JP3589177B2 - Method for producing inorganic oxynitride - Google Patents
Method for producing inorganic oxynitride Download PDFInfo
- Publication number
- JP3589177B2 JP3589177B2 JP2000343655A JP2000343655A JP3589177B2 JP 3589177 B2 JP3589177 B2 JP 3589177B2 JP 2000343655 A JP2000343655 A JP 2000343655A JP 2000343655 A JP2000343655 A JP 2000343655A JP 3589177 B2 JP3589177 B2 JP 3589177B2
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- Prior art keywords
- oxide
- oxynitride
- nitrogen
- heating
- titanium
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Links
- 238000004519 manufacturing process Methods 0.000 title description 9
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- 238000010438 heat treatment Methods 0.000 claims description 46
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 38
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 37
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- RYYXDZDBXNUPOG-UHFFFAOYSA-N 4,5,6,7-tetrahydro-1,3-benzothiazole-2,6-diamine;dihydrochloride Chemical compound Cl.Cl.C1C(N)CCC2=C1SC(N)=N2 RYYXDZDBXNUPOG-UHFFFAOYSA-N 0.000 claims description 5
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- ZFSLODLOARCGLH-UHFFFAOYSA-N isocyanuric acid Chemical compound OC1=NC(O)=NC(O)=N1 ZFSLODLOARCGLH-UHFFFAOYSA-N 0.000 claims description 3
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- -1 amino compound Chemical class 0.000 claims 1
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- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 8
- 125000004433 nitrogen atom Chemical group N* 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 125000004430 oxygen atom Chemical group O* 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 239000011941 photocatalyst Substances 0.000 description 6
- 238000003756 stirring Methods 0.000 description 6
- 229910021529 ammonia Inorganic materials 0.000 description 5
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- OAKJQQAXSVQMHS-UHFFFAOYSA-N Hydrazine Chemical compound NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 description 4
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
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- 229910001873 dinitrogen Inorganic materials 0.000 description 4
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- 239000003153 chemical reaction reagent Substances 0.000 description 3
- 125000002485 formyl group Chemical class [H]C(*)=O 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
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- 238000006467 substitution reaction Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
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- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 2
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- 239000003054 catalyst Substances 0.000 description 2
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- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 2
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- 238000010405 reoxidation reaction Methods 0.000 description 2
