JP3790222B2

JP3790222B2 - Visible light active photocatalyst

Info

Publication number: JP3790222B2
Application number: JP2003064162A
Authority: JP
Inventors: 崇本多
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-02-04
Filing date: 2003-02-04
Publication date: 2006-06-28
Anticipated expiration: 2023-02-04
Also published as: JP2004237267A

Description

【０００１】
【発明の属する技術分野】
本発明は、可視光にて活性化可能な光触媒に関する。
【０００２】
【従来の技術】
従来、光触媒としてはアナターゼやルチル型の酸化チタンが知られているが、約３８０ｎｍ以下の紫外線でしか活性化しないため、太陽光または紫外線放射ランプ等を用いる必要があった。このため、光触媒が活性化できる波長を可視光領域にまで広げる研究が活発に行われている。
【０００３】
例えば、様々な金属を光触媒にドーピングしたりイオン注入する試み（特開平９−１９２４９６号公報や表面化学２０巻２号６０〜６５項１９９９年など）や、酸素欠陥または構造欠陥を発生させて可視光活性化させる試み（工業材料４８巻６号２６〜４４項２０００年など）が行われている。しかし、吸収波長が限られており、高活性を示す可視光活性光触媒は得られていない。
【０００４】
特開平１１−１０４５００号公報には、可視光領域でプラズマ共鳴による吸収（プラズモン吸収）を示すクラスター状態の金属を光触媒物質中に分散させた光触媒が記載されている。しかし、金属微粒子が媒体となる光触媒中に分散しているため、媒体との相互作用を誘起し光電場による分極に影響を与え、プラズモン吸収が不鮮明になる欠点がある。また、プラズモン吸収はそれぞれの金属に固有の波長しか吸収できないため、例えば、媒体中または空気中で安定で明確なプラズモン吸収を示す金属であるＡｇ、Ａｕ、Ｃｕの微粒子の場合、４２０、５２０、５７０ｎｍ付近の波長は吸収できるが、６２０〜８００ｎｍの領域の光では活性化できない欠点がある。
【０００５】
特開平１０−１４６５３１号公報には、平均粒径１〜１０ｎｍの金属微粒子を光触媒表面に担持する事により触媒活性を向上させた光触媒が記載されているが、紫外線による活性向上のみしか得られていない。
【０００６】
一方、光触媒中に半導体微粒子を分散させて、半導体微粒子のサブバンド吸収を利用した可視光活性光触媒も報告されている。しかし、吸収強度が低く、ＣｄＳｅ、ＣｄＴｅ等の半導体のように、６９０、７６０ｎｍ付近の光を吸収できるが、水の存在下で光をあてると自己溶解現象を起こし、光触媒表面を覆ってしまうような不安定なものがほとんどで、高活性な可視光活性光触媒は得られていない。
【０００７】
【発明が解決しようとしている課題】
本発明の目的は、可視光領域の光を効率良く吸収して高い触媒活性を示す可視光活性光触媒を提供することにある。
【０００８】
【問題を解決するための手段】
明確なプラズモン吸収を示す金属としては、Ｌｉ、Ｎａ、Ｋ、Ａｕ、Ａｇ、Ｃｕなどが知られているが、媒体中または空気中で安定な金属としてはＡｕ、ＡｇおよびＣｕが挙げられる。これらの金属のプラズモン吸収波長は５２０、４２０、５７０ｎｍである。このようなプラズモン吸収は、一般に数ｎｍ〜数十ｎｍ程度の金属微粒子において見られる。しかし、これらの金属微粒子を２〜３個凝集させて二次粒子化すると異なる吸収波長ピークが出現し、Ａｕは５２０と７２０ｎｍ、Ａｇは４２０と６２０ｎｍ、Ｃｕは５７０と８００ｎｍの吸収波長ピークを示すことが判った。
【０００９】
また、ＡｕとＡｇからなる二次粒子には５２０と４２０ｎｍの吸収ピークの他に６６０ｎｍの吸収ピークが出現し、ＡｇとＣｕからなる二次粒子には４２０と５７０ｎｍの吸収ピークの他に６９０ｎｍの吸収ピークが出現し、ＡｕとＣｕからなる二次粒子には５２０と５７０ｎｍの吸収ピークの他に７６０ｎｍの吸収ピークが出現し、ＡｕとＡｇとＣｕからなる二次粒子には５２０と４２０と５７０ｎｍの吸収ピークの他に７００ｎｍの吸収ピークが出現することが判った。
【００１０】
このように、Ａｕ、Ａｇ、Ｃｕなどの金属微粒子を２〜３個凝集させた二次粒子化金属微粒子を光触媒中に分散または光触媒表面に担持することにより、可視光領域の光を効率よく吸収して活性化できる可視光活性光触媒が得られることを見出した。
【００１１】
二次粒子化金属微粒子は、光触媒中に分散させても可視光域の光を吸収して光触媒活性を示すが、光触媒表面に担持した方が活性が高いことを確認した。詳しい触媒反応機構は不明だが、光触媒中に分散させた金属微粒子は媒体との相互作用により、光電場による分極に影響が生じることが考えられ、また、金属微粒子で分極した電荷が実際に反応が起こる光触媒表面に十分に達していない事が考えられる。金属微粒子を光媒触表面に担持した場合は、プラズマ共鳴により金属微粒子表面に生じた分極の電荷が光触媒に有効に移行して光触媒表面に電子と正孔を生じるため、高い活性が得られると考えられる。
【００１２】
さらに、金属微粒子の組成や粒径を変化させることによってプラズモン吸収ピークを変化させることができる。Ａｕ，Ａｇ，またはＣｕに、Ｐｔ、Ｒｈ、Ｐｄ、Ｉｒ、Ｚｎ、ＰｂまたはＢｉ等の金属を３０重量％まで混合して合金化することによりプラズモン吸収波長ピークを約５０ｎｍ長波長側にシフトさせることが可能であることを見い出した。このように合金化した金属微粒子を二次粒子化した場合に新たに発生する吸収ピークも同様に長波長側にシフトすることも見い出した。
