JP3592727B2 - Photocatalyst - Google Patents

Photocatalyst Download PDF

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JP3592727B2
JP3592727B2 JP14661692A JP14661692A JP3592727B2 JP 3592727 B2 JP3592727 B2 JP 3592727B2 JP 14661692 A JP14661692 A JP 14661692A JP 14661692 A JP14661692 A JP 14661692A JP 3592727 B2 JP3592727 B2 JP 3592727B2
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photocatalyst
powder
titanium oxide
substrate
metal oxide
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JPH05309267A (en
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雅紀 北村
雄耕 藤田
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日本電池株式会社
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Description

【0001】
【産業上の利用分野】
本発明は、浄水,脱臭,殺菌,排水処理,水分解,藻の成育抑止,各種有機化学反応等に用いられる光触媒体に関するものである。
【0002】
【従来の技術】
半導体にそのバンドギャップ以上のエネルギーを有するしかるべき波長の光を照射すると、光励起により、価電子帯から伝導体に電子が遷移すると同時に、価電子帯に正孔が生成し、いわゆる電荷分離が起こる。また半導体に光を照射しつつ水あるいは溶液を接触させると、ショットキーバリヤに類似した接合が形成され、半導体がn型の場合には正孔が、p型の場合には電子が、それぞれ半導体の固−液界面側の表面に集まってくることはよく知られている。そして、n型半導体の場合には、正孔が水あるいは溶液種から電子を引き抜き、その結果、水が分解したり、溶液中の溶質が酸化される。また、p型半導体の場合には、電子が隣接する水あるいは溶液種に付与され、その水あるいは溶液種の還元反応が起こる。このように、光酸化還元反応を促進する半導体を特に半導体光触媒あるいは、単に光触媒という。
【0003】
従来、光触媒を用いた酸化還元反応もしくは酸化還元反応操作としては、水の分解反応、微生物を殺す反応、脱臭反応、殺菌反応、水の浄化排水処理その他各種有機化学反応などが提案されている。光触媒としては、具体的には、n型半導体としての酸化チタンが、その化学的安定性の故に最も広く使用されている。酸化チタンは、粉末状で溶液に懸濁された形で用いられる場合と、何らかの基体上に担持した形で使用される場合とがある。光触媒の活性という見地からみると、その表面積の大きさから、一般に前者の方がより活性であるが、実用的見地からすると、その取扱い易さからいって前者より後者の方を採用せざるを得ない場合が多い。
【0004】
光触媒を基体に担持する方法としては、種々提案されている。例えば、(A)ニトロセルロース、ガラス、ポリ塩化ビニル、ナイロン、メタクリル樹脂,ポリプロピレン等の光透過性物質材料からなるフィルム状、ビーズ状、ボード状、繊維状等の形状の基体に酸化チタン微粉末を付着させる方法(特開昭62−66861)、(B)多孔性ガラス支持体にチタン(IV)テトラブトキシオキサイドのアルコール溶液を含浸し、加熱して、アナターゼ型の酸化チタンにすることによって多孔性ガラス支持体に保持・固定する方法(特開平2−50154)、(C)色素または金属錯体などの光増感剤を側鎖としてもつ多孔性高分子膜(例えば、ポリフッ化エチレン樹脂)中に圧入、含浸、沈着等の方法により、半導体触媒粉末を保持・固定する方法(特開昭58−125602)、(D)ポリプロピレン繊維あるいはセラミックからなる濾過フィルターに酸化チタンを担持する方法(特開平2−68190)、(E)石英、ガラス、プラスチックの繊維のからみの中に酸化チタン粉末を保持・固定しその両面を光透過性のガラスでおさえつける方法(アメリカ特許、4,888,101)、(F)アルミナ基板に白金をスパッタリング法により固着させ、その上にアナターゼ型の酸化チタン粉末とメチルメタクリレートの有機溶媒溶液との混合分散液をスピンコーティング法により塗着し、しかるのちに結着剤としてのメチルメタクリレートを加熱分解するとともにアナターゼ型の酸化チタンをルチル型の酸化チタンにする方法《ロバート,イー,ヘトリック−Robert