JP2007070188A - Method for producing zinc oxide fine particle and aggregate and dispersion solution of the same - Google Patents
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本発明は、酸化亜鉛ナノ粒子分散溶液の製造方法および新規な酸化亜鉛ナノ粒子集合体に関する。 The present invention relates to a method for producing a zinc oxide nanoparticle dispersion solution and a novel zinc oxide nanoparticle aggregate.
酸化亜鉛（ＺｎＯ）は、代表的なｎ半導酸化物半導体であり、その半導体特性や圧電性および蛍光発光特性などにより、重要な電子セラミックス材料である。近年、光触媒、各種の表示装置のための透明導電性薄膜、蛍光体、色素増感太陽電池用電極材料、あるいはｐ型酸化物半導体として、様々な応用が注目されている。このために、一般的には、約１００ｎｍ未満の直径を有する酸化亜鉛微粒子（以下ナノ粒子という）を製造する方法が検討されている。従来、この酸化亜鉛ナノ粒子を製造するには、以下のような方法が提案されている。
（１）従来技術１（非特許文献１）
酢酸亜鉛2水和物のエタノール溶液に水酸化リチウムのエタノール溶液を加え0℃にて静置する方法で、平均粒径が3nmから10nmの酸化亜鉛ナノ粒子が得られること、またその平均粒径は、静置時間により制御可能である事が報告されている。
（２）従来技術２（特許文献１）
また、アルコールに溶解させた亜鉛化合物およびアルミニウム化合物を加水分解させることによりアルコールを分散媒とする水酸化亜鉛および水酸化アルミニウムのゾルを調製し、得られたゾルをゲル化させると同時に成形し、形成されたゲルの成形物を焼成して含アルミナ酸化亜鉛セラミックスを生じさせることが開示されている。
（３）従来技術３（特許文献２）
ナノ粒子状で再分散可能な平均粒径１５ｎｍ以下の酸化亜鉛、水およびアルコールを含む酸化亜鉛ゲルを製造して、これを、ジクロロメタン及び／またはクロロホルムあるいは、場合によっては表面改質物質を含んで成る水または水／エチレングリコール混合物である溶媒で、再分散することで酸化亜鉛ゾルを製造する方法が開示されている。
(1) Prior art 1 (Non-patent document 1)
By adding a solution of lithium hydroxide in ethanol solution of zinc acetate dihydrate and allowing to stand at 0 ° C, zinc oxide nanoparticles with an average particle size of 3 nm to 10 nm can be obtained. It is reported that can be controlled by the standing time.
(2) Prior art 2 (Patent Document 1)
In addition, a zinc sol and an aluminum hydroxide sol using an alcohol as a dispersion medium are prepared by hydrolyzing a zinc compound and an aluminum compound dissolved in an alcohol, and the obtained sol is gelled and simultaneously molded. It is disclosed that the formed gel product is fired to produce an alumina-containing zinc oxide ceramic.
(3) Prior art 3 (Patent Document 2)
A nanoparticulate and redispersible zinc oxide gel having an average particle size of 15 nm or less, water and alcohol is produced, which is mixed with dichloromethane and / or chloroform or, optionally, a surface modifying substance. A method of producing a zinc oxide sol by redispersing with a solvent which is water or a water / ethylene glycol mixture is disclosed.
しかし、これらの方法では、以下のような課題がある。
（１）反応に用いた亜鉛化合物がすべて酸化亜鉛に変化せずに未反応物が多く残留する場合があり、酸化亜鉛ナノ粒子の収率が低い方法が多い。
（２）水溶液中での反応では酸化亜鉛の結晶成長速度の制御が困難であり、100nm以下の粒径を有するナノ粒子を得る事が困難である。
（３）数ヶ月から数年程度の長期間に渡って溶液中に安定に酸化亜鉛ナノ粒子が分散したゾルを得る事が困難である。
（４）反応に用いる溶媒中の水分含有量などを厳密に制御する必要があり、反応操作が煩雑である。
本発明は、かかる事情に鑑みなされたものであって、低環境負荷であり非常に簡便な高収率の酸化亜鉛ナノ粒子分散溶液の製造方法および新規な酸化亜鉛ナノ粒子集合体の製造方法を提供することにある。
However, these methods have the following problems.
(1) All zinc compounds used in the reaction may not be changed to zinc oxide, and many unreacted substances may remain, and there are many methods in which the yield of zinc oxide nanoparticles is low.
(2) In the reaction in an aqueous solution, it is difficult to control the crystal growth rate of zinc oxide, and it is difficult to obtain nanoparticles having a particle size of 100 nm or less.
(3) It is difficult to obtain a sol in which zinc oxide nanoparticles are stably dispersed in a solution for a long period of several months to several years.
(4) It is necessary to strictly control the water content in the solvent used for the reaction, and the reaction operation is complicated.
The present invention has been made in view of such circumstances, and provides a method for producing a zinc oxide nanoparticle dispersion solution having a low environmental load and a very simple and high yield and a novel method for producing a zinc oxide nanoparticle aggregate. It is to provide.