【００１３】
Ａｕ，ＡｇおよびＣｕの微粒子の粒径を、６０ｎｍ以上にするとプラズモン吸収ピークが長波長側にシフトし、１７０ｎｍ以上になるとプラズモン吸収ピークが見られなくなることも見い出した。このような６０〜１６０ｎｍの粒径の金属微粒子を二次粒子化した場合に発生する吸収ピークも同様に長波長側にシフトすることも見い出した。
【００１４】
以下、本発明の詳細について説明する。光触媒にはチタンテトライソプロポキシドを加水分解して合成した酸化チタン粉末を用いたが、これ以外にも、粉砕により粉末化したのもや、テルミット法やＣＶＤ等で合成した酸化チタン粉末やコーティング膜、チョコラルスキー法やスカル・メルティング法等で合成された酸化チタン単結晶や多結晶も用いる事ができる。Ａｕ，Ａｇ，Ｃｕの金属微粒子の合成には多くの方法が提案されており、どのような方法で合成した金属微粒子を用いても良い。例えば、クエン酸、アスコルビン酸、ＰＶＡ、ポリビニルピロリドン等のコロイド安定化剤を加えた水溶液中で金属塩化物等の金属化合物を還元する方法等がある。金属微粒子の粒径を変化させるには、コロイド安定化剤や金属化合物の濃度を変化させる事により７．５ｎｍから１８０ｎｍ以上の粒径の金属微粒子が得られる。
【００１５】
金属微粒子を二次粒子化するには、塩や電解質を少量添加する方法や、一度乾燥凝集させたものを再度分散させる再分散法などを用いる事ができる。例えば、Ａｕ微粒子が分散したコロイド溶液に硝酸アルミニウムを０．００２〜０．００５％程度添加する事により２から３個のＡｕ微粒子が凝集した二次粒子分散コロイド溶液が得られる。
【００１６】
二次粒子化金属微粒子を酸化チタン光触媒上に担持する方法としては、酸化チタン分散溶液に二次粒子化金属微粒子コロイド溶液を混合して酸化チタンに吸着担持させたのち乾燥させる方法や、粉末状酸化チタンに二次粒子化金属微粒子コロイド溶液を含浸または噴霧させたのち乾燥させる方法等を用いて担持できる。
【００１７】
二次粒子化した金属微粒子を酸化チタン光触媒中に分散させる方法としては、二次粒子化金属微粒子オルガノゾルにチタンテトライソプロポキシドを加えた後、加水分解して、二次粒子化金属微粒子分散酸化チタン光触媒を合成する方法等を用いる事ができる。二次粒子化金属微粒子オルガノゾルは、エタノール等の有機溶媒中で二次粒子化金属微粒子を合成する方法や、一度乾燥凝集した金属微粒子を有機溶媒中で再分散させる方法等で作成できる。
【００１８】
【発明の実施の形態】
発明の実施の形態を実施例にもとづき説明する。
【００１９】
金属微粒子の粒径や凝集状態は透過型電子顕微鏡にて測定した。可視光活性光触媒の吸収スペクトルはダブルモノクロメータ可視紫外近赤外分光光度計を用いて測定した。
【００２０】
本発明の実施例および比較例で用いる酸化チタンコロイド溶液は、エタノール２００ｃｃに純水０．７２ｇを加えて良く混合した後、チタンテトライソプロポキシド６．２６ｇを添加し、１０℃で撹拌してゆっくりと加水分解を行うことにより作成した。
【００２１】
可視光活性光触媒の浄化能力測定には、シリカウール２．５ｇに本発明の可視光活性光触媒を０．１ｇ担持したものを用いた。外表面を紫外線吸収膜で覆った１ｌガラス容器中に、アセトアルデヒドを３０００ｐｐｍ含有させた標準空気（酸素２１％、窒素７９％）と可視光活性光触媒担持シリカウールを密閉し、紫外線カットガラスを介して４０Ｗの白熱灯を照射した。アセトアルデヒドの濃度変化はガスクロマトグラフにて測定した。比較にはシリカウール２．５ｇに酸化チタンのみを０．１ｇ担持したものを用いた。
【００２２】
実施例１
９５ｇの純水にテトラクロロ金酸４水和物２０．５９ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金庫微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図１に示す。酸化チタン上に担持した二次粒子化金微粒子は、約４０ｎｍの金微粒子が２から３個凝集した二次粒子を形成していた。
【００２３】
実施例２
テトラクロロ金酸４水和物２０．５９ｍｇの代わりに塩素酸銀９．５７ｍｇを用いたこと以外は、実施例１と同様にして、酸化チタン粒子上に二次粒子化銀微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図１に示す。酸化チタン上に担持した二次粒子化銀微粒子は、約４０ｎｍの銀微粒子が２から３個凝集した二次粒子を形成していた。
【００２４】
実施例３
９０ｇの純水に塩化銅（ＩＩ）二水和物８．５２ｍｇと分子量１００００のポリビニルピロリドン５５．５ｍｇを加えて十分に容解した後、水素化ホウ素ナトリウム３．７８ｍｇを純水１０ｇに溶解した水溶液を加えて良く撹拌した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化銅微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図１に示す。酸化チタン上に担持した二次粒子化銅微粒子は、約３５ｎｍの銅微粒子が２から３個凝集した二次粒子を形成していた。
【００２５】
実施例４
９５ｇの純水にテトラクロロ金酸４水和物２０．５９ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却して金微粒子コロイドを得た。９５ｇの純水に塩素酸銀９．５７ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却して銀微粒子コロイドを得た。得られた金微粒子コロイドと銀微粒子コロイドを混合した後、硝酸アルミニウム９水和物１０ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液２００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金属微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図２に示す。酸化チタン上に担持した金と銀の複合二次粒子化金属微粒子は、約４０ｎｍの金属微粒子が２から３個凝集した二次粒子を形成していた。