E. Hetrick, Applied Physics Communications,, (3), 177−187(1985)》, (G)ポリエステル布の表面に酸化チタンを低温溶射方法で溶射担持する方法(桜田司、表面技術41巻,10号,P60(1990)、などが提案されている。
【0005】
【発明が解決すべき課題】
上述のような従来の光触媒の基体への保持・固定方法を検討すると、まず(B)あるいは(G)の方法では、光触媒としての酸化チタンそのものが微粉末というよりは大きなかたまりであるバルク半導体であるため、その光触媒としての活性は、粉末半導体光触媒を固定化した光触媒体に比べて相対的に低い。
【0006】
また、(A),(D),(E)あるいは(F)の方法においては、結着剤を含まないため、あるいは最終的に結着剤がのこらないため、光触媒粉末が基体に保持固定される強度は実用上不十分である。さらに、これらの系に例えばポリテトラフルオロエチレンの乳化重合懸濁液のような有機高分子エマルジョンなどを結着剤として添加すると、触媒表面の活性点をこれらの結着剤が被覆したり、光触媒の強力な酸化力によりこれらの結着剤そのものが分解されたり、あるいはその分解生成物により光触媒粉末が被毒を受けて触媒活性が著しく低下するといった問題点があった。
【0007】
また、上述のいずれの方法を実施した場合にも光触媒を粉末のまま用いた場合に比して、光触媒粉末の結着強度が弱いといった問題点以外に、光触媒を粉末状のまま用いる場合に比べるとその触媒活性が相対的に低下するという問題点があった。
【0008】
【課題を解決するための手段】
本発明は、光触媒粉末を基体に担持固定化してなる光触媒体において、光触媒粉末の担持固定化剤として金属酸化物のゾルを400℃以下の温度で加熱処理して生成する多孔性金属酸化物を用いることによって上述の如き問題を解決しようとするものである。
【0009】
【作用】
本発明にかかる光触媒体の特徴は光触媒粉末を基体上に担持固定化し、一定の機械的強度を持っていて、なおかつ、粉末のままの高い光触媒活性を維持している点にある。以下、本発明にかかる光触媒体の製造過程、構成およびその意義について詳述する。
【0010】
本発明にかかる光触媒体を製造する過程にはさまざまな方法がある。
まず、基体として用いられる材料は、光触媒粉末を塗着、含浸などの方法で担持したりあるいは、ディップコーティング、スピンコーティング、などの方法で皮膜を形成できるものであれば何でも適用できる。例えば、ガラスやセラミックの繊維を水中に分散し、紙すきの要領で抄造して得られるセラミックマット、多孔性ガラス、または、ナイロン,アクリル,ポリエステルなどの繊維製品、などのような三次元的な空孔をもつものあるいは、ガラス、PMMAなどの透光性の板状、線状、管状、のもの、セラミック、金属、プラスチックの成形品などである。
【0011】
次に、半導体光触媒粉末としては、TiO,ZnO,SrTiO,CdS,GaP,InP,GaAs,BaTiO,KNbO,Fe,Ta,WO,SnO,Bi,NiO,CuO,SiC,SiO,MoS,InPb,RuO,CeO,などおよび、これらの光触媒粉末にPt,Rh,RuO,Nb,Cu,Sn,NiOなどの金属及び金属酸化物を担持した従来公知のものがすべて適応できる。
【0012】
