JP3793806B2 - Layered restructured aggregate of layered compound nanosheet and method for producing the same - Google Patents
Layered restructured aggregate of layered compound nanosheet and method for producing the same Download PDFInfo
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- JP3793806B2 JP3793806B2 JP2002062474A JP2002062474A JP3793806B2 JP 3793806 B2 JP3793806 B2 JP 3793806B2 JP 2002062474 A JP2002062474 A JP 2002062474A JP 2002062474 A JP2002062474 A JP 2002062474A JP 3793806 B2 JP3793806 B2 JP 3793806B2
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- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 239000002135 nanosheet Substances 0.000 title description 49
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- 239000010955 niobium Substances 0.000 claims description 33
- 150000001768 cations Chemical class 0.000 claims description 28
- 239000000243 solution Substances 0.000 claims description 28
- 239000001257 hydrogen Substances 0.000 claims description 26
- 229910052707 ruthenium Inorganic materials 0.000 claims description 26
- 229910052758 niobium Inorganic materials 0.000 claims description 24
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 24
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 23
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- 229910021645 metal ion Inorganic materials 0.000 claims description 19
- 239000007864 aqueous solution Substances 0.000 claims description 18
- 239000010410 layer Substances 0.000 claims description 18
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- 239000002245 particle Substances 0.000 claims description 17
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- 229910052759 nickel Inorganic materials 0.000 claims description 14
- 229910052700 potassium Inorganic materials 0.000 claims description 13
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- 229910052741 iridium Inorganic materials 0.000 claims description 10
- 229910052697 platinum Inorganic materials 0.000 claims description 10
- 229910052802 copper Inorganic materials 0.000 claims description 9
- 229910052744 lithium Inorganic materials 0.000 claims description 9
- 239000013078 crystal Substances 0.000 claims description 7
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- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 16
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 14
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 12
- 229910001414 potassium ion Inorganic materials 0.000 description 11
- 239000000843 powder Substances 0.000 description 10
- GOOXRYWLNNXLFL-UHFFFAOYSA-H azane oxygen(2-) ruthenium(3+) ruthenium(4+) hexachloride Chemical compound N.N.N.N.N.N.N.N.N.N.N.N.N.N.[O--].[O--].[Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[Cl-].[Ru+3].[Ru+3].[Ru+4] GOOXRYWLNNXLFL-UHFFFAOYSA-H 0.000 description 7
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- 238000002441 X-ray diffraction Methods 0.000 description 6
- 239000001103 potassium chloride Substances 0.000 description 6
- 235000011164 potassium chloride Nutrition 0.000 description 6
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- 239000000084 colloidal system Substances 0.000 description 4
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- 229910052753 mercury Inorganic materials 0.000 description 4
- 229910052701 rubidium Inorganic materials 0.000 description 4