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Images
Description
【０００１】
【発明の属する技術分野】
本発明は、無機系酸窒化物の製造方法および無機系酸窒化物、特に光触媒活性を有する無機系酸窒化物に関する。
【０００２】
【従来の技術】
従来より、光触媒として酸化チタン（ＴｉＯ２）が広く利用されている。しかし、この酸化チタンは、紫外光において触媒活性を示すが、可視光においてはほとんど触媒活性を示さない。
【０００３】
【発明が解決しようとする課題】
一方、太陽光における紫外線領域の光は、数％程度であり、蛍光灯の光などは紫外線領域の光をほとんど含まない。従って、可視光においても光触媒活性を示す物質が望まれている。
【０００４】
本出願人は、酸化チタンの酸素を部分的に窒素と置換した酸窒化チタン（Ｔｉ−Ｏ−Ｎ）が、可視光においても良好な光触媒活性を示すことを発見した。この酸窒化チタンは、酸化チタンなどのチタン化合物をターゲットとして窒素雰囲気でスパッタリングすることにより薄膜として形成することができる。これについては、特願平１１−２２３００３号において提案した。また、特願２０００−１９３１５号において、酸窒化物の製造方法について各種の提案をした。
【０００５】
また、光触媒物質としては、粉末形状のものなどが利用しやすい。すなわち、粉末形状であれば、接着剤などと一緒に必要な場所に塗布するなどの方法で、所望の場所に容易に光触媒の膜を形成することができる。そこで、粉末状の酸窒化物を効率的に製造することが望まれている。
【０００６】
本発明は、光触媒として機能する粉末形状の無機系酸窒化物を効率的に製造する方法および製造された無機系酸窒化物に関する。
【０００７】
なお、特開２０００−８６２１０号公報には、ホウ酸と尿素の混合物を加熱して窒化ホウ素を得る方法が示されており、また特開２０００−１４４３９４号公報には、ホウ酸と酸化チタンと尿素の混合物から熱処理で窒化チタンを得ることが示されているが、これらは条件および結果生成物の両方が本発明と異なるものである。
【０００８】
【課題を解決するための手段】
本発明は、無機系酸窒化物の製造方法であって、比表面積が５ｍ２／ｇ以上の酸化物と、常温で酸化物に吸着する窒素化合物の混合物を加熱して光触媒活性を有する無機系酸窒化物を製造することを特徴とする。
【０００９】
このように、窒素供給源として、酸化物に常温で吸着する窒素化合物を使用し、これらの混合物を加熱することによって、原料酸化物内へ窒素を侵入させることができる。これによって、酸化物の酸素の一部が窒素に置換され酸窒化物が生成される。すなわち、酸窒化物の形成が比較的低温（例えば、１５０℃〜６００℃程度）で、かつ短時間の加熱で達成できる。また、原料酸化物結晶の表面に窒素化合物の吸着され、原料酸化物結晶の表面が窒素化合物で覆われる。この結果、加熱処理によって形成される酸窒化物の結晶の粗大化が抑制され、原料酸化物とほぼ同じ比表面積を有する酸窒化物が得られる。これにより、生成された酸窒化物において、原料酸化物と同様の紫外光触媒活性が得られるとともに、可視光においても高い光触媒活性を得ることができる。
【００１０】
また、前記酸化物は、酸化チタン、酸化亜鉛から選ばれた１以上の物質であることが好適である。これらの物質は、元々紫外線照射下において光触媒機能を有しており、窒素を導入することで、可視光による光触媒機能を発揮するようになる。
【００１１】
また、前記窒素化合物は、各種アミノ化合物、アミド等が使用できるが、尿素であることが好適である。尿素は、酸化物の表面に吸着されやすく、また加熱することによって窒素が酸化物中に効果的に侵入する。
【００１２】
なお、窒素化合物としては、上述の尿素の他、チオ尿素、二酸化チオ尿素、１，１−ジメチル尿素、シアヌル酸など還元力を有するもの（特に、尿素類似化合物）が利用可能である。これは、炭酸アンモニウムのように還元力のないものであると、酸化物と反応せず、酸化物中に窒素が侵入しないからである。
【００１３】
また、前記加熱は、アンモニアガス雰囲気において行われることが好適である。アンモニアガスからの窒素が酸化物中に侵入し、さらに窒素含有量の多い酸窒化物を形成することができる。
【００１４】
本発明に係る無機系酸窒化物は、比表面積が５ｍ２／ｇ以上の酸化物と、常温で液体もしくは固体の窒素化合物の混合物を加熱して製造された光触媒活性を有する粉末状の無機系酸窒化物であって、窒素原子による酸素原子の置換割合が、０．１〜２５％であることを特徴とする。窒素含有量が多いため、可視光において十分な光触媒活性を得ることができる。例えば、酸窒化チタンであれば、ＴｉＯ１．９９８Ｎ０．００２〜Ｔｉ１．５Ｎ０．５の範囲である。
【００１５】
【発明の実施の形態】
以下、本発明の実施形態について、図面に基づいて説明する。
【００１６】
本実施形態の処理について図１に基づいて説明する。まず、粉末状の酸化チタンと、尿素を用意する（Ｓ１１）。酸化チタンは、比表面積が５ｍ２／ｇ以上のものとし、好ましくは３００ｍ２／ｇ以上のものとする。このような粉末状の酸化チタンは市販されているので、それを利用すればよい。ただし、粉末粒子の大きさが上述のようなものであれば問題はないため、市販されているものでなくてもよい。なお、表面積の小さなものは、その分だけ触媒としての能力が劣ってしまうため、好ましくない。さらに、尿素からの窒素の侵入も十分なものにできない。
【００１７】
また、尿素は試薬として市販されている粉末状のものを利用すればよい。
【００１８】
次に、粉末状の酸化チタンと尿素を混合する（Ｓ１２）。尿素は、常温で酸化チタンの表面に吸着される。そこで、両者を攪拌混合することで、尿素が酸化チタンの表面に付着する。量的には、両者をほぼ同重量ずつ混合すればよく、これによって十分な尿素を酸化チタンの表面全体に吸着させることができる。なお、尿素などの窒素化合物の水溶液を作り、これを酸化チタン粉末の表面に付着させてもよい。
【００１９】
このようにして、酸化チタンと尿素が攪拌混合され、酸化チタン粉末の表面に尿素が吸着された場合には、その混合物を加熱する。温度は５００℃程度、時間は３０分程度が好適であり、さらに加熱中も攪拌を継続することが好ましい。このような加熱処理によって、酸化チタンの内部に窒素が侵入し、酸窒化チタンが生成される。
【００２０】
特に、加熱前から尿素が酸化チタンの表面に吸着されており、窒素の侵入が非常に容易に行われる。そこで、６００℃未満という低温でかつ短時間での酸窒化チタンの生成が可能になる。
【００２１】
そして、このような６００℃未満での短時間の加熱により、酸窒化チタンの結晶の粗大化が抑制され、原料の酸化チタンと同じ比表面積を有する酸窒化チタンが得られる。特に、酸化チタンの表面に尿素が吸着されており、酸化チタンの粉末粒子同士が直接接触していない。そこで、加熱されたときに、粉末粒子同士が合体して結晶化が進むのが防止され、粒子の粗大化が抑制される。
