JP3790189B2 - Novel synthesis method of visible light responsive BiVO4 fine powder, photocatalyst comprising the BiVO4 fine powder, and purification method using the photocatalyst - Google Patents
Novel synthesis method of visible light responsive BiVO4 fine powder, photocatalyst comprising the BiVO4 fine powder, and purification method using the photocatalyst Download PDFInfo
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- JP3790189B2 JP3790189B2 JP2002181107A JP2002181107A JP3790189B2 JP 3790189 B2 JP3790189 B2 JP 3790189B2 JP 2002181107 A JP2002181107 A JP 2002181107A JP 2002181107 A JP2002181107 A JP 2002181107A JP 3790189 B2 JP3790189 B2 JP 3790189B2
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- 239000000843 powder Substances 0.000 title claims description 55
- 239000011941 photocatalyst Substances 0.000 title claims description 49
- 238000000034 method Methods 0.000 title claims description 20
- 238000000746 purification Methods 0.000 title claims description 7
- 229910002915 BiVO4 Inorganic materials 0.000 title 2
- 238000001308 synthesis method Methods 0.000 title 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 24
- 239000001301 oxygen Substances 0.000 claims description 24
- 229910052760 oxygen Inorganic materials 0.000 claims description 24
- 239000000126 substance Substances 0.000 claims description 23
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- 238000000862 absorption spectrum Methods 0.000 claims description 2
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- IGFHQQFPSIBGKE-UHFFFAOYSA-N Nonylphenol Natural products CCCCCCCCCC1=CC=C(O)C=C1 IGFHQQFPSIBGKE-UHFFFAOYSA-N 0.000 description 30
- SNQQPOLDUKLAAF-UHFFFAOYSA-N nonylphenol Chemical compound CCCCCCCCCC1=CC=CC=C1O SNQQPOLDUKLAAF-UHFFFAOYSA-N 0.000 description 30
- IISBACLAFKSPIT-UHFFFAOYSA-N bisphenol A Chemical compound C=1C=C(O)C=CC=1C(C)(C)C1=CC=C(O)C=C1 IISBACLAFKSPIT-UHFFFAOYSA-N 0.000 description 24
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- LSGOVYNHVSXFFJ-UHFFFAOYSA-N vanadate(3-) Chemical compound [O-][V]([O-])([O-])=O LSGOVYNHVSXFFJ-UHFFFAOYSA-N 0.000 description 4
- DNXHEGUUPJUMQT-UHFFFAOYSA-N (+)-estrone Natural products OC1=CC=C2C3CCC(C)(C(CC4)=O)C4C3CCC2=C1 DNXHEGUUPJUMQT-UHFFFAOYSA-N 0.000 description 3
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- 101710134784 Agnoprotein Proteins 0.000 description 3
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- 238000002441 X-ray diffraction Methods 0.000 description 3
- 229910052797 bismuth Inorganic materials 0.000 description 3
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 3
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- PROQIPRRNZUXQM-ZXXIGWHRSA-N estriol Chemical compound OC1=CC=C2[C@H]3CC[C@](C)([C@H]([C@H](O)C4)O)[C@@H]4[C@@H]3CCC2=C1 PROQIPRRNZUXQM-ZXXIGWHRSA-N 0.000 description 3
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
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- XKGLSKVNOSHTAD-UHFFFAOYSA-N valerophenone Chemical compound CCCCC(=O)C1=CC=CC=C1 XKGLSKVNOSHTAD-UHFFFAOYSA-N 0.000 description 2
- RNMDNPCBIKJCQP-UHFFFAOYSA-N 5-nonyl-7-oxabicyclo[4.1.0]hepta-1,3,5-trien-2-ol Chemical compound C(CCCCCCCC)C1=C2C(=C(C=C1)O)O2 RNMDNPCBIKJCQP-UHFFFAOYSA-N 0.000 description 1