本発明者らは、鋭意研究の結果、水酸化亜鉛ゲルを中性溶液で、中低温で加熱する非常に簡便な方法により、高い収率で酸化亜鉛ナノ粒子が安定に分散したゾルを製造する方法（請求項１、２および３、４、５、６）を開発した。さらに、反応条件を調整することによって、酸化亜鉛ナノ粒子の粒径を制御し、さらに酸化亜鉛ナノ粒子が球状に凝集した特異な構造体（請求項７、８）を形成した。本発明は、以下のようにして構成して、上記課題を解決する。 As a result of diligent research, the inventors of the present invention produce a sol in which zinc oxide nanoparticles are stably dispersed in a high yield by a very simple method of heating zinc hydroxide gel in a neutral solution at medium and low temperatures. A method (claims 1, 2 and 3, 4, 5, 6) was developed. Furthermore, by adjusting the reaction conditions, the particle size of the zinc oxide nanoparticles was controlled, and a specific structure (claims 7 and 8) in which the zinc oxide nanoparticles were aggregated spherically was formed. The present invention is configured as follows to solve the above problems.
（１）課題１の解決
請求項１により、酸化亜鉛の合成原料として酸化亜鉛に結晶化しやすい水酸化亜鉛を使用する事によって、他の亜鉛化合物から合成する場合よりも高収率で酸化亜鉛粒子を得る事ができる。
（２）課題２の解決
請求項１により、水酸化亜鉛の加熱処理に用いる溶液を2価以上の多価アルコールまたはそれらのアルキルエーテルまたはそれらの混合溶液もしくはそれらの水溶液もしくはそれらのアルコール溶液とすることで、溶液中の多価アルコール分子またはそれらのアルキルエーテル分子が亜鉛イオンに配位して、水酸化亜鉛から酸化亜鉛への反応速度が抑制されるために、粒径が100nm以下の酸化亜鉛ナノ粒子を得る事が可能となる。
（３）課題３の解決
請求項１により、水酸化亜鉛の加熱処理に用いる溶液を2価以上の多価アルコールまたはそれらのアルキルエーテルまたはそれらの混合溶液もしくはそれらの水溶液もしくはそれらのアルコール溶液とすることで、溶液中の多価アルコール分子またはそれらのアルキルエーテル分子が生成した酸化亜鉛ナノ粒子表面に配位し溶液中の分子との相互作用することで、粒子間の凝集が抑制される事が期待される。
（４）課題４の解決
請求項１により、水分子の存在により酸化亜鉛の生成反応が阻害されることのない水酸化亜鉛を原料物質として用いることによって、反応系内の水分含有量に敏感でない条件下で酸化亜鉛粒子の生成反応を行う事ができる。
(1) Solution to Problem 1 According to claim 1, zinc oxide particles can be produced in a higher yield than when synthesized from other zinc compounds by using zinc hydroxide which is easily crystallized into zinc oxide as a raw material for zinc oxide synthesis. Can be obtained.
(2) Solution to Problem 2 According to claim 1, the solution used for the heat treatment of zinc hydroxide is a dihydric or higher polyhydric alcohol, an alkyl ether thereof, a mixed solution thereof, an aqueous solution thereof or an alcohol solution thereof. In this way, the polyhydric alcohol molecules or their alkyl ether molecules in the solution are coordinated to zinc ions, and the reaction rate from zinc hydroxide to zinc oxide is suppressed, so that the zinc oxide having a particle size of 100 nm or less Nanoparticles can be obtained.
(3) Solution to Problem 3 According to claim 1, the solution used for the heat treatment of zinc hydroxide is a dihydric or higher polyhydric alcohol, an alkyl ether thereof, a mixed solution thereof, an aqueous solution thereof or an alcohol solution thereof. By coordinating with the surface of the zinc oxide nanoparticles where the polyhydric alcohol molecules in the solution or their alkyl ether molecules are formed and interacting with the molecules in the solution, aggregation between the particles may be suppressed. Be expected.
(4) Solution to Problem 4 According to claim 1, by using zinc hydroxide as a raw material that does not inhibit the formation reaction of zinc oxide due to the presence of water molecules, it is not sensitive to the water content in the reaction system. The formation reaction of zinc oxide particles can be performed under the conditions.
以下に、図に示す本発明の実施形態（以下、単に本発明という）を説明する。しかし、本願発明はここに挙げる実施例によって何ら制限を受けるものではない。 Hereinafter, embodiments of the present invention shown in the drawings (hereinafter simply referred to as the present invention) will be described. However, the present invention is not limited in any way by the examples given here.
