JP2004255684A - High-quality titania nano-sheet ultra-thin membrane and its manufacturing process - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、光触媒薄膜や紫外線遮断コーティングに利用でき、光電変換用薄膜やフォトクロミック材料、各種センサーなどへの利用も期待できる、ｎｍレベルで膜厚制御された緻密で高品位なチタニアナノシート超薄膜とその製造方法に関する。
【０００２】
【従来の技術】
一般に、酸化チタン薄膜を得る方法として、分子線エピタキシー（ＭＢＥ）、有機金属気相成長法（ＭＯＣＶＤ）などによる気相成長法、あるいはチタンアルコキシド等のチタン化合物を加水分解して得られるチタニアゾルをディッピングやスピンコートなどによって基板表面に塗布する方法が知られている。
前者の方法では、サブｎｍレベルで膜厚が制御された高品位な薄膜が得られるが、高真空設備など高価で特殊な装置を必要とし、また、その薄膜作製までには長時間を要する等、コストや作業効率等に問題があった。これに対して、後者の方法では、特殊な装置を要することもなく、しかも操作が容易であり、低コストで酸化チタン薄膜を得ることが出来るが、その膜厚はサブミクロン以上であり、ナノレベルで膜厚や膜質を制御することは極めて困難であった。
【０００３】
一方、これらの手法とは全く異なった方法が提案されている。すなわち、層状チタン酸化物を剥離して得られるチタニアナノシートを有機ポリマーと交互に吸着させることにより基板表面に累積させてチタニア超薄膜を得る方法が提案され（非特許文献１）、複雑な装置を使用せずに簡便な方法で、サブｎｍからｎｍレンジで膜厚が制御されたチタニア超薄膜の作製が可能である。これらのチタニア超薄膜は、この出願前の先行技術である「チタニア超薄膜およびその製造方法」（特許文献１）に開示されているような交互積層法、あるいはＬａｎｇｍｕｉｒ−Ｂｌｏｄｇｅｔｔ製膜法などにより作製することが可能である。
【０００４】
しかしながら、これらの手段によって作製されたチタニア超薄膜では、通常横サイズがサブμｍ〜μｍの粉末サンプル由来のナノシートが使用されていたため、このサイズのナノシートでは基板表面を隙間なく被覆することは困難であり、また、ナノシート同士の重複被覆が避けられないという欠点があり（非特許文献１）、このため種々の応用展開に問題があった。
【０００５】
【非特許文献１】Ｔ．Ｓａｓａｋｉ ｅｔ．ａｌ、Ｃｈｅｍ．Ｍａｔ、１３（２００１）４６６１
【特許文献１】特開２００１−２７００２２号公報
【０００６】
【発明が解決しようとする課題】
本発明は厚み約１ｎｍのナノレベル、横サイズ１μｍ〜１ｍｍのチタニアナノシートが隙間なく累積した、重複被覆が極めて少ない高品位チタニア超薄膜とその製造方法を提供しようと言うものである。
【０００７】
【課題を解決するための手段】
そのため、本発明者等は上記課題に対して鋭意研究を重ねた結果、ポリマーとの交互積層に横サイズが１μｍ〜１ｍｍのチタニアナノシートを用いることにより基板表面がナノシートにより隙間なく被覆されたチタニア超薄膜を作製することが可能であること、また、得られた薄膜をアルカリ水酸化物やアミン、アンモニア塩などの塩基性物質を含むｐＨ９以上の水溶液中で超音波処理を行うことにより、ナノシートの重複被覆部が除去可能である事を見いだしたものであり、これらの知見に基づいて本発明を成すに至った。すなわち、本発明は厚み約１ｎｍ、横サイズ１μｍ〜１ｍｍのチタニアナノシートが隙間なく累積し、しかも重複した被覆が極めて少ないチタニア超薄膜とその製造方法に関するものであり、その構成は以下に記載する通りの事項からなるものである。
【０００８】
（１） 層状チタン酸化物単結晶を剥離して得られる薄片粒子（ナノシート）を基板表面上に隙間なく被覆し、且つ、薄片粒子同士の重複を除去、低減してなることを特徴とした、チタニア超薄膜。
（２） 該薄片粒子が厚み約１ｎｍ、横サイズ１μｍ〜１ｍｍの粒子サイズのナノシートであることを特徴とした、前記（１）項に記載のチタニア超薄膜。
（３） 該薄片粒子が組成式Ｔｉ１−δＯ２（０＜δ＜０．５）で表されるチタニアナノシート、あるいはＴｉ１−ｘ／２ｎＭｘ／２ｎＯ２〔Ｍは、Ｌｉ、Ｍｇ、Ｆｅ、Ｎｉ、Ｚｎ、Ｃｏ、Ｃｒ、Ｍｎ、Ｃｕ、Ａｌより選ばれる１種又は２種以上の金属、ｎは（４−Ｍの平均価数）、０．５≦ｘ≦１〕で表されるチタニアを主成分としてなるナノシートであることを特徴とした、前記（１）又は（２）項に記載のチタニア超薄膜。
（４） 層状チタン酸化物単結晶を剥離して薄片粒子（ナノシート）を得、これを基板上に隙間なく被覆し、次いで薄片粒子同士の重複部分を除去、低減する処理を施し、薄片粒子同士の重複部分が除去、低減されたチタニア超薄膜を得ることを特徴とした、チタニア超薄膜の製造方法。
（５） 該薄片粒子が厚み約１ｎｍ、横サイズ１μｍ〜１ｍｍの粒子サイズのナノシートであることを特徴とした、前記（４）項に記載のチタニア超薄膜の製造方法。
（６） 該薄片粒子が組成式Ｔｉ１−δＯ２（０＜δ＜０．５）で表されるチタニアナノシート、あるいはＴｉ１−ｘ／２ｎＭｘ／２ｎＯ２〔Ｍは、Ｌｉ、Ｍｇ、Ｆｅ、Ｎｉ、Ｚｎ、Ｃｏ、Ｃｒ、Ｍｎ、Ｃｕ、Ａｌより選ばれる１種又は２種以上の金属、ｎは（４−Ｍの平均価数）、０．５≦ｘ≦１〕で表されるチタニアを主成分としてなるナノシートであることを特徴とした、前記（４）又は（５）記載のチタニア超薄膜の製造方法。