- VDZOOKBUILJEDG-UHFFFAOYSA-M tetrabutylammonium hydroxide Chemical compound [OH-].CCCC[N+](CCCC)(CCCC)CCCC VDZOOKBUILJEDG-UHFFFAOYSA-M 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
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- 238000003756 stirring Methods 0.000 description 3
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- 229910021586 Nickel(II) chloride Inorganic materials 0.000 description 2
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- 239000012298 atmosphere Substances 0.000 description 2
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- QMMRZOWCJAIUJA-UHFFFAOYSA-L nickel dichloride Chemical compound Cl[Ni]Cl QMMRZOWCJAIUJA-UHFFFAOYSA-L 0.000 description 2
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- 239000002253 acid Substances 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
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- 229910052783 alkali metal Inorganic materials 0.000 description 1
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- 229910052786 argon Inorganic materials 0.000 description 1
- 239000012300 argon atmosphere Substances 0.000 description 1
- 229910001423 beryllium ion Inorganic materials 0.000 description 1
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- FVIZARNDLVOMSU-UHFFFAOYSA-N ginsenoside K Natural products C1CC(C2(CCC3C(C)(C)C(O)CCC3(C)C2CC2O)C)(C)C2C1C(C)(CCC=C(C)C)OC1OC(CO)C(O)C(O)C1O FVIZARNDLVOMSU-UHFFFAOYSA-N 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
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- 238000011068 loading method Methods 0.000 description 1
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- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(iv) oxide Chemical compound O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
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- 229910052725 zinc Inorganic materials 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
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- Inorganic Compounds Of Heavy Metals (AREA)
- Oxygen, Ozone, And Oxides In General (AREA)
- Catalysts (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、様々な層状化合物微結晶を剥離して得られる薄片粒子（以下、ナノシートと呼ぶ）を１価または多価の陽イオンにより層状化合物を再構築した凝集体、該凝集体の製造方法、および該凝集体の触媒、特に光触媒としての利用に関する。
【０００２】
【従来の技術】
ニッケル酸化物を担持した層状化合物Ｋ4Ｎｂ6Ｏ17は水を分解して水素を発生する光触媒として知られている。また、アルカリ金属元素と５Ａ族元素からなる層状化合物をゲル化反応により形成し、熱処理して粉砕して得られた粉末にＮｉ，Ｐｔ，Ｉｒ，Ｒｕまたはそれらの酸化物を０．１〜５重量％担持させる光触媒の製造方法が知られている（特開平１０−９９６９４号公報、特開平１０−１６５８２０号公報）。
【０００３】
【発明が解決しようとする課題】
従来、層状化合物を剥離し、ナノシート化することは知られていたが、このナノシートを用いた用途としては多層薄膜の製造に限られていた。ナノシートを用いて高比表面積、多孔質の層状凝集体に構築する例はほとんどない。さらに、２成分以上のイオンを制御して層間に導入する技術という切り口で見た場合、通常、一般的に行われている水溶液あるいは溶融塩による方法ではイオンに制限があるとともに制御性も充分ではない。また、水の光分解触媒としてルテニウムを担持する方法は含浸法などの方法があるが、分散性の制御が困難である。
【０００４】
【課題を解決するための手段】
本発明者らは、層状化合物を剥離したナノシートを再構築した凝集体からなる層状化合物により従来のものよりも高効率、高活性化した触媒、特に光触媒が得られることを見出した。
【０００５】
すなわち、本発明は、（１）ニオブ系層状ペロブスカイト型複合酸化物またはチタン系層状酸化物の微結晶を剥離して得られる薄片粒子を、層間に入ったＨ，Ｌｉ，Ｎａ，Ｋから選ばれる陽イオンによって層状再構築したことを特徴とする層状再構築凝集体である。
また、本発明は、（２）Ｃｏ，Ｎｉ，Ｃｕ，Ｒｕ，Ｉｒ，Ｐｔからなる群から選ばれる少なくとも１種の金属イオンを前記陽イオンと共存させたことを特徴とする上記の層状再構築凝集体、である。
また、本発明は、（３）上記（２）の層状再構築凝集体を焼成して得られる層間に金属酸化物を含有することを特徴とする層状再構築凝集体である。
また、本発明は、（４）光照射下で水から水素および酸素あるいは少なくとも水素を生成する光触媒能を有することを特徴とする上記（１）ないし（３）のいずれかの層状再構築凝集体である。
【０００６】
さらに、本発明は、（５）ニオブ系層状ペロブスカイト型複合酸化物またはチタン系層状酸化物の微結晶を剥離して得られる薄片粒子が分散したコロイド溶液を薄片粒子の全電荷数よりも過剰のＨ，Ｌｉ，Ｎａ，Ｋから選ばれる陽イオンを含む水溶液と混合して、薄片粒子と陽イオンが層状に積層した凝集体を得ることを特徴とする再構築凝集体の製造方法である。
【０００７】