図１は、本発明における製造方法を以下に詳細を説明する。
（１）硝酸亜鉛６水和物とアンモニア水溶液を混合して水酸化亜鉛ゲルを得る工程。
硝酸亜鉛６水和物2.97g（0.01mol）を蒸留水に溶解し全体積を100mlとし0.1mol/lの硝酸亜鉛水溶液100mlを調製した。次に濃アンモニア水（15mol/l）0.66mlを蒸留水に溶解し全体積を100mlとし0.1mol/lのアンモニア水100mlを調製した。このアンモニア水を先の硝酸亜鉛水溶液に加えると直ちに白色ゲル状の水酸化亜鉛の沈殿が生じた。この沈殿を遠心分離（3000r.p.m，5min）した後、蒸留水100ml中に分散し、先と同じ条件にて遠心分離を行った。更に蒸留水中に分散した後遠心分離の操作を行い水酸化亜鉛のゲル状沈殿中に含まれる未反応のアンモニウムイオン、硝酸イオンを除去した。また、この工程での洗浄操作が不十分であると、次の溶液中での加熱処理において安定なゾルを得ることはできない。
FIG. 1 explains in detail the manufacturing method according to the present invention.
(1) A step of obtaining zinc hydroxide gel by mixing zinc nitrate hexahydrate and aqueous ammonia solution.
2.97 g (0.01 mol) of zinc nitrate hexahydrate was dissolved in distilled water to make the total volume 100 ml, and 100 ml of a 0.1 mol / l zinc nitrate aqueous solution was prepared. Next, 0.66 ml of concentrated ammonia water (15 mol / l) was dissolved in distilled water to make the total volume 100 ml, and 100 ml of 0.1 mol / l ammonia water was prepared. When this aqueous ammonia was added to the aqueous zinc nitrate solution, white gel-like zinc hydroxide was immediately precipitated. This precipitate was centrifuged (3000 rpm, 5 min), then dispersed in 100 ml of distilled water, and centrifuged under the same conditions as above. Further, after being dispersed in distilled water, the centrifugal operation was performed to remove unreacted ammonium ions and nitrate ions contained in the zinc hydroxide gel precipitate. If the washing operation in this step is insufficient, a stable sol cannot be obtained in the heat treatment in the next solution.
（２）水酸化亜鉛ゲルをエチレグリコール中で分散する工程。
300mlビーカーにエチレングリコール100mlを入れ、さらに水酸化亜鉛のゲル状沈殿を加えガラス棒で攪拌し均一に分散した後、密栓をした。
(2) A step of dispersing zinc hydroxide gel in ethylene glycol.
Into a 300 ml beaker, 100 ml of ethylene glycol was added, and a gelatinous precipitate of zinc hydroxide was further added. The mixture was stirred and dispersed uniformly with a glass rod, and then sealed.
（３）分散した水酸化亜鉛ゲルを加熱して酸化亜鉛ナノ粒子分散ゾルを得る工程。（温度３５℃の場合）
エチレングリコール中に水酸化亜鉛のゲル状沈殿が分散した溶液を、35℃に恒温に保たれている恒温槽中に入れ24時間静置した。これにより乳白色のゾルが得られた。得られたゾルは6ヶ月以上沈殿することなく安定な分散状態を保持した。
(3) A step of heating the dispersed zinc hydroxide gel to obtain a zinc oxide nanoparticle-dispersed sol. (When temperature is 35 ° C)
A solution in which a gelatinous precipitate of zinc hydroxide was dispersed in ethylene glycol was placed in a constant temperature bath maintained at a constant temperature of 35 ° C. and allowed to stand for 24 hours. This gave a milky white sol. The obtained sol maintained a stable dispersed state without precipitation for more than 6 months.
（４）上記工程より得られる酸化亜鉛ナノ粒子分散ゾル、球状二次粒子の集合の評価。
得られたゾル中に含まれるナノ粒子についてそのキャラクタリゼーションを行うために、得られたゾル100mlに0.2mol/lのアンモニア水100mlを加えよく攪拌し、ゾル中に含まれる酸化亜鉛ナノ粒子を凝集沈殿させた。生成した沈殿を3000r.p.m.で5min遠心分離を行い分離した後、沈殿に残留しているエチレングリコールおよびアンモニウムイオンを除去洗浄するために、該沈殿を蒸留水100ml中に分散し更に先と同様の条件にて遠心分離を行った。
(4) Evaluation of the aggregate of zinc oxide nanoparticle-dispersed sol and spherical secondary particles obtained from the above steps.
In order to characterize the nanoparticles contained in the obtained sol, 100 ml of 0.2 mol / l ammonia water was added to 100 ml of the obtained sol and stirred well to aggregate the zinc oxide nanoparticles contained in the sol. Precipitated. The resulting precipitate is separated by centrifuging at 3000 rpm for 5 minutes, and then the precipitate is dispersed in 100 ml of distilled water to remove ethylene glycol and ammonium ions remaining in the precipitate. Centrifugation was performed under conditions.