【００２６】
実施例５
９５ｇの純水にテトラクロロ金酸４水和物２０．５９ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却して金微粒子コロイドを得た。９０ｇの純水に塩化銅（ＩＩ）二水和物８．５２ｍｇと分子量１００００のポリビニルピロリドン５５．５ｍｇを加えて十分に溶解した後、水素化ホウ素ナトリウム３．７８ｍｇを純水１０ｇに溶解した水溶液を加えて良く撹拌して銅微粒子コロイドを得た。得られた金微粒子コロイドと銅微粒子コロイドを混合した後、硝酸アルミニウム９水和物１０ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液２００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金属微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図２に示す。酸化チタン上に担持した金と銅の複合二次粒子化金属微粒子は、約３５ｎｍの金属微粒子が２から３個凝集した二次粒子を形成していた。
【００２７】
実施例６
９５ｇの純水に塩素酸銀９．５７ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却して銀微粒子コロイドを得た。９０ｇの純水に塩化銅（ＩＩ）二水和物８．５２ｍｇと分子量１００００のポリビニルピロリドン５５．５ｍｇを加えて十分に溶解した後、水素化ホウ素ナトリウム３．７８ｍｇを純水１０ｇに溶解した水溶液を加えて良く撹拌して銅微粒子コロイドを得た。得られた銀微粒子コロイドと銅微粒子コロイドを混合した後、硝酸アルミニウム９水和物１０ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶２００ｃｃ液とを混合し、酸化チタン粒子上に二次粒子化金属微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図２に示す。酸化チタン上に担持した銀と銅の複合二次粒子化金属微粒子は、約３５ｎｍの金属微粒子が２から３個凝集した二次粒子を形成していた。
【００２８】
実施例７
９５ｇの純水にテトラクロロ金酸４水和物６９．４９ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物２９．４ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図３に示す。酸化チタン上に担持した二次粒子化金微粒子は、約６０ｎｍの金微粒子が２から３個凝集した二次粒子を形成していた。
【００２９】
実施例８
９５ｇの純水にテトラクロロ金酸４水和物１．３２ｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物１４．７ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図３に示す。酸化チタン上に担持した二次粒子化金微粒子は、約１６０ｎｍの金微粒子が２から３個凝集した二次粒子を形成していた。
【００３０】
実施例９
合成後の金属微粒子の組成が金７０重量％、白金３０重量％となる様に、９５ｇの純水にテトラクロロ金酸４水和物１４．３７ｍｇとヘキサクロロ白金酸６水和物７．８３ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金属微粒子を吸着担持し、可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図３に示す。酸化チタン上に担持した二次粒子化金属微粒子は、約４０ｎｍの金属微粒子が２から３個凝集した二次粒子を形成していた。
【００３１】
実施例１０
７９．３ｇのエタノールに分子量１００００のポリビニルピロリドン５５．５ｍｇとテトラクロロ金酸４水和物２０．５９ｍｇを加えて加熱し、１０分間還流沸騰させた後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液にチタンテトライソプロポキシド３．１３ｇを加えて良く混合した後、エタノール１００ｃｃと純水０．３６ｇを添加し、１０℃で撹拌してゆっくりと加水分解を行い、酸化チタン粒子中に２次粒子化金微粒子が分散した可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図３に示す。酸化チタン中に分散した二次粒子化金微粒子は、約４０ｎｍの金微粒子が２から３個凝集した二次粒子を形成していた。
【００３２】
比較例１
９５ｇの純水にテトラクロロ金酸４水和物１．５８ｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物１０ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金微粒子を吸着担持して可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図４に示す。酸化チタン上に担持した二次粒子化金微粒子は、約１７０ｎｍの金微粒子が２から３個凝集した二次粒子を形成していた。
【００３３】
比較例２