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 1
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 235000002597 Solanum melongena Nutrition 0.000 description 1
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910001413 alkali metal ion Inorganic materials 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
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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
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/30—Wastewater or sewage treatment systems using renewable energies
- Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy
Description
【0001】
【発明の属する技術分野】
本発明は、可視光応答性のバナジン酸ビスマス(BiVO4)微粉末の改良された製造方法、前記方法により得られた改善された可視光応答性を示す新規な可視光応答性バナジン酸ビスマス微粉末光触媒、および可視光応答性バナジン酸ビスマス(BiVO4)微粉末光触媒を利用して、少なくとも可視光下に有機系環境汚染物質、例えばノニルフェノール、ビスフェノールA、天然エストロゲンなどの低濃度で内分泌攪乱作用をする環境汚染物質を可視光分解して環境、特に水系を浄化する方法に関する。
【0002】
【従来技術】
オクチルフェノール、ノニルフェノール、ビスフェノールA、天然エストロゲンなどの化学物質は環境ホルモン作用があることが発見されて以来、その浄化処理が問題とされている。中でも、エストロゲン類は、前記ホルモン活性においても、また、水処理設備での除去が難しいことにおいても、非常に問題とされている。すなわち、前記女性ホルモン活性のエストロゲン類は、前記ノニルフェノール、ビスフェノールAに比べ、約1000倍から100000倍強い活性を有していると報告されている〔松井三郎:環境技術,vol.27,No.9,p665〜675(1998年)、文献1〕。また、前記女性ホルモン類は下水処理施設においても、その除去率は80%以下と低いだけでなく、活性汚泥を脱水する時に得られる脱水濾液から高濃度の女性ホルモン類が検出されることから、女性ホルモン類は一次的に生物吸着した状態で除去されているだけで、活性汚泥中の微生物による実際の分解率はかなり低いと推定されるとの報告もある〔松井三郎:環境技術,vol.27,No.9,p665〜675(1998年)文献2、建設省都市局下水道部流域下水道課「下水道における内分泌攪乱化学物質に関する調査・中間報告について」、平成11年6月22日、文献3〕
また、前記ノニルフェノール(NP)は、下水処理過程において工業用非イオン性界面活性剤であるノニルフェノールポリエトキシレート(NPEO)のバクテリアによる生分解を経て生成することが報告されている〔Giger, W., et al, Science 225. 623 (1984)、文献4〕。また、NPは下水処理の生物処理工程で活性汚泥に取り込まれて除去されるが、生分解して無毒化することが出来ず、活性汚泥中に蓄積しているとの報告もある〔Tateda, M., et al, Water Sci. Technol. 44. 101 (2001)、文献5〕。
【0003】
こんな中で、PelizzettiらはTiO2を用いて光分解によりNPおよびNPEOをCO2にまで完全酸化されることを示した〔Pelizzetti, E.,et al,Environ.Sci.Technol.23.1380 (1989)、文献6〕。
また、前記女性ホルモン類を含有する液体に前記物質の酸化分解力を有する物質、例えば酸化チタン(TiO2)や酸化亜鉛(ZnO)に代表される光触媒材料により発生する酸素、およびオゾン、過酸化水素水、次亜塩素酸などの酸化剤、紫外線やエキシマレーザー等から発する酸化力を有する光、及び女性ホルモン特有のステロイド構造を分解したり酸化することができる微生物等を接触させることにより、女性ホルモン類をホルモン活性のない物質に分解することが報告、または提案されている〔(特開2001−149929、平成13年6月5日公開(文献7)、2001−198584、平成13年7月24日公開(文献8)〕。
【0004】
文献8では、排水中に含まれる前記女性ホルモン類等の環境汚染化合物の問題を取り除くために、酸化チタン光触媒の優れた有機物分解活性に着目し、前記女性ホルモン類の処理に酸化チタン光触媒を活用することを提案している。また、静岡工業技術センターの鈴木光彰、松本豊等は研究報告45の報告24(2001年12月1日)では、ガラスビーズにゾルゲル法で酸化チタン薄膜を形成した光触媒を用いてメチレンブルー、非イオン系界面活性剤のポリオキシエチレンノニルフェノールエーテル(PONE)の光分解を試みており、特に後者の分解機構として、初期のPONEの細分化段階と、その後の二酸化炭素までへの分解からなる2段階分解を推測している。
その他、2002年3月の日本化学会第81春季年会において、日高久夫等は二酸化チタンを用いた内分泌攪乱物質の光分解のメカニズムなどを発表している。
このように光触媒を用いて、内分泌攪乱物質等の環境汚染物質を分解する研究も盛んに行われている。
【0005】
一方、光触媒については、太陽の光をクリーンなエネルギーを製造するのに利用しようという観点から、水を光分解して水素および/または酸素を製造ための触媒として利用することの研究も活発になされている。ところで、太陽光の約95%は可視光であることを考えると、前記酸化チタン光触媒は紫外光で活性であるが、可視光に応答しないので太陽光の利用効率の観点から十分とはいえないという問題がある。そこで、前記問題を改善するために可視光応答性の多くの新規な光触媒が提案されている。そのような中に、BiVO4を水の光化学的分解反応の触媒として使用することが既に報告されている(Catalysis Letters 53(1998).229-230、文献9)。また、従来のBiVO4製造方法は、前記文献9に記載されているようにBi3O3(関東化学(株)、純度98%)およびNH4VO3(関東化学(株)、純度99%)からなる混合物をアルミナるつぼ中で、大気圧下において700℃または900℃で5時間焼成することによって合成されていた(固相法)。しかし、前記BiVO4の製造方法はエネルギー的にも、製造装置的にもコストパフォーマンスがあまり良くない、および得られたBiVO4の活性も高くないという問題があった。
【0006】
