JP2011112359A - METHOD OF MANUFACTURING SnO2 GAS SENSOR - Google Patents
METHOD OF MANUFACTURING SnO2 GAS SENSOR Download PDFInfo
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この発明は、ＶＯＣに高感度なＳｎＯ２ガスセンサの製造方法に関する。 The present invention relates to a method of manufacturing a SnO 2 gas sensor having high sensitivity to VOC.
発明者らは、Ｓｎ(ＯＨ)６ ２−を内包する逆ミセル溶液に硝酸の逆ミセル溶液を混合し、Ｓｎ(ＯＨ)４を析出させ、焼成してＳｎＯ２とすることを提案した(特許文献１：特開2004-64674)。発明者はさらに、微細なＳｎＯ２粒子を調製することにより、ＶＯＣ(揮発性有機化合物)への感度を増し、かつガスセンサでのＳｎＯ２膜の成膜を容易にすることを検討した。即ち、ＳｎＯ２の粒径がｎｍオーダーになると、酸素イオンの吸着による電子欠乏層がＳｎＯ２粒子の全体に及び、周囲の有機物ガスへの感度が増すと考えられる。また有機溶媒中に懸濁した状態で安定なＳｎＯ２ナノクリスタルが得られると、この溶液を基板に塗布し焼成することにより、簡単にＳｎＯ２膜を成膜できる。 The inventors have proposed that a reverse micelle solution of nitric acid is mixed with a reverse micelle solution containing Sn (OH) 6 2− to precipitate Sn (OH) 4 and calcined to form SnO 2 (patent) Literature 1: JP 2004-64674). The inventor further studied to increase the sensitivity to VOC (volatile organic compound) by preparing fine SnO 2 particles and to facilitate the formation of the SnO 2 film with a gas sensor. That is, when the particle diameter of SnO 2 is on the order of nm, the electron-deficient layer due to adsorption of oxygen ions extends to the entire SnO 2 particles, and the sensitivity to surrounding organic gas is considered to increase. Further, when stable SnO 2 nanocrystals can be obtained in a state suspended in an organic solvent, by applying firing the solution to the substrate, it can be easily deposited SnO 2 film.
この発明の課題は，ＶＯＣに高感度でかつ成膜が容易なＳｎＯ２ガスセンサの製造方法を提供することにある。 An object of the present invention is to provide a method of manufacturing a SnO 2 gas sensor that is highly sensitive to VOC and easy to form.
この発明のＳｎＯ２ガスセンサの製造方法では、スズの有機化合物を、水に不溶な有機溶媒中に界面活性剤と共に溶解した溶液を調製し、次いで前記溶液を加熱することによりスズの有機化合物を熱分解して、ＳｎＯ２微粒子の懸濁液を調製すると共に、前記懸濁液から得られたＳｎＯ２によりガスセンサを製造する。 In the manufacturing method of the SnO 2 gas sensor of this invention, a solution in which an organic compound of tin is dissolved together with a surfactant in an organic solvent insoluble in water is prepared, and then the organic compound of tin is heated by heating the solution. By decomposing, a suspension of SnO 2 fine particles is prepared, and a gas sensor is manufactured from SnO 2 obtained from the suspension.
この発明では、ガスセンサとして成膜後も結晶子径が小さく、結晶成長が緩やかなＳｎＯ２ナノクリスタルが得られる。そしてこのＳｎＯ２ナノクリスタルを用いたガスセンサは、結晶子径が小さいため、ＶＯＣに高感度である。これは、有機溶媒中でスズの有機化合物を熱分解してＳｎＯ２ナノクリスタルとし、その表面に界面活性剤を吸着ないしは配位させるためで、界面活性剤はＳｎＯ２ナノクリスタルを有機溶媒中に分散させると共に、焼成時の結晶成長を妨げる。 In the present invention, a SnO 2 nanocrystal having a small crystallite diameter and a slow crystal growth can be obtained as a gas sensor after film formation. And the gas sensor using this SnO 2 nanocrystal has high sensitivity to VOC because the crystallite diameter is small. This is because the organic compound of tin is thermally decomposed into an SnO 2 nanocrystal in an organic solvent, and the surfactant is adsorbed or coordinated on the surface thereof. The surfactant is used to put the SnO 2 nanocrystal in the organic solvent. Disperse and hinder crystal growth during firing.
好ましくは、熱分解前の前記溶液が、スズの有機化合物と、水に不溶な有機溶媒と、界面活性剤と、酸素供与性の有機化合物とからなる。酸素供与性の有機化合物はスズの有機化合物の熱分解時に酸素を供与し、ＳｎＯ２ナノクリスタルの生成を容易にする。 Preferably, the solution before thermal decomposition comprises a tin organic compound, an organic solvent insoluble in water, a surfactant, and an oxygen-donating organic compound. The oxygen-donating organic compound donates oxygen during the thermal decomposition of the tin organic compound and facilitates the formation of SnO 2 nanocrystals.