また、本発明は、（６）ニオブ系層状ペロブスカイト型複合酸化物またはチタン系層状酸化物の微結晶を剥離して得られる薄片粒子が分散したコロイド溶液をＣｏ，Ｎｉ，Ｃｕ，Ｒｕ，Ｉｒ，Ｐｔからなる群から選ばれる少なくとも１種の金属イオンとＨ，Ｌｉ，Ｎａ，Ｋから選ばれる陽イオンとを含む水溶液と混合して、該薄片粒子と該金属イオンおよび該陽イオンが層状に積層した凝集体を得ることを特徴とする層状再構築凝集体の製造方法である。
【０００８】
また、本発明は、（７）ニオブ系層状ペロブスカイト型複合酸化物またはチタン系層状酸化物の微結晶を剥離して得られる薄片粒子が分散したコロイド溶液をＣｏ，Ｎｉ，Ｃｕ，Ｒｕ，Ｉｒ，Ｐｔからなる群から選ばれる少なくとも１種の金属イオンとＨ，Ｌｉ，Ｎａ，Ｋから選ばれる陽イオンとを含む水溶液と混合して、該薄片粒子と該金属イオンおよび該陽イオンが層状に積層した凝集体を得た後、該凝集体を焼成して金属酸化物を層間に形成することを特徴とする層状再構築凝集体の製造方法である。
【０００９】
本発明は、ナノシートを１価または多価の陽イオン水溶液で層状化合物に再構築すること、また、再構築した層状化合物を触媒あるいは光触媒反応に利用することを特徴とする。
本発明により、ナノシートの新たな物性の付加、高比表面積化した層状化合物の合成ができる。また、従来、イオン交換できなかった層間内へのイオンの挿入ができる。また、層状化合物微結晶の剥離−再構築によって生成された当該層状化合物は、通常のバルク結晶からなる粉体と比較して高比表面積化するため、触媒、光触媒、または吸着剤としての利用において、さらなる高効率化が可能となる。
【００１０】
【発明の実施の形態】
ナノシートの原料となるニオブ系層状ペロブスカイト型複合酸化物は、組成式ＡＭ2Ｎｂ3Ｏ10（ここで、Ａ＝Ｋ,Ｒｂ,Ｃｓ；Ｍ＝Ｃａ,Ｓｒ,Ｂａ,Ｐｂ,Ｂｉ）、Ａ1-xＭ2-xＭ'xＮｂ3Ｏ10（ここで、Ａ＝Ｋ,Ｒｂ,Ｃｓ；Ｍ＝Ｃａ,Ｓｒ,Ｂａ,Ｐｂ,Ｂｉ；Ｍ'＝ランタノイド元素）、またはチタン系層状酸化物ＡＭＴｉＯ4（ここで、Ａ＝Ｎａ,Ｋ,Ｒｂ,Ｃｓ；Ｍ＝Ｍｎ,Ｃｏなどの遷移金属化合物）などで表せるもので、これを塩酸、硝酸等の酸溶液の中でイオン交換することにより層間内のＡを水素イオンに置換後、適当なアルキルアンモニウムイオンなどの水溶液中で振盪して単層剥離することでナノシートとする。
【００１１】
このナノシートを分散したコロイド溶液（以下ナノシート溶液という）をナノシートの全電荷数よりも過剰の１価あるいは多価の陽イオンを含む水溶液と混合すると凝集物が生成する。１価あるいは多価の陽イオンとしては、Ｈ，Ｌｉ，Ｎａ，Ｋ，Ｒｂ，Ｃｓ，Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ，Ｒｕ，Ｉｒ，Ｐｔが挙げられる。陽イオンを過剰とすることにより、全てのナノシートは凝集し、沈殿物となる。
【００１２】
この時、過剰の１価あるいは多価の陽イオンを含む水溶液にナノシート溶液を１ｃｍ3／ｍｉｎ程度でゆっくりと滴下すると、粉末Ｘ線回折により底面反射系列が出現し層状構造が構築されたと考えられる凝集体を回収することができる。
この時、この層状化合物の層間には１価あるいは多価の陽イオンが理論値の９０％以上入り、従来のイオン交換法では困難であった２価以上の陽イオンが層間内に存在するニオブ系層状ペロブスカイト型複合酸化物もこの手法により得ることができる。また、これによって得られた層状化合物はナノシート化する前のバルク体の比表面積１〜３ｍ2／ｇに比べて、２０〜３０ｍ2／ｇと１０倍以上の高比表面積となる。
【００１３】
２種類以上のナノシート溶液を混合して再構築を行っても層状化合物凝集体が得られる。この時の再構築凝集体は複数のナノシートがランダムに層状構造を形成するよりは同種類のナノシートが数層再積層し、その種々の再積層体がさらに凝集した２次粒子になった。すなわち、ニオブ系層状ペロブスカイトのナノシートのみでは、図１ａに示す層間距離１．６５ｎｍを有する層状再構築凝集体が得られ、チタン酸化物のナノシートのみから再構築した場合は、図１の（ｄ）に示す層間距離０．８３ｎｍの層状再構築凝集体が得られた。
【００１４】
これらの層間距離は出発原料のバルク体の層状化合物の層間距離と非常に近い値を示しているため層状再構築凝集体が得られたことを表している。また、ニオブ系、チタン系のナノシートを同時に再構築した凝集体のＸ線回折パターンは図１の（ｂ）、（ｃ）に見られるように、ニオブ系の層状再構築凝集体とチタン系の層状再構築凝集体が混合したピークを与えている。
【００１５】
再構築する際に、溶液中に、Ｃｏ，Ｎｉ，Ｃｕ，Ｒｕ，Ｉｒ，Ｐｔからなる群から選ばれる少なくとも１種の金属イオンとこれら以外の、ナノシートに比較して過剰に存在するＮａ，Ｋなどの陽イオンとを組み合わせて、溶液中にナノシートに比べて１０重量％以下のＲｕ、Ｎｉなどの金属イオンを共存させた場合も、同様に層状化合物を再構築することができる。この時、少量の金属イオンはイオン価数が２価以上で、過剰に存在する陽イオンが１価の場合は少量の金属イオンがより優先的に層間に取り込まれた層状化合物凝集体となる。
【００１６】
例えば、ルテニウムレッドあるいは塩化ルテニウムを溶液に添加することによってルテニウム金属イオンをナノシートから再構築された凝集体に含有させた場合、水を水素と酸素に分解する光触媒活性がある。
【００１７】
過剰量の塩化カリウムとナノシートの１重量％に当たるルテニウムレッドを含む水溶液にＣａ2Ｎｂ3Ｏ10のナノシート溶液を滴下して得られた層状再構築凝集体０．３ｇを純水３００ｍｌ中に懸濁してアルゴン雰囲気下で４５０Ｗ高圧水銀灯で光照射したところ、水素を２７μｍｏｌ／ｈ、酸素を８．５μｍｏｌ／ｈの割合で発生した。ルテニウムレッドを用いないで再構築した凝集体で同様な水分解の光触媒反応を行うと、水素のみが７．１μｍｏｌ／ｈの割合で発生するのみだった。
【００１８】
このように、溶液中に、Ｃｏ，Ｎｉ，Ｃｕ，Ｒｕ，Ｉｒ，Ｐｔからなる群から選ばれる少なくとも１種の金属イオンとこれら以外の陽イオンを組み合わせて形成した層状再構築凝集体は、１００℃〜６００℃で１０分〜数時間空気中で加熱しても層状構造を維持しており、添加した金属イオンを酸化物に変化させることができる。例えば、ルテニウムレッドを含む層状再構築凝集体を空気中５００℃で１時間 焼成してルテニウム酸化物（ＲｕＯ2）を形成したものを用いて、水の光分解反応を行うと分解速度が上昇し、水素が４８μｍｏｌ／ｈ、酸素が２３μｍｏｌ／ｈの割合で発生し、水素／酸素比が２となる水の全分解反応が進行した。
【００１９】
その他のアルカリ金属イオン、水素イオンで行った結果を表１（ニオブ系ナノシートと陽イオン、ルテニウムからなる層状再構築凝集体Ａ−Ｃａ2Ｎｂ3Ｏ10の紫外光照射による純水からの水素および酸素生成速度。ルテニウム担持量はルテニウムレッドとして１重量％。）に示す。また、ルテニウム以外の金属イオン、例えば塩化ニッケルを使用した場合も、水素と酸素に分解する光触媒能があった（水素２１μｍｏｌ／ｈ、酸素４μｍｏｌ／ｈ）。
【００２０】
【表１】
これらから、再構築を行う際に凝集体にルテニウムを含有させること、さらに焼成によってルテニウムを酸化させることにより水素と酸素の発生量を増大させることができることが明らかである。また、複数のナノシートで層状再構築凝集体の作製を行った時でも、ルテニウムを少量加えた凝集体が水の光分解において水素と酸素を２：１で発生させる全分解反応に有効であることが分かった。
【００２２】
Ｃａ2Ｎｂ3Ｏ10とＴｉ1.825□0.175Ｏ4（□は八面体の空孔）とを過剰量の塩化カリウムと１重量％の塩化ルテニウムで層状再構築凝集体とし、空気中５００℃で焼成した後での水の光分解における水素および酸素の生成速度を表２（ルテニウムを担持したニオブ系ナノシート、チタン系ナノシートおよびこれらの混合ナノシートから得られた層状再構築凝集体の紫外光照射による純水からの水素および酸素生成速度。比は重量比。）に示す。表２に示すとおり、どのような混合比でも水素と酸素は同時に生成している。