合成後の金属微粒子の組成が金６０重量％、白金４０重量％となる様に、９５ｇの純水にテトラクロロ金酸４水和物１２．３１ｍｇとヘキサクロロ白金酸６水和物１０．４２ｍｇを加えて加熱し、還流沸騰させながら、５ｇの純水にクエン酸ナトリウム２水和物５８．８ｍｇを溶解した水溶液を加え、１０分間撹拌した後、室温まで冷却した。その後、硝酸アルミニウム９水和物５ｍｇを加えて撹拌し、２次粒子化金属微粒子コロイド溶液を作成した。この２次粒子化金属微粒子コロイド溶液と酸化チタンコロイド溶液１００ｃｃとを混合し、酸化チタン粒子上に二次粒子化金属微粒子を吸着担持し、可視光活性光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図４に示す。酸化チタン上に担持した二次粒子化金属微粒子は、約４０ｎｍの金属微粒子が２から３個凝集した二次粒子を形成していた。
【００３４】
比較例３
エタノール１００ｃｃに純水０．３６ｇを加えて良く混合した後、チタンテトライソプロポキシド３．１３ｇを添加し、１０℃で撹拌してゆっくりと加水分解を行い、酸化チタン光触媒を作成した。得られた酸化チタン光触媒の可視光域での吸収スペクトルを測定した結果を図４に示す。
【００３５】
比較例４
７９．３ｇのエタノールに分子量１００００のポリビニルピロリドン５５．５ｍｇとテトラクロロ金酸４水和物２０．５９ｍｇを加えて加熱し、１０分間還流沸騰させた後、室温まで冷却して金属微粒子コロイド溶液を作成した。この金属微粒子コロイド溶液にチタンテトライソプロポキシド３．１３ｇを加えて良く混合した後、エタノール１００ｃｃと純水０．３６ｇを添加し、１０℃で撹拌してゆっくりと加水分解を行い、酸化チタン粒子中に金微粒子が分散した光触媒を作成した。可視光域での吸収スペクトルを測定した結果を図４に示す。酸化チタン中に分散した金微粒子の粒径は約４０ｎｍであった。
【００３６】
実施例１から３で作成した可視光活性光触媒の浄化能力測定を行った結果を図５に、実施例４から６で作成した可視光活性光触媒の浄化能力測定を行った結果を図６に、実施例７から１０で作成した可視光活性光触媒の浄化能力測定を行った結果を図７に、比較例１から４で作成した光触媒および可視光活性光触媒の浄化能力測定を行った結果を図８に示す。このように、実施例１から１０の可視光活性光触媒は、可視光にて高い光触媒活性を示した。一方、比較例１から４の光触媒は、可視光にて低い光触媒活性を示した。
【００３７】
【発明の効果】
以上説明した様に、プラズモン吸収を示すＡｕ、Ａｇ、Ｃｕの金属微粒子が２〜３個凝集した二次粒子を、酸化チタン等の光触媒中に分散または光触媒表面に担持する事により、今まで吸収が困難であった６２０〜８００ｎｍの光を吸収して高い触媒活性を示す可視光活性光触媒を作成した。
【００３８】
Ａｕ，Ａｇ，またはＣｕに、Ｐｔ、Ｒｈ、Ｐｄ、Ｉｒ、Ｚｎ、ＰｂまたはＢｉ等の金属を３０重量％まで混合して合金化することによりプラズモン吸収波長ピークを約５０ｎｍ長波長側にシフトさせることが可能であり、このように合金化した金属微粒子を二次粒子化した場合に新たに発生する吸収ピークも同様に長波長側にシフトすることも見い出した。
【００３９】
さらに、Ａｕ，ＡｇまたはＣｕの微粒子の粒径を、６０ｎｍ以上１６０ｎｍ以下にすることにより、波長吸収ピークが最大で約１００ｎｍ長波長側にシフトし、このように粒径を多きくした金属微粒子を二次粒子化した場合に新たに発生する吸収ピークも同様に長波長側にシフトすることも見い出した。これらの可視光活性光触媒を組み合わせる事により、可視光域全体で効率良く光を吸収でき、高い触媒活性を示す可視光活性光触媒を作成できる。この可視光活性光触媒は可視光で活性化できるため、蛍光灯や白熱灯の様に紫外線をほとんど含まない光源でも使用でき、近年問題となっているシックハウス症候群の原因物質や悪臭等を、室内の光だけで分解除去できる様になる。
【図面の簡単な説明】
【図１】実施例１、２、３の可視光吸収スペクトルを示す図である。
【図２】実施例４、５、６の可視光吸収スペクトルを示す図である。
【図３】実施例７、８、９、１０の可視光吸収スペクトルを示す図である。
【図４】比較例１、２、３、４の可視光吸収スペクトルを示す図である。
【図５】実施例１、２、３の可視光活性光触媒のアセトアルデヒド浄化能力測定結果を示す図である。
【図６】実施例４、５、６の可視光活性光触媒のアセトアルデヒド浄化能力測定結果を示す図である。
【図７】実施例７、８、９、１０の可視光活性光触媒のアセトアルデヒド浄化能力測定結果を示す図である。
【図８】比較例１、２、３、４の光触媒のアセトアルデヒド浄化能力測定結果を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocatalyst that can be activated by visible light.
[0002]
[Prior art]
Conventionally, anatase and rutile type titanium oxide are known as photocatalysts. However, since they are activated only by ultraviolet rays of about 380 nm or less, it is necessary to use sunlight or an ultraviolet radiation lamp. For this reason, research is actively conducted to extend the wavelength at which the photocatalyst can be activated to the visible light region.