さて、一つの典型的な製造方法はこのような基体にまず、半導体光触媒粉末を担持し、しかるのちに金属酸化物ゾルを含浸などの方法で作用させる方法である。つまり、まず、セラミックマットや繊維製品のような三次元的な空孔をもつものであれば、あらかじめこの基体の空孔に半導体光触媒粉末を塗着、含浸などの方法で担持しておく。また、ガラス、PMMA、セラミック、金属、プラスチックの成形品、などの比較的滑らかな表面を持つものであれば、あらかじめその表面に、スプレー吹き付け法、ディップコーティング法、スピンコーティング法などの方法で、光触媒粉末層を形成しておく。この光触媒粉末を付着せしめただけの光触媒粉末担持体に、ゾルゲル法で採用されるような金属のアルコキシド、アセチルアセトネート、カルボキシレートなどの金属有機化合物や、四塩化チタンといった塩化物のアルコール溶液を酸あるいはアルカリ触媒存在下加水分解することにより得られた金属酸化物のゾルを含浸し、溶媒成分を飛ばしてゲル化し金属酸化物ゲルとし、目的の光触媒体を得る。
【0013】
しかし、他の方法として、ゾルゲル法で採用されるような金属のアルコキシド、アセチルアセトネート、カルボキシレートなどの金属有機化合物や、四塩化チタンといった塩化物のアルコール溶液を酸あるいはアルカリ触媒存在下加水分解することにより得られた金属酸化物のゾルと光触媒粉末との混合液を調製し、基体に半導体光触媒粉末のみを担持するかわりにこの混合液を含浸、塗布あるいは、さまざまなコーティング法などにて担持し、ゲル化する方法においても同様の効果を持つ光触媒体を得る。
【0014】
あるいは、金属酸化物ゾルを得る前に、前述の金属有機化合物や、塩化物のアルコール溶液に光触媒粉末をまず混合し、酸あるいはアルカリ触媒存在下加水分解することにより得られる光触媒粉末−金属酸化物混合ゾルを基体に含浸、塗布あるいはさまざまなコーティング法にて担持し、ゲル化する方法においても同様の効果が得られることがある。
【0015】
また、これらいずれの方法において用いられる金属酸化物ゾルも、2種類以上の金属酸化物のゾルを混合して、金属複合酸化物のゾルとして用いると有効なことがある。
【0016】
以上詳述してきたように、本発明にかかる光触媒体の製造過程においては、光触媒粉末と金属酸化物ゾルより生成する多孔性金属酸化物を良好な構成とすることが最も重要な点であって、この両者の原料、取扱い方法などをなんら限定するものではない。
【0017】
ここで、この光触媒粉末と、担持固定化剤の良好な構成とは、次のようなものであるとも考えられる。すなわち、塗着,含浸などの方法で基体に担持された光触媒粉末は、その基体への付着力こそ非常に弱いものの、大きな多孔度と表面積をもっており比較的粉末状態に近い触媒活性が維持されている。次に、粉末光触媒担持体に金属酸化物ゾルを含浸しゲル化すると、多数の孔をもつあるいは、光触媒粉末粒子と基体とのあいだに入り込んだ金属酸化物ゲルのネットワークとなり、基体に担持された粉末光触媒をいわば網目の中に取り込むように保持し、強固な結着剤となる。ここで危惧される点は、金属酸化物ゾル由来の金属酸化物ゲルあるいはこれを熱処理して得られる金属酸化物そのものが光触媒として作用したりあるいは、光触媒粉末表面を被覆して光触媒粉末を光励起するために照射された紫外光を散乱あるいは吸収し、光触媒粉末の光励起を妨げたりする可能性があることである。しかしながら、本発明にかかる光触媒体においては実施例においても示すように、たとえば金属酸化物のゾルに酸化チタンを用いる場合には、酸化チタンゾル由来のチタン酸ポリマーあるいは酸化チタンは、光触媒粉末の固定化剤としての役割を果たしつつ、このようないわば妨害作用を発現することは全くなかった。つまりその結果、光触媒粉末の表面は充分に溶液界面に接しており、この金属酸化物ゲルは光触媒反応の活性点を被覆してしまわないような構成となっている。
【0018】
残念ながら、上述の構成は一つの推測にすぎず、本発明者らは本発明品の作用機構について解明できていない点もある。しかしながら、従来公知の光触媒粉末のみ、および金属酸化物ゲルのみでは得られなかった、触媒活性に優れかつ一定の機械的強度をもつ光触媒体が、光触媒粉末と金属酸化物ゾルを組み合わせることによってはじめて得ることが可能となったのである。
【0019】
【実施例】
<実施例1>
繊維径19μm のガラス繊維1.5gを1リットルの水中に分散し、これを抄造して面積100cm2(100mm×100mm)、厚さ1.1mmのガラスマットを基体として得た。、光触媒粉末としてアナターゼ型酸化チタン(比表面積50m3/g、粒子径0.03μm)10gを100ミリリットルの水に懸濁し、水スラリーとし、これをあらかじめ準備した基体に含浸し、乾燥して光触媒粉末を担持した。酸化チタンの担持量は2.0gであった。次に、チタンイソプロポキシド10gを100ミリリットルのエタノールに溶解しここに、50ミリリットルのエタノール、5ミリリットルの水及び、0.7ミリリットルの濃塩酸の混合溶液を加え加水分解し酸化チタンゾルを得た。この酸化チタンゾルに、あらかじめ酸化チタン粉末を含浸したガラスマットを浸積し、すばやく引き上げて50℃、1時間乾燥処理し溶媒のアルコールを飛ばした後、350℃、2時間熱処理して光触媒体とした。酸化チタンの担持量は2.06gであった。