【００２２】
このようにして、尿素からの窒素が導入された酸窒化チタンの粉末が生成される。この粉末の粒子径は、基本的に原料の酸化チタンと同一であり、従って酸化チタンと同様の紫外光における光触媒を維持することができる。そして、窒素が導入されて得られた酸窒化チタンは、紫外光だけでなく可視光において触媒活性を有する。そこで、屋外、屋内における防曇、防汚材として広く利用できる。特に接着剤などのバインダを利用して所望の表面に塗布することができ、広範囲な利用が期待できる。
【００２３】
なお、酸窒化チタンの窒素は、酸素との置換により、Ｔｉ原子とＮ原子との間の化学結合が存在する状態で導入されている。
【００２４】
ここで、使用する酸化物は、比表面積が５ｍ２／ｇ以上を有する酸化物であればいかなるものでのよいが、光触媒などに使用できる、酸化チタン、酸化亜鉛、酸化錫、酸化鉄、酸化タングステン、酸化ケイ素の中から選ばれた１種または２種以上が好適である。酸化物の表面積が上記値を下回る場合、窒素化合物の吸着量が不足して酸窒化物の形成に支障をきたし、結晶粒子の粗大化を抑制できる温度範囲の加熱では酸窒化物が形成できなくなる。
【００２５】
また、酸化物の形態は、湿式法あるいは乾式法で製造される粉末や膜、あるいは内部に微細孔を有するメソポア多孔質材料などいかなるものでもよい。さらに、本発明でいう酸化物とは、非酸化性雰囲気中での加熱によって酸化物になるものを含み、含水酸化物、水酸化物であってもよい。
【００２６】
また、酸化物の比表面積は、５ｍ２／ｇ以上であることが好適である。これは、この程度の比表面積がないと、窒素の侵入を十分なものとできず、また生成された酸窒化物が触媒活性を十分発揮することができないからである。
【００２７】
酸化物の比表面積がこの値を下回ると、窒素化合物の吸着量が不足して、酸窒化物の形成に支障をきたし、また結晶粒子の粗大化を抑制できる温度範囲での加熱では酸窒化物の形成が困難になるからである。
【００２８】
また、尿素に代えて他の窒素化合物、例えばチオ尿素、二酸化チオ尿素、１，１−ジメチル尿素、シアヌル酸など各種のアミノ化合物やアミド等の還元力のある窒素化合物を利用することもできる。なお、限定されるわけではないが、窒素化合物は常温で固体のものが好ましい。これは、アンモニアやヒドラジン等の常温で気体のものは酸化物の表面への吸着が効果的に行えないからである。
【００２９】
また、窒素化合物と酸化物の混合には、任意の混合方法が選択できる。例えば、粉末同士であれば、上述のように、そのまま両者を混合すればよい。また、窒素化合物を適当な溶媒に溶解してから酸化物粉末と混合してもよい。さらに、酸化物が基体上の膜である場合には、窒素化合物溶液をスプレーなどで塗布してもよい。
【００３０】
さらに、加熱処理時の雰囲気は、大気中でもよが、酸窒化物の再酸化を防止するために、窒素ガス、アルゴンガスなどの不活性ガス雰囲気あるいは、水素ガス、アンモニアガス、ヒドラジンガスなど従来公知の還元性ガス雰囲気が好ましい。特に、アンモニアガス雰囲気では、酸窒化物の酸化防止されるとともに、雰囲気ガスからも窒素が供給され、酸窒化物の生成効率が高まるため、特に好ましい。 ここで、加熱中は原料の酸化物が還元力のある窒素化合物に均一に曝されるのが好ましく、原料酸化物が粉末の場合は、加熱炉は流動層炉やロータリーキルンなどの連続攪拌機構を持つものが好ましい。しかし、連続攪拌機構を持たない炉であっても、原料の酸化物と窒素化合物の混合物を、一度大気中で１５０℃程度まで加熱し、攪拌具を使って原料をよく混ぜ合わせ、その後所望の温度および雰囲気ガス中で加熱すれば、最初から流動層炉などを用いた場合と同様の酸窒化反応を行わせることができる。
【００３１】
加熱処理は、上記のように既成の酸化物と窒素化合物との混合物を加熱するのが簡便であるが、原料の酸化物の製造段階における加熱工程を利用してもよい。例えば、酸化チタンの粉末を得る一般的な製造方法では、四塩化チタンや硫化チタニルなどのチタン塩水溶液を加熱あるいはアルカリを添加して加水分解させて酸化チタンの微結晶を沈殿させた後、ろ過、洗浄を経て加熱乾燥される。さらに、場合によっては、この微結晶をオートクレーブ中で１００℃以上の温度で水熱処理して所望の結晶体にまで成長させる。
【００３２】
よって、この酸化物製造の加熱工程を本発明の加熱工程と兼ねてもよい。すなわち、酸化物粉末の乾燥やオートクレーブ処理などの加熱工程に入る前に尿素やチオ尿素などの還元力のある窒素化合物を混合し、しかるのちに加熱を行う。この方法によれば、加熱温度やガス雰囲気は従来条件から適宜変更する必要はあるが、省エネルギー、低コストの酸窒化物製造方法となり好ましい。
【００３３】
また、本発明の酸窒化物粉末を光触媒などに利用する場合には、酸窒化物粉末を水や有機溶媒に分散させてゾルあるいはスラリーとし、これをコーティング液として基体に塗布した後、加熱して酸窒化物粉末を膜状に基体に密着させるのが一般的である。そこで、この密着加熱工程を本発明の酸窒化物製造の加熱工程と兼ねてもよい。すなわち、原料の酸化物粉末と尿素などの還元力のある窒素化合物との混合物をゾルあるいはスラリーとして基体に塗布した後に加熱を行い、酸窒化物の製造とコーティング膜化を同時に行ってもよい。この方法では、酸窒化物の種類および基体の種類によって加熱温度やガス雰囲気を従来条件から適宜変更する必要はあるが、低コストの酸窒化物コーティング液が得られるという利点がある。また、処理が全体として簡略化されるため、コーティングが低コストで行える。
【００３４】
このように、窒素供給源として、酸化物に常温で吸着する尿素などの窒素化合物を使用し、これらの混合物を加熱することによって、原料酸化物内へ窒素を侵入させ酸素原子を窒素原子に置換させることができる。すなわち、酸窒化物の形成が６００℃未満の低温で、かつ短時間の加熱で達成できる。また、原料酸化物結晶の表面に窒素化合物が吸着され、原料酸化物結晶の表面が窒素化合物で覆われる。この結果、加熱処理によって形成される酸窒化物の結晶の粗大化が抑制され、原料酸化物とほぼ同じ比表面積を有する酸窒化物が得られる。これにより、生成された酸窒化物において、原料酸化物と同様の紫外光触媒活性が得られるとともに、可視光においても高い光触媒活性を得ることができる。
【００３５】
【実施例】
「実施例１」
酸化物として、比表面積が１〜３２０ｍ２／ｇのアナターゼ型酸化チタン粉末を５種類用意した。酸化チタン粉末を５０ｇずつガラスビーカに入れ、さらに試薬の二酸化チオ尿素粉末を２５ｇ添加した。そして、両者をへらで、十分攪拌混合した。このとき、混合物は、純白色を呈していた。
【００３６】
ここで、酸化チタン粉末の比表面積は、サンプル１が３２０ｍ２／ｇ、サンプル２が９０ｍ２／ｇサンプル３が７ｍ２／ｇ、サンプル４が４ｍ２／ｇ、サンプル５が１ｍ２／ｇである。
【００３７】
次に、大気開放下で、ガラスビーカをマントルヒータにより加熱し、混合物の温度が２００℃に達するまでへらでかき混ぜながら混合物の色調変化を目視観察した。その結果を表１に示す。