[0003]
For example, doping with various metals into the photocatalyst or attempts to implant ions (Japanese Patent Laid-Open No. Hei 9-19296, Surface Chemistry Vol. 20, No. 2, 60-65, 1999, etc.), visible oxygen defects or structural defects are generated. Attempts to photoactivate (Industrial Materials, Vol. 48, No. 6, 26-44, 2000, etc.) have been made. However, the absorption wavelength is limited, and a visible light active photocatalyst exhibiting high activity has not been obtained.
[0004]
Japanese Patent Application Laid-Open No. 11-104500 describes a photocatalyst in which a metal in a cluster state exhibiting absorption (plasmon absorption) by plasma resonance in the visible light region is dispersed in a photocatalytic substance. However, since the metal fine particles are dispersed in the photocatalyst serving as a medium, there is a drawback in that the interaction with the medium is induced to affect the polarization due to the photoelectric field, and the plasmon absorption becomes unclear. In addition, since plasmon absorption can only absorb wavelengths unique to each metal, for example, in the case of fine particles of Ag, Au, and Cu, which are metals that exhibit stable and clear plasmon absorption in a medium or in air, 420, 520, Although the wavelength near 570 nm can be absorbed, there is a drawback that it cannot be activated by light in the region of 620 to 800 nm.
[0005]
Japanese Patent Application Laid-Open No. 10-146531 discloses a photocatalyst having improved catalytic activity by supporting metal fine particles having an average particle diameter of 1 to 10 nm on the surface of the photocatalyst, but only an activity improvement by ultraviolet rays is obtained. Absent.
[0006]
On the other hand, a visible light active photocatalyst using semiconductor fine particles dispersed in the photocatalyst and utilizing subband absorption of the semiconductor fine particles has also been reported. However, the absorption intensity is low, and it can absorb light around 690 and 760 nm like semiconductors such as CdSe, CdTe, etc., but if it is exposed to light in the presence of water, it will cause a self-dissolution phenomenon and cover the photocatalytic surface Most of these are unstable, and a highly active visible light active photocatalyst has not been obtained.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a visible light active photocatalyst exhibiting high catalytic activity by efficiently absorbing light in the visible light region.
[0008]
[Means for solving problems]
Li, Na, K, Au, Ag, Cu, and the like are known as metals that exhibit clear plasmon absorption, and Au, Ag, and Cu are examples of metals that are stable in a medium or in air. These metals have plasmon absorption wavelengths of 520, 420, and 570 nm. Such plasmon absorption is generally observed in metal fine particles of about several nm to several tens of nm. However, when 2 to 3 of these metal fine particles are aggregated to form secondary particles, different absorption wavelength peaks appear, Au shows absorption wavelength peaks of 520 and 720 nm, Ag shows 420 and 620 nm, and Cu shows 570 and 800 nm. I found out.
[0009]
In addition to the absorption peaks at 520 and 420 nm, the absorption peak at 660 nm appears in the secondary particles composed of Au and Ag, and in the secondary particle composed of Ag and Cu, the absorption peaks at 690 nm are observed in addition to the absorption peaks at 420 and 570 nm. An absorption peak appears, an absorption peak at 760 nm appears in addition to the absorption peaks at 520 and 570 nm in the secondary particles made of Au and Cu, and 520, 420 and 570 nm in the secondary particles made of Au, Ag and Cu. It was found that an absorption peak at 700 nm appeared in addition to the absorption peak of.
[0010]
In this way, by dispersing secondary particulate metal fine particles in which 2 or 3 metal fine particles such as Au, Ag, and Cu are aggregated in the photocatalyst or supporting the photocatalyst surface, light in the visible light region is efficiently absorbed. The present inventors have found that a visible light active photocatalyst that can be activated is obtained.
[0011]
Even when dispersed into the photocatalyst, the secondary particulate metal fine particles absorb light in the visible light region and show photocatalytic activity, but it was confirmed that the activity was higher when supported on the photocatalyst surface. Although the detailed catalytic reaction mechanism is unknown, it is thought that the metal fine particles dispersed in the photocatalyst may affect the polarization due to the photoelectric field due to the interaction with the medium, and the charges polarized by the metal fine particles actually react. It is considered that the surface of the photocatalyst that occurs is not sufficiently reached. When metal fine particles are supported on the photocatalyst surface, the charge of polarization generated on the surface of the metal fine particles by plasma resonance is effectively transferred to the photocatalyst to generate electrons and holes on the photocatalyst surface. Conceivable.
[0012]
Furthermore, the plasmon absorption peak can be changed by changing the composition and particle size of the metal fine particles. Placing a metal such as Pt, Rh, Pd, Ir, Zn, Pb or Bi into Au, Ag, or Cu up to 30% by weight and alloying them shifts the plasmon absorption wavelength peak to the long wavelength side by about 50 nm. I found that it was possible. It has also been found that the absorption peak newly generated when the alloyed metal fine particles are converted into secondary particles similarly shifts to the longer wavelength side.
[0013]
It has also been found that the plasmon absorption peak shifts to the long wavelength side when the particle size of the Au, Ag and Cu fine particles is 60 nm or more, and that the plasmon absorption peak is not seen when the particle diameter is 170 nm or more. It has also been found that the absorption peak generated when such metal fine particles having a particle diameter of 60 to 160 nm are made into secondary particles is similarly shifted to the longer wavelength side.