【0020】
<実施例2>
シリコンテトラエトキシド5gを100ミリリットルのエタノールに溶解しここに、50ミリリットルのエタノール、5ミリリットルの水及び、0.7ミリリットルの濃塩酸の混合溶液を加え加水分解しシリカゾルを得た。このシリカゾルに、実施例1と同様にあらかじめ酸化チタンの水スラリーを含浸し酸化チタンを担持したガラスマットを浸積し、すばやく引き上げて50℃、1時間乾燥処理し溶媒のアルコールを飛ばした後、400℃、2時間熱処理して光触媒体とした。酸化チタンの担持量は2.0gであった。
【0021】
<実施例3>
チタンイソプロポキシド3gを50ミリリットルのエタノールに溶解しここに、20ミリリットルのエタノール、2ミリリットルの水及び、0.3ミリリットルの濃塩酸の混合溶液を加え酸化チタンゾルを得た。これに、あらかじめ350℃で2時間熱処理したアナターゼ型酸化チタン(粒子径0.2μm )5gを分散してこれを、30mm×30mmのガラス板にディップコーティング法にて光触媒層を形成した。このときの酸化チタンの担持量は1.1mgであった。
【0022】
[触媒体の効力に関する試験例]
<試験例1>
実施例1及び実施例2において得られた光触媒体を30mm×30mmに切り出しそれぞれ(a)、(b)とし(酸化チタン量(a):0.18g,(b):0.17g)、200mlビーカーの底面に配置した。ここに、濃度0.1mmol/lのフェノール水溶液100ミリリットルをいれ、ビーカー底面より1kW高圧水銀ランプの400nm−300nmの紫外光を照射し、この水溶液の光照射時間に対するフェノール濃度の経時変化を検討した。このときの紫外線強度は8.79μアインシュタイン/分であった。
【0023】
その結果(a),(b)ともに光照射開始後約20分でフェノールの濃度は半減し、約3時間で検出限界以下に分解された。比較のために、光触媒体に担持した酸化チタン粉末0.18gを粉末のまま懸濁したもの(c)、チタンイソプロポキシドの加水分解により得られた酸化チタンをガラスマットに担持したもの(d)、および光触媒粉末0.18gをPTFEディスパージョンと混合し固形物とし200℃で熱処理したもの(e)、について同様の検討を行ったところ粉末懸濁系では同程度の分解特性を示し、図1にこれらの光触媒体のフェノール分解特性を示す。その他の光触媒体については4時間の光照射後も分解されなかった。
【0024】
<試験例2>
実施例3において得られた光触媒体を直径50mmのガラス管内部に配置し密閉系とし、アセトアルデヒド20ppm.を含む空気を還流させながら光触媒体に300Wのキセノンランプの400−300nmの紫外光を30μアインシュタイン/分で照射したところ、光照射開始後約15分でアセトアルデヒドはほぼ分解された。比較のために、ゾルゲル法にて調製した酸化チタン1.1mgについて同様の検討を行ったところ4時間の光照射後も分解されなかった。
【0025】
【発明の効果】
以上詳述したように、本発明にかかる光触媒体は、光触媒粉末を基体上に担持固定化し、一定の機械的強度を持っていて、なおかつ、粉末のままの高い光触媒活性を維持している新規な光触媒体であり、その工業的価値は極めて大きい。
【図面の詳細な説明】
【図1】本発明の実施例にかかる光触媒体の、試験例1の光触媒分解特性の図である。
[0001]
[Industrial applications]
The present invention relates to a photocatalyst used for water purification, deodorization, sterilization, wastewater treatment, water decomposition, growth suppression of algae, various organic chemical reactions, and the like.