【００２３】
【表２】
【実施例】
次に本発明の実施例を示す。
（実施例１）
組成式ＫＣａ2Ｎｂ3Ｏ10で示されるニオブ系層状ペロブスカイト型複合酸化物を酸処理して得られるＨＣａ2Ｎｂ3Ｏ10・１．５Ｈ2Ｏ粉末１．２ｇを水酸化テトラブチルアンモニウム水溶液３００ｃｍ3に加え、室温で１週間程度振盪（１８０ｒｐｍ）し、乳白色のコロイド溶液を得た。
【００２５】
得られたナノシートのコロイド溶液を２ＭのＫＣｌ水溶液３００ｃｍ3に約１ｍ3／ｍｉｎの速度で滴下して生成した凝集物を吸引ろ過し、純水で洗浄後、大気中で風乾して固体粉末を得た。得られたカリウムイオンで再構築した層状化合物からなる凝集体のＸ線回折パターンを図１の（ａ）に示す。
【００２６】
（実施例２）
組成式Ｃｓ0.7Ｔｉ1.825□0.175Ｏ4で示されるチタン系層状酸化物を酸処理して得られるＨ0.7Ｔｉ1.825□0.175Ｏ4・Ｈ2Ｏ粉末１．２ｇを水酸化テトラブチルアンモニウム水溶液３００ｃｍ3に加え、室温で１週間程度振盪（１８０ｒｐｍ）し、乳白色のコロイド溶液を得た。このコロイド溶液１００ｍｌと実施例１で生成したニオブ系酸化物のナノシートのコロイド溶液を２００ｍｌの割合で混合し２種類のナノシートが存在するコロイド溶液を得た。
【００２７】
得られた混合ナノシートのコロイド溶液を２ＭのＫＣｌ水溶液３００ｃｍ3に約１ｃｍ3／ｍｉｎの速度で滴下して生成した凝集物を吸引ろ過し、純水で洗浄後、大気中で風乾して固体粉末を得た。得られたカリウムイオンで再構築した層状化合物からなる凝集体のＸ線回折パターンを図１の（ｂ）に示す。
【００２８】
（実施例３）
実施例２のチタン系ナノシートコロイド溶液１００ｍｌを２００ｍｌに、ニオブ系ナノシートコロイド溶液２００ｍｌを１００ｍｌに代えて使用した他は同じ条件で凝集体を製造した。凝集体のＸ線回折パターンを図１の（ｃ）に示す。
【００２９】
（実施例４）
実施例１のＨＣａ2Ｎｂ3Ｏ10・１．５Ｈ2Ｏに代えてＨ0.7Ｔｉ1.825□0.175Ｏ4・Ｈ2Ｏを使用した他は同じ条件で凝集体を製造した。凝集体のＸ線回折パターンを図１の（ｄ）に示す。
【００３０】
（実施例５）
実施例１で得られた乳白色のニオブ系酸化物のナノシートのコロイド溶液を１２ｍｇのルテニウムレッドが存在する２ｍｏｌ／ｌのＫＣｌ水溶液３００ｃｍ3に約１ｃｍ3／ｍｉｎの速度で滴下して生成した凝集物を吸引ろ過し、純水で洗浄後、大気中で風乾して固体粉末を得た。さらに、この固体粉末を空気中５００℃で１時間焼成した。得られたルテニウムを含有したカリウムイオンで再構築した層状化合物からなる凝集体を純水３００ｍｌと共に石英ガラス製反応管に入れ、閉鎖循環型反応装置に取り付け十分に溶存空気を除いた後、アルゴンガスを１３．３ｋＰａを導入した。
【００３１】
ルテニウムを含有したカリウムイオンで再構築した層状化合物からなる凝集体を十分に撹拌しながら４５０Ｗ高圧水銀灯で光照射して光触媒反応を進行させた。生成したガスを閉鎖循環系に直結したガスクロマトグラフィーによって定性定量した結果、４８μｍｏｌ／ｈで水素が、２３μｍｏｌ／ｈで酸素が発生していることが確認できた。図２に、得られたニオブ系ナノシートからのルテニウムを含有したカリウムイオンで再構築した層状化合物からなる凝集体の水の光分解の経時変化（○：水素、●：酸素）を示す。
【００３２】
（実施例６）
実施例１および実施例２で調製したニオブ系酸化物のコロイド溶液２００ｍｌとチタン系酸化物１００ｍｌの混合ナノシートのコロイド溶液を５．６ｍｇの塩化ルテニウムが存在する２ＭのＫＣｌ水溶液３００ｃｍ3に約１ｃｍ3／ｍｉｎの速度で滴下して生成した凝集物を吸引ろ過し、純水で洗浄後、大気中で風乾して固体粉末を得た。さらに、この固体粉末を空気中５００℃で１時間焼成した。
【００３３】
得られたルテニウムを含有したカリウムイオンで再構築した層状化合物からなる凝集体を純水３００ｍｌと共に石英ガラス製反応管に入れ、閉鎖循環型反応装置に取り付け十分に溶存空気を除いた後、アルゴンガスを１３．３ｋＰａを導入した。
【００３４】
ルテニウムを含有したカリウムイオンで再構築した層状化合物からなる凝集体を十分に撹拌しながら４５０Ｗ高圧水銀灯で光照射して光触媒反応を進行させた。生成したガスを閉鎖循環系に直結したガスクロマトグラフィーによって定性定量した結果、２１μｍｏｌ／ｈで水素が、１０μｍｏｌ／ｈで酸素が発生していることが確認できた。図３に、得られたニオブ系ナノシートとチタン系ナノシート混合系からのルテニウムを含有したカリウムイオンで再構築した層状化合物からなる凝集体の水の光分解の経時変化（○：水素、●：酸素）を示す。
【００３５】
（実施例７）
実施例５のルテニウムレッドに代えて塩化ニッケル２６ｍｇを使用し、空気中で１時間焼成に代えて水素５０ｋＰａ雰囲気下で２時間還元した後、酸素１５ｋＰａ雰囲気下で１時間酸化処理を行った他は同じ条件でニッケルを含有したカリウムイオンで再構築した層状化合物からなる凝集体を製造した。
【００３６】
得られたニッケルを含有したカリウムイオンで再構築した層状化合物からなる凝集体を純水３００ｍｌと共に石英ガラス製反応管に入れ、閉鎖循環型反応装置に取り付け十分に溶存空気を除いた後，アルゴンガスを１３．３ｋＰａを導入した。ニッケルを含有したカリウムイオンで再構築した層状化合物からなる凝集体を十分に撹拌しながら４５０Ｗ高圧水銀灯で光照射して光触媒反応を進行させた。生成したガスを閉鎖循環系に直結したガスクロマトグラフィーによって定性定量した結果、２１μｍｏｌ／ｈで水素が、４ μｍｏｌ／ｈで酸素が発生していることが確認できた。
【図面の簡単な説明】
【図１】ニオブ系ナノシート、チタン系ナノシートおよびこれらの混合ナノシートから得られた層状再構築凝集体のＸ線回折パターン（ａ＝実施例１、ｂ＝実施例２、ｃ＝実施例３、ｄ＝実施例４）を示すグラフである。
【図２】実施例５において得られたニオブ系ナノシートからのルテニウム含有層状再構築凝集体の水の光分解の経時変化を示すグラフである。
【図３】実施例６において得られたニオブ系ナノシートとチタン系ナノシート混合系からのルテニウム含有層状再構築凝集体の水の光分解の経時変化を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aggregate in which lamellar particles obtained by peeling various layered compound microcrystals (hereinafter referred to as nanosheets) are reconstructed with a monovalent or polyvalent cation, and a method for producing the aggregate And the use of the aggregate as a catalyst, particularly as a photocatalyst.
[0002]
[Prior art]
The layered compound K 4 Nb 6 O 17 carrying nickel oxide is known as a photocatalyst that decomposes water to generate hydrogen. In addition, Ni, Pt, Ir, Ru or their oxides are added to a powder obtained by forming a layered compound comprising an alkali metal element and a 5A group element by a gelation reaction, and pulverizing by heat treatment. A method for producing a photocatalyst supported by weight percent is known (Japanese Patent Laid-Open Nos. 10-99694 and 10-165820).