[0014]
Details of the present invention will be described below. As the photocatalyst, titanium oxide powder synthesized by hydrolyzing titanium tetraisopropoxide was used, but in addition to this, it was pulverized, titanium oxide powder synthesized by thermite method or CVD, coating film, Titanium oxide single crystals and polycrystals synthesized by the chocolate skiing method or the skull melting method can also be used. Many methods have been proposed for the synthesis of Au, Ag, Cu metal fine particles, and the metal fine particles synthesized by any method may be used. For example, there is a method of reducing a metal compound such as a metal chloride in an aqueous solution to which a colloid stabilizer such as citric acid, ascorbic acid, PVA, or polyvinylpyrrolidone is added. In order to change the particle diameter of the metal fine particles, the metal fine particles having a particle diameter of 7.5 nm to 180 nm or more can be obtained by changing the concentration of the colloid stabilizer or the metal compound.
[0015]
In order to convert the metal fine particles into secondary particles, a method of adding a small amount of a salt or an electrolyte, a redispersion method of once dispersing and aggregating once again, or the like can be used. For example, by adding about 0.002 to 0.005% of aluminum nitrate to a colloidal solution in which Au fine particles are dispersed, a secondary particle-dispersed colloidal solution in which 2 to 3 Au fine particles are aggregated can be obtained.
[0016]
As a method for supporting the secondary particulate metal fine particles on the titanium oxide photocatalyst, the secondary particulate metal fine particle colloidal solution is mixed with the titanium oxide dispersion solution and adsorbed and supported on the titanium oxide, and then dried. It can be supported by using a method in which titanium oxide is impregnated or sprayed with a colloidal solution of secondary metal fine particles and then dried.
[0017]
To disperse the secondary metal particles into the titanium oxide photocatalyst, add titanium tetraisopropoxide to the secondary metal particle organosol and then hydrolyze it to disperse oxidized secondary particle metal particles. A method of synthesizing a titanium photocatalyst can be used. The secondary particulate metal fine particle organosol can be prepared by a method of synthesizing secondary particulate metal fine particles in an organic solvent such as ethanol, or a method of redispersing once finely aggregated metal fine particles in an organic solvent.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described based on examples.
[0019]
The particle size and aggregation state of the metal fine particles were measured with a transmission electron microscope. The absorption spectrum of the visible light active photocatalyst was measured using a double monochromator visible ultraviolet near infrared spectrophotometer.
[0020]
Titanium oxide colloidal solutions used in the examples and comparative examples of the present invention were mixed thoroughly by adding 0.72 g of pure water to 200 cc of ethanol, added with 6.26 g of titanium tetraisopropoxide, and stirred at 10 ° C. Prepared by slow hydrolysis.
[0021]
For measuring the purification ability of the visible light active photocatalyst, 2.5 g of silica wool carrying 0.1 g of the visible light active photocatalyst of the present invention was used. Standard air (oxygen 21%, nitrogen 79%) containing 3000 ppm acetaldehyde and visible light active photocatalyst-supported silica wool are sealed in a 1 liter glass container whose outer surface is covered with an ultraviolet ray absorbing film, and the ultraviolet ray cut glass is used. A 40 W incandescent lamp was irradiated. Changes in the concentration of acetaldehyde were measured with a gas chromatograph. For comparison, 2.5 g of silica wool carrying 0.1 g of titanium oxide alone was used.
[0022]
Example 1
In 95 g of pure water, 20.59 mg of tetrachloroauric acid tetrahydrate was added and heated, and while refluxing and boiling, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added. After stirring for minutes, it was cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particleized safe particulate colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 100 cc were mixed, and the secondary gold oxide fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary particulate gold fine particles supported on titanium oxide formed secondary particles in which 2 to 3 gold fine particles of about 40 nm were aggregated.
[0023]
Example 2
In the same manner as in Example 1 except that 9.57 mg of silver chlorate was used instead of 20.59 mg of tetrachloroauric acid tetrahydrate, the silver secondary particles were adsorbed and supported on the titanium oxide particles. A visible light active photocatalyst was prepared. The result of measuring the absorption spectrum in the visible light region is shown in FIG. Secondary grained silver fine particles supported on titanium oxide formed secondary particles in which 2 to 3 silver fine particles of about 40 nm were aggregated.
[0024]
Example 3
To 90 g of pure water, 8.52 mg of copper (II) chloride dihydrate and 55.5 mg of polyvinylpyrrolidone having a molecular weight of 10000 were added to completely dissolve, and then 3.78 mg of sodium borohydride was dissolved in 10 g of pure water. The aqueous solution was added and stirred well. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The colloidal solution of the secondary particle metal fine particles and 100 cc of the titanium oxide colloid solution were mixed, and the secondary particleized copper fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary particulate copper fine particles supported on titanium oxide formed secondary particles in which 2 to 3 copper fine particles of about 35 nm were aggregated.
[0025]
Example 4
In 95 g of pure water, 20.59 mg of tetrachloroauric acid tetrahydrate was added and heated, and while refluxing and boiling, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added. After stirring for minutes, the mixture was cooled to room temperature to obtain a gold fine particle colloid. After adding 957 mg of silver chlorate to 95 g of pure water and heating and refluxing and boiling, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added and stirred for 10 minutes. After cooling to room temperature, a silver fine particle colloid was obtained. After mixing the obtained gold fine particle colloid and silver fine particle colloid, 10 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 200 cc were mixed, and the secondary particle metal fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The gold and silver composite secondary particle metal fine particles supported on titanium oxide formed secondary particles in which 2 to 3 metal fine particles of about 40 nm were aggregated.