[0002]
[Prior art]
When a semiconductor is irradiated with light of an appropriate wavelength having energy equal to or greater than its band gap, photoexcitation causes transition of electrons from the valence band to the conductor, and at the same time, generation of holes in the valence band, so-called charge separation occurs. . In addition, when water or a solution is brought into contact with a semiconductor while being irradiated with light, a junction similar to a Schottky barrier is formed. When the semiconductor is an n-type, holes are produced, and when the semiconductor is a p-type, electrons are produced. It is well known that they gather on the surface on the solid-liquid interface side. In the case of an n-type semiconductor, holes extract electrons from water or a solution species, and as a result, water is decomposed or a solute in the solution is oxidized. In the case of a p-type semiconductor, electrons are given to adjacent water or solution species, and a reduction reaction of the water or solution species occurs. Such a semiconductor that promotes the photooxidation-reduction reaction is particularly called a semiconductor photocatalyst or simply a photocatalyst.
[0003]
Conventionally, as a redox reaction or a redox reaction operation using a photocatalyst, a decomposition reaction of water, a reaction for killing microorganisms, a deodorization reaction, a sterilization reaction, a water purification wastewater treatment, and various other organic chemical reactions have been proposed. As a photocatalyst, specifically, titanium oxide as an n-type semiconductor is most widely used because of its chemical stability. Titanium oxide may be used in the form of a powder suspended in a solution or in the form of being supported on some substrate. From the viewpoint of photocatalytic activity, the former is generally more active due to its large surface area, but from a practical standpoint, the latter must be adopted from the viewpoint of ease of handling. Often not.
[0004]
Various methods have been proposed for supporting a photocatalyst on a substrate. For example, (A) a titanium oxide fine powder is applied to a substrate made of a light-transmitting substance such as nitrocellulose, glass, polyvinyl chloride, nylon, methacrylic resin, polypropylene, etc. in the form of a film, beads, board, fiber, etc. (B) A porous glass support is impregnated with an alcohol solution of titanium (IV) tetrabutoxy oxide and heated to form an anatase type titanium oxide. (Japanese Patent Laid-Open No. 50154/1990), (C) In a porous polymer membrane (for example, polyfluoroethylene resin) having a photosensitizer such as a dye or a metal complex as a side chain. For holding and fixing the semiconductor catalyst powder by press-fitting, impregnation, deposition, etc. (Japanese Patent Application Laid-Open No. 58-125602), (D) polypropylene A method of supporting titanium oxide on a filter made of fiber or ceramic (Japanese Patent Application Laid-Open No. 2-68190). (E) Titanium oxide powder is held and fixed in the entanglement of quartz, glass, and plastic fibers, and light is transmitted through both surfaces. (U.S. Pat. No. 4,888,101). (F) Platinum is fixed to an alumina substrate by a sputtering method, and anatase-type titanium oxide powder and an organic solvent solution of methyl methacrylate are further placed thereon. A method in which the mixed dispersion is applied by a spin coating method, and thereafter, methyl methacrylate as a binder is thermally decomposed and anatase-type titanium oxide is converted to rutile-type titanium oxide << Robert, E, Hetric-Robert E . Hetric, Applied Physics Communications, 5 , (3), 177-187 (1985) >>, (G) A method of spray-supporting titanium oxide on the surface of a polyester cloth by a low-temperature spraying method (Takashi Sakurada, Surface Technology Vol. 41, No. 10) , P60 (1990), and the like.
[0005]
[Problems to be solved by the invention]
Considering the conventional method of holding and fixing the photocatalyst to the substrate as described above, first, in the method (B) or (G), the titanium oxide itself as the photocatalyst is a bulk semiconductor that is a large lump rather than a fine powder. Therefore, its activity as a photocatalyst is relatively lower than that of a photocatalyst in which a powdered semiconductor photocatalyst is immobilized.
