group. A step of mixing and stirring a metal salt aqueous solution and an organic solvent that is incompatible with water in the presence of the selected phase transfer agent to cause phase transfer of metal ions to the organic solvent; (2) a step selected from a nitrile compound or an amine compound A step of preparing a metal fine particle colloid solution by stirring and mixing an organic solvent containing a metal ion and a reducing agent in the presence of a protective agent to form a metal fine particle colloid solution; and (3) removing the solvent to obtain surface-protected metal fine particles. And producing stable metal fine particles easily. In addition, it has been found that when the metal is silver, the use of a specific phase transfer agent increases the phase transfer speed of metal ions and increases productivity. Furthermore, it has been found that by using a specific protective agent, more stable metal fine particles can be obtained with less by-products.
[Brief description of the drawings]
FIG. 1 is an ultraviolet-visible absorption spectrum (UV-VIS) of a substance obtained by redispersing a precipitate obtained in an example in toluene.
FIG. 2 is a transmission electron microscope (TEM) image of a substance obtained by redispersing a precipitate obtained in an example in toluene.
Claims (5)
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