（７） 前記基板上に薄片粒子を隙間なく被覆する手段が、カチオン性有機ポリマー溶液中に基板を浸漬して基板表面に有機ポリマーを吸着させた後、該薄片粒子が懸濁したナノシートコロイド溶液中に浸漬することにより、薄片状粒子を静電気的作用によって基板上に自己組織的に吸着させるプロセスによるものであることを特徴とする、請求項４ないし６記載の何れか１項に記載のチタニア超薄膜の製造方法。
（８） 前記薄片粒子同士の重複部分を除去、低減する処理手段が、アルカリ水溶液中で超音波処理することによることを特徴とする、前記（４）ないし（６）の何れか１項に記載のチタニア超薄膜の製造方法。
（９） 前記アルカリ水溶液が、ｐＨが９以上に調製されたアルカリ溶液であることを特徴とする、前記（８）項に記載のチタニア超薄膜の製造方法。
【０００９】
【発明の実施の形態】
本発明のチタニア超薄膜を形成する出発チタニアナノシートは、厚みｎｍレベル、横サイズ１μｍ〜１ｍｍ、好ましくは１０μｍ以上のものが使用される。
この横サイズのナノシートを用いて超薄膜を作製した場合、ナノシート同士の重複被覆が多くみられるものの、基板表面をほぼ完全に被覆した超薄膜が得られる。１μｍ以下の横サイズのナノシートを用いた場合、ナノシート間に隙間が生じることにより基板表面への被覆率が減少するため好ましくない。
【００１０】
このチタニアナノシートは、粒子径が１μｍ〜１ｍｍである層状構造を有するチタン酸化物単結晶に、後述する特殊な化学反応処理を施すことにより得ることが出来る。ここに、層状チタン酸化物としては、レピドクロサイト型チタン酸塩〔ＡｘＴｉ２−ｘ／ｎＭｘ／ｎＯ４、但し、Ａは、Ｋ、Ｒｂ、Ｃｓよりなる１種又は２種以上のアルカリ金属、Ｍは□（空孔）あるいは、Ｌｉ、Ｍｇ、Ｆｅ、Ｎｉ、Ｚｎ、Ｃｏ、Ｃｒ、Ｍｎ、Ｃｕ、Ａｌよりなる１種又は２種以上の金属、ｎは（４−Ｍの平均価数）あるいは４（Ｍが空孔□の場合）、０．５≦ｘ≦１〕を始めとして、Ｎａ２Ｔｉ３Ｏ７などの三チタン酸塩、Ｋ２Ｔｉ４Ｏ９などの四チタン酸塩、Ｃｓ２Ｔｉ５Ｏ１１などの五チタン酸塩などを挙げることが出来るが、要するに酸化チタンを主成分としたホスト層により構成される層状チタン酸塩であればよく、特に限定されるものではない。チタニアナノシートの出発原料としては、これらの化合物をフラックス法や溶融法などの方法により作製した、粒子径が１μｍ〜１ｍｍ、好ましくは１０μｍ〜１ｍｍの単結晶サンプルを使用する。
【００１１】
ここに、特殊な化学反応処理とは、「斜方晶の層状構造を有するチタン酸およびその製造方法」（特許文献２）及び「組成式Ｈ２Ｔｉ５Ｏ１１・ｎＨ２Ｏで示される単斜晶の層状構造を有する化合物およびその製造方法」（特許文献３）に開示されている酸処理や、「チタニアゾルとその製造方法」（特許文献４）に開示されているコロイド化処理を指すものである。すなわち、層状チタン酸化物単結晶に酸処理を行うことにより層間のアルカリ金属イオンを水素イオンに置き換えて水素型物質を作製し、該水素型物質を水溶液中でアミンなどの塩基性物質と反応させることによりコロイド化し、層状構造を構成するホスト層が一枚一枚にまで剥離したチタニアナノシートゾル溶液を得ることが出来るものである。これにより１μｍ〜１ｍｍサイズの大型ナノシートが得られる。
【００１２】
【特許文献２】特公平６−８８７８６号公報
【特許文献３】特公平６−７８１６６号公報
【特許文献４】特開平９−２５１２３号公報
【００１３】
これらのチタニアナノシートを用いたチタニア超薄膜は、前記特許文献１（「チタニア超薄膜およびその製造方法」）において開示された交互積層法による膜製造プロセスによる手段を適用することによって作製される。このチタニア超薄膜では前記の大型ナノシートを用いることにより基板表面を隙間なく被覆することが可能であるが、基板表面にナノシート同士の重複被覆部分が多くみられる。これを解決するため鋭意研究した結果、該超薄膜で被覆された基板をアルカリ水溶液中で超音波処理を行うことによって、ナノシートの重複被覆部分を除去することが充分に可能であることを見出したものである。
その原理は、以下のように説明することが出来る。すなわち、この交互積層法によって得られたチタニア超薄膜では負電荷を有したチタニアナノシートが正電荷を有するポリマーと組み合わされて累積されているため、基板表面上に累積したナノシートはポリマーとの間に働く静電気的作用により基板表面に比較的強固に吸着しているが、ナノシートが他のナノシートの上に重複被覆した部分ではナノシートが負電荷を持つことによって反発力が働くため、その付着力は弱くなっていると考えられる。このような重複部分がある超薄膜に対して、アルカリ水溶液中で超音波処理するとアルカリ水溶液中で生じるキャビテーションによる洗浄効果により、ナノシートの重複被覆部は水溶液中に除去されるが、基板表面に累積した部分は基板表面への引力が強いために除去されることなく残る。
【００１４】
このように特定の処理を講ずることによってナノシートの重複被覆部を除去することにより、単層のナノシートにより基板表面が隙間なく被覆された高品位チタニア超薄膜を得ることが出来る。本研究で使用されるアルカリ水溶液の成分は、例えば、アミンやアンモニウム、アルカリ金属水酸化物などが挙げられるが、特に特定の成分に限定されるものではない。また、アルカリ水溶液のｐＨはｐＨ９以上、好ましくはｐＨ１０〜１１である。ｐＨ９未満では、ナノシートの重複被覆部の付着力が強くなるため、超音波処理による重複被覆部の除去ができない。
【００１５】
また、該超音波処理方法は、その処理手段には特に制約はなく、要するに結果的にキャビテーション効果が得られるものであればよく、例えば、一般に市販され、使用されている超音波洗浄機などを使用することができる。その照射する超音波の周波数についても、特に制約はないが、キャビテーションが発生する周波数であればよい。好ましくは２０Ｈｚ以上である。超音波の出力はキャビテーションの発生量に影響するため、高すぎると基板表面に累積したナノシートの脱離や損傷を引き起こすおそれがあるため、１００Ｗ以下が望ましい。また、超音波照射時間は、１分以上が望ましい。