【００３８】
【表１】
【００３９】
これに対し、実施例である比表面積が５ｍ２／ｇ以上であるサンプル１，２および３では、１５０℃以上において、混合物の色調が黄色に変化し、酸化チタンに窒素が導入されて酸窒化チタンが生成されることが確認された。
【００４０】
また、得られた酸窒化チタンの窒素原子による酸素原子の置換割合をＸ線光電子分光分析で調べたところ、実施例では、０．２％以上という値を示した。また、比較例では０．１％以下であった。
【００４１】
「実施例２」
表２に示すように、酸化物として、実施例１のサンプル１で使用したものと同じ比表面積が３２０ｍ２／ｇのアナターゼ型酸化チタン粉末を用意した。比較例であるサンプル１０〜１２ではこれをそのまま使用した。また、実施例であるサンプル６〜９では、尿素試薬を等量混合した。
【００４２】
【表２】
【００４３】
一方、尿素を混合しない比較例であるサンプル１０〜１２については、サンプル１０は加熱なし、サンプル１１はアンモニアガス中で４５０℃：３０分、サンプル１２は、アンモニアガス中６００℃：３時間加熱した。
【００４４】
そして、各サンプル６〜９，１１，１２を表２に示す条件で加熱処理した。その結果、粉末の色調は、白色から、薄い黄色〜橙色に変化した。サンプル１０は、酸化チタンの原料粉末のまま加熱しないものであり、色調は白色のままであった。
【００４５】
加熱処理の後、尿素を混合して加熱したサンプル６〜９については、脱イオン水で洗浄し、酸窒化物以外の残留物を除去して乾燥した。
【００４６】
各サンプルについて、Ｘ線回折法により結晶形の調査を行った結果、いずれの加熱サンプルもサンプル１０の原料酸化物と同じアナターゼ型酸化チタンの結晶形を維持していた。その平均結晶粒径は、実施例であるサンプル６〜９では、原料酸化物（サンプル１０）と同じ７ｎｍであった。これに対し、比較例であるサンプル１１では、１２ｎｍ、サンプル１２では２０ｎｍと結晶成長を起こしていた。
【００４７】
また、Ｘ線光電子分光法により原料酸化物の酸素原子の窒素原子による置換割合を測定した結果、表２に示すように、サンプル６〜９における窒素原子による酸素原子の置換割合は、それぞれ、サンプル６：０．３％、サンプル７：７．８％、サンプル８：８．７％、サンプル９：１０．５％であった。一方、比較例であるサンプル１１，１２では、それぞれ０．０６％、０．０９％であった。このように、実施例の酸窒化物では、比較例より低温の加熱条件でも高い置換割合を示した。
【００４８】
次に、各サンプルについて、紫外光線および可視光線の照射下での光触媒能の測定を行った。この測定は、定法に従い、アセトアルデヒドガスの光分解能を測定した。すなわち、アセトアルデヒドの初期濃度を５０ｐｐｍとし、１０Ｗのブラックライトを１時間照射後のアセトアルデヒドの残留濃度を測定することで紫外光線による光触媒活性を測定した。また、紫外線カットフィルタ付１０Ｗ白色蛍光灯を７時間照射後のアセトアルデヒドの残留濃度により、可視光線による光触媒活性を測定した。
【００４９】
その結果を表２に示す。
【００５０】
これより、実施例であるサンプル６〜９および比較例であるサンプル１０では、紫外光線照射により残留アルデヒド濃度は２ｐｐｍとなった。これより、６００℃以下の加熱により、結晶粒子が粗大化することなく、酸窒化物が形成された結果、紫外光線照射下での光触媒作用が原料粉末であるサンプル１０（比較例）と同等に維持されることが確認された。一方、サンプル１１および１２では、残留アルデヒド濃度がそれぞれ５ｐｐｍ、８ｐｐｍであり、紫外光線活性が損なわれていることがわかる。これは、酸化チタンが粗大化したためである。
【００５１】
また、７時間の可視光照射後の残留アルデヒド濃度は、サンプル６で２０ｐｐｍ、サンプル７で１５ｐｐｍ、サンプル８で１２ｐｐｍ、サンプル９で８ｐｐｍとなった。これより、粗大化が起こらない範囲では、加熱温度は高い方がよく、また窒素中よりはアンモニア中が好ましいことがわかった。
【００５２】
これは、大気中では酸窒化物の再酸化が進むが、窒素ガス雰囲気中ではこれが防止されること、およびアンモニア雰囲気においてはアンモニアからの窒素が酸化チタン中に侵入するためと考えられる。
【００５３】
また、サンプル１２（比較例）では、色調は、黄色で酸窒化物が形成されているものの、結集粒子の粗大化が起こっており、可視光活性が認められる反面、紫外光活性が損なわれていた。
【００５４】
なお、実施例である上述のサンプル６〜９の酸窒化炭素について分析したところ、表２に示すように、窒素原子による酸素原子の置換割合で０．３％以上の窒素が含まれていた。一方、比較例であるサンプル１１，１２では、窒素含有率は０．１％以下である。このように、本発明により、従来に比べ、酸化チタンへの窒素の導入を効率的なものとして、窒素含有率の大きな酸窒化物を得ることができる。
【００５５】
【発明の効果】
以上説明したように、本発明によれば、窒素供給源として、酸化物に常温で吸着する窒素化合物を使用し、これらの混合物を加熱することによって、原料酸化物内へ窒素を侵入させることができる。すなわち、酸窒化物の形成が比較的低温で、かつ短時間の加熱で達成できる。また、原料酸化物結晶の表面に窒素化合物が吸着され、原料酸化物結晶の表面が窒素化合物で覆われる。この結果、加熱処理によって形成される酸窒化物の結晶の粗大化が抑制され、原料酸化物とほぼ同じ比表面積を有する酸窒化物が得られる。これにより、生成された酸窒化物において、原料酸化物と同様の紫外光触媒活性が得られるとともに、可視光においても高い光触媒活性を得ることができる。
【図面の簡単な説明】
【図１】実施形態の処理を示すフローチャートである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an inorganic oxynitride and an inorganic oxynitride, particularly to an inorganic oxynitride having photocatalytic activity.
[0002]
[Prior art]
Conventionally, titanium oxide (TiO 2 ) has been widely used as a photocatalyst. However, this titanium oxide shows catalytic activity in ultraviolet light, but shows almost no catalytic activity in visible light.
[0003]
[Problems to be solved by the invention]
On the other hand, light in the ultraviolet region in sunlight is about several percent, and light from a fluorescent lamp or the like hardly contains light in the ultraviolet region. Therefore, a substance exhibiting photocatalytic activity even in visible light is desired.