[0006]
In the methods (A), (D), (E) and (F), the photocatalyst powder is held and fixed on the substrate because the binder is not contained or the binder is not finally deposited. The required strength is not practically sufficient. Further, when an organic polymer emulsion such as an emulsion polymerization suspension of polytetrafluoroethylene is added as a binder to these systems, the active sites on the catalyst surface can be covered with the binder, or the photocatalyst can be coated. However, there is a problem that these binders themselves are decomposed due to the strong oxidizing power of the photocatalyst, or the photocatalyst powder is poisoned by the decomposition products and the catalytic activity is remarkably reduced.
[0007]
In addition, when compared to the case where the photocatalyst is used in powder form, the photocatalyst powder has a weaker binding strength than the case where the photocatalyst is used as powder in any of the above-described methods. In addition, there is a problem that the catalyst activity is relatively reduced.
[0008]
[Means for Solving the Problems]
The present invention relates to a photocatalyst obtained by supporting and fixing a photocatalyst powder on a substrate, wherein a porous metal oxide produced by heat-treating a sol of a metal oxide at a temperature of 400 ° C. or lower is used as a photocatalyst powder support and fixing agent. It is intended to solve the above-mentioned problem by using the same.
[0009]
[Action]
A feature of the photocatalyst according to the present invention is that the photocatalyst powder is supported and fixed on a substrate, has a certain mechanical strength, and maintains a high photocatalytic activity as a powder. Hereinafter, the production process, configuration, and significance of the photocatalyst according to the present invention will be described in detail.
[0010]
There are various methods for producing the photocatalyst according to the present invention.
First, as the material used as the base, any material can be applied as long as it can support the photocatalyst powder by coating, impregnation, or the like, or can form a film by dip coating, spin coating, or the like. For example, a three-dimensional space such as a ceramic mat, porous glass, or a fiber product such as nylon, acrylic, or polyester obtained by dispersing glass or ceramic fibers in water and forming the paper in a papermaking manner. Examples thereof include those having a hole, glass, and translucent plate-like, linear, and tubular materials such as PMMA, and molded products of ceramic, metal, and plastic.
[0011]
Next, as the semiconductor photocatalyst powder, TiO 2 , ZnO, SrTiO 3 , CdS, GaP, InP, GaAs, BaTiO 3 , K 2 NbO 3 , Fe 2 O 3 , Ta 2 O 5 , WO 3 , SnO 2 , Bi 2 O 3 , NiO, Cu 2 O, SiC, SiO 2 , MoS 2 , InPb, RuO 2 , CeO 2 , etc., and Pt, Rh, RuO 2 , Nb, Cu, Sn, NiO, etc. All conventionally known materials supporting metals and metal oxides can be applied.
[0012]
One typical production method is a method in which a semiconductor photocatalyst powder is first supported on such a substrate, and then a metal oxide sol is applied by a method such as impregnation. That is, first, if the substrate has three-dimensional pores such as a ceramic mat or a fiber product, the semiconductor photocatalyst powder is applied to the pores of the substrate in advance by a method such as coating and impregnation. In addition, if the surface has a relatively smooth surface, such as glass, PMMA, ceramic, metal, or plastic moldings, the surface is sprayed in advance by a method such as spraying, dip coating, or spin coating. A photocatalyst powder layer is formed in advance. A metal organic compound such as a metal alkoxide, acetylacetonate, carboxylate or the like employed in a sol-gel method, or a chloride alcohol solution such as titanium tetrachloride is applied to the photocatalyst powder carrier to which the photocatalyst powder is merely attached. A sol of a metal oxide obtained by hydrolysis in the presence of an acid or an alkali catalyst is impregnated, and a solvent component is skipped to gel to form a metal oxide gel, thereby obtaining a desired photocatalyst.