【００１６】
【実施例】
以下、本発明を実施例および比較例に基づいてさらに具体的に説明するが、本発明はこれら実施例に限定されるものではない。
【００１７】
実施例１；
炭酸カリウム、炭酸リチウム、酸化チタンおよび三酸化モリブデンをモル比で１．６７：０．１３：１．７３：１．２７の割合に混合し、１２００度で１０時間焼成した後、９５０度まで毎時４℃の速度で徐冷し、純水中にてフラックス成分であるモリブデン酸カリウムを除去し、風乾してチタン酸リチウムカリウム （ＫｘＴｉ２−ｘ／３Ｌｉｘ／３Ｏ４、ｘ〜０．８）単結晶（層状化合物）を得た。
この単結晶３０ｇを室温にて０．５規定の塩酸溶液２ｄｍ３中で酸処理を行なった。塩酸溶液を１日ごとに取り替え、５日間反応を行った後、濾過し、１晩風乾して１００μｍ〜２ｍｍの大きさの層状チタン酸結晶（Ｈ１．０７Ｔｉ１．７３Ｏ４・１．２Ｈ２Ｏ）を得た。
この層状チタン酸化物結晶０．４ｇに０．４ｗｔ％のテトラブチルアンモニウム水酸化物（以下、ＴＢＡＯＨと記載する）水溶液１００ｃｍ３を加えて室温にて２週間静置状態にて反応させて乳白色状のゾルを作製した。このゾルをＴＥＭにて観察したところ長辺約７０μｍ、短辺約２０μｍの長方形状のナノシートが得られていることが確認できた。そのゾルを５０倍に希釈してｐＨ９に調整したチタニアゾル溶液を作製した。また、２ｗｔ％のポリジアリルジメチルアンモニウムクロライド；ｐｏｌｙｄｉａｌｌｙｌｄｉｍｅｔｈｙｌａｍｍｏｎｉｕｍ ｃｈｌｏｒｉｄｅ溶液（以下ＰＤＤＡ溶液という）１００ｃｍ３に０．５ｍｏｌｄｍ−３に相当する量のＮａＣｌを加え、ｐＨ９に調整した。
５ｃｍ×１ｃｍの短冊状のＳｉウェハーと石英ガラス板を塩酸：メタノール＝１：１の溶液に２０分間浸漬した後、濃硫酸中に２０分間浸漬することにより親水化処理を行った。この基板を上記ＰＤＤＡ溶液に２０分間浸漬した後、Ｍｉｌｌｉ−Ｑ純水で充分に洗浄した後、撹拌した上記チタニアゾル溶液中に浸漬し、２０分経過後にＭｉｌｌｉ−Ｑ純水で充分に洗浄し、窒素気流を吹き付けて乾燥させ、チタニア超薄膜を作製した。得られた超薄膜をｐＨ１１のＴＢＡＯＨ水溶液中に浸漬しながら、超音波洗浄槽（４２ｋＨｚ、９０Ｗ、１５１０Ｊ−ＤＴＨ；型式商品名、日本エマソン（株）ブランソン事業本部製）にて１０分間の超音波処理を行った。こうして得られたチタニア超薄膜の超音波処理前後の原子間力顕微鏡（ＡＦＭ；Ａｔｏｍｉｃ Ｆｏｒｃｅ Ｍｉｃｒｏｓｃｏｐｅ）表面観察像を図１に、ＡＦＭ表面観察像から解析された基板表面の被覆面積率と重複被覆部の面積率を表１に示す。図１と表１より、超音波処理前では基板表面はナノシートにより隙間なく被覆されるとともにナノシートの重複被覆が非常に多いが、超音波処理後では重複被覆部が除去された緻密なチタニア超薄膜が得られることが確認された。ＡＦＭ観察像から得られるこのチタニア超薄膜の厚みは約１ｎｍであり、これは単層のナノシート一枚の厚みにほぼ一致する。
また、基板表面へのチタニアナノシートの累積量は紫外可視吸収スペクトロスコピーによる２６５ｎｍの吸光度で確認することが可能であり（非特許文献２）、基板表面を単層のナノシートが完全に被覆したと仮定した場合の吸光度は約０．１１である。
表２に示す様に超音波処理前のチタニア超薄膜の吸光度は０．２７であり、ナノシートの重複被覆が非常に多いことが裏付けられるが、超音波処理後では０．１２まで低減しており、重複被覆部の除去が進んでいることが判明した。以上のような吸光度の変化とＡＦＭ表面観察像から、重複被覆がほとんど除去された単層のナノシートから成る緻密なチタニア超薄膜が得られていることが確認できた。
【００１８】
【非特許文献２】Ｔ．Ｓａｓａｋｉ、Ｍ．Ｗａｔａｎａｂｅ、Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ、１２０、４６８２（１９９８）
【００１９】
比較例１；
チタニアナノシートの横サイズがサブμｍ〜μｍであること以外は、実施例１と同様に行い、チタニア超薄膜を作製した。超音波処理前後のチタニア超薄膜のＡＦＭ表面観察像を図２（ａ）および（ｂ）示す。
吸光度から超音波処理前のチタニア超薄膜では基板表面を完全に被覆し得る量のナノシートが累積しているが（表２）、ＡＦＭ表面観察像からこのチタニア超薄膜ではチタニアナノシート間の隙間がみられ、基板表面の被覆率は８１％（表１）であることから、横サイズがサブμｍ〜μｍのナノシートでは基板表面を隙間なく被覆することは困難であることが分かる。
また、超音波処理後のチタニア超薄膜では吸光度は０．０６であり、図２および表１から、重複被覆部とともに基板表面の被覆率も減少していることから、横サイズがサブμｍ〜μｍのチタニアナノシートでは超音波処理より、重複被覆部の除去と同時にナノシートの脱離が生じており、本発明の効果は得られないことが確認された。
【００２０】
比較例２；
超音波処理時にｍｉｌｌｉ−Ｑ純水（ｐＨ６．５）に浸漬した以外は実施例１と同様に行い、チタニア超薄膜を作製した。超音波処理前後のチタニア超薄膜のＡＦＭ表面観察像を図３（ａ）および（ｂ）に示す。
表２から超音波処理前後の吸光度は各々０．２８と０．２７でほとんど変化しておらず、また、図３のＡＦＭ表面観察像においてもナノシートの累積状態はほとんど変化していないことから、ｍｉｌｌｉ−Ｑ純水中で超音波処理をした場合は、ナノシートの重複被覆部の除去に効果がないことが確認された。
【００２１】