[0004]
The present applicant has discovered that titanium oxynitride (Ti-ON) in which oxygen of titanium oxide is partially substituted with nitrogen exhibits good photocatalytic activity even in visible light. This titanium oxynitride can be formed as a thin film by sputtering in a nitrogen atmosphere using a titanium compound such as titanium oxide as a target. This was proposed in Japanese Patent Application No. 11-223003. In Japanese Patent Application No. 2000-19315, various proposals were made on a method for producing an oxynitride.
[0005]
Further, as the photocatalyst substance, a powdery one or the like is easily used. That is, in the case of a powder form, a photocatalyst film can be easily formed at a desired place by a method such as applying it to a necessary place together with an adhesive or the like. Therefore, it is desired to efficiently produce powdery oxynitride.
[0006]
The present invention relates to a method for efficiently producing a powdery inorganic oxynitride that functions as a photocatalyst, and to the produced inorganic oxynitride.
[0007]
JP-A-2000-86210 discloses a method of heating a mixture of boric acid and urea to obtain boron nitride. JP-A-2000-144394 discloses a method in which boric acid and titanium oxide are used. It has been shown that heat treatment of titanium nitride from a mixture of ureas results in both conditions and resulting products differing from the present invention.
[0008]
[Means for Solving the Problems]
The present invention relates to a method for producing an inorganic oxynitride, comprising heating a mixture of an oxide having a specific surface area of 5 m 2 / g or more and a nitrogen compound adsorbed on the oxide at room temperature to thereby obtain an inorganic oxynitride having photocatalytic activity. It is characterized by producing oxynitride.
[0009]
As described above, by using a nitrogen compound which is adsorbed on an oxide at normal temperature as a nitrogen supply source and heating a mixture thereof, nitrogen can be introduced into the raw material oxide. As a result, part of the oxygen of the oxide is replaced with nitrogen, and oxynitride is generated. That is, formation of oxynitride can be achieved by heating at a relatively low temperature (for example, about 150 ° C. to 600 ° C.) and for a short time. Further, the nitrogen compound is adsorbed on the surface of the raw material oxide crystal, and the surface of the raw material oxide crystal is covered with the nitrogen compound. As a result, coarsening of the crystal of the oxynitride formed by the heat treatment is suppressed, and an oxynitride having substantially the same specific surface area as the raw material oxide is obtained. Thereby, in the generated oxynitride, an ultraviolet photocatalytic activity similar to that of the raw material oxide can be obtained, and a high photocatalytic activity can be obtained even in visible light.