[0003]
[Problems to be solved by the invention]
Conventionally, it has been known that a layered compound is peeled off to form a nanosheet, but the use using the nanosheet has been limited to the production of a multilayer thin film. There are almost no examples of using nanosheets to form porous layered aggregates with a high specific surface area. Furthermore, when viewed from the viewpoint of a technique of controlling ions of two or more components and introducing them between layers, the generally used method using an aqueous solution or molten salt has limited ions and sufficient controllability. Absent. Further, as a method for supporting ruthenium as a photolysis catalyst for water, there is a method such as an impregnation method, but it is difficult to control dispersibility.
[0004]
[Means for Solving the Problems]
The present inventors have found that a highly efficient and highly active catalyst, particularly a photocatalyst, can be obtained by using a layered compound comprising an aggregate obtained by restructuring a nanosheet from which a layered compound has been peeled.
[0005]
That is, the present invention selects (1) flake particles obtained by exfoliating fine crystals of a niobium-based layered perovskite complex oxide or a titanium-based layered oxide from H, Li, Na, and K entering between layers. a layer-like reconstruction aggregates, characterized in that reconstructed layered by cation.
Further, the present invention provides (2) the layered reconstruction described above, wherein at least one metal ion selected from the group consisting of Co, Ni, Cu, Ru, Ir, and Pt coexists with the cation. Agglomerates.
Moreover, this invention is (3) The layered reconstruction aggregate characterized by containing a metal oxide between the layers obtained by baking the layered reconstruction aggregate of said (2) .
The present invention also provides: (4) The layered reconstituted aggregate according to any one of (1) to (3) above, which has a photocatalytic ability to generate hydrogen and oxygen or at least hydrogen from water under light irradiation. It is.
[0006]
Furthermore, the present invention provides (5) a colloidal solution in which flake particles obtained by exfoliating fine crystals of niobium layered perovskite complex oxide or titanium layered oxide are dispersed in excess of the total number of charges of the flake particles . It is a method for producing a reconstructed aggregate characterized in that it is mixed with an aqueous solution containing a cation selected from H, Li, Na, and K to obtain an aggregate in which thin particles and cations are laminated in layers.
[0007]
The present invention also provides (6) a colloidal solution in which flake particles obtained by exfoliating fine crystals of a niobium layered perovskite complex oxide or a titanium layered oxide are dispersed in Co, Ni, Cu, Ru, Ir, Mixing with an aqueous solution containing at least one metal ion selected from the group consisting of Pt and a cation selected from H, Li, Na, K, and laminating the flake particles, the metal ion and the cation in layers It is a method for producing a lamellar restructured aggregate characterized in that the obtained aggregate is obtained.