【表１】
【表２】
【発明の効果】
ｎｍレベルで膜厚制御された緻密で高品質なチタニアナノシート超薄膜は、各種用途、例えば光触媒、紫外線カットコーティング、光電変換素子、フォトクロミック材料、センサー等多岐にわたる用途に供され、優れた作用効果を奏するものと期待されている。本発明は、このように各種技術分野から期待されているチタニアナノシート超薄膜を、従来のように特殊な装置を使用することなく極めて簡便な手段に基づいて高品質で提供することを可能とするものであり、これによって極めて品質の高いチタニアナノシート超薄膜を、簡単に、時間にも、費用的にも大幅にダウンを図ることを可能としたことに加え、大型化を可能とし、また複雑形状体に対しても対応できる超薄膜の形成を可能とするものであり、これまでのものに比して際だった品質、形態のものを実現、提供したものであって、その技術的意義は、極めて大きい。その結果、今後、各種技術分野の発展に大いに貢献し、寄与するものと期待される。
【図面の簡単な説明】
【図１】（ａ） 超音波処理前の実施例１のチタニア超薄膜のＡＦＭ像
（ｂ） 超音波処理後の実施例１のチタニア超薄膜のＡＦＭ像
【図２】（ａ） 超音波処理前の比較例１のチタニア超薄膜のＡＦＭ像
（ｂ） 超音波処理後の比較例１のチタニア超薄膜のＡＦＭ像
【図３】（ａ） 超音波処理前の比較例２のチタニア超薄膜のＡＦＭ像
（ｂ） 超音波処理後の比較例２のチタニア超薄膜のＡＦＭ像[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention can be used for a photocatalytic thin film or an ultraviolet blocking coating, and can be expected to be used for a photoelectric conversion thin film, a photochromic material, various sensors, and the like. It relates to the manufacturing method.
[0002]
[Prior art]
Generally, as a method for obtaining a titanium oxide thin film, a vapor phase growth method such as molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD), or dipping a titania sol obtained by hydrolyzing a titanium compound such as a titanium alkoxide. There is known a method of coating the substrate surface by spin coating or spin coating.
In the former method, a high-quality thin film whose film thickness is controlled at the sub-nm level can be obtained, but it requires expensive and special equipment such as high vacuum equipment, and it takes a long time to produce the thin film. There was a problem in cost, work efficiency, and the like. In contrast, the latter method does not require special equipment, is easy to operate, and can produce a titanium oxide thin film at low cost. It was extremely difficult to control the film thickness and film quality at the level.
[0003]
On the other hand, a method completely different from these methods has been proposed. That is, a method of obtaining an ultrathin titania thin film by accumulating on the substrate surface by alternately adsorbing titania nanosheets obtained by exfoliating the layered titanium oxide with an organic polymer has been proposed (Non-Patent Document 1). It is possible to produce an ultra-thin titania film whose film thickness is controlled in the sub-nm to nm range by a simple method without using it. These titania ultrathin films are prepared by an alternate lamination method as disclosed in the prior art “Titania ultrathin film and a method for producing the same” (Patent Document 1) or a Langmuir-Blodgett film forming method. It is possible to do.