[0010]
The oxide is preferably at least one substance selected from titanium oxide and zinc oxide . These substances originally have a photocatalytic function under ultraviolet irradiation, and can exhibit a photocatalytic function by visible light by introducing nitrogen.
[0011]
As the nitrogen compound, various amino compounds, amides and the like can be used, but urea is preferred. Urea is easily adsorbed on the surface of the oxide, and nitrogen effectively enters the oxide by heating.
[0012]
As the nitrogen compound, in addition to the above-mentioned urea, thiourea, thiourea dioxide, 1,1-dimethylurea, cyanuric acid, and other compounds having a reducing power (particularly, urea-like compounds) can be used. The reason for this is that if the material has no reducing power, such as ammonium carbonate, it does not react with the oxide and nitrogen does not enter the oxide.
[0013]
Preferably, the heating is performed in an ammonia gas atmosphere. Nitrogen from the ammonia gas enters the oxide, and an oxynitride having a high nitrogen content can be formed.
[0014]
The inorganic oxynitride according to the present invention is a powdery inorganic oxynitride having a photocatalytic activity produced by heating a mixture of an oxide having a specific surface area of 5 m 2 / g or more and a liquid or solid nitrogen compound at room temperature. An oxynitride, wherein a substitution ratio of oxygen atoms by nitrogen atoms is 0.1 to 25%. Since the nitrogen content is large, sufficient photocatalytic activity can be obtained in visible light. For example, in the case of titanium oxynitride, the range is TiO 1.998 N 0.002 to Ti 1.5 N 0.5 .
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
The processing of the present embodiment will be described with reference to FIG. First, powdery titanium oxide and urea are prepared (S11). Titanium oxide has a specific surface area of 5 m 2 / g or more, preferably 300 m 2 / g or more. Since such powdered titanium oxide is commercially available, it may be used. However, as long as the size of the powder particles is as described above, there is no problem. A catalyst having a small surface area is not preferred because the performance as a catalyst is inferior to that extent. Furthermore, the entry of nitrogen from urea cannot be sufficient.
[0017]
Urea may be a commercially available powdery reagent.
[0018]
Next, powdery titanium oxide and urea are mixed (S12). Urea is adsorbed on the surface of titanium oxide at room temperature. Then, by stirring and mixing both, urea adheres to the surface of titanium oxide. Quantitatively, the two may be mixed by almost the same weight, whereby sufficient urea can be adsorbed on the entire surface of the titanium oxide. Note that an aqueous solution of a nitrogen compound such as urea may be prepared and attached to the surface of the titanium oxide powder.
[0019]
In this way, the titanium oxide and the urea are stirred and mixed, and when the urea is adsorbed on the surface of the titanium oxide powder, the mixture is heated. The temperature is preferably about 500 ° C., and the time is preferably about 30 minutes, and it is preferable that stirring be continued during heating. By such a heat treatment, nitrogen enters the inside of the titanium oxide, and titanium oxynitride is generated.
[0020]
In particular, urea is adsorbed on the surface of the titanium oxide before heating, and nitrogen intrusion is performed very easily. Therefore, it is possible to generate titanium oxynitride at a low temperature of less than 600 ° C. and in a short time.
[0021]
Such short-time heating at less than 600 ° C. suppresses the coarsening of the crystal of titanium oxynitride, and obtains titanium oxynitride having the same specific surface area as the raw material titanium oxide. In particular, urea is adsorbed on the surface of titanium oxide, and powder particles of titanium oxide are not in direct contact with each other. Thus, when heated, the powder particles are prevented from coalescing and the crystallization is prevented, and the coarsening of the particles is suppressed.
[0022]
In this manner, a powder of titanium oxynitride into which nitrogen from urea has been introduced is generated. The particle size of this powder is basically the same as that of the raw material titanium oxide, and therefore, the same photocatalyst in ultraviolet light as titanium oxide can be maintained. The titanium oxynitride obtained by introducing nitrogen has catalytic activity not only in ultraviolet light but also in visible light. Therefore, it can be widely used as an antifogging and antifouling material outdoors and indoors. In particular, it can be applied to a desired surface using a binder such as an adhesive, and wide use can be expected.
[0023]
Note that nitrogen of titanium oxynitride is introduced in a state where a chemical bond exists between a Ti atom and an N atom by substitution with oxygen.
[0024]
Here, any oxide may be used as long as it has an specific surface area of 5 m 2 / g or more, but titanium oxide, zinc oxide, tin oxide, iron oxide, oxide One or two or more selected from tungsten and silicon oxide are preferable. When the surface area of the oxide is less than the above value, the amount of adsorption of the nitrogen compound is insufficient, which hinders the formation of the oxynitride, and the oxynitride cannot be formed by heating in a temperature range in which the coarsening of the crystal grains can be suppressed. .
[0025]
The oxide may be in any form such as a powder or film produced by a wet method or a dry method, or a mesoporous material having fine pores therein. Furthermore, the oxide referred to in the present invention includes those that become oxides by heating in a non-oxidizing atmosphere, and may be hydrated oxides or hydroxides.
[0026]
Further, the specific surface area of the oxide is preferably 5 m 2 / g or more. This is because, if there is no such specific surface area, it is impossible to sufficiently infiltrate nitrogen, and the generated oxynitride cannot exhibit sufficient catalytic activity.