[0008]
The present invention also provides (7) a colloidal solution in which flake particles obtained by exfoliating fine crystals of a niobium-based layered perovskite complex oxide or a titanium-based layered oxide are dispersed in Co, Ni, Cu, Ru, Ir, Mixing with an aqueous solution containing at least one metal ion selected from the group consisting of Pt and a cation selected from H, Li, Na, K, and laminating the flake particles, the metal ion and the cation in layers After the obtained aggregate is obtained, the aggregate is fired to form a metal oxide between the layers.
[0009]
The present invention is characterized in that the nanosheet is reconstructed into a layered compound with a monovalent or polyvalent cation aqueous solution, and the reconstructed layered compound is used for a catalyst or photocatalytic reaction.
According to the present invention, new physical properties of nanosheets can be added, and a layered compound having a high specific surface area can be synthesized. Further, it is possible to insert ions into the layers that could not be ion exchanged conventionally. In addition, since the layered compound produced by exfoliation-reconstruction of the layered compound microcrystal has a higher specific surface area than a powder composed of ordinary bulk crystals, it can be used as a catalyst, photocatalyst, or adsorbent. Further efficiency improvement is possible.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The niobium layered perovskite complex oxide used as the raw material of the nanosheet has a composition formula AM 2 Nb 3 O 10 (where A = K, Rb, Cs; M = Ca, Sr, Ba, Pb, Bi), A 1. -x M 2-x M 'x Nb 3 O 10 ( where, A = K, Rb, Cs ; M = Ca, Sr, Ba, Pb, Bi; M' = lanthanides), or titanium-based layered oxides AMTiO 4 (where A = Na, K, Rb, Cs; M = transition metal compound such as Mn, Co), etc., and by ion exchange in an acid solution such as hydrochloric acid or nitric acid After substituting A in the layer with hydrogen ions, the layer is shaken in an aqueous solution of an appropriate alkylammonium ion or the like to peel off the monolayer to form a nanosheet.
[0011]
When this colloidal solution in which nanosheets are dispersed (hereinafter referred to as nanosheet solution) is mixed with an aqueous solution containing monovalent or polyvalent cations in excess of the total number of charges of nanosheets, aggregates are formed. Examples of monovalent or polyvalent cations include H, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Fe, Co, Ni, Cu, Zn, Ru, Ir, and Pt. By making the cation excessive, all the nanosheets aggregate and become a precipitate.
[0012]
At this time, when the nanosheet solution was slowly dropped at about 1 cm 3 / min into an aqueous solution containing an excess of monovalent or polyvalent cations, it is considered that a bottom reflection series appeared by powder X-ray diffraction and a layered structure was constructed. Aggregates can be recovered.
At this time, niobium in which monovalent or polyvalent cations enter 90% or more of the theoretical value between the layers of this layered compound, and divalent or more cations that were difficult in the conventional ion exchange method exist in the interlayer. A layered perovskite complex oxide can also be obtained by this method. Moreover, the layered compound obtained by this becomes 20-30 m < 2 > / g and a high specific surface area of 10 times or more compared with the specific surface area 1-3 m < 2 > / g of the bulk body before making a nanosheet.
[0013]
Even when two or more kinds of nanosheet solutions are mixed and reconstructed, a layered compound aggregate can be obtained. The reconstructed aggregates at this time were secondary particles in which several nanosheets formed a layered structure randomly, and several layers of the same kind of nanosheets were restacked, and the various restacked bodies further aggregated. That is, the layered reconstructed aggregate having the interlayer distance of 1.65 nm shown in FIG. 1a is obtained only with the niobium-based layered perovskite nanosheet, and when reconstructed only from the titanium oxide nanosheet, FIG. A layered restructured aggregate having an interlayer distance of 0.83 nm shown in FIG.
[0014]
Since these interlayer distances are very close to the interlayer distance of the layered compound in the bulk material of the starting material, it indicates that a layered restructured aggregate was obtained. In addition, the X-ray diffraction pattern of the aggregate obtained by simultaneously reconstructing the niobium-based and titanium-based nanosheets can be seen in FIGS. 1B and 1C. The layered reconstituted aggregate gives a mixed peak.
[0015]
When reconstructing, at least one metal ion selected from the group consisting of Co, Ni, Cu, Ru, Ir, and Pt in the solution and other Na, K present in excess than the nanosheet other than these. In the case where a metal ion such as Ru or Ni of 10 wt% or less as compared with the nanosheet is coexisted in the solution in combination with cations such as, the layered compound can be similarly reconstructed. At this time, a small amount of metal ions has a ionic valence of 2 or more, and when the excess cation is monovalent, a small amount of metal ions become a layered compound aggregate in which a small amount of metal ions are preferentially taken in between layers.
[0016]
For example, when ruthenium metal ions are contained in an aggregate reconstructed from a nanosheet by adding ruthenium red or ruthenium chloride to a solution, there is a photocatalytic activity for decomposing water into hydrogen and oxygen.
[0017]
Suspended in 300 ml of pure water 0.3 g of layered reconstituted aggregate obtained by dropping a nanosheet solution of Ca 2 Nb 3 O 10 into an aqueous solution containing an excess amount of potassium chloride and ruthenium red equivalent to 1% by weight of the nanosheet. When irradiated with a 450 W high pressure mercury lamp in an argon atmosphere, hydrogen was generated at a rate of 27 μmol / h and oxygen at a rate of 8.5 μmol / h. When a similar water-splitting photocatalytic reaction was performed on the aggregate reconstructed without using ruthenium red, only hydrogen was generated at a rate of 7.1 μmol / h.