[0026]
Example 5
In 95 g of pure water, 20.59 mg of tetrachloroauric acid tetrahydrate was added and heated, and while refluxing and boiling, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added. After stirring for minutes, the mixture was cooled to room temperature to obtain a gold fine particle colloid. An aqueous solution in which 8.52 mg of copper (II) chloride dihydrate and 55.5 mg of polyvinylpyrrolidone having a molecular weight of 10000 are sufficiently dissolved in 90 g of pure water, and then 3.78 mg of sodium borohydride is dissolved in 10 g of pure water. Was added and stirred well to obtain a copper fine particle colloid. After mixing the obtained gold fine particle colloid and copper fine particle colloid, 10 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 200 cc were mixed, and the secondary particle metal fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The composite secondary particulate metal fine particles of gold and copper supported on titanium oxide formed secondary particles in which 2 to 3 metal fine particles of about 35 nm were aggregated.
[0027]
Example 6
After adding 957 mg of silver chlorate to 95 g of pure water and heating and refluxing and boiling, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added and stirred for 10 minutes. After cooling to room temperature, a silver fine particle colloid was obtained. An aqueous solution in which 8.52 mg of copper (II) chloride dihydrate and 55.5 mg of polyvinylpyrrolidone having a molecular weight of 10000 are sufficiently dissolved in 90 g of pure water, and then 3.78 mg of sodium borohydride is dissolved in 10 g of pure water. Was added and stirred well to obtain a copper fine particle colloid. After the obtained silver fine particle colloid and copper fine particle colloid were mixed, 10 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 200 cc were mixed, and the secondary particle metal fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The composite secondary particle metal fine particles of silver and copper supported on titanium oxide formed secondary particles in which 2 to 3 metal particles of about 35 nm were aggregated.
[0028]
Example 7
In 95 g of pure water, 69.49 mg of tetrachloroauric acid tetrahydrate was added and heated. While refluxing and boiling, an aqueous solution of 29.4 mg of sodium citrate dihydrate dissolved in 5 g of pure water was added. After stirring for minutes, it was cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 100 cc were mixed, and the secondary gold oxide fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary-particle gold fine particles supported on titanium oxide formed secondary particles in which 2 to 3 gold fine particles of about 60 nm were aggregated.
[0029]
Example 8
While adding 1.32 g of tetrachloroauric acid tetrahydrate to 95 g of pure water and heating and refluxing and boiling, an aqueous solution in which 14.7 mg of sodium citrate dihydrate is dissolved in 5 g of pure water is added. After stirring for minutes, it was cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 100 cc were mixed, and the secondary gold oxide fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary-particle gold fine particles supported on titanium oxide formed secondary particles in which 2 to 3 gold fine particles of about 160 nm were aggregated.
[0030]
Example 9
95 g of pure water was charged with 14.37 mg of tetrachloroauric acid tetrahydrate and 7.83 mg of hexachloroplatinic acid hexahydrate so that the composition of the fine metal particles after synthesis was 70 wt% gold and 30 wt% platinum. In addition, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added while heating to reflux and boiling, and the mixture was stirred for 10 minutes and then cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particulate metal fine particle colloid solution and the titanium oxide colloid solution 100 cc were mixed, and the secondary particulate metal fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary particulate metal fine particles supported on titanium oxide formed secondary particles in which 2 to 3 metal fine particles of about 40 nm were aggregated.
[0031]
Example 10
To 79.3 g of ethanol, 55.5 mg of polyvinylpyrrolidone having a molecular weight of 10,000 and 20.59 mg of tetrachloroauric acid tetrahydrate were added, heated, refluxed and boiled for 10 minutes, and then cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. After adding 3.13 g of titanium tetraisopropoxide to this secondary metal fine particle colloid solution and mixing well, 100 cc of ethanol and 0.36 g of pure water are added and stirred at 10 ° C. to slowly hydrolyze. A visible light active photocatalyst in which secondary gold fine particles were dispersed in titanium oxide particles was prepared. The result of measuring the absorption spectrum in the visible light region is shown in FIG. Secondary-particle gold fine particles dispersed in titanium oxide formed secondary particles in which 2 to 3 gold particles of about 40 nm were aggregated.
[0032]
Comparative Example 1
While adding 1.58 g of tetrachloroauric acid tetrahydrate to 95 g of pure water and heating it to reflux boiling, an aqueous solution of 10 mg of sodium citrate dihydrate dissolved in 5 g of pure water was added and stirred for 10 minutes. And then cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particle metal fine particle colloid solution and the titanium oxide colloid solution 100 cc were mixed, and the secondary gold oxide fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary-particle gold fine particles supported on titanium oxide formed secondary particles in which 2 to 3 gold fine particles of about 170 nm were aggregated.
[0033]
Comparative Example 2
95 g of pure water was charged with 12.31 mg of tetrachloroauric acid tetrahydrate and 10.42 mg of hexachloroplatinic acid hexahydrate so that the composition of the fine metal particles after synthesis was 60% by weight of gold and 40% by weight of platinum. In addition, an aqueous solution in which 58.8 mg of sodium citrate dihydrate was dissolved in 5 g of pure water was added while heating to reflux and boiling, and the mixture was stirred for 10 minutes and then cooled to room temperature. Thereafter, 5 mg of aluminum nitrate nonahydrate was added and stirred to prepare a secondary particle metal fine particle colloid solution. The secondary particulate metal fine particle colloid solution and the titanium oxide colloid solution 100 cc were mixed, and the secondary particulate metal fine particles were adsorbed and supported on the titanium oxide particles to prepare a visible light active photocatalyst. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The secondary particulate metal fine particles supported on titanium oxide formed secondary particles in which 2 to 3 metal fine particles of about 40 nm were aggregated.