[0013]
However, as another method, a metal organic compound such as metal alkoxide, acetylacetonate, carboxylate or the like employed in the sol-gel method, or a chloride alcohol solution such as titanium tetrachloride is hydrolyzed in the presence of an acid or alkali catalyst. A mixed solution of the metal oxide sol and the photocatalyst powder obtained by the above is prepared, and instead of supporting only the semiconductor photocatalyst powder on the substrate, the mixed solution is impregnated, coated, or supported by various coating methods. Then, a photocatalyst having the same effect is obtained in the method of gelation.
[0014]
Alternatively, before obtaining a metal oxide sol, a photocatalyst powder obtained by first mixing a photocatalyst powder with an alcohol solution of the above-mentioned metal organic compound or chloride and hydrolyzing in the presence of an acid or alkali catalyst. A similar effect may be obtained by a method in which the mixed sol is impregnated on a substrate, coated or supported by various coating methods, and gelled.
[0015]
The metal oxide sol used in any of these methods may be effective when two or more metal oxide sols are mixed and used as a metal composite oxide sol.
[0016]
As described above in detail, in the production process of the photocatalyst according to the present invention, it is most important that the porous metal oxide formed from the photocatalyst powder and the metal oxide sol has a good structure. However, there is no limitation on the raw materials, handling methods, and the like of the two.
[0017]
Here, it is considered that the favorable configuration of the photocatalyst powder and the supported fixing agent is as follows. In other words, the photocatalyst powder supported on the substrate by a method such as coating or impregnation has a very low adhesion to the substrate, but has a large porosity and surface area and maintains a catalytic activity relatively close to a powder state. I have. Next, when the metal oxide sol was impregnated into the powder photocatalyst carrier and gelled, it became a network of metal oxide gel having a large number of pores or penetrating between the photocatalyst powder particles and the substrate, and was carried on the substrate. The powder photocatalyst is held so as to be taken into the so-called mesh, so that it becomes a strong binder. The concern here is that the metal oxide gel derived from the metal oxide sol or the metal oxide itself obtained by heat treatment acts as a photocatalyst or coats the surface of the photocatalyst powder to photoexcit the photocatalyst powder. UV light scattered or absorbed, and may hinder photoexcitation of the photocatalyst powder. However, in the photocatalyst according to the present invention, as shown in Examples, for example, when titanium oxide is used for the metal oxide sol, the titanic acid polymer or titanium oxide derived from the titanium oxide sol is immobilized on the photocatalyst powder. While acting as an agent, it did not exhibit such a so-called obstructive effect at all. That is, as a result, the surface of the photocatalyst powder is sufficiently in contact with the solution interface, and the metal oxide gel is configured not to cover the active sites of the photocatalytic reaction.
[0018]
Unfortunately, the above configuration is only one guess, and the present inventors have not been able to elucidate the mechanism of action of the product of the present invention. However, a photocatalyst having excellent catalytic activity and a certain mechanical strength, which cannot be obtained only with a conventionally known photocatalyst powder and a metal oxide gel alone, can be obtained only by combining a photocatalyst powder and a metal oxide sol. It became possible.
[0019]
【Example】
<Example 1>
1.5 g of glass fiber having a fiber diameter of 19 μm was dispersed in 1 liter of water, and the resultant was made into a paper to obtain a glass mat having an area of 100 cm 2 (100 mm × 100 mm) and a thickness of 1.1 mm as a substrate. 10 g of anatase-type titanium oxide (specific surface area: 50 m3 / g, particle size: 0.03 μm) as a photocatalyst powder was suspended in 100 ml of water to form a water slurry, which was impregnated into a substrate prepared in advance, and dried to obtain a photocatalyst powder. Was carried. The supported amount of titanium oxide was 2.0 g. Next, 10 g of titanium isopropoxide was dissolved in 100 ml of ethanol, and a mixed solution of 50 ml of ethanol, 5 ml of water, and 0.7 ml of concentrated hydrochloric acid was added thereto and hydrolyzed to obtain a titanium oxide sol. . A glass mat pre-impregnated with titanium oxide powder was immersed in the titanium oxide sol, quickly pulled up, dried at 50 ° C. for 1 hour to remove solvent alcohol, and then heat-treated at 350 ° C. for 2 hours to form a photocatalyst. . The supported amount of titanium oxide was 2.06 g.