また好ましくは、界面活性剤が、脂肪酸と脂肪族アミン化合物との混合物である。脂肪族アミン化合物は脂肪酸から水素を引き抜き、脂肪酸のＳｎＯ２ナノクリスタルへの配位〜吸着を容易にする。 Preferably, the surfactant is a mixture of a fatty acid and an aliphatic amine compound. The aliphatic amine compound extracts hydrogen from the fatty acid and facilitates the coordination to adsorption of the fatty acid to the SnO 2 nanocrystal.
特に好ましくは、前記懸濁液に極性の有機溶媒を加えてＳｎＯ２微粒子を沈殿させた後に、ＳｎＯ２微粒子を遠心分離し、次いで電子供与性基を備えた有機溶媒と混合する。生成したＳｎＯ２ナノクリスタルは有機物の残査を含んでおり、極性溶媒に不溶で、非極性溶媒に可溶である。生成したＳｎＯ２ナノクリスタルは、コロイド溶液として長期間保存しにくい。そこで遠心分離により不純物を除き、電子供与性基を備えた有機溶媒と混合すると極性溶媒に可溶となり、かつ長期間保存できる。
Particularly preferably, after precipitation of SnO 2 fine particles by adding a polar organic solvent to the suspension, the SnO 2 particles were centrifuged and then mixed with an organic solvent having an electron donating group. The resulting SnO 2 nanocrystals contain organic residues and are insoluble in polar solvents and soluble in nonpolar solvents. The produced SnO 2 nanocrystal is difficult to store for a long time as a colloidal solution. Therefore, if impurities are removed by centrifugation and mixed with an organic solvent having an electron donating group, it becomes soluble in a polar solvent and can be stored for a long time.
以下に本発明を実施するための最適実施例を示す。 In the following, an optimum embodiment for carrying out the present invention will be shown.
図１〜図１４に、実施例のＳｎＯ２ガスセンサとその特性とを示す。図１，図２にＳｎＯ２の調製を示し、図３に貴金属触媒の担持を示す。ＳｎＯ２の調製では、スズの有機化合物としてＳｎ(IV)アセチルアセトナト２塩化物(Ｓｎ(Ｃ５Ｈ７Ｏ２)２Ｃｌ2)を用い、アセチルアセトンの沸点は約１４０℃である。有機スズ化合物は、上記のものに限らず、無水酢酸スズ(II)，ステアリン酸スズ，オクタン酸スズ，オクチル酸スズ，ラウリル酸スズ，オレイン酸スズ，酢酸トリフェニルスズ，塩化トリフェニルスズなどでもよく、実質上任意の有機スズ化合物を用いることができる。 In FIGS. 1 to 14 show a SnO 2 gas sensor of Example and its properties. 1 and 2 show the preparation of SnO 2 and FIG. 3 shows the loading of a noble metal catalyst. In the preparation of SnO 2 , Sn (IV) acetylacetonate dichloride (Sn (C 5 H 7 O 2 ) 2 Cl 2 ) is used as an organic compound of tin, and the boiling point of acetylacetone is about 140 ° C. Organotin compounds are not limited to the above, but also with anhydrous tin acetate (II), stearate, stannous octoate, stannous octoate, stannous laurate, stannous oleate, triphenyltin acetate, triphenyltin chloride, etc. Well, virtually any organotin compound can be used.