得られた沈殿を、35℃で12時間静置して乾燥し得られた粉体についてＸ線回折測定装置（ブルカーエイエックスエス製 ＭＰＸ１８）によって銅ターゲットを用い、加速電圧４０ｋＶ、電流２００ｍＡの測定条件で測定した。その結果を図２に示す。本X線回折パターン中に見られるピークはすべて酸化亜鉛によるものである。これより、水酸化亜鉛をエチレングリコール中で35℃で24時間加熱処理することによって酸化亜鉛に結晶化したことがわかる。 The obtained precipitate was left to stand at 35 ° C. for 12 hours and dried, and the powder obtained was measured with an X-ray diffractometer (MPX18 manufactured by Bruker AXS) at an acceleration voltage of 40 kV and a current of 200 mA. Measured under conditions. The result is shown in FIG. All peaks seen in this X-ray diffraction pattern are due to zinc oxide. This indicates that zinc hydroxide was crystallized into zinc oxide by heat treatment at 35 ° C. for 24 hours in ethylene glycol.
また、得られた粉体に含まれる酸化亜鉛粒子の形態を電解放射型走査型電子顕微鏡（日本電子製 ＪＳＭ）により加速電圧５ｋＶ、エミッション電流１２μＡの条件で観察した。図３にその像を示す。平均粒径が10nmの一次粒子が球状に集合して平均直径が160nm程度の球状の二次粒子を形成している事が分かった。 Moreover, the form of the zinc oxide particles contained in the obtained powder was observed under the conditions of an acceleration voltage of 5 kV and an emission current of 12 μA with an electrolytic emission scanning electron microscope (JSM JSM). The image is shown in FIG. It was found that primary particles having an average particle diameter of 10 nm gathered in a spherical shape to form spherical secondary particles having an average diameter of about 160 nm.
さらに、ガラス真空ラインを用い、本実施例で得られた酸化亜鉛粉体を1mPaの真空過で110℃，２時間、前処理した後、容量法にて７７Kでの窒素吸着等温線の測定を行った。測定から得られた等温線をBET法にて解析した所、比表面積が39.7m2/gである事が分かった。 Furthermore, using a glass vacuum line, the zinc oxide powder obtained in this example was pretreated at 110 ° C. for 2 hours under a vacuum of 1 mPa, and then the nitrogen adsorption isotherm was measured at 77 K by the volumetric method. went. When the isotherm obtained from the measurement was analyzed by the BET method, it was found that the specific surface area was 39.7 m 2 / g.
加えて、BJH法にて細孔径分布解析を行った結果を図４に示した。この結果より本実施例において得られた球状の酸化亜鉛ナノ粒子集合体中には5nmから２７nmのメソ孔領域の細孔を多く有する事が分かった。この細孔は図３のFE-SEM像から一次粒子の粒子間細孔と二次粒子同士の間の粒子間細孔からなるものと推測される。従って、本実施例より得られた球状酸化亜鉛ナノ粒子集合体中は、一次粒子である酸化亜鉛ナノ粒子が密に凝集した構造ではなく、酸化ナノ粒子が亜鉛疎に凝集し粒子間細孔を多く含む新規な集合構造を形成している事が分かった。 In addition, the results of pore size distribution analysis by the BJH method are shown in FIG. From this result, it was found that the spherical zinc oxide nanoparticle aggregate obtained in this example had many pores in the mesopore region of 5 nm to 27 nm. From the FE-SEM image in FIG. 3, it is assumed that the pores are composed of interparticle pores between primary particles and secondary particles. Therefore, the aggregate of spherical zinc oxide nanoparticles obtained from this example does not have a structure in which zinc oxide nanoparticles, which are primary particles, are densely aggregated, but the oxide nanoparticles are loosely aggregated to form interparticle pores. It was found that a new aggregate structure including many was formed.
以上から、エチレグリコール中で、３５℃以上２４時間で加熱処理することにより、図３に示すように、少なくとも、平均粒径１５ｎｍ以下の酸化亜鉛一次粒子が集合した粒径が50nmから200ｎｍの球状二次粒子が凝集した特異な集合体より形成された酸化亜鉛ゾルを得ることができた。 From the above, by performing heat treatment in ethyl glycol at 35 ° C. or more for 24 hours, as shown in FIG. A zinc oxide sol formed from a unique aggregate in which secondary particles aggregated was obtained.
以下に、本発明の第２の実施例を述べる。実施例１に示された方法と同じ方法により水酸化亜鉛のゲル状沈殿を調製した後、エチレングリコール中に分散した。そして、この溶液を75℃の空気恒温相中で２４時間静置した。これにより、透明で僅かに白色に着色したゾルが得られた。またこのゾルは６ヶ月以上室温で沈殿を生成することなく安定であった。このゾルに実施例１と同様に0.2mol/lのアンモニア水100mlを加えてゾル中の粒子を凝集沈殿した後遠心分離し蒸留水で洗浄し乾燥することによって粉体を得た。 The second embodiment of the present invention will be described below. A zinc hydroxide gel-like precipitate was prepared by the same method as shown in Example 1, and then dispersed in ethylene glycol. And this solution was left still for 24 hours in an 75 degreeC air constant temperature phase. Thereby, a transparent and slightly colored sol was obtained. The sol was stable for 6 months or more without forming a precipitate at room temperature. In the same manner as in Example 1, 100 ml of 0.2 mol / l aqueous ammonia was added to this sol to coagulate and precipitate particles in the sol, followed by centrifugation, washing with distilled water, and drying to obtain a powder.