[0034]
Comparative Example 3
After adding 0.36 g of pure water to 100 cc of ethanol and mixing well, 3.13 g of titanium tetraisopropoxide was added, and the mixture was stirred at 10 ° C. and slowly hydrolyzed to prepare a titanium oxide photocatalyst. The result of having measured the absorption spectrum in the visible light region of the obtained titanium oxide photocatalyst is shown in FIG.
[0035]
Comparative Example 4
75.5 g of ethanol, 55.5 mg of polyvinylpyrrolidone having a molecular weight of 10,000 and 20.59 mg of tetrachloroauric acid tetrahydrate are added and heated, boiled at reflux for 10 minutes, and then cooled to room temperature to obtain a metal fine particle colloidal solution. Created. After adding titanium tetraisopropoxide 3.13g to this metal fine particle colloid solution and mixing well, add 100cc of ethanol and 0.36g of pure water, stir at 10 ° C and slowly hydrolyze, titanium oxide particles A photocatalyst having gold fine particles dispersed therein was prepared. The result of measuring the absorption spectrum in the visible light region is shown in FIG. The particle size of the gold fine particles dispersed in titanium oxide was about 40 nm.
[0036]
FIG. 5 shows the results of measuring the purification ability of the visible light active photocatalysts prepared in Examples 1 to 3, and FIG. 6 shows the results of measuring the purification ability of the visible light active photocatalysts prepared in Examples 4 to 6. FIG. 7 shows the results of measuring the cleaning ability of the visible light active photocatalysts prepared in Examples 7 to 10, and FIG. 8 shows the results of measuring the cleaning ability of the photocatalysts prepared in Comparative Examples 1 to 4 and the visible light active photocatalyst. Shown in Thus, the visible light active photocatalysts of Examples 1 to 10 exhibited high photocatalytic activity in visible light. On the other hand, the photocatalysts of Comparative Examples 1 to 4 showed low photocatalytic activity in visible light.
[0037]
【The invention's effect】
As described above, secondary particles, in which 2 to 3 metal fine particles of Au, Ag, and Cu that exhibit plasmon absorption are aggregated, are dispersed in a photocatalyst such as titanium oxide or absorbed on the surface of the photocatalyst so far. Thus, a visible light active photocatalyst exhibiting high catalytic activity by absorbing light at 620 to 800 nm was prepared.
[0038]
Placing a metal such as Pt, Rh, Pd, Ir, Zn, Pb or Bi into Au, Ag, or Cu up to 30% by weight and alloying them shifts the plasmon absorption wavelength peak to the long wavelength side by about 50 nm. It has also been found that when the alloyed metal fine particles are converted into secondary particles, the newly generated absorption peak is similarly shifted to the longer wavelength side.
[0039]
Furthermore, by setting the particle diameter of the Au, Ag, or Cu fine particles to 60 nm or more and 160 nm or less, the wavelength absorption peak is shifted to the long wavelength side by about 100 nm at the maximum. It was also found that the absorption peak newly generated when secondary particles are formed is similarly shifted to the longer wavelength side. By combining these visible light active photocatalysts, light can be efficiently absorbed in the entire visible light region, and a visible light active photocatalyst exhibiting high catalytic activity can be produced. Since this visible light activated photocatalyst can be activated by visible light, it can be used with light sources that contain almost no ultraviolet rays, such as fluorescent lamps and incandescent lamps. It can be decomposed and removed only by light.
[Brief description of the drawings]
1 is a view showing visible light absorption spectra of Examples 1, 2, and 3. FIG.
2 is a view showing visible light absorption spectra of Examples 4, 5, and 6. FIG.
FIG. 3 is a view showing visible light absorption spectra of Examples 7, 8, 9, and 10;
4 is a view showing visible light absorption spectra of Comparative Examples 1, 2, 3, and 4. FIG.
FIG. 5 is a graph showing measurement results of acetaldehyde purification ability of visible light active photocatalysts of Examples 1, 2, and 3;
6 is a graph showing measurement results of acetaldehyde purification ability of visible light active photocatalysts of Examples 4, 5, and 6. FIG.
7 is a graph showing measurement results of acetaldehyde purification ability of visible light active photocatalysts of Examples 7, 8, 9, and 10. FIG.
FIG. 8 is a graph showing the measurement results of the acetaldehyde purification ability of the photocatalysts of Comparative Examples 1, 2, 3, and 4.

Claims

A visible light active photocatalyst characterized in that secondary particles in which 2 to 3 metal fine particles exhibiting plasmon absorption are aggregated are dispersed or supported on the photocatalyst surface.

2. The visible light active photocatalyst according to claim 1, wherein metal fine particles containing 70% by weight or more of one or more metals selected from the group consisting of Au, Ag and Cu are used as the metal fine particles exhibiting plasmon absorption.

The visible light active photocatalyst according to claim 1 or 2, wherein the metal fine particles have a particle size of 60 to 160 nm.