そこで、工藤等は、前記問題点を改善したBiVO4の製造方法として、層状バナジン酸アルカリと硝酸ビスマス五水和物とを水中で室温において撹拌して反応させBiVO4結晶を製造するソフト溶液プロセスを提案している〔特開2001−2419、平成13年1月9日公開、文献10〕。文献10の製造プロセスで得られたBiVO4結晶は、前記焼成工程を経て合成されたBiVO4よりも高い光触媒活性を持つものが得られるという利点がある。しかしながら、(1)BiVO4を製造するのに三日間という長時間を必要とする、および(2)出発原料の構成元素であるアルカリ金属イオンが微量不純物として残留する恐れがある、という問題がある。また、BiVO4については、水の光分解における420nmより長波長の可視光下での活性効果については検討されているが、前記内分泌攪乱物質等を光分解する活性については未検討である。
【0007】
【発明が解決しようとする課題】
本発明の第1の課題は、前記問題が改善された効率的な可視光活性を有するBiVO4を製造する方法を提供することであり、第2の課題は、前記内分泌攪乱物質に有用な可視光活性を示す新規光分解用触媒を提供することである。
前記第1の課題を解決するために、従来、触媒調製において、下記式1の反応工程による、尿素の加水分解により放出されるアンモニアによるpHの上昇を利用した均一沈殿法がしばしば用いられる。
(NH2)2CO + H2O → 2NH3 + CO2↑ 式1
そこで,前記ソフト溶液プロセスの2つの問題を改善するために、前記方法を利用することを発想し、尿素を用いた均一沈殿法によるBiVO4の合成を試みた。その結果、約6時間という短時間で可視光応答性があるBiVO4を合成できること、また、得られたBiVO4のX線回折と拡散反射スペクトル測定から、欠陥が少ない結晶性のよいBiVO4粉末が得られることがわかり、前記課題の1を解決することができた。
【0008】
また、前記第2の課題は、光触媒BiVO4微粉末を、前記内分泌攪乱物質であるノニルフェノール(NP)、ビスフェノールA、天然エストロゲンを含む水中に分散し、400nmより長波長の疑似太陽光を照射して、前記可視光活性下での前記内分泌攪乱物質の光分解性を調べたところ、ノニルフェノール(NP)は太陽光照射並びに可視光照射により分解できること、光分解は水中の溶存酸素の影響を受けること、天然エストロゲンは可視光で分解できること、また、ビスフェノールAの可視光分解においては、特に、NaOH水溶液を溶媒としたアルカリ条件下で分解反応が進むことを確認でき、前記第2の課題を解決することができた。
【0009】
【課題を解決するための手段】
本発明の第1は、尿素の存在下にNH4VO3とBi(NO3)3を反応させる工程を含むことを特徴とする可視光応答性のBiVO4微粉末を製造する方法である。好ましくは、前記反応工程を60℃〜90℃の範囲で実施することを特徴とする前記可視光応答性のBiVO4微粉末を製造する方法であり、より好ましくは、前記反応工程が90℃±5℃の温度で最長12時間の熟成工程を含むことを特徴とする前記可視光応答性のBiVO4微粉末を製造する方法である。
本発明の第2は、60℃〜95℃の温度範囲で尿素の存在下にNH 4 VO 3 とBi(NO 3 ) 3 を反応させて得られた微粉末を90℃以上において熟成したXRDの18.8°、35°及び46°のピークの分裂が明瞭に観察され、吸収スペクトル特性において300nm〜400nmにおいて平坦であり、可視光領域に急な吸収端を示し、550nmより長波長において裾引きのない2.37eVのバンドギャップを持つことを特徴とするBiVO4微粉末から成る可視光応答性光触媒前記各製造方法によって得られたBiVO4微粉末から成る可視光応答性光触媒である。
【0010】
本発明の第3は、前記第2の発明の可視光応答性のBiVO4微粉末光触媒を用いて少なくとも可視光を含む光の照射下で内分泌攪乱物質を含有する被浄化水を処理して前記内分泌攪乱物質を光分解することを特徴とする浄化方法である。好ましくは、被浄化系をアルカリ性とするおよび/または酸素を溶存させることを特徴とする前記各浄化方法である。
【0011】
【本発明の実施の態様】
本発明をより詳細に説明する。
I.本発明の新規なBiVO4微粉末の製造方法において、熟成時の温度および時間は重要な条件である。例えば、熟成時間が短いと、正方晶系(tetragonal)の結晶のものが多く存在し、熟成時間が長くなるにつれて純粋な単斜晶系(monoclinic)の結晶のものが得られる。したがって、熟成時間は温度とも関連するが最長12時間、好ましくは2−12時間であり、2−3時間でも目的化合物が得られる。また、熟成時の温度も重要であり90±5℃が好ましい。
II.添加する尿素の量は得られるBiVO4微粉末の特性にほとんど影響しない。
添加量は原料のNH4VO3が1.40gとBi(NO3)3・5H2Oが5.82gに対し5−10gの範囲とすればよい。
【0012】
【実施例】
以下、実施例により本発明を具体的に説明するが、この例示により本発明が限定的に解釈されるものではない。
得られた光触媒の特性の測定装置の説明;
XRDは、理学社製のMiniFlexを用いた。
BETは、Coulter社製のSA3100Bを用いた。
拡散反射スペクトル測定は、日本分光社製のUbest V570を用いた。
光源;酸素発生光源は420nm以下の波長の光をカットオフするフィルターとXeランプを組み合わせたもの。または内分泌撹乱物質を分解する光源は400nm以下の波長の光をカットオフするフィルターとXeランプを組み合わせたものである、あるいは、ORIEL社製の68820型とエアマスフィルターAM2Dを組み合わせた擬似太陽光を放射する光源(太陽光シミュレーター)。太陽光シミュレーターのスペクトルを図12に示す。
【0013】
実施例1
新規なBiVO4光触媒粉末の製造方法
2モル/Lの硝酸にNH4VO3と(99.0%)とBi(NO3)3・5H2O(関東化学99.9%)を 0.12モル/L溶解させた水溶液をそれぞれ調製した。これらの水溶液(100mL)を混合した後,尿素を溶解させ、ホットスターラー上で90℃(363K)に加熱した。尿素量や熟成時間を変えて合成した。得られたBiVO4沈殿を濾過洗浄乾燥した。得られた粉末をXRD(RIGAKU;RINT−1400)を用いて同定した。拡散反射スペクトル計(DRS)(JASCO;Ubet V−570)を用いて吸収スペクトル特性を調べた。BET法による表面積測定(COULTER;SA−3100)を行った。
光触媒的酸素生成反応は閉鎖循環系内で行った。パイレックス(登録商標である)反応管に触媒1gと犠牲試薬AgNO3水溶液(0.05モル/L、320mL)を入れ、可視光(>420nm)を照射した。光源には、波長420nm以下の光をカットするフィルター(L42)を備えた300WXeランプを用いた。生成した酸素は,ガスクロで定量した。
【0014】
図1に90℃(363K)での熟成時間を変えた〔(a)1.5時間、(b)2時間、(c)3時間、(d)6時間、(e)8時間、(f)12時間〕ときに得られた粉末のX線回折パターンを示す。いずれもシーライト(灰重石)(scheelite)構造を持つBiVO4であることがわかった。これらのXRDピークの鋭さは、この水溶液中での低温合成において,結晶性のよい粉末が得られることを示している。
BET表面積は、0.3m2g−1であった。熟成時間が長くなるにつれて、18.8、35、46°のピークの分裂が明瞭になった。このことは、熟成時間が短いときには正方晶系(tetragonal)の結晶構造を持ったものが得られるのに対して、長くなるにつれて純粋な単斜晶系(monoclinic)の結晶構造を持ったものが得られることを示している。