得られた粉体について、実施例１と同様にＸ線回折パターンを測定した。図５にそのパターンを示す。
本図中に見られるピークはすべて酸化亜鉛によるものである。これより、水酸化亜鉛をエチレングリコール中で75℃で24時間加熱処理することによっても酸化亜鉛に結晶化したことがわかった。
About the obtained powder, the X-ray diffraction pattern was measured in the same manner as in Example 1. FIG. 5 shows the pattern.
All peaks seen in this figure are due to zinc oxide. Thus, it was found that zinc hydroxide was crystallized into zinc oxide by heat treatment in ethylene glycol at 75 ° C. for 24 hours.
得られた粉体に含まれる酸化亜鉛粒子の形態を、実施例１と同様の条件で電解放射型走査型電子顕微鏡で観察した。図６にその像を示す。平均粒径が20nmの酸化亜鉛ナノ粒子が生成している事が分かった。また、実施例１において35℃で加熱処理した場合とは異なり、75℃で加熱処理した本実施例においては一次粒子である酸化亜鉛ナノ粒子が球状に集合した二次粒子の形成は見られなかった。
（比較例１）
The form of zinc oxide particles contained in the obtained powder was observed with an electrolytic emission scanning electron microscope under the same conditions as in Example 1. The image is shown in FIG. It was found that zinc oxide nanoparticles with an average particle size of 20 nm were formed. In addition, unlike the case where the heat treatment was performed at 35 ° C. in Example 1, in the present example where the heat treatment was performed at 75 ° C., the formation of secondary particles in which the zinc oxide nanoparticles as the primary particles were assembled in a spherical shape was not observed. It was.
(Comparative Example 1)
以下に、上記実施例で用いたエチレングリコールに代えて、蒸留水中に水酸化亜鉛を分散した比較例を述べる。
実施例１に示された方法と同じ方法により水酸化亜鉛のゲル状沈殿を調製した後、蒸留水100ml中に水酸化亜鉛を分散した。次に、この溶液を75℃の空気恒温相中で24時間静置した。これにより、白色の沈殿物が得られた。この沈殿物を遠心分離し蒸留水で洗浄した後乾燥することによって粉体を得た。
In the following, a comparative example in which zinc hydroxide is dispersed in distilled water instead of ethylene glycol used in the above examples will be described.
A gel precipitate of zinc hydroxide was prepared by the same method as shown in Example 1, and then zinc hydroxide was dispersed in 100 ml of distilled water. Next, this solution was allowed to stand for 24 hours in an air constant temperature phase of 75 ° C. As a result, a white precipitate was obtained. The precipitate was centrifuged, washed with distilled water and dried to obtain a powder.
得られた粉体について実施例１と同様にＸ線回折パターンを測定した所酸化亜鉛による回折ピークのみが見られた事から本実施例において酸化亜鉛が得られる事が分かった。得られた酸化亜鉛粒子の形態を実施例１と同様の条件にて電解放射型走査型電子顕微鏡で観察した。図７にその像を示す。エチレングリコールを溶媒として用いた実施例２とは全く異なり針状の粒子が得られた。また長軸方向の平均長さは4.5μmでありナノ粒子は生成しなかった。
（比較例２）
When the X-ray diffraction pattern of the obtained powder was measured in the same manner as in Example 1, only the diffraction peak due to zinc oxide was observed, indicating that zinc oxide was obtained in this example. The form of the obtained zinc oxide particles was observed with an electrolytic emission scanning electron microscope under the same conditions as in Example 1. The image is shown in FIG. Unlike Example 2 using ethylene glycol as a solvent, acicular particles were obtained. The average length in the major axis direction was 4.5 μm, and no nanoparticles were produced.
(Comparative Example 2)
以下に、上記実施例で用いたエチレングリコールに代えて、エタノール中に水酸化亜鉛を分散した比較例を述べる。
実施例１に示された方法と同じ方法により水酸化亜鉛のゲル状沈殿を調製した後、エタノール100ml中に水酸化亜鉛を分散した。次に、この溶液を75℃の空気恒温相中で24時間静置した。これにより、白色の沈殿物が得られた。この沈殿物を遠心分離し蒸留水で洗浄した後乾燥することによって粉体を得た。得られた粉体について実施例１と同様にＸ線回折パターンを測定した所酸化亜鉛による回折ピークのみが見られた事から本実施例において酸化亜鉛が得られる事が分かった。得られた酸化亜鉛粒子の形態を実施例１と同様の条件にて電解放射型走査型電子顕微鏡で観察した。図８にその像を示す。平均粒径が35nmの酸化亜鉛ナノ粒子が生成している事がわかった。しかし本実施例によりエタノール中に水酸化亜鉛を分散して加熱処理を行って得られた酸化亜鉛ナノ粒子は凝集しビーカーのそこに沈殿した状態でしか得られず、溶液中に安定に分散したゾルを得ることはできなかった。
（比較例３）
In the following, a comparative example in which zinc hydroxide is dispersed in ethanol instead of ethylene glycol used in the above examples will be described.