水に不溶性の高沸点有機溶媒として、ジベンジルエーテル(Ｃ6Ｈ5-ＣＨ2-Ｏ-ＣＨ2-Ｃ6Ｈ5)を用い、沸点は約２９５℃である。ジベンジルエーテルに代えて、テトラフェニルエーテル(Ｃ6Ｈ5-Ｏ-Ｃ6Ｈ4-Ｏ-Ｃ6Ｈ4-Ｏ-Ｃ6Ｈ5)，ペンタフェニルエーテル(Ｃ6Ｈ5-Ｏ-Ｃ6Ｈ4-Ｏ-Ｃ6Ｈ4-Ｏ-Ｃ6Ｈ4-Ｏ-Ｃ6Ｈ5)などでもよく、これらの沸点は３００℃以上である。これらのフェニルエーテルを用いると、後述のように、スズの有機化合物を例えば２８０℃などで熱分解する際に、還流下で反応させることができる。沸点がスズの有機化合物の熱分解温度よりも低い場合、例えばオートクレーブ中で熱分解する。有機溶媒の沸点は２００℃以上が好ましく、より好ましくは２５０℃以上とする。 Dibenzyl ether (C 6 H 5 —CH 2 —O—CH 2 —C 6 H 5 ) is used as a high-boiling organic solvent insoluble in water, and the boiling point is about 295 ° C. Instead of dibenzyl ether, tetraphenyl ether (C 6 H 5 —O—C 6 H 4 —O—C 6 H 4 —O—C 6 H 5 ), pentaphenyl ether (C 6 H 5 —O—C) 6 H 4 —O—C 6 H 4 —O—C 6 H 4 —O—C 6 H 5 ) or the like, and the boiling point thereof is 300 ° C. or more. When these phenyl ethers are used, when the organic compound of tin is thermally decomposed at, for example, 280 ° C. as described later, it can be reacted under reflux. When the boiling point is lower than the thermal decomposition temperature of the organic compound of tin, for example, it is thermally decomposed in an autoclave. The boiling point of the organic solvent is preferably 200 ° C. or higher, more preferably 250 ° C. or higher.
界面活性剤として、オレイン酸とオレイルアミンとの等モル混合物を用い、これらのモル比は好ましくは２：１〜１：２とする。オレイン酸とオレイルアミンの組み合わせは脂肪酸と脂肪族アミンとの混合物の例で、脂肪酸と脂肪族アミンとの間で炭素数が異なっていても良い。脂肪酸並びに脂肪族アミンの好ましい炭素数は、例えば１０〜２５、好ましくは１２〜２０、より好ましくは１５〜１８で、オレイン酸とオレイルアミンは炭素数がいずれも１８である。また脂肪酸や脂肪族アミンは不飽和もしくは飽和を問わない。オレイン酸とオレイルアミンの混合物の役割は、オレイン酸がスズの有機化合物にカルボキシル基により配位することで、熱分解後にもＳｎＯ２のナノクリスタルにオレイン酸が吸着していた。そして吸着ないし配位したオレイン酸は、焼成などの過程でＳｎＯ２の結晶成長を妨げる。オレイン酸は電子供与性基として熱分解後のＳｎＯ２ナノクリスタルに配位ないしは吸着するものと考えられ、オレイルアミンの役割は、オレイン酸から水素を引き抜き、オレイン酸イオンを形成させて配位を容易にすることにある。 As the surfactant, an equimolar mixture of oleic acid and oleylamine is used, and the molar ratio thereof is preferably 2: 1 to 1: 2. The combination of oleic acid and oleylamine is an example of a mixture of a fatty acid and an aliphatic amine, and the number of carbon atoms may be different between the fatty acid and the aliphatic amine. The preferable carbon number of the fatty acid and the aliphatic amine is, for example, 10 to 25, preferably 12 to 20, and more preferably 15 to 18. Both oleic acid and oleylamine have 18 carbon atoms. Fatty acids and aliphatic amines may be unsaturated or saturated. The role of the mixture of oleic acid and oleylamine was that oleic acid was adsorbed on the SnO 2 nanocrystals even after thermal decomposition, because oleic acid was coordinated to a tin organic compound by a carboxyl group. The adsorbed or coordinated oleic acid prevents SnO 2 crystal growth in the course of firing or the like. Oleic acid is considered to be coordinated or adsorbed on the pyrolyzed SnO 2 nanocrystal as an electron donating group, and the role of oleylamine is to extract hydrogen from oleic acid and form oleic acid ions for easy coordination. Is to make it.
界面活性剤としては、オレイン酸，ステアリン酸、メリスチル酸などの脂肪酸あるいはこれらと脂肪族アミンとの組合せの他に、テトラエチレングリコール，ドデシルベンゼンスルホン酸ナトリウム，フェニルホスホン酸，ドデカンチオール，ドデシルアミンなどがある。実施例では、スズアセチルアセトナト２塩化物を０.４mmol，ジベンジルエーテルを７ml，オレイン酸とオレイルアミンとを共に各０.６ml用いた(ステップ１)。 Surfactants include fatty acids such as oleic acid, stearic acid and meristyl acid, or combinations of these with aliphatic amines, tetraethylene glycol, sodium dodecylbenzenesulfonate, phenylphosphonic acid, dodecanethiol, dodecylamine, etc. There is. In the examples, 0.4 mmol of tin acetylacetonate dichloride, 7 ml of dibenzyl ether, and 0.6 ml of each of oleic acid and oleylamine were used (Step 1).