表1に,合成条件を変えて得られたBiVO4の可視光照射下での酸素生成反応活性を示す.室温でも長時間反応させることによりBiVO4は得られたが、90℃(363K)で3時間以上熟成して得られたBiVO4が、高い光触媒活性を示した.熟成時間が短いBiVO4の活性が低いのは、前記図1で示されたように不活性な正方晶系のBiVO4が混ざっているためである。一方,光触媒活性は、尿素の添加量の影響を受けなかった。
【0015】
【表1】
【0016】
図2は、熟成を含む反応時間を8時間かけて、90℃で合成して得られたBiVO4(連続線で示す)と827℃(1100K)での固相法で合成されたBiVO4の拡散反射スペクトルである。固相法で合成したものでは吸収端が裾を引いている(点線で示す)。これは、高温合成のため構成元素の一部が揮発し、欠陥を生成していることを示唆している。これに対して、本発明の水溶液プロセスにより合成されたBiVO4は、可視光領域に急な吸収端を持つスペクトルが得られた。この吸収端から見積もられたバンドギャップは、2.37eVであった。このことから、尿素を用いた加水分解により欠陥が少ない結晶性のよいBiVO4粉末が、前記先行技術の水溶液プロセスに比べて、短時間で合成できることがわかった。
因みに、光触媒TiO2粉末(点線)と光触媒BiVO4微粉末(連続線)の拡散反射スペクトルを図11に示す。
【0017】
図3は、尿素5gを用いて熟成を含む反応時間を8時間かけて合成で得られたBiVO4粉末(8時間熟成)を用いて犠牲試薬AgNO3水溶液の光触媒的(λ>420nmの可視光における)酸素生成反応の経時変化を示す。効率良く酸素が光触媒的に生成していることがわかった。すなわち、可視光応答性の光触媒活性があることを示している。
【0018】
実施例2
可視光応答性光触媒BiVO4粉末のNPの光分解特性
1,太陽光照射によるNPの光分解特性
50mLのナスフラスコに、NaOH(ナカライテスク,試薬特級)水溶液(pH=11.6)に溶かしたNP(関東化学,99.5%)2.0×10−4Mの試料溶液25mLを入れ、光触媒BiVO40.2gを加えた。1時間暗室で攪拌した後、そのまま攪拌しながら太陽光〔2001年10月15日(金沢、快晴、21-23℃)の太陽光、線量;照射直前:90.6mW/cm2、照射停止直後:98.4mW/cm2〕を照射した。
NPの濃度変化を図4に示す。NPの光分解が確認できる。
【0019】
2,太陽光シミュレーターによる反応
NaOH(ナカライテスク,試薬特級)水溶液(pH=13.0)に溶かしたNP(関東化学,99.5%)2.0×10−4Mの試料溶液、または蒸留水に溶かしたNP(関東化学,99.5%)2.0×10−4Mの試料溶液25mLを85mLの円筒型石英セルに入れ、光触媒BiVO4またはTiO20.2gを加えて、1時間暗室で攪拌させた後、そのまま攪拌しながら太陽光シミュレーター〔ORIEL 68820型,エアマスフィルター;AM2D、線量;26mW/cm2〕で反応させた。その放射光スペクトルを図12に示す。
NPの濃度変化を図5に示す。図5における空気飽和(酸素分圧 0.2atm)させた場合の光触媒BiVO4(◆)、光触媒TiO2(◇)、と酸素飽和(酸素分圧 1atm)させた場合の光触媒BiVO4(▲)、光触媒TiO2(△)の結果から、NPの光分解が確認でき、かつ、光触媒BiVO4活性は溶存酸素に影響を受けることが分かる。また、酸素飽和の条件下では、光触媒BiVO4のほうが光触媒TiO2よりも分解が速く、活性が高いのは明らかである。
【0020】
3,2×10−4MのNP溶液に可視光応答性光触媒BiVO4微粉末を分散し、光照射をしないで攪拌だけを行ったときの濃度変化(■)、400nmより長波長の可視光を照射したときの濃度変化(●)、および光触媒を加えないで光照射した場合の濃度変化(▲)を図6に示す。この結果から、可視光応答性光触媒BiVO4微粉末が400nm以上の可視光で作用して、NPを分解することは明らかである。
【0021】
4,可視光応答性光触媒BiVO4微粉末を分散した2×10−4MのNP溶液における、可視光照射(400nmより長波長)による光触媒BiVO4微粉末のNP分解に対する酸素の効果を調べるために、空気飽和(■)、酸素飽和(▲)、窒素飽和(◆)の条件でのNPの濃度変化を検討した。その結果を図7に示す。それぞれの条件における分解速度定数を表2に示す通り算出した。酸素の効果は明らかである。
【0022】
【表2】
【0023】
実施例3
可視光応答性光触媒BiVO4微粉末のビスフェノールAの光分解特性
図8は、ビスフェノールA(関東化学,環境分析用)を水またはNaOH(pH12.8)水溶液に1.0×10−4M溶かした溶液に、可視光応答性光触媒BiVO4微粉末を分散させ、これに可視光(>400nm)(水銀灯の線量は30mW/cm2)を照射したときのビスフェノールAの濃度変化を示す。なお、原料の濃度はHPLC法でバレロフェノンを内部標準とした検量線から求めた。溶媒に水を用いた時はなかなか反応が進まなかったのに対し、NaOHを加えた場合には、光分解反応が活発であり、光照射7時間後にビスフェノールAの濃度は、照射前の約1/5まで減少していた。前記光分解は、1次の反応速度式に従うとして、分解速度定数をもとめ、表3にまとめた。このことより、溶媒のpHの違いで分解速度が大きく変化することがわかった。
【0024】
【表3】
【0025】
実施例4
可視光応答性光触媒BiVO4微粉末を用いたエストロゲン(17β−エストラジオール,エストロン,エストリオール)の可視光による分解
エストロゲンをpH12.8の水に溶かした溶液にBiVO4微粉末を分散し、これに可視光(>400nm)を照射したときのエストロゲンの濃度変化図9に示す。なお、エストロゲンの濃度はHPLC法でバレロフェノンを内部標準とした検量線から求めた。光照射8時間後の濃度はいずれも約1/4となり、可視光で3つの天然エストロゲンを分解できることが明らかとなった。分解は、1次の反応速度式に従うとして、速度定数をもとめ、逆数をとることにより、寿命を求めた。これらの値を表4にまとめた。これより、エストラジオール,エストロン,エストリオールの反応速度は、多少の違いはあるもののほとんど変わらないことがわかった。すなわち、これらエストロゲンの分解では17位での置換基の変化による影響は、ほとんど受けないということが確認できた。
【0026】
【表4】
【0027】
実施例5
可視光応答性光触媒BiVO4微粉末を用いた17β−エストラジオールの太陽光による分解
図10は晴天下で光触媒BiVO4微粉末を加えた場合と、加えなかった場合の17β−エストラジオールの濃度変化である。光触媒BiVO4微粉末が存在する場合、2時間後に溶液中の17β−エストラジオールはほぼ完全に消失している。一方、光触媒BiVO4微粉末が存在しない場合は、若干の減少はみられるものの分解速度はかなり遅いことがわかる。従って、17β−エストラジオールは、太陽光照射によるBiVO4微粉末の光触媒作用により効率よく分解できることが明らかとなった。
【0028】
【発明の効果】
以上のことから、可視光応答性BiVO4微粉末光触媒、特に本発明により製造された新規な可視光応答性BiVO4微粉末光触媒は、可視光を利用して被浄化系、特に被浄化水系に存在する内分泌攪乱物質であるノニルフェノール、ビスフェノールA、天然エストロゲン等を光分解できるという、現在の社会で非常に問題とされている環境汚染物質を浄化する手段として貢献すること大である。特に、新規なBiVO4微粉末の製造方法は効率よく、太陽光の利用効率を改善できる可視光応答性の光触媒を合成できることも、実用可能性が大きい。