[0018]
Thus, the layered reconstituted aggregate formed by combining at least one metal ion selected from the group consisting of Co, Ni, Cu, Ru, Ir, and Pt and a cation other than these in the solution is 100 The layered structure is maintained even when heated in the air at 10 to 600 ° C. for 10 minutes to several hours, and the added metal ions can be changed into oxides. For example, when a layered reconstituted agglomerate containing ruthenium red is fired in air at 500 ° C. for 1 hour to form ruthenium oxide (RuO 2 ) and water is photolyzed, the decomposition rate increases. Hydrogen was generated at a rate of 48 μmol / h and oxygen at a rate of 23 μmol / h, and the total decomposition reaction of water with a hydrogen / oxygen ratio of 2 proceeded.
[0019]
The results obtained with other alkali metal ions and hydrogen ions are shown in Table 1 (hydrogen from pure water by irradiation with ultraviolet light of layered reconstructed aggregate A-Ca 2 Nb 3 O 10 composed of niobium-based nanosheets, cations and ruthenium, and (Oxygen production rate, ruthenium loading is 1% by weight as ruthenium red.) Further, when metal ions other than ruthenium, such as nickel chloride, were used, there was a photocatalytic ability to decompose into hydrogen and oxygen (hydrogen 21 μmol / h,
[0020]
[Table 1]
From these, it is clear that the generation amount of hydrogen and oxygen can be increased by incorporating ruthenium into the aggregate during the reconstruction and oxidizing the ruthenium by firing. In addition, even when a layered restructured aggregate is produced with a plurality of nanosheets, the aggregate with a small amount of ruthenium is effective for the total decomposition reaction that generates hydrogen and oxygen at a ratio of 2: 1 in the photolysis of water. I understood.
[0022]
Ca 2 Nb 3 O 10 and Ti 1.825 □ 0.175 O 4 (□ is octahedral vacancy) are layered reconstituted aggregates with excess potassium chloride and 1 wt% ruthenium chloride, and fired at 500 ° C in air Table 2 shows the generation rate of hydrogen and oxygen in the photolysis of water after heating. The purity of layered reconstituted aggregates obtained from ruthenium-supported niobium-based nanosheets, titanium-based nanosheets and mixed nanosheets by ultraviolet light irradiation Hydrogen and oxygen production rate from water, ratio is weight ratio.) As shown in Table 2, hydrogen and oxygen are generated simultaneously at any mixing ratio.
[0023]
[Table 2]
【Example】
Next, examples of the present invention will be described.
Example 1
1.2 g of HCa 2 Nb 3 O 10 · 1.5H 2 O powder obtained by acid treatment of a niobium-based layered perovskite type complex oxide represented by the composition formula KCa 2 Nb 3 O 10 is added to a tetrabutylammonium hydroxide
[0025]
The resulting nanosheet colloidal solution was dropped into 300 cm 3 of 2M KCl aqueous solution at a rate of about 1 m 3 / min, and the resulting aggregate was suction filtered, washed with pure water, and then air-dried in the air to obtain a solid powder. Obtained. The X-ray diffraction pattern of the aggregate composed of the layered compound reconstructed with the obtained potassium ion is shown in FIG.
[0026]
(Example 2)
1.2 g of H 0.7 Ti 1.825 □ 0.175 O 4 · H 2 O powder obtained by acid-treating a titanium-based layered oxide represented by the composition formula Cs 0.7 Ti 1.825 □ 0.175 O 4 was added to a 300 cm 3 aqueous solution of tetrabutylammonium hydroxide. In addition, the mixture was shaken (180 rpm) at room temperature for about 1 week to obtain a milky white colloidal solution. The colloid solution of 100 ml of this colloid solution and the colloidal solution of the niobium-based oxide nanosheet produced in Example 1 were mixed at a ratio of 200 ml to obtain a colloidal solution containing two kinds of nanosheets.
[0027]
The resulting colloidal solution of mixed nanosheets was dropped into 300 cm 3 of 2M KCl aqueous solution at a rate of about 1 cm 3 / min, and the resulting aggregate was suction filtered, washed with pure water, air-dried in the air, and then solid powder Got. The X-ray diffraction pattern of the aggregate composed of the layered compound reconstructed with the obtained potassium ion is shown in FIG.
[0028]
Example 3
Aggregates were produced under the same conditions except that 100 ml of the titanium nanosheet colloid solution of Example 2 was used in place of 200 ml, and 200 ml of the niobium nanosheet colloid solution was used in place of 100 ml. The X-ray diffraction pattern of the aggregate is shown in FIG.
[0029]
(Example 4)
Other using H 0.7 Ti 1.825 □ 0.175 O 4 · H 2 O in place of the HCa 2 Nb 3 O 10 · 1.5H 2 O of Example 1 was produced aggregates under the same conditions. The X-ray diffraction pattern of the aggregate is shown in FIG.
[0030]
(Example 5)
Agglomerates produced by dropping the colloidal solution of the milky white niobium-based oxide nanosheet obtained in Example 1 into 300 cm 3 of a 2 mol / l KCl aqueous solution containing 12 mg of ruthenium red at a rate of about 1 cm 3 / min. Was filtered with suction, washed with pure water, and then air-dried in the air to obtain a solid powder. Further, this solid powder was fired at 500 ° C. for 1 hour in the air. The resulting aggregate composed of a layered compound reconstituted with potassium ions containing ruthenium is placed in a quartz glass reaction tube together with 300 ml of pure water, attached to a closed circulation reactor, and sufficiently dissolved air is removed. 13.3 kPa was introduced.