上記の溶液を例えば１４０℃で１時間Ｎ２中で加熱した。この温度はアセチルアセトンの沸点にほぼ等しく、アセチルアセトンと塩素とが一部失われて、スズ原子にオクチル酸が配位することが考えられる(ステップ２)。熱処理後の溶液を冷却し、酸素の供与剤としてトリメチルアミンオキシド(Ｃ3Ｈ9ＮＯ)を例えば０.１５ml添加した(ステップ３)。次いで例えば還流下に２８０℃に３０分間溶液を加熱し、スズの有機化合物を熱分解し、ＳｎＯ２ナノクリスタルを生成させた(ステップ４)。ＳｎＯ２のコロイドは通常白色であるが、得られた溶液は褐色で、これは熱分解による有機物の残渣が含まれていることを示唆している。酸素供与性の有機化合物は、オクタデカノール，ペンタデカノール，ヘキサデカノール，ヘプタデカノールなどの、炭素数１２〜２０程度の脂肪族アルコールでもよく、これらは酸素を含む弱い酸化剤で、脂肪族のアルデヒドなどでも良い。なおアセチルアセトンあるいはオレイン酸も、酸素の供給源として作用することが考えられ、トリメチルアミンオキシドを添加しないでも、ＳｎＯ２ナノクリスタルが生成することがあった。従って酸素供与性の有機化合物は、添加しなくても良い。 The above solution was heated, for example, at 140 ° C. for 1 hour in N 2 . This temperature is almost equal to the boiling point of acetylacetone, and it is considered that acetylacetone and chlorine are partially lost, and octylic acid is coordinated to the tin atom (step 2). The solution after the heat treatment was cooled, and 0.15 ml of trimethylamine oxide (C 3 H 9 NO) was added as an oxygen donor (step 3). The solution was then heated to 280 ° C. for 30 minutes, for example, under reflux to thermally decompose the tin organic compound to produce SnO 2 nanocrystals (step 4). The colloid of SnO 2 is usually white, but the resulting solution is brown, suggesting that it contains organic residue from pyrolysis. The oxygen-donating organic compound may be an aliphatic alcohol having about 12 to 20 carbon atoms such as octadecanol, pentadecanol, hexadecanol, heptadecanol, etc., and these are weak oxidizing agents containing oxygen, Aldehyde aldehydes may also be used. In addition, it is considered that acetylacetone or oleic acid also acts as a supply source of oxygen, and SnO 2 nanocrystals may be formed without adding trimethylamine oxide. Therefore, it is not necessary to add an oxygen-donating organic compound.
ＳｎＯ２ナノクリスタルに貴金属触媒を添加する場合、結合子Ａから図３の処理に移り、添加しない場合にはステップ５〜ステップ９を実行する。生成したＳｎＯ２ナノクリスタルはエタノール、テトラヒドロフラン等の極性溶媒には不溶で、n-ヘキサンあるいはベンゼンなどの非極性溶媒に可溶である。ＳｎＯ２ナノクリスタルの懸濁液に例えばエタノールを加えて沈殿させ、遠心分離後にn-ヘキサンを加えてＳｎＯ２ナノクリスタルを抽出し、再度エタノールを加えて沈殿させ遠心分離した。遠心分離による洗浄を例えば３回行い、n-ヘキサンに分散させて保存した（ステップ５）。 When a noble metal catalyst is added to the SnO 2 nanocrystal, the process proceeds from the connector A to the process of FIG. 3, and when not added, Steps 5 to 9 are executed. The produced SnO 2 nanocrystals are insoluble in polar solvents such as ethanol and tetrahydrofuran, and are soluble in nonpolar solvents such as n-hexane and benzene. For example, ethanol was added to the suspension of SnO 2 nanocrystals to precipitate, and after centrifugation, n-hexane was added to extract SnO 2 nanocrystals, and ethanol was added again to precipitate and centrifuged. Washing by centrifugation, for example, was performed 3 times, and dispersed and stored in n-hexane (step 5).
ステップ４で得られたＳｎＯ２ナノクリスタルをn-ヘキサン等の非極性溶媒に分散させて保存すると、１〜２日で沈殿の生成が見られた。このことはＳｎＯ２ナノクリスタルが凝集しやすいことを示唆している。そこで電子供与性基を備えた有機溶媒、ここではピリジン１０mlを加え、還流下にＮ2雰囲気で例えば１１０℃に１２時間加熱した（ステップ６）。電子供与性基を備えた有機溶媒としては、ピリジンの他に、プロピルアミン，ブチルアミン，ペンチルアミン，へキシルアミンなどのアミン化合物、チオフェン，フェニレンジアミン，アニリン，トリブチルホスホン，1,6ジアミノヘキサンなどがある。これらの化合物はアミン類等の配位子ということができ、配位は非共有電子対で行われる。 When the SnO 2 nanocrystals obtained in Step 4 were dispersed and stored in a nonpolar solvent such as n-hexane, precipitation was observed in 1 to 2 days. This suggests that SnO 2 nanocrystals tend to aggregate. Therefore, an organic solvent having an electron donating group, here 10 ml of pyridine, was added, and the mixture was heated to 110 ° C., for example, for 12 hours under reflux in an N 2 atmosphere (step 6). In addition to pyridine, organic solvents with electron-donating groups include amine compounds such as propylamine, butylamine, pentylamine, and hexylamine, thiophene, phenylenediamine, aniline, tributylphosphone, and 1,6-diaminohexane. . These compounds can be referred to as ligands such as amines, and the coordination is carried out by unshared electron pairs.