[0004]
However, in the ultra-thin titania thin film produced by these means, since a nanosheet derived from a powder sample having a sub-μm to μm lateral size is usually used, it is difficult to coat the substrate surface without gaps with a nanosheet of this size. In addition, there is a drawback that overlapping coating between nanosheets cannot be avoided (Non-Patent Document 1), and therefore, there has been a problem in various application developments.
[0005]
[Non-Patent Document 1] Sasaki et. al, Chem. Mat, 13 (2001) 4661
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-270022
[Problems to be solved by the invention]
An object of the present invention is to provide a high-grade titania ultra-thin film having very little overlapping coating, in which nanometer-sized titania nanosheets having a thickness of about 1 nm and a horizontal size of 1 μm to 1 mm are accumulated without gaps, and a method for producing the same.
[0007]
[Means for Solving the Problems]
Therefore, the present inventors have conducted intensive studies on the above-mentioned problems, and as a result, by using titania nanosheets having a lateral size of 1 μm to 1 mm for alternate lamination with a polymer, the titania nanosheet in which the substrate surface is covered with nanosheets without gaps is used. It is possible to produce a thin film, and the obtained thin film is subjected to ultrasonic treatment in an aqueous solution having a pH of 9 or more containing a basic substance such as an alkali hydroxide, an amine, or an ammonium salt, so that a nanosheet is obtained. It has been found that the overlapping covering portion can be removed, and the present invention has been accomplished based on these findings. That is, the present invention relates to an ultrathin titania thin film in which titania nanosheets having a thickness of about 1 nm and a horizontal size of 1 μm to 1 mm are accumulated without gaps, and in which the number of overlapping coatings is extremely small, and a method for producing the same. It consists of the following items.
[0008]
(1) The method is characterized in that flake particles (nanosheets) obtained by peeling a layered titanium oxide single crystal are coated on the substrate surface without gaps, and that overlap of flake particles is removed and reduced. Ultra thin film of titania.