A gel-like precipitate of zinc hydroxide was prepared by the same method as shown in Example 1, and then zinc hydroxide was dispersed in 100 ml of ethanol. Next, this solution was allowed to stand for 24 hours in an air constant temperature phase of 75 ° C. As a result, a white precipitate was obtained. The precipitate was centrifuged, washed with distilled water and dried to obtain a powder. When the X-ray diffraction pattern of the obtained powder was measured in the same manner as in Example 1, only the diffraction peak due to zinc oxide was observed, indicating that zinc oxide was obtained in this example. The form of the obtained zinc oxide particles was observed with an electrolytic emission scanning electron microscope under the same conditions as in Example 1. FIG. 8 shows the image. It was found that zinc oxide nanoparticles with an average particle size of 35 nm were formed. However, according to this example, zinc oxide nanoparticles obtained by dispersing zinc hydroxide in ethanol and performing a heat treatment were obtained only in a state where they aggregated and precipitated in a beaker, and were stably dispersed in the solution. The sol could not be obtained.
(Comparative Example 3)
以下に、本発明に係る水酸化亜鉛をエチレングリコールに分散した例と、エタノールまたは水に分散した比較例における相違を述べる。 実施例１から４に示された方法により、水酸化亜鉛をエチレングリコール、エタノール、水の各溶液中に分散し24時間加熱処理して得られた酸化亜鉛粒子分散溶液中に含まれる亜鉛イオン（Zn2+）濃度を測定した。具体的には以下のような実験操作を行った。
酸化亜鉛粒子が分散している溶液100mlに0.2mol/lのアンモニア水を100ml加え溶液に含まれている酸化亜鉛粒子を凝集沈殿させた後、3000 r.p.m.で5分間遠心分離し酸化亜鉛粒子を完全に沈殿させた。上澄みの溶液を5ml採取し、pH6の酢酸−酢酸ナトリウム緩衝液を10ml加えさらにキシレノールオレンジの0.001mol/l 10％エタノール水溶液を3ml加えさらに蒸留水を加えて全体の体積を50mlにした。
Below, the difference in the example which disperse | distributed the zinc hydroxide based on this invention to ethylene glycol, and the comparative example disperse | distributed to ethanol or water is described. According to the method shown in Examples 1 to 4, zinc ions contained in a zinc oxide particle dispersion obtained by dispersing zinc hydroxide in each solution of ethylene glycol, ethanol and water and heat-treating for 24 hours ( Zn 2+ ) concentration was measured. Specifically, the following experimental operation was performed.
Add 100 ml of 0.2 mol / l ammonia water to 100 ml of the solution in which zinc oxide particles are dispersed, coagulate and precipitate the zinc oxide particles contained in the solution, and then centrifuge at 3000 rpm for 5 minutes to complete the zinc oxide particles. Precipitated. 5 ml of the supernatant solution was collected, 10 ml of pH 6 acetic acid-sodium acetate buffer was added, 3 ml of 0.001 mol / l 10% ethanol aqueous solution of xylenol orange was added, and distilled water was added to make the total volume 50 ml.
この溶液の波長570nmにおける吸光度を測定し溶液中の亜鉛イオン濃度を求めた。図９に加熱処理温度と溶液中の亜鉛イオン濃度の関係を示す。エチレングリコールを用いた場合の方が蒸留水やエタノールを溶液として用いた場合よりも亜鉛イオン濃度が高かった。これは、エチレングリコール分子の亜鉛イオンに対する錯生成定数が大きく水分子やエタノール分子が配位する場合よりも安定な錯体を形成するためであると考えられる。従って、エチレングリコールを用いた場合は、亜鉛イオンと安定な錯体を形成するために、酸化亜鉛粒子の成長速度が遅くなり粒径の小さなナノ粒子が得られたと考えられる。また、酸化亜鉛ナノ粒子表面にエチレングリコール分子が配位する事によって分酸溶液との相互作用が大きくなり安定なゾルを形成したと考えられる。 The absorbance of this solution at a wavelength of 570 nm was measured to determine the zinc ion concentration in the solution. FIG. 9 shows the relationship between the heat treatment temperature and the zinc ion concentration in the solution. The zinc ion concentration was higher when ethylene glycol was used than when distilled water or ethanol was used as the solution. This is considered to be because the complex formation constant of ethylene glycol molecules with respect to zinc ions is large and forms a more stable complex than when water molecules or ethanol molecules are coordinated. Therefore, it is considered that when ethylene glycol was used, the growth rate of zinc oxide particles was slowed to form nanoparticles having a small particle size in order to form a stable complex with zinc ions. In addition, it is considered that the interaction with the diacid solution was increased by the coordination of ethylene glycol molecules on the surface of the zinc oxide nanoparticles, and a stable sol was formed.