ピリジンと反応させると、ＳｎＯ２ナノクリスタルは非極性溶媒に不溶となり、例えばn-ヘキサンを加えて沈殿させ、遠心分離により洗浄し、例えばＴＨＦ(テトラヒドロフラン)によりＳｎＯ２ナノクリスタルを抽出し、ヘキサンで再度沈殿させて遠心分離した。遠心分離を例えば３回繰り返して、ＳｎＯ２ナノクリスタルを洗浄した(ステップ７)。この洗浄により過剰のピリジンが除かれるが、ステップ５でＳｎＯ２ナノクリスタル自体は洗浄済みなので、ステップ７を省略しても良い。 Reacted with pyridine, SnO 2 nanocrystals become insoluble in non-polar solvents, for example, precipitated by addition of n- hexane, and washed by centrifugation, extract the SnO 2 nanocrystals example by THF (tetrahydrofuran), with hexane Precipitated again and centrifuged. Centrifugation was repeated, for example, three times to wash the SnO 2 nanocrystals (step 7). Excess pyridine is removed by this washing, but since the SnO 2 nanocrystal itself has been washed in step 5, step 7 may be omitted.
遠心分離により洗浄したＳｎＯ２ナノクリスタルを、テトラヒドロフランにより抽出しコロイド溶液として保存した（ステップ８）。このコロイド溶液は安定で、基板上に塗布し、乾燥後に焼成することにより、ＳｎＯ２膜が得られる(ステップ９)。実施例では、ＳｎＯ２ナノクリスタルのＴＨＦ溶液をアルミナ基板に５回塗布・乾燥し、空気中６００℃で３時間焼成して膜厚約７μｍのＳｎＯ２膜とした。 SnO 2 nanocrystals washed by centrifugation were extracted with tetrahydrofuran and stored as a colloidal solution (step 8). This colloidal solution is stable, and is applied onto a substrate, dried and fired to obtain a SnO 2 film (step 9). In this example, a THF solution of SnO 2 nanocrystals was applied to an alumina substrate five times, dried, and fired in air at 600 ° C. for 3 hours to form a SnO 2 film having a thickness of about 7 μm.
上記の工程を整理する。スズの有機化合物を界面活性剤と共に高沸点の水に不溶な有機溶媒中に溶解させる。次いで、好ましくは酸素の供給源の存在下に、スズの有機化合物を熱分解し、ＳｎＯ２ナノクリスタルとする。このＳｎＯ２ナノクリスタルにはオレイン酸などの界面活性剤が吸着ないし配位しており、ＳｎＯ２ナノクリスタルは褐色で非極性溶媒に可溶であるが、１〜２日程度で沈殿する。ＳｎＯ２ナノクリスタルの調製後に直ちにガスセンサを製造する場合、例えば上記の溶液をエタノールなどの極性溶媒と遠心分離などにより洗浄し、基板上に塗布乾燥した後に焼成してＳｎＯ２膜を成膜する。ＳｎＯ２ナノクリスタルの保存性を高める場合、ピリジン等の配位子とＳｎＯ２ナノクリスタルとを反応させ、ＴＨＦ，エタノールなどの極性溶媒に可溶で、非極性溶媒に不溶にする。そして好ましくは遠心分離などにより洗浄した後、ＴＨＦ中などで保存し、基板上に塗布・乾燥して焼成する。 Organize the above process. An organic compound of tin is dissolved together with a surfactant in an organic solvent insoluble in high boiling water. The organic compound of tin is then pyrolyzed into SnO 2 nanocrystals, preferably in the presence of a source of oxygen. This is the SnO 2 nanocrystals are adsorbed or coordinated surfactants such as oleic acid, SnO 2 nanocrystals are soluble in non-polar solvents in brown precipitate in about 1-2 days. When a gas sensor is manufactured immediately after the SnO 2 nanocrystals are prepared, for example, the above solution is washed with a polar solvent such as ethanol and centrifugation, applied and dried on a substrate, and then fired to form a SnO 2 film. When increasing the SnO 2 nanocrystals storability, reacting the ligand with SnO 2 nanocrystals such as pyridine, THF, it is soluble in a polar solvent such as ethanol, is insoluble in non-polar solvents. Preferably, after washing by centrifugation or the like, it is stored in THF or the like, coated on a substrate, dried and baked.