[0020]
<Example 2>
5 g of silicon tetraethoxide was dissolved in 100 ml of ethanol, and a mixed solution of 50 ml of ethanol, 5 ml of water and 0.7 ml of concentrated hydrochloric acid was added thereto and hydrolyzed to obtain a silica sol. This silica sol was impregnated with a water slurry of titanium oxide in advance and immersed in a glass mat carrying titanium oxide in the same manner as in Example 1, and was quickly pulled up and dried at 50 ° C. for 1 hour to evaporate the solvent alcohol. Heat treatment was performed at 400 ° C. for 2 hours to obtain a photocatalyst. The supported amount of titanium oxide was 2.0 g.
[0021]
<Example 3>
3 g of titanium isopropoxide was dissolved in 50 ml of ethanol, and a mixed solution of 20 ml of ethanol, 2 ml of water and 0.3 ml of concentrated hydrochloric acid was added thereto to obtain a titanium oxide sol. 5 g of anatase-type titanium oxide (particle size: 0.2 μm), which had been heat-treated at 350 ° C. for 2 hours, was dispersed therein, and a photocatalyst layer was formed on a 30 mm × 30 mm glass plate by dip coating. At this time, the supported amount of titanium oxide was 1.1 mg.
[0022]
[Test Example on Effectiveness of Catalyst Body]
<Test Example 1>
The photocatalyst bodies obtained in Example 1 and Example 2 were cut into 30 mm × 30 mm and each was taken as (a) and (b) (amount of titanium oxide (a): 0.18 g, (b): 0.17 g), 200 ml Placed on the bottom of the beaker. 100 ml of a phenol aqueous solution having a concentration of 0.1 mmol / l was added thereto, and ultraviolet light of 400 nm to 300 nm from a 1 kW high-pressure mercury lamp was irradiated from the bottom of the beaker. . The ultraviolet intensity at this time was 8.79 μe Einstein / min.
[0023]
As a result, in both (a) and (b), the concentration of phenol was reduced by half about 20 minutes after the start of light irradiation, and decomposed below the detection limit in about 3 hours. For comparison, 0.18 g of titanium oxide powder supported on a photocatalyst was suspended as powder (c), and titanium oxide obtained by hydrolysis of titanium isopropoxide was supported on a glass mat (d). ) And 0.18 g of a photocatalyst powder mixed with a PTFE dispersion to form a solid and heat-treated at 200 ° C. (e). The same examination was performed. FIG. 1 shows the phenol decomposition characteristics of these photocatalysts. Other photocatalysts were not decomposed even after irradiation for 4 hours.
[0024]
<Test Example 2>
The photocatalyst obtained in Example 3 was placed inside a glass tube having a diameter of 50 mm to form a closed system. When the photocatalyst was irradiated with 400-300 nm ultraviolet light of a 300 W xenon lamp at 30 μE / min while refluxing air containing, acetaldehyde was almost decomposed in about 15 minutes after the start of light irradiation. For comparison, 1.1 mg of titanium oxide prepared by the sol-gel method was subjected to the same examination, and was not decomposed even after irradiation for 4 hours.
[0025]
【The invention's effect】
As described in detail above, the photocatalyst according to the present invention is a novel photocatalyst having a photocatalyst powder supported and fixed on a substrate, having a certain mechanical strength, and maintaining a high photocatalytic activity as a powder. Photocatalyst, and its industrial value is extremely large.
[Detailed description of drawings]
FIG. 1 is a graph showing the photocatalytic decomposition characteristics of Test Example 1 of a photocatalyst according to an example of the present invention.

Claims (1)

光触媒粉末を基体に担持固定化してなる光触媒体であって、光触媒粉末の担持固定化材として金属酸化物ゾルを400℃以下の温度で加熱処理して生成する多孔性金属酸化物を用いてなることを特徴とする光触媒体。A photocatalyst obtained by supporting and fixing a photocatalyst powder on a substrate, wherein a porous metal oxide produced by heat-treating a metal oxide sol at a temperature of 400 ° C. or lower is used as a support and fixing material for the photocatalyst powder. A photocatalyst comprising:
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