(2) The titania ultrathin film according to the above (1), wherein the flake particles are nanosheets having a particle size of about 1 nm in thickness and 1 μm to 1 mm in lateral size.
(3) thin piece particles formula Ti 1-delta O.D. 2 titania nanosheet represented by (0 <δ <0.5) or Ti 1-x / 2n M x / 2n O 2 [M, is, Li, Mg , Fe, Ni, Zn, Co, Cr, Mn, Cu, Al, at least one metal selected from the group consisting of n and (n = (4-M average valence), 0.5 ≦ x ≦ 1] The ultrathin titania thin film according to the above (1) or (2), characterized in that it is a nanosheet containing titania as a main component.
(4) The layered titanium oxide single crystal is peeled to obtain flake particles (nanosheets), which are coated on the substrate without gaps, and then subjected to a process of removing and reducing the overlapping portions of the flake particles. A method for producing an ultra-thin titania thin film, characterized by obtaining an ultra-thin titania thin film in which overlapping portions of (i) are removed and reduced.
(5) The method for producing an ultrathin titania thin film according to the above (4), wherein the flake particles are nanosheets having a particle size of about 1 nm in thickness and 1 μm to 1 mm in lateral size.
(6) The flake particles are titania nanosheets represented by the composition formula Ti 1- δO 2 (0 <δ <0.5) or Ti 1-x / 2n M x / 2n O 2 [M is Li, Mg , Fe, Ni, Zn, Co, Cr, Mn, Cu, Al, at least one metal selected from the group consisting of n and (n = (4-M average valence), 0.5 ≦ x ≦ 1] The ultra-thin titania thin film production method according to the above (4) or (5), characterized in that it is a nanosheet containing titania as a main component.
(7) The means for coating the flake particles on the substrate without gaps is such that the nanosheet colloid solution in which the flake particles are suspended after the substrate is immersed in the cationic organic polymer solution to adsorb the organic polymer on the substrate surface The titania according to any one of claims 4 to 6, wherein the titania is obtained by a process of self-organizingly adsorbing the flaky particles on the substrate by electrostatic action by immersing the titania in the titania. Ultra thin film manufacturing method.
(8) The treatment means for removing and reducing the overlapping portion between the flake particles is performed by ultrasonic treatment in an alkaline aqueous solution, according to any one of (4) to (6). Of producing ultra-thin titania film.
(9) The method for producing a titania ultrathin film according to the above item (8), wherein the alkaline aqueous solution is an alkaline solution having a pH adjusted to 9 or more.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The starting titania nanosheet for forming the titania ultrathin film of the present invention has a thickness of nm level and a lateral size of 1 μm to 1 mm, preferably 10 μm or more.
When an ultrathin film is produced using this laterally sized nanosheet, an ultrathin film that almost completely covers the substrate surface can be obtained, although the nanosheets often overlap each other. It is not preferable to use a nanosheet having a lateral size of 1 μm or less, because a gap is generated between the nanosheets and the coverage of the substrate surface is reduced.
[0010]
This titania nanosheet can be obtained by subjecting a titanium oxide single crystal having a layered structure having a particle diameter of 1 μm to 1 mm to a special chemical reaction treatment described later. Here, the layered titanic oxide, lepidocrocite type titanate [A x Ti 2-x / n M x / n O 4, where, A is, K, Rb, 1 or consisting of Cs or two The above alkali metal, M is □ (vacancy) or one or more metals composed of Li, Mg, Fe, Ni, Zn, Co, Cr, Mn, Cu, Al, and n is (4-M Average valence) or 4 (when M is a void □), 0.5 ≦ x ≦ 1], trititanate such as Na 2 Ti 3 O 7 , K 2 Ti 4 O 9, etc. Examples thereof include tetratitanate and pentatitanate such as Cs 2 Ti 5 O 11. In short, a layer titanate composed of a host layer containing titanium oxide as a main component may be used. It is not done. As a starting material for the titania nanosheet, a single crystal sample having a particle diameter of 1 μm to 1 mm, preferably 10 μm to 1 mm, prepared by a method such as a flux method or a melting method of these compounds is used.
[0011]
Here, the special chemical reaction treatment refers to “titanic acid having an orthorhombic layered structure and a method for producing the same” (Patent Document 2) and “simple composition represented by composition formula H 2 Ti 5 O 11 .nH 2 O”. Compounds having a layered structure of a clinic structure and a method for producing the same "(Patent Document 3) and an acid treatment disclosed in" Titania sol and a method for producing the same "(Patent Document 4). It is. That is, an acid treatment is performed on the layered titanium oxide single crystal to replace the alkali metal ions between the layers with hydrogen ions to produce a hydrogen-type substance, and react the hydrogen-type substance with a basic substance such as an amine in an aqueous solution. This makes it possible to obtain a titania nanosheet sol solution in which the host layers constituting the layer structure are exfoliated one by one into colloids. Thereby, a large nanosheet having a size of 1 μm to 1 mm is obtained.