ＳｎＯ２ナノクリスタルに貴金属を担持する場合、図３のステップ１０を実行する。例えばＰｄやＡｇの場合、それらのアセチルアセトナトを、ステップ４で得られた懸濁液に添加し、例えば１５０〜１８０℃で、Ｎ2気流下に１０分〜１時間程度加熱すると、ＰｄあるいはＡｇのアセチルアセトナト化合物が分解し、ＳｎＯ２ナノクリスタルにＰｄあるいはＡｇを担持させることができる。 When a noble metal is supported on the SnO 2 nanocrystal, step 10 in FIG. 3 is executed. For example, in the case of Pd or Ag, when those acetylacetonates are added to the suspension obtained in Step 4 and heated at 150 to 180 ° C. for 10 minutes to 1 hour under N 2 stream, The Ag acetylacetonate compound is decomposed, and Pd or Ag can be supported on the SnO 2 nanocrystal.
Ｐｔ，Ａｕを担持する場合、例えばヘキサクロロ白金酸，塩化金酸を例えばオレイルアミンとn-ヘキサンの混合溶媒などに溶かし、加熱してn-ヘキサンを蒸発させ、ステップ４で得られた溶液に加える。次いで例えばＮ2気流下に１２０〜１８０℃に１０分〜１時間程度加熱する。この過程でヘキサクロロ白金酸，塩化金酸などが分解し、ＳｎＯ２ナノクリスタルにＰｔあるいはＡｕを担持することができる。貴金属触媒の担持後、図１のステップ５に戻り、図２のステップ９までを実行してＳｎＯ２ガスセンサを製造する。 In the case of supporting Pt and Au, for example, hexachloroplatinic acid and chloroauric acid are dissolved in, for example, a mixed solvent of oleylamine and n-hexane, and the n-hexane is evaporated by heating and added to the solution obtained in Step 4. Next, for example, heating is performed at 120 to 180 ° C. for about 10 minutes to 1 hour under a N 2 stream. In this process, hexachloroplatinic acid, chloroauric acid and the like are decomposed and Pt or Au can be supported on the SnO 2 nanocrystal. After loading the noble metal catalyst, the process returns to step 5 in FIG. 1, and the processes up to step 9 in FIG. 2 are executed to manufacture the SnO 2 gas sensor.
得られたＳｎＯ２ナノクリスタル(貴金属触媒無担持)の性状を図４〜図７に示す。図４の下側の(a)は、ピリジンと接触させ、ＴＨＦ中に保存したＳｎＯ２ナノクリスタルのＸ線回折パターンである。また上側の(b)は６００℃で焼成後のＳｎＯ２のＸ線回折パターンである。両者とも明瞭なＳｎＯ２の結晶を示し、６００℃で焼成しても回折パターンのピークの半値幅が余り減少していない。このことは、得られたＳｎＯ２ナノクリスタルは結晶成長が遅く、高温で焼成してもガス感度を保つことができることを示している。 Properties of the obtained SnO 2 nanocrystal (no precious metal catalyst supported) are shown in FIGS. The lower (a) of FIG. 4 is an X-ray diffraction pattern of SnO 2 nanocrystals contacted with pyridine and stored in THF. Upper (b) is an X-ray diffraction pattern of SnO 2 after firing at 600 ° C. Both show clear SnO 2 crystals, and the half-value width of the peak of the diffraction pattern is not significantly reduced even when fired at 600 ° C. This indicates that the obtained SnO 2 nanocrystals have a slow crystal growth and can maintain gas sensitivity even when fired at a high temperature.
図５の(a)，(b)は、ピリジンで処理後のＳｎＯ２ナノクリスタルの透過電子顕微鏡画像を示し、(a)は低倍率画像で、(b)は高倍率画像である。また(a)には図２のステップ８で得られた懸濁液を示し、溶液は褐色である。(b)ではＳｎＯ２(１１０)に対応する格子が見え、結晶は単分散して凝集しておらず、平均結晶子径は３.５nmである。 5A and 5B show transmission electron microscope images of SnO 2 nanocrystals treated with pyridine. FIG. 5A shows a low-magnification image and FIG. 5B shows a high-magnification image. (A) shows the suspension obtained in Step 8 of FIG. 2, and the solution is brown. In (b), a lattice corresponding to SnO 2 (110) is seen, the crystals are monodispersed and not aggregated, and the average crystallite diameter is 3.5 nm.