【図面の簡単な説明】
【図1】熟成時間を変えたXRDパターン;(a)1.5時間、(b)2時間、(c)3時間、(d)6時間、(e)8時間、(f)12時間
【図2】BiVO4の拡散反射スペクトル;連続線は尿素を用いて製造したもの、点線は固相反応で得られたもの
【図3】本発明で製造されたBiVO4の420nmより波長可視光下における犠牲試薬AgNO3水溶液からの酸素発生光触媒活性(300Wキセノンランプ)
【図4】実施例2の可視光応答性光触媒BiVO4粉末を用いた太陽光照射(平成13年10月15日,金沢,快晴,21−23℃)によるNPの光分解特性
【図5】11 太陽光シミュレーターを用いたNaOH水溶液(pH=13.0)に溶かしたNPの分解特性;空気飽和(酸素分圧 0.2atm)させた場合の光触媒BiVO4(◆)、光触媒TiO2(◇)、酸素飽和(酸素分圧 1atm)させた場合の光触媒BiVO4(▲)、光触媒TiO2(△)
【図6】光触媒BiVO4微粉末のNP分解に対する可視光照射の効果
【図7】可視光照射による光触媒BiVO4微粉末のNP分解に対する被浄化水中の酸素の効果
【図8】実施例3のビスフェノールAを水またはNaOH(pH12.8)水溶液に1.0×10−4Mを溶かした溶液中での光触媒BiVO4微粉末のビスフェノールAの光分解特性
【図9】実施例4の可視光応答性光触媒BiVO4微粉末を用いたエストロゲン(176−エストラジオール,エストロン,エストリオール)の可視光による分解特性
【図10】晴天下(平成13年10月30日,金沢,快晴,16−21℃)での光触媒BiVO4微粉末による176−エストラジオールの分解特性
【図11】光触媒TiO2粉末(点線)と光触媒BiVO4微粉末(連続線)の拡散反射スペクトル
【図12】太陽光シミュレーターの放射光スペクトル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improved method for producing visible light responsive bismuth vanadate (BiVO 4 ) fine powder, and a novel visible light responsive bismuth vanadate fine powder exhibiting improved visible light responsiveness obtained by the method. Utilizing powder photocatalyst and visible light responsive bismuth vanadate (BiVO 4 ) fine powder photocatalyst, endocrine disrupting action at low concentration of organic environmental pollutants such as nonylphenol, bisphenol A, natural estrogen at least under visible light The present invention relates to a method for purifying the environment, particularly an aqueous system, by decomposing visible environmental pollutants.
[0002]
[Prior art]
Since chemical substances such as octylphenol, nonylphenol, bisphenol A, and natural estrogens have been discovered to have environmental hormonal effects, purification treatment has been a problem. Among them, estrogens are considered to be very problematic both in the hormonal activity and in the difficulty of removal with water treatment facilities. That is, it is reported that the female hormone-active estrogens have about 1000 to 100,000 times stronger activity than the nonylphenol and bisphenol A [Saburo Matsui: Environmental Technology, vol. 27, no. 9, p665-675 (1998), literature 1]. In addition, the female hormones are not only low in the sewage treatment facility, but the removal rate is as low as 80% or less, and high concentrations of female hormones are detected from the dehydrated filtrate obtained when dewatering the activated sludge. It has been reported that female hormones are only removed primarily in the state of bioadsorption, and that the actual degradation rate by microorganisms in activated sludge is estimated to be considerably low [Saburo Matsui: Environmental Technology, vol. 27, no. 9, p665-675 (1998)
In addition, it has been reported that nonylphenol (NP) is produced through biodegradation by bacteria of nonylphenol polyethoxylate (NPEO), which is an industrial nonionic surfactant, in the sewage treatment process [Giger, W. , et al, Science 225. 623 (1984), literature 4]. In addition, although NP is taken up and removed by activated sludge in the biological treatment process of sewage treatment, there is a report that it cannot be biodegraded and detoxified and accumulates in activated sludge [Tateda, M., et al, Water Sci. Technol. 44. 101 (2001), literature 5].