[0027]
If the specific surface area of the oxide falls below this value, the amount of adsorbed nitrogen compounds becomes insufficient, which hinders the formation of oxynitrides. This makes it difficult to form
[0028]
Instead of urea, other nitrogen compounds, for example, various amino compounds such as thiourea , thiourea dioxide, 1,1-dimethylurea, and cyanuric acid, and reducing nitrogen compounds such as amides can be used. Although not limited, the nitrogen compound is preferably solid at room temperature. This is because gaseous substances such as ammonia and hydrazine at normal temperature cannot effectively adsorb to the oxide surface.
[0029]
In addition, an arbitrary mixing method can be selected for mixing the nitrogen compound and the oxide. For example, in the case of powders, both may be mixed as they are as described above. Alternatively, the nitrogen compound may be dissolved in an appropriate solvent and then mixed with the oxide powder. Further, when the oxide is a film on the substrate, a nitrogen compound solution may be applied by spraying or the like.
[0030]
Furthermore, the atmosphere during the heat treatment may be in the air, but in order to prevent reoxidation of oxynitride, an inert gas atmosphere such as nitrogen gas, argon gas, or a conventionally known gas such as hydrogen gas, ammonia gas, hydrazine gas, etc. Is preferable. In particular, in an ammonia gas atmosphere, oxidation of the oxynitride is prevented, and nitrogen is also supplied from the atmosphere gas, so that the efficiency of oxynitride generation is increased. Here, it is preferable that the oxide of the raw material is uniformly exposed to a nitrogen compound having a reducing power during heating, and when the raw material oxide is a powder, the heating furnace is a continuous stirring mechanism such as a fluidized bed furnace or a rotary kiln. Having one is preferred. However, even in a furnace without a continuous stirring mechanism, the mixture of the oxide and the nitrogen compound as the raw materials is heated once to about 150 ° C. in the air, and the raw materials are mixed well using a stirrer, and then the desired mixture is obtained. By heating in a temperature and atmosphere gas, the same oxynitriding reaction as in the case of using a fluidized bed furnace or the like can be performed from the beginning.
[0031]
In the heat treatment, it is convenient to heat the mixture of the existing oxide and the nitrogen compound as described above, but a heating step in the stage of manufacturing the raw material oxide may be used. For example, in a general production method for obtaining a powder of titanium oxide, an aqueous solution of a titanium salt such as titanium tetrachloride or titanyl sulfide is heated or added with an alkali to hydrolyze to precipitate fine crystals of titanium oxide, and then filtered. After washing, it is dried by heating. Further, in some cases, the microcrystal is subjected to hydrothermal treatment in an autoclave at a temperature of 100 ° C. or more to grow to a desired crystal.
[0032]
Therefore, the heating step of producing the oxide may also serve as the heating step of the present invention. That is, a nitrogen compound having a reducing power such as urea or thiourea is mixed before the heating step such as drying of the oxide powder or autoclave treatment, and then heating is performed. According to this method, it is necessary to appropriately change the heating temperature and the gas atmosphere from the conventional conditions. However, this method is preferable because it is an energy-saving and low-cost oxynitride production method.
[0033]
When the oxynitride powder of the present invention is used for a photocatalyst or the like, the oxynitride powder is dispersed in water or an organic solvent to form a sol or a slurry, which is applied to a substrate as a coating liquid, and then heated. Generally, the oxynitride powder is adhered to the substrate in a film form. Therefore, this contact heating step may also serve as the heating step of the oxynitride production of the present invention. That is, a mixture of a raw material oxide powder and a nitrogen compound having a reducing power such as urea may be applied as a sol or a slurry to a substrate, followed by heating to simultaneously perform production of an oxynitride and formation of a coating film. In this method, it is necessary to appropriately change the heating temperature and the gas atmosphere from the conventional conditions depending on the type of the oxynitride and the type of the base, but there is an advantage that a low-cost oxynitride coating solution can be obtained. Further, since the processing is simplified as a whole, coating can be performed at low cost.
[0034]
As described above, a nitrogen compound such as urea that is adsorbed on an oxide at room temperature is used as a nitrogen supply source, and by heating these mixtures, nitrogen enters the raw material oxide to replace oxygen atoms with nitrogen atoms. Can be done. That is, the formation of oxynitride can be achieved at a low temperature of less than 600 ° C. and by heating for a short time. Further, the nitrogen compound is adsorbed on the surface of the raw material oxide crystal, and the surface of the raw material oxide crystal is covered with the nitrogen compound. As a result, coarsening of the crystal of the oxynitride formed by the heat treatment is suppressed, and an oxynitride having substantially the same specific surface area as the raw material oxide is obtained. Thereby, in the generated oxynitride, an ultraviolet photocatalytic activity similar to that of the raw material oxide can be obtained, and a high photocatalytic activity can be obtained even in visible light.
[0035]
【Example】
"Example 1"
As the oxide, five types of anatase-type titanium oxide powder having a specific surface area of 1 to 320 m 2 / g were prepared. 50 g of the titanium oxide powder was put into a glass beaker, and 25 g of thiourea dioxide powder as a reagent was further added. Then, both were sufficiently stirred and mixed with a spatula. At this time, the mixture had a pure white color.
[0036]
Here, the specific surface area of the titanium oxide powder, the sample 1 is 320 m 2 / g, the sample 2 is 90m 2 / g sample 3 7m 2 / g, sample 4 is 4m 2 / g, the sample 5 with 1 m 2 / g is there.