なお、実施例１および２に示されたエチレグリコール中での加熱温度による酸化亜鉛ナノ粒子の集合状態の違いは、これは、上記比色定量分析の結果から、エチレグリコール中に溶解している亜鉛イオンから酸化亜鉛粒子の核が生成する際の生成機構の相違によると推測される。従って、加熱温度または加熱時間等を設定することで、様々な空隙率を有する酸化亜鉛二次粒子集合体を製造することが可能である。 In addition, the difference in the aggregation state of the zinc oxide nanoparticles depending on the heating temperature in the ethylene glycol shown in Examples 1 and 2 is dissolved in the ethylene glycol from the result of the colorimetric quantitative analysis. This is presumed to be due to the difference in the mechanism of formation of nuclei of zinc oxide particles from zinc ions. Accordingly, by setting the heating temperature or the heating time, it is possible to produce zinc oxide secondary particle aggregates having various porosity.
以下に、本発明の第３の実施例を述べる。実施例１に示された方法と同じ方法により水酸化亜鉛のゲル状沈殿を調製した後、2価の多価アルコールであるエチレングリコールのモノメチルエーテルである2−メトキシエタノール100ml中に水酸化亜鉛を分散した。次に、この溶液を75℃の空気恒温相中で24時間静置した。これにより、乳白色の安定なゾルが得られた。 The third embodiment of the present invention will be described below. After preparing a gel-like precipitate of zinc hydroxide by the same method as shown in Example 1, zinc hydroxide was added to 100 ml of 2-methoxyethanol, which is a monomethyl ether of ethylene glycol, which is a divalent polyhydric alcohol. Distributed. Next, this solution was allowed to stand for 24 hours in an air constant temperature phase of 75 ° C. Thereby, a milky white stable sol was obtained.
このゾルに実施例１と同様に0.2mol/lのアンモニア水100mlを加えてゾル中の粒子を凝集沈殿した後遠心分離し蒸留水で洗浄乾燥することによって粉体を得た。得られた粉体について実施例１と同様にＸ線回折パターンを測定した所、酸化亜鉛による回折ピークのみが見られた事から本実施例において酸化亜鉛が得られる事が分かった。得られた酸化亜鉛粒子の形態を実施例１と同様の条件にて電解放射型走査型電子顕微鏡で観察した。図１０にその像を示す。平均粒径が32nmの酸化亜鉛ナノ粒子が生成している事がわかった。また得られたゾルは６ヶ月以上安定に沈殿することなく分散状態を保持した。これより多価アルコールであるエチレングリコールなどのグリコール類だけでなくそのアルキルエーテルを溶液として用いても酸化亜鉛ナノ粒子が安定に分散したゾルが得られる事が明らかとなった。 In the same manner as in Example 1, 100 ml of 0.2 mol / l ammonia water was added to this sol to coagulate and precipitate particles in the sol, followed by centrifugation, washing with distilled water, and drying to obtain a powder. When the X-ray diffraction pattern of the obtained powder was measured in the same manner as in Example 1, only the diffraction peak due to zinc oxide was observed, and it was found that zinc oxide was obtained in this example. The form of the obtained zinc oxide particles was observed with an electrolytic emission scanning electron microscope under the same conditions as in Example 1. The image is shown in FIG. It was found that zinc oxide nanoparticles with an average particle size of 32 nm were formed. Further, the obtained sol maintained a dispersed state without being stably precipitated for 6 months or more. From this, it has been clarified that a sol in which zinc oxide nanoparticles are stably dispersed can be obtained not only by using glycols such as ethylene glycol, which is a polyhydric alcohol, but also by using the alkyl ether as a solution.
本発明による方法で製造された酸化亜鉛ナノ粒子の分散されたゾルあるいは酸化亜鉛ナノ粒子の二次粒子集合体は極めて安定しているので、例えば、ディップコーティング、スピンコーティング、スプレー等の薄膜形成方法で、例えば、ソーダガラス、無アルカリガラス、石英ガラス等の板）の表面に均一にコーティングして、所望の厚さの膜を基板上に生じさせる。このゲルを焼成して酸化亜鉛の結晶を生成させ、液晶用基板電極、エレクトロクロミック用電極、太陽電池用電極等に実施することができる。 Since the dispersed sol of zinc oxide nanoparticles or the secondary particle aggregate of zinc oxide nanoparticles produced by the method according to the present invention is extremely stable, for example, a thin film forming method such as dip coating, spin coating, spraying, etc. Then, for example, a surface of a plate of soda glass, non-alkali glass, quartz glass, or the like) is uniformly coated to form a film having a desired thickness on the substrate. This gel is baked to produce a zinc oxide crystal, which can be applied to a liquid crystal substrate electrode, an electrochromic electrode, a solar cell electrode, or the like.