図６はＳｎＯ２ガスセンサとＳｎＯ２膜とを示し、(a)はガスセンサの構造を示し、アルミナ基板２上に櫛の歯状の金電極４を設け、電極４を覆うようにＳｎＯ２膜６を成膜してある。実施例では、ＳｎＯ２溶液の塗布と乾燥を５回繰り返し、６００℃で焼成することにより、膜厚７μmのＳｎＯ２膜６を得た。(b)〜(d)は６００℃で焼成後のＳｎＯ２膜を示し、(b)は原子間力顕微鏡画像を示し、(c)と(d)は２次電子顕微鏡画像で、(c)は低倍率画像で、(d)は高倍率画像である。別の高倍率原子間力電子顕微鏡画像並びに２次電子顕微鏡画像から、ＳｎＯ２の平均結晶子径は約９nmであることが分かった。 FIG. 6 shows a SnO 2 gas sensor and a SnO 2 film. FIG. 6A shows the structure of the gas sensor. A comb-like gold electrode 4 is provided on an alumina substrate 2 and the SnO 2 film 6 is covered so as to cover the electrode 4. Is deposited. In the example, SnO 2 film 6 having a thickness of 7 μm was obtained by repeating application and drying of the SnO 2 solution five times and baking at 600 ° C. (b)-(d) shows the SnO 2 film after baking at 600 ° C., (b) shows an atomic force microscope image, (c) and (d) are secondary electron microscope images, (c) Is a low-magnification image, and (d) is a high-magnification image. From another high-magnification atomic force electron microscope image and a secondary electron microscope image, it was found that the average crystallite diameter of SnO 2 was about 9 nm.
図７はＳｎＯ２ナノクリスタルのＦＴ−ＩＲスペクトルを示し、(a)はピリジン処理前のスペクトルを、(b)は６００℃焼成後（ピリジン無添加）のスペクトルを、(c)はピリジン処理後で焼成前のスペクトルを示している。(d)は市販のＳｎＯ２のスペクトルである。 FIG. 7 shows an FT-IR spectrum of SnO 2 nanocrystals, (a) is a spectrum before pyridine treatment, (b) is a spectrum after baking at 600 ° C. (no pyridine added), (c) is after pyridine treatment. Shows the spectrum before firing. (d) is a spectrum of commercially available SnO 2 .
焼成前の(a)のスペクトルでは、Ｃ＝Ｏ並びにＣ＝Ｃの吸収が１７００cm−１及び１６３０cm−１に見られ、アミノ基に関する吸収が見られない点から、オレイン酸がＳｎＯ２ナノクリスタルに吸着していることが分かる。(b)の６００℃焼成後のスペクトル並びに(c)のピリジン処理後のスペクトルでも、Ｃ＝Ｃの吸収が消えておらず、焼成後もオレイン酸がＳｎＯ２ナノクリスタル中に存在することが分かる。そしてこのことは、オレイン酸がＳｎＯ２ナノクリスタルの結晶成長を妨げ、６００℃焼成でも９nm程度の結晶子径までしか成長しなかったことを説明している。 The spectrum of the before firing (a), C = the absorption of O and C = C was observed at 1700 cm -1 and 1630 cm -1, from the viewpoint of not observed absorption about amino group, the oleic acid SnO 2 nanocrystals It can be seen that it is adsorbed. In the spectrum after baking at 600 ° C. in (b) and the spectrum after pyridine treatment in (c), C = C absorption is not lost, and it can be seen that oleic acid is still present in the SnO 2 nanocrystals after firing. . This explains that oleic acid hindered the crystal growth of SnO 2 nanocrystals, and even when sintered at 600 ° C., it grew only to a crystallite diameter of about 9 nm.
図８は、ピリジン処理前のＳｎＯ２ナノクリスタル４.５mgを焼成した際の、重量変化(ＴＧ)並びに示差熱(ＤＴＡ)分析の結果を示す。６００℃焼成によりＳｎＯ２ナノクリスタルは約２０％減量し、示差熱分析は３００℃強と４００℃強とに吸熱のピークを示している。このことは焼成の過程でのオレイン酸の熱分解を示しているものと考えられる。 FIG. 8 shows the results of weight change (TG) and differential heat (DTA) analysis when 4.5 mg of SnO 2 nanocrystals before pyridine treatment were fired. SnO 2 nanocrystals are reduced by about 20% by firing at 600 ° C., and differential thermal analysis shows endothermic peaks at slightly higher than 300 ° C. and slightly higher than 400 ° C. This is considered to indicate thermal decomposition of oleic acid during the firing process.