[0003]
In this, Pelizzetti et al. Showed that NP and NPEO were completely oxidized to CO 2 by photolysis using TiO 2 [Pelizzetti, E., et al, Environ. Sci. Technol. 23.1380 (1989). Reference 6].
Further, a substance having the oxidative decomposition ability of the substance in the liquid containing the female hormones, for example, oxygen generated by a photocatalytic material typified by titanium oxide (TiO 2 ) and zinc oxide (ZnO), ozone, and peroxidation By contacting oxidants such as hydrogen water and hypochlorous acid, light having an oxidizing power emitted from ultraviolet rays, excimer lasers, etc., and microorganisms that can decompose or oxidize the steroid structure peculiar to female hormones. It has been reported or proposed to decompose hormones into substances having no hormone activity [(JP 2001-149929, published June 5, 2001 (Reference 7), 2001-198584, July 2001]. Released on 24th (Reference 8)].
[0004]
Reference 8 focuses on the excellent organic substance decomposing activity of the titanium oxide photocatalyst to remove the problem of environmental pollutants such as the female hormones contained in the wastewater, and uses the titanium oxide photocatalyst for the treatment of the female hormones. Propose to do. In addition, Mitsuaki Suzuki, Yutaka Matsumoto, et al. Of Shizuoka Industrial Technology Center reported in Research Report 45 Report 24 (December 1, 2001) using a photocatalyst in which a titanium oxide thin film was formed on a glass bead by a sol-gel method. Photo-decomposition of polyoxyethylene nonylphenol ether (PONE), a surfactant based on surfactants. In particular, as the latter decomposition mechanism, two-stage decomposition consisting of initial PONE fragmentation and subsequent decomposition to carbon dioxide I guess.
In addition, at the 81st Spring Meeting of the Chemical Society of Japan in March 2002, Hisao Hidaka and others presented the mechanism of photolysis of endocrine disrupting substances using titanium dioxide.
In this way, research on decomposing environmental pollutants such as endocrine disrupting substances using photocatalysts has been actively conducted.
[0005]
On the other hand, with regard to photocatalysts, from the viewpoint of using solar light to produce clean energy, research on using water as a catalyst for producing hydrogen and / or oxygen by photodegrading water is also actively conducted. ing. By the way, considering that about 95% of sunlight is visible light, the titanium oxide photocatalyst is active in ultraviolet light, but it does not respond to visible light, so it cannot be said that it is sufficient from the viewpoint of utilization efficiency of sunlight. There is a problem. Therefore, many novel photocatalysts with visible light responsiveness have been proposed in order to improve the problem. Under such circumstances, it has already been reported that BiVO 4 is used as a catalyst for the photochemical decomposition reaction of water (Catalysis Letters 53 (1998). 229-230, Reference 9). In addition, the conventional BiVO 4 production method includes Bi 3 O 3 (Kanto Chemical Co., Ltd., purity 98%) and NH 4 VO 3 (Kanto Chemical Co., Ltd., purity 99%, as described in Reference 9 above. ) In an alumina crucible for 5 hours at 700 ° C. or 900 ° C. under atmospheric pressure (solid phase method). However, the production method of the BiVO 4 is also energetically poor cost in production apparatus manner is much, and the resulting activity of BiVO 4 also has a problem that not high.
[0006]
Therefore, Kudo et al., As a method for producing BiVO 4 with improved problems, is a soft solution process for producing BiVO 4 crystals by stirring and reacting a layered alkali vanadate and bismuth nitrate pentahydrate at room temperature in water. [JP 2001-2419, published on January 9, 2001, reference 10]. The BiVO 4 crystal obtained by the production process of
[0007]
[Problems to be solved by the invention]
The first object of the present invention is to provide a method for producing BiVO 4 having an efficient visible light activity in which the above problems are improved, and the second object is to provide a visible light useful for the endocrine disrupting substance. It is to provide a novel photolysis catalyst exhibiting photoactivity.
In order to solve the first problem, conventionally, in the catalyst preparation, a uniform precipitation method using a pH increase due to ammonia released by hydrolysis of urea by a reaction step of the following
(NH 2 ) 2 CO + H 2 O → 2NH 3 + CO 2 ↑
Then, in order to improve the two problems of the soft solution process, the idea was to use the method, and an attempt was made to synthesize BiVO 4 by the homogeneous precipitation method using urea. As a result, it is possible to synthesize BiVO 4 having visible light responsiveness in a short time of about 6 hours. From the X-ray diffraction and diffuse reflection spectrum measurement of the obtained BiVO 4 , BiVO 4 powder having good crystallinity with few defects. As a result, it was possible to solve the first problem.
[0008]
The second problem is that the photocatalytic BiVO 4 fine powder is dispersed in water containing nonylphenol (NP), bisphenol A, and natural estrogen, which are the endocrine disrupting substances, and irradiated with simulated sunlight having a wavelength longer than 400 nm. As a result of examining the photodegradability of the endocrine disrupting substance under the visible light activity, nonylphenol (NP) can be decomposed by sunlight irradiation and visible light irradiation, and photolysis is affected by dissolved oxygen in water. Natural estrogen can be decomposed by visible light, and in the visible light decomposition of bisphenol A, it can be confirmed that the decomposition reaction proceeds particularly under alkaline conditions using an aqueous NaOH solution as a solvent, thereby solving the second problem. I was able to.
[0009]
[Means for Solving the Problems]
A first aspect of the present invention is a method for producing a visible light responsive BiVO 4 fine powder comprising a step of reacting NH 4 VO 3 and Bi (NO 3 ) 3 in the presence of urea. Preferably, the reaction step is performed in a range of 60 ° C. to 90 ° C., and the method for producing the visible light responsive BiVO 4 fine powder is more preferable. More preferably, the reaction step is 90 ° C. ± at 5 ° C. temperature is a method for producing the visible light response of BiVO 4 powder, characterized in that it comprises a maturation step of up to 12 hours.