なお、上記実施例において、硝酸亜鉛６水和物とアンモニア水溶液を混合して水酸化亜鉛ゲルを得たがこれに限定されるものではなく、亜鉛化合物は、例えば、塩化亜鉛、酢酸亜鉛、およびそれらの水和物等を用いることができる。塩基性溶液に含まれる塩基もアンモニアだけではなく。水酸化ナトリウム、水酸化リチウム、水酸化カリウム、炭酸ナトリウム、炭酸リチウム、炭酸カリウム、水酸化カルシウム、水酸化セシウム、ヒドロキシテトラメチルアンモニウムを用いることができる。 In the above examples, zinc nitrate hexahydrate and an aqueous ammonia solution were mixed to obtain a zinc hydroxide gel. However, the present invention is not limited thereto, and zinc compounds include, for example, zinc chloride, zinc acetate, and Their hydrates can be used. The base contained in the basic solution is not only ammonia. Sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium carbonate, lithium carbonate, potassium carbonate, calcium hydroxide, cesium hydroxide, and hydroxytetramethylammonium can be used.
また、多価アルコールとしては、エチレグリコールを用いた。上記発明の効果で述べたように、二個のヒドロキシ基が異なる炭素原子（一般には隣接した炭素原子だが、必ずしも限定しない）に結合した二価アルコール、またはそれらのアルキルエーテルもしくはそれらの混合溶液もしくはそれらの水溶液もしくはそれらのアルコール溶液とすることで、溶液中の多価アルコール分子またはそれらのアルキルエーテル分子が亜鉛イオンに配位して、水酸化亜鉛から酸化亜鉛への反応速度が抑制されるために、粒径が100nm以下の酸化亜鉛ナノ粒子を得る事が可能となる。従って、プロピレングリコール、１，３−ブタンジオール、１，４−ブタンジオール、グリセリン等も用いることができる。 Ethylene glycol was used as the polyhydric alcohol. As described in the effect of the invention above, dihydric alcohols in which two hydroxy groups are bonded to different carbon atoms (generally, but not necessarily limited to), alkyl ethers thereof or mixed solutions thereof or By using these aqueous solutions or alcohol solutions thereof, polyhydric alcohol molecules or alkyl ether molecules in the solution are coordinated to zinc ions, and the reaction rate from zinc hydroxide to zinc oxide is suppressed. In addition, it is possible to obtain zinc oxide nanoparticles having a particle size of 100 nm or less. Accordingly, propylene glycol, 1,3-butanediol, 1,4-butanediol, glycerin and the like can also be used.
さらに、上記溶液中で分散した水酸化亜鉛を加熱処理して酸化亜鉛ナノ粒子およびそれらが分散した溶液を得る工程において、加熱温度および加熱時間は、用いる溶液の沸点と反応速度との関係において得ようとする二次粒子の空隙率を考慮しつつ適宜に選択する。加熱温度は、望ましくは１５℃以上１８０℃以下であり、中低温で可能である。 Further, in the step of heat-treating zinc hydroxide dispersed in the above solution to obtain zinc oxide nanoparticles and a solution in which they are dispersed, the heating temperature and heating time are obtained in relation to the boiling point of the solution used and the reaction rate. It selects suitably considering the porosity of the secondary particle to be made. The heating temperature is preferably 15 ° C. or higher and 180 ° C. or lower, and can be a medium low temperature.
以上説明したように、本発明は、中性溶液中で、中低温で加熱する、低環境負荷であり非常に簡便な高収率の製造方法を提供することができるので、光触媒、各種の表示装置のための透明導電性薄膜、蛍光体、色素増感太陽電池用電極材料、あるいはｐ型酸化物半導体の製造など、様々な応用が可能である。また、様々な空隙率を有する酸化亜鉛二次粒子集合体を製造することが可能となり、ドーピング可能が飛躍的に高まるので、酸化アルミニウム（Al2O3）をドーピングして、大型液晶の透明電極、ガス放電型カラー表示パネルの陰極構造などに好都合である。さらに、ビスマス、コバルト、マンガン、アンチモン、ニッケル、クロム、スズ、アルミニウム、チタンなどの金属元素または半金属元素でドープして、バリスタ等の電子部品を製造することができ、極めて有用である。 As described above, the present invention can provide a production method with a low environmental load and a very simple and high yield that is heated in a neutral solution at a medium to low temperature. Various applications such as production of transparent conductive thin films for devices, phosphors, dye-sensitized solar cell electrode materials, or p-type oxide semiconductors are possible. In addition, it becomes possible to produce zinc oxide secondary particle aggregates having various porosity, and the doping ability is dramatically increased. Therefore, a transparent electrode of a large liquid crystal is doped with aluminum oxide (Al 2 O 3 ). It is convenient for the cathode structure of a gas discharge type color display panel. Furthermore, it is possible to produce electronic parts such as varistors by doping with metal elements or metalloid elements such as bismuth, cobalt, manganese, antimony, nickel, chromium, tin, aluminum and titanium.
Claims (8)
A thin film formed from the secondary particles of claim 7.
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