[0012]
[Patent Document 2] Japanese Patent Publication No. 6-88786 [Patent Document 3] Japanese Patent Publication No. 6-78166 [Patent Document 4] Japanese Patent Application Laid-Open No. 9-25123
The titania ultrathin film using these titania nanosheets is produced by applying the means by the film manufacturing process by the alternate lamination method disclosed in Patent Document 1 (“Titania ultrathin film and its manufacturing method”). In this ultra-thin titania thin film, it is possible to coat the substrate surface without gaps by using the large nanosheets described above, but there are many overlapping portions of the nanosheets on the substrate surface. As a result of intensive research to solve this, it has been found that by subjecting the substrate coated with the ultra-thin film to ultrasonic treatment in an alkaline aqueous solution, it is possible to sufficiently remove the overlapping coating portion of the nanosheet. Things.
The principle can be explained as follows. In other words, in the titania ultrathin film obtained by this alternate lamination method, the titania nanosheets having negative charges are accumulated in combination with the polymer having positive charges, and the nanosheets accumulated on the substrate surface are between the polymer and the polymer. Although it is relatively strongly adsorbed on the substrate surface due to the working electrostatic effect, the nanosheet has a negative charge at the part where the nanosheet overlaps another nanosheet, so the repulsive force acts due to the negative charge, so the adhesion is weak It is thought that it has become. When an ultrathin film with such an overlapping portion is subjected to ultrasonic treatment in an alkaline aqueous solution, the cavitation generated in the alkaline aqueous solution removes the overlapping coating portion of the nanosheets in the aqueous solution, but the accumulated effect on the substrate surface is reduced. The removed portion remains without being removed because of strong attraction to the substrate surface.
[0014]
By removing the overlapped portion of the nanosheet by performing the specific treatment in this way, a high-grade titania ultrathin film in which the substrate surface is covered with a single-layer nanosheet without gaps can be obtained. The components of the aqueous alkali solution used in this study include, for example, amines, ammonium, and alkali metal hydroxides, but are not particularly limited to specific components. The pH of the alkaline aqueous solution is pH 9 or more, preferably
[0015]
In addition, the ultrasonic treatment method is not particularly limited in its treatment means, in other words, any method can be used as long as the resulting cavitation effect can be obtained, for example, generally commercially available ultrasonic cleaners and the like used Can be used. There is no particular limitation on the frequency of the ultrasonic wave to be applied, but any frequency may be used as long as cavitation occurs. Preferably it is 20 Hz or more. Since the output of the ultrasonic wave affects the amount of cavitation, if it is too high, the nanosheets accumulated on the substrate surface may be detached or damaged. The ultrasonic irradiation time is desirably 1 minute or more.
[0016]
【Example】
Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to these examples.
[0017]
Example 1;
Potassium carbonate, lithium carbonate, titanium oxide and molybdenum trioxide are mixed in a molar ratio of 1.67: 0.13: 1.73: 1.27, and calcined at 1200 ° C. for 10 hours, then every hour until 950 ° The solution was gradually cooled at a rate of 4 ° C., potassium molybdate as a flux component was removed in pure water, and air-dried, and lithium potassium titanate (K x Ti 2-x / 3 Li x / 3 O 4 , xｘ 0.8) A single crystal (layered compound) was obtained.
30 g of this single crystal was subjected to an acid treatment at room temperature in 2 dm 3 of a 0.5 N hydrochloric acid solution. It replaced hydrochloric acid solution each day, after 5 days reaction, filtered and layered titanate crystal size of dried overnight air 100μm~2mm (H 1.07 Ti 1.73 O 4 · 1. 2H 2 O).
To 0.4 g of the layered titanium oxide crystal was added 100 cm 3 of a 0.4 wt% aqueous solution of tetrabutylammonium hydroxide (hereinafter, referred to as TBAOH), and the mixture was allowed to react at room temperature for 2 weeks and left milky white. Was prepared. Observation of this sol with a TEM confirmed that a rectangular nanosheet having a long side of about 70 μm and a short side of about 20 μm was obtained. The sol was diluted 50-fold to prepare a titania sol solution adjusted to pH 9. Further, NaCl in an amount equivalent to 0.5 moldm -3 was added to 100 cm 3 of 2 wt% polydiallyldimethylammonium chloride; polydiallyldimethylammonium chloride solution (hereinafter referred to as PDDA solution) to adjust the pH to 9.