[0031]
The agglomerates composed of layered compounds reconstituted with potassium ions containing ruthenium were irradiated with light with a 450 W high-pressure mercury lamp with sufficient stirring to advance the photocatalytic reaction. As a result of qualitative determination of the generated gas by gas chromatography directly connected to a closed circulation system, it was confirmed that hydrogen was generated at 48 μmol / h and oxygen was generated at 23 μmol / h. FIG. 2 shows time-dependent changes in water photolysis of aggregates composed of layered compounds reconstituted with potassium ions containing ruthenium from the obtained niobium-based nanosheets (◯: hydrogen, ●: oxygen).
[0032]
(Example 6)
The colloidal solution of the mixed nanosheet of 200 ml of niobium-based oxide and 100 ml of titanium-based oxide prepared in Example 1 and Example 2 was added to 300 cm 3 of 2M KCl aqueous solution containing 5.6 mg of ruthenium chloride and about 1 cm 3. Aggregates produced by dropping at a rate of / min were suction filtered, washed with pure water, and then air-dried in the air to obtain a solid powder. Further, this solid powder was fired at 500 ° C. for 1 hour in the air.
[0033]
The resulting aggregate composed of a layered compound reconstituted with potassium ions containing ruthenium is placed in a quartz glass reaction tube together with 300 ml of pure water, attached to a closed circulation reactor, and sufficiently dissolved air is removed. 13.3 kPa was introduced.
[0034]
The agglomerates composed of layered compounds reconstituted with potassium ions containing ruthenium were irradiated with light with a 450 W high-pressure mercury lamp with sufficient stirring to advance the photocatalytic reaction. As a result of qualitative determination of the generated gas by gas chromatography directly connected to a closed circulation system, it was confirmed that hydrogen was generated at 21 μmol / h and oxygen was generated at 10 μmol / h. FIG. 3 shows the time-dependent changes in water photolysis of aggregates composed of layered compounds reconstituted with potassium ions containing ruthenium from the mixed system of niobium-based nanosheets and titanium-based nanosheets (○: hydrogen, ●: oxygen) ).
[0035]
(Example 7)
26 mg of nickel chloride was used in place of the ruthenium red of Example 5, and after reducing for 2 hours in an atmosphere of 50 kPa of hydrogen instead of firing for 1 hour in air, oxidation treatment was performed for 1 hour in an atmosphere of 15 kPa of oxygen. Aggregates composed of layered compounds reconstructed with potassium ions containing nickel under the same conditions were produced.
[0036]
Aggregates made of layered compounds reconstituted with potassium ions containing nickel were put into a quartz glass reaction tube together with 300 ml of pure water, attached to a closed circulation reactor, and after sufficiently removing dissolved air, argon gas 13.3 kPa was introduced. The agglomerates composed of layered compounds reconstituted with potassium ions containing nickel were irradiated with light with a 450 W high-pressure mercury lamp with sufficient stirring to advance the photocatalytic reaction. As a result of qualitative determination of the generated gas by gas chromatography directly connected to a closed circulation system, it was confirmed that hydrogen was generated at 21 μmol / h and oxygen was generated at 4 μmol / h.
[Brief description of the drawings]
1 is an X-ray diffraction pattern (a = Example 1, b = Example 2, c = Example 3, d) of layered restructured aggregates obtained from niobium-based nanosheets, titanium-based nanosheets, and mixed nanosheets thereof. = A graph showing Example 4).
FIG. 2 is a graph showing time-dependent changes in water photolysis of ruthenium-containing layered reconstituted aggregates from niobium-based nanosheets obtained in Example 5.
FIG. 3 is a graph showing the time course of water photolysis of ruthenium-containing layered reconstituted aggregates from a mixed system of niobium nanosheets and titanium nanosheets obtained in Example 6.
Claims (7)
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| JP4752048B2 (en) * | 2005-02-22 | 2011-08-17 | 国立大学法人信州大学 | Layered ruthenic acid compound film |
| JP4749007B2 (en) * | 2005-03-16 | 2011-08-17 | 大塚化学株式会社 | Bright pigment aqueous medium dispersion and bright paint |
| JP4948802B2 (en) * | 2005-08-25 | 2012-06-06 | 大塚化学株式会社 | Light-resistant titanic acid coating film and light-resistant titanic acid film coating resin substrate |
| JP4979211B2 (en) * | 2005-08-25 | 2012-07-18 | 大塚化学株式会社 | Composite titanic acid coating film and composite titanic acid film coating resin substrate |
| JP5429843B2 (en) * | 2007-08-31 | 2014-02-26 | 独立行政法人物質・材料研究機構 | Photocatalytic material having octahedral sheet structure |
| JP5205675B2 (en) * | 2008-06-05 | 2013-06-05 | 独立行政法人物質・材料研究機構 | Photocatalyst nanosheet and photocatalyst material |
| JP5582464B2 (en) * | 2009-06-08 | 2014-09-03 | 国立大学法人信州大学 | Method for producing metal nanosheet, and metal nanosheet |
| JP5515115B2 (en) * | 2010-05-31 | 2014-06-11 | 独立行政法人物質・材料研究機構 | Fuel cell electrode catalyst and method for producing the same |
| JP6103524B2 (en) * | 2013-02-06 | 2017-03-29 | 国立研究開発法人物質・材料研究機構 | Perovskite nanosheets based on homologous series layered perovskite oxide and uses thereof |
| JP5963000B2 (en) * | 2013-03-14 | 2016-08-03 | 株式会社豊田中央研究所 | Exhaust gas purification catalyst, method for producing the same, and exhaust gas purification method using the same |
| JP6466744B2 (en) | 2014-03-11 | 2019-02-06 | パナソニック株式会社 | Turbulent structure material, active material for electricity storage device, electrode and electricity storage device |
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