The second aspect of the present invention is an XRD obtained by aging a fine powder obtained by reacting NH 4 VO 3 and Bi (NO 3 ) 3 in the presence of urea in the temperature range of 60 ° C. to 95 ° C. at 90 ° C. or higher. The splitting of peaks at 18.8 °, 35 ° and 46 ° is clearly observed, the absorption spectrum is flat from 300 nm to 400 nm, shows a sharp absorption edge in the visible light region, and is tailed at wavelengths longer than 550 nm. having a band gap of no 2.37eV visible light responsive photocatalyst consisting of BiVO 4 fine powder obtained by BiVO 4 visible light responsive photocatalysts each manufacturing process comprising fine powder wherein a.
[0010]
According to a third aspect of the present invention, by using the visible light responsive BiVO 4 fine powder photocatalyst according to the second aspect of the present invention, the purified water containing an endocrine disrupting substance is treated under the irradiation of light containing at least visible light, A purification method characterized by photodegrading an endocrine disrupting substance. Preferably, each of the purification methods is characterized in that the system to be purified is made alkaline and / or oxygen is dissolved.
[0011]
[Embodiments of the present invention]
The present invention will be described in more detail.
I. In the production method of the novel BiVO 4 fine powder of the present invention, the temperature and time during aging are important conditions. For example, when the aging time is short, many exist as crystalline tetragonal (tetragonal), is obtained as crystals of pure monoclinic as aging time increases (monoclinic). Therefore, although the aging time is related to the temperature, it is a maximum of 12 hours, preferably 2-12 hours, and the target compound can be obtained even in 2-3 hours. Moreover, the temperature at the time of aging is also important, and 90 ± 5 ° C. is preferable.
II. The amount of urea added has little effect on the properties of the resulting BiVO 4 fine powder.
The addition amount may be in the range of 5-10 g with respect to 1.40 g of raw material NH 4 VO 3 and 5.82 g of Bi (NO 3 ) 3 .5H 2 O.
[0012]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not interpreted limitedly by this illustration.
Description of the device for measuring the characteristics of the obtained photocatalyst;
For XRD, MiniFlex manufactured by Rigaku Corporation was used.
As BET, Coulter SA3100B was used.
The diffuse reflection spectrum was measured using Ubest V570 manufactured by JASCO Corporation.
Light source: The oxygen generation light source is a combination of a filter that cuts off light with a wavelength of 420 nm or less and an Xe lamp. Alternatively, the light source for decomposing endocrine disrupting substances is a combination of a filter that cuts off light with a wavelength of 400 nm or less and an Xe lamp, or a simulated sunlight that combines an ORIEL 68820 model and an air mass filter AM2D. Light source (sunlight simulator). The spectrum of the solar simulator is shown in FIG.
[0013]
Example 1
Production Method of Novel BiVO 4 Photocatalyst Powder NH 4 VO 3 (99.0%) and Bi (NO 3 ) 3 · 5H 2 O (Kanto Chemical 99.9%) were added to 2 mol / L nitric acid. Mole / L dissolved aqueous solutions were respectively prepared. After mixing these aqueous solutions (100 mL), urea was dissolved and heated to 90 ° C. (363 K) on a hot stirrer. They were synthesized with varying amounts of urea and aging time. The resulting BiVO 4 precipitate was filtered washed and dried. The obtained powder was identified using XRD (RIGAKU; RINT-1400). Absorption spectral characteristics were examined using a diffuse reflectance spectrometer (DRS) (JASCO; Ubet V-570). The surface area was measured by the BET method (COULTER; SA-3100).
The photocatalytic oxygen production reaction was carried out in a closed circulation system. Pyrex (registered trademark) reaction tube was charged with 1 g of catalyst and an aqueous solution of sacrificial reagent AgNO 3 (0.05 mol / L, 320 mL), and irradiated with visible light (> 420 nm). As a light source, a 300WXe lamp provided with a filter (L42) that cuts off light having a wavelength of 420 nm or less was used. The generated oxygen was quantified by gas chromatography.
[0014]
The aging time at 90 ° C. (363 K) was changed in FIG. 1 [(a) 1.5 hours, (b) 2 hours, (c) 3 hours, (d) 6 hours, (e) 8 hours, (f ) 12 hours] shows the X-ray diffraction pattern of the resulting powder. Both were found to be BiVO 4 having a scheelite structure. The sharpness of these XRD peaks indicates that a powder with good crystallinity can be obtained in low-temperature synthesis in this aqueous solution.
The BET surface area was 0.3 m 2 g −1 . As the aging time increased, the 18.8, 35, and 46 ° peak splits became apparent. This means that when the ripening time is short, a tetragonal crystal structure is obtained, whereas as it is longer, a pure monoclinic crystal structure is obtained. It shows that it is obtained.
Table 1 shows the oxygen production reaction activity of BiVO 4 obtained by changing the synthesis conditions under visible light irradiation. Although BiVO 4 were obtained by long reaction time at room temperature, 90 ° C. BiVO 4 obtained was aged 3 hours or more (363K) showed high photocatalytic activity. The reason for the low activity of BiVO 4 with a short ripening time is that inactive tetragonal BiVO 4 is mixed as shown in FIG. On the other hand, the photocatalytic activity was not affected by the amount of urea added.