A 5 cm × 1 cm strip-shaped Si wafer and a quartz glass plate were immersed in a solution of hydrochloric acid: methanol = 1: 1 for 20 minutes, and then immersed in concentrated sulfuric acid for 20 minutes to perform a hydrophilic treatment. After immersing this substrate in the PDDA solution for 20 minutes, thoroughly washing with Milli-Q pure water, immersing in the stirred titania sol solution, and after 20 minutes, sufficiently washing with Milli-Q pure water, A nitrogen stream was blown and dried to produce a titania ultrathin film. While immersing the obtained ultrathin film in a TBAOH aqueous solution having a pH of 11, an ultrasonic cleaning tank (42 kHz, 90W, 1510J-DTH; model name, manufactured by Branson Business Headquarters, Emerson Japan Ltd.) for 10 minutes of ultrasonic wave Processing was performed. FIG. 1 shows an atomic force microscope (AFM) surface observation image of the ultrathin titania thin film thus obtained before and after the ultrasonic treatment, and FIG. 1 shows the coverage ratio of the substrate surface analyzed from the AFM surface observation image and the overlapping coating portion. Table 1 shows the area ratio. From FIG. 1 and Table 1, it can be seen that before the ultrasonic treatment, the substrate surface is covered with the nanosheets without any gaps, and the nanosheets have very many overlapping coatings. Was obtained. The thickness of the titania ultrathin film obtained from the AFM observation image is about 1 nm, which is almost equal to the thickness of one single-layer nanosheet.
In addition, the accumulated amount of titania nanosheets on the substrate surface can be confirmed by absorbance at 265 nm by ultraviolet-visible absorption spectroscopy (Non-Patent Document 2), and it is assumed that a single-layer nanosheet completely covers the substrate surface. The absorbance in this case is about 0.11.
As shown in Table 2, the absorbance of the ultrathin titania film before sonication is 0.27, which confirms that the nanosheets have a very large number of overlapping coatings. It was found that the removal of the overlapping covering part was advanced. From the change in absorbance and the AFM surface observation image as described above, it was confirmed that a dense ultrathin titania thin film composed of a single-layer nanosheet from which the overlapping coating was almost completely removed was obtained.
[0018]
[Non-Patent Document 2] Sasaki, M .; Watanabe, J .; Am. Chem. Soc, 120, 4682 (1998)
[0019]
Comparative Example 1;
An ultrathin titania thin film was prepared in the same manner as in Example 1, except that the lateral size of the titania nanosheet was sub-μm to μm. FIGS. 2A and 2B show AFM surface observation images of the ultrathin titania thin film before and after the ultrasonic treatment.
From the absorbance, nanosheets that can completely cover the substrate surface are accumulated in the ultrathin titania thin film before the ultrasonic treatment (Table 2), but the gap between the titania nanosheets in the ultrathin titania thin film is observed from the AFM surface observation image. Since the coverage of the substrate surface is 81% (Table 1), it can be seen that it is difficult to cover the substrate surface without gaps with a nanosheet having a lateral size of sub μm to μm.
In addition, the absorbance of the ultrathin titania film after the ultrasonic treatment was 0.06, and from FIG. 2 and Table 1, since the coverage of the substrate surface was reduced together with the overlapped coating, the lateral size was sub-μm to μm. In the titania nanosheet, the nanosheet was detached simultaneously with the removal of the overlapped coating portion by the ultrasonic treatment, and it was confirmed that the effect of the present invention was not obtained.
[0020]
Comparative Example 2;
An ultrathin titania thin film was prepared in the same manner as in Example 1 except that the substrate was immersed in milli-Q pure water (pH 6.5) during the ultrasonic treatment. FIGS. 3A and 3B show AFM surface observation images of the ultrathin titania thin film before and after the ultrasonic treatment.
From Table 2, the absorbances before and after the ultrasonic treatment hardly changed at 0.28 and 0.27, respectively, and the accumulated state of the nanosheets hardly changed in the AFM surface observation image in FIG. It was confirmed that when ultrasonic treatment was performed in milli-Q pure water, there was no effect in removing the overlapped portion of the nanosheet.
[0021]
[Table 1]
[Table 2]
【The invention's effect】
Dense and high-quality titania nanosheet ultra-thin films with controlled film thickness at the nm level are used in a wide variety of applications such as photocatalysts, UV cut coatings, photoelectric conversion devices, photochromic materials, sensors, etc. It is expected to play. The present invention makes it possible to provide a titania nanosheet ultrathin film expected from various technical fields in high quality based on extremely simple means without using a special device as in the past. In addition to making it possible to significantly reduce the quality of ultra-high-quality titania nanosheet thin films easily, in terms of time and cost, it is also possible to increase the size and form It enables the formation of ultra-thin films that can be applied to the body, and realizes and provides products of outstanding quality and form compared to the past, and its technical significance is , Extremely large. As a result, it is expected to greatly contribute to the development of various technical fields in the future.
[Brief description of the drawings]
FIG. 1 (a) AFM image of ultrathin titania film of Example 1 before ultrasonic treatment (b) AFM image of ultrathin titania film of Example 1 after ultrasonic treatment FIG. 2 (a) Ultrasonic treatment AFM image of ultra-thin titania film of Comparative Example 1 before (b) AFM image of ultra-thin titania film of Comparative Example 1 after ultrasonic treatment [FIG. 3 (a)] AFM image of ultra-thin titania film of Comparative Example 2 before ultrasonic treatment AFM image (b) AFM image of ultra-thin titania film of Comparative Example 2 after ultrasonic treatment
Claims (9)
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| Publication number | Priority date | Publication date | Assignee | Title |
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