図９はＰｄを担持したＳｎＯ２の２次電子顕微鏡画像を示し、見やすくするため白黒を反転してある。Ｐｄの担持量はＳｎＯ２に対し１０mol％で、Ｐｄのアセチルアセトナトを遠心分離前のＳｎＯ２ナノクリスタルの懸濁液（ジベンジルエーテル溶媒）に溶解させて、Ｎ2気流下１７０℃で３０分加熱して担持させたものである。 FIG. 9 shows a secondary electron microscope image of SnO 2 carrying Pd, with black and white reversed for ease of viewing. The amount of Pd supported was 10 mol% with respect to SnO 2 , and Pd acetylacetonate was dissolved in a suspension of SnO 2 nanocrystals (dibenzyl ether solvent) before centrifugation and dissolved at 170 ° C. under N 2 stream at 30 ° C. It is supported by heating for a few minutes.
図１０〜図１４は、得られたＳｎＯ２ガスセンサの特性を示し、周囲の環境は室温の空気で、図１０，１１，１４では測定温度は３５０℃である。図１０はトルエン，ホルムアルデヒド，エタノールに対する感度を示し、図１１はトルエンへの応答パターンを示している。図１２は水素への感度を、図１３はＣＯへの感度を示している。図１０から明らかなように、３５０℃で１０ppmのエタノール及びホルムアルデヒドへの感度は、２００ppmの水素あるいは２００ppmのＣＯよりも充分に高い。また図１０でトルエンの感度がホルムアルデヒド及びエタノールに対して小さいのは、ＳｎＯ２膜中でのトルエンの拡散が遅いことに起因するものと思われる。 10 to 14 show the characteristics of the obtained SnO 2 gas sensor. The ambient environment is air at room temperature, and the measurement temperature is 350 ° C. in FIGS. FIG. 10 shows the sensitivity to toluene, formaldehyde, and ethanol, and FIG. 11 shows the response pattern to toluene. FIG. 12 shows sensitivity to hydrogen, and FIG. 13 shows sensitivity to CO. As is apparent from FIG. 10, the sensitivity to 10 ppm ethanol and formaldehyde at 350 ° C. is sufficiently higher than 200 ppm hydrogen or 200 ppm CO. In addition, in FIG. 10, the sensitivity of toluene is lower than that of formaldehyde and ethanol. This is probably due to the slow diffusion of toluene in the SnO 2 film.
図１４は図１０の特性を低濃度側へ外挿したもので、図での値が１となる濃度が理論的な検出下限である。この図から、実施例のＳｎＯ２ガスセンサはＶＯＣを例えば１ppb程度の検出下限で検出できることが分かる。 FIG. 14 extrapolates the characteristics of FIG. 10 to the low concentration side, and the concentration at which the value in the figure is 1 is the theoretical lower limit of detection. From this figure, it can be seen that the SnO 2 gas sensor of the embodiment can detect VOC with a detection lower limit of about 1 ppb, for example.
実施例での好ましい配合比を以下に示し、単位はＳｎの有機化合物１mmol当たりの量である。
高沸点有機溶媒 ５〜５００mＬ 特に１０〜１００mＬ
オレイン酸等の配位化合物 ０.１〜１０mＬ 特に１〜５mL
トリメチルアミンオキシド等の酸素源 ０〜１０mＬ 特に０.1〜５mL
ピリジン等の配位子 ５〜５００mＬ 特に１０〜１００mＬ
Preferred blending ratios in the examples are shown below, and the unit is the amount of Sn per 1 mmol of the organic compound.
High boiling point organic solvent 5 to 500 mL, especially 10 to 100 mL
Coordination compounds such as oleic acid 0.1 to 10 mL, especially 1 to 5 mL
Oxygen source such as trimethylamine oxide 0-10mL Especially 0.1-5mL
Ligands such as pyridine 5 to 500 mL, especially 10 to 100 mL
２ アルミナ基板
４ 櫛の歯金電極
６ ＳｎＯ２膜
2 Alumina substrate 4 Comb tooth electrode 6 SnO 2 film
Claims (4)
次いで前記溶液を加熱することによりスズの有機化合物を熱分解して、ＳｎＯ２微粒子の懸濁液を調製すると共に、
前記懸濁液から得られたＳｎＯ２によりガスセンサを製造する、ＳｎＯ２ガスセンサの製造方法。 Prepare a solution in which the organic compound of tin is dissolved together with the surfactant in an organic solvent insoluble in water,
Then, the organic solution of tin is thermally decomposed by heating the solution to prepare a suspension of SnO 2 fine particles,
Producing the gas sensor by SnO 2 obtained from the suspension, SnO 2 gas sensor manufacturing method.
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