[0015]
[Table 1]
[0016]
2, over a period of 8 hours reaction time including the aging, 90 ° C. BiVO 4 obtained by combining with (shown in continuous line) and 827 ° C. (1100K) solid phase methods have been of BiVO 4 synthesized in It is a diffuse reflection spectrum. The one synthesized by the solid phase method has a trailing edge at the absorption edge (indicated by a dotted line). This suggests that some of the constituent elements are volatilized due to high-temperature synthesis, and defects are generated. In contrast, BiVO 4 synthesized by the aqueous solution process of the present invention obtained a spectrum having a steep absorption edge in the visible light region. The band gap estimated from this absorption edge was 2.37 eV. From this, it was found that BiVO 4 powder having good crystallinity with few defects by hydrolysis using urea can be synthesized in a shorter time than the aqueous solution process of the prior art.
Incidentally, showing the diffuse reflectance spectrum of the photocatalyst TiO 2 powder (dotted line) and a photocatalyst BiVO 4 powder (continuous line) in FIG. 11.
[0017]
FIG. 3 shows a photocatalytic (λ> 420 nm visible light of a sacrificial reagent AgNO 3 aqueous solution using BiVO 4 powder (aged for 8 hours) obtained by synthesis using 5 g of urea and a reaction time including aging for 8 hours. Shows the time course of the oxygen production reaction. It was found that oxygen was efficiently generated photocatalytically. That is, it shows that there is a photocatalytic activity that is responsive to visible light.
[0018]
Example 2
NP photodecomposition characteristics of visible light responsive photocatalyst BiVO 4 powder 1, photodegradation characteristics of NP by sunlight irradiation dissolved in NaOH (Nacalai Tesque, reagent grade) aqueous solution (pH = 11.6) in 50
The concentration change of NP is shown in FIG. NP photolysis can be confirmed.
[0019]
2. Reaction by solar simulator NP (Kanto Chemical, 99.5%) dissolved in NaOH (Nacalai Tesque, reagent grade) aqueous solution (pH = 13.0) 2.0 × 10 −4 M sample solution or distilled
The concentration change of NP is shown in FIG. Photocatalyst BiVO 4 (♦) and photocatalyst TiO 2 (◇) in the case of air saturation (oxygen partial pressure 0.2 atm) in FIG. 5 and photocatalyst BiVO 4 (▲) in the case of oxygen saturation (oxygen
[0020]
Concentration change (■) when visible light responsive photocatalyst BiVO 4 fine powder is dispersed in 3,2 × 10 −4 M NP solution and stirring is performed without light irradiation, visible light having a wavelength longer than 400 nm FIG. 6 shows the change in concentration (●) when irradiated with, and the change in concentration (▲) when irradiated with light without adding a photocatalyst. From this result, it is clear that the visible light responsive photocatalyst BiVO 4 fine powder acts with visible light of 400 nm or more to decompose NP.
[0021]
4, To examine the effect of oxygen on NP decomposition of photocatalytic BiVO 4 fine powder by irradiation with visible light (wavelength longer than 400 nm) in a 2 × 10 −4 M NP solution in which the visible light responsive photocatalytic BiVO 4 fine powder is dispersed Further, changes in the concentration of NP under the conditions of air saturation (■), oxygen saturation (▲), and nitrogen saturation (♦) were examined. The result is shown in FIG. The decomposition rate constant under each condition was calculated as shown in Table 2. The effect of oxygen is obvious.
[0022]
[Table 2]
[0023]
Example 3
Photodecomposition characteristics of bisphenol A in visible light responsive photocatalyst BiVO 4 fine powder FIG. 8 shows bisphenol A (Kanto Chemical, for environmental analysis) dissolved in water or aqueous NaOH (pH 12.8) 1.0 × 10 −4 M solution. The concentration change of bisphenol A when visible light responsive photocatalyst BiVO 4 fine powder is dispersed in this solution and irradiated with visible light (> 400 nm) (mercury lamp dose is 30 mW / cm 2 ) is shown. The concentration of the raw material was determined from a calibration curve using valerophenone as an internal standard by the HPLC method. When water was used as the solvent, the reaction did not progress easily, but when NaOH was added, the photodecomposition reaction was active, and the concentration of bisphenol A was about 1 before irradiation after 7 hours of light irradiation. / 5. The photodegradation is summarized in Table 3 by determining the decomposition rate constants according to the first-order reaction rate equation. From this, it was found that the decomposition rate greatly changes depending on the pH of the solvent.
[0024]
[Table 3]
[0025]
Example 4
BiVO 4 fine powder is dispersed in a solution in which estrogen (17β-estradiol, estrone, estriol) using visible light responsive photocatalyst BiVO 4 fine powder is dissolved in water having a pH of 12.8. FIG. 9 shows changes in estrogen concentration when irradiated with visible light (> 400 nm). The estrogen concentration was determined by a HPLC method from a calibration curve using valerophenone as an internal standard. The concentrations after 8 hours of light irradiation were all about ¼, and it was revealed that the three natural estrogens could be decomposed by visible light. Decomposition was determined according to a first-order reaction rate equation, and the lifetime was determined by determining the rate constant and taking the reciprocal. These values are summarized in Table 4. From these results, it was found that the reaction rates of estradiol, estrone, and estriol remained almost unchanged with some differences. That is, it was confirmed that the degradation of these estrogens was hardly affected by the change of the substituent at the 17-position.
[0026]
[Table 4]
[0027]
Example 5
And if a visible light responsive photocatalyst BiVO 4 exploded
[0028]
【The invention's effect】
From the above, the visible light responsive BiVO 4 fine powder photocatalyst, particularly the novel visible light responsive BiVO 4 fine powder photocatalyst produced according to the present invention, can be applied to the system to be purified, particularly the water to be purified using visible light. It is important to contribute as a means of purifying environmental pollutants, which are extremely problematic in today's society, and are capable of photodegrading existing endocrine disrupters such as nonylphenol, bisphenol A, and natural estrogens. In particular, the novel method of producing BiVO 4 fine powder is highly practical, and the possibility of synthesizing a visible light-responsive photocatalyst capable of improving the utilization efficiency of sunlight is also highly practical.
[Brief description of the drawings