[0037]
Next, the glass beaker was heated with a mantle heater under the open air, and the color tone change of the mixture was visually observed while stirring with a spatula until the temperature of the mixture reached 200 ° C. Table 1 shows the results.
[0038]
[Table 1]
[0039]
On the other hand, in Samples 1, 2, and 3, which have specific surface areas of 5 m 2 / g or more, the color tone of the mixture changes to yellow at 150 ° C. or more, and nitrogen is introduced into titanium oxide to cause oxynitridation. It was confirmed that titanium was produced.
[0040]
Further, when the replacement ratio of oxygen atoms by nitrogen atoms in the obtained titanium oxynitride was examined by X-ray photoelectron spectroscopy, it was found to be 0.2% or more in Examples. Moreover, in the comparative example, it was 0.1% or less.
[0041]
"Example 2"
As shown in Table 2, as the oxide, an anatase type titanium oxide powder having the same specific surface area as that used in Sample 1 of Example 1 was 320 m 2 / g. This was used as it was in Samples 10 to 12 as comparative examples. In Samples 6 to 9 as examples, urea reagents were mixed in equal amounts.
[0042]
[Table 2]
[0043]
On the other hand, with respect to Samples 10 to 12 which are comparative examples not mixed with urea, Sample 10 was heated without heating, Sample 11 was heated in ammonia gas at 450 ° C. for 30 minutes, and
[0044]
The samples 6 to 9, 11, and 12 were heat-treated under the conditions shown in Table 2. As a result, the color tone of the powder changed from white to pale yellow to orange. In Sample 10, the raw material powder of titanium oxide was not heated, and the color tone remained white.
[0045]
After the heat treatment, Samples 6 to 9 heated by mixing urea were washed with deionized water to remove residues other than oxynitride and dried.
[0046]
As a result of investigating the crystal form of each sample by an X-ray diffraction method, all the heated samples maintained the same crystal form of the anatase-type titanium oxide as the raw material oxide of Sample 10. The average crystal grain size of Samples 6 to 9 as Examples was 7 nm, which is the same as that of the raw material oxide (Sample 10). On the other hand, the crystal growth of sample 11 as a comparative example was 12 nm, and that of
[0047]
In addition, as a result of measuring the replacement ratio of oxygen atoms of the raw material oxides by nitrogen atoms by X-ray photoelectron spectroscopy, as shown in Table 2, the replacement ratio of oxygen atoms by nitrogen atoms in Samples 6 to 9 was as follows: 6: 0.3%, Sample 7: 7.8%, Sample 8: 8.7%, Sample 9: 10.5%. On the other hand, in
[0048]
Next, the photocatalytic ability of each sample was measured under irradiation of ultraviolet light and visible light. In this measurement, the optical resolution of acetaldehyde gas was measured according to a standard method. That is, the initial concentration of acetaldehyde was set to 50 ppm, and the photocatalytic activity by ultraviolet light was measured by measuring the residual concentration of acetaldehyde after irradiating 10 W black light for 1 hour. The photocatalytic activity by visible light was measured based on the residual concentration of acetaldehyde after irradiating a 10 W white fluorescent lamp with an ultraviolet cut filter for 7 hours.
[0049]
Table 2 shows the results.
[0050]
Thus, in Samples 6 to 9 as Examples and Sample 10 as Comparative Example, the residual aldehyde concentration was 2 ppm by irradiation with ultraviolet light. From this, the oxynitride was formed without the crystal grains being coarsened by heating at 600 ° C. or less. As a result, the photocatalysis under ultraviolet light irradiation was equivalent to that of Sample 10 (comparative example) as the raw material powder. It was confirmed that it would be maintained. On the other hand, in
[0051]
The residual aldehyde concentration after 7 hours of visible light irradiation was 20 ppm for sample 6, 15 ppm for
[0052]
This is presumably because the reoxidation of the oxynitride proceeds in the atmosphere, but is prevented in a nitrogen gas atmosphere, and nitrogen from ammonia enters titanium oxide in an ammonia atmosphere.
[0053]
In Sample 12 (Comparative Example), although the color tone was yellow and oxynitride was formed, the aggregated particles were coarsened and visible light activity was observed, but ultraviolet light activity was impaired. Was.
[0054]
In addition, when the carbon oxynitrides of the above-mentioned samples 6 to 9 as examples were analyzed, as shown in Table 2, nitrogen was contained in an amount of 0.3% or more as a replacement ratio of oxygen atoms by nitrogen atoms. On the other hand, in
[0055]
【The invention's effect】
As described above, according to the present invention, as a nitrogen supply source, a nitrogen compound adsorbed on an oxide at normal temperature is used, and by heating these mixtures, nitrogen can be introduced into the raw material oxide. it can. That is, the formation of oxynitride can be achieved by heating at a relatively low temperature for a short time. Further, the nitrogen compound is adsorbed on the surface of the raw material oxide crystal, and the surface of the raw material oxide crystal is covered with the nitrogen compound. As a result, coarsening of the crystal of the oxynitride formed by the heat treatment is suppressed, and an oxynitride having substantially the same specific surface area as the raw material oxide is obtained. Thereby, in the generated oxynitride, an ultraviolet photocatalytic activity similar to that of the raw material oxide can be obtained, and a high photocatalytic activity can be obtained even in visible light.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a process according to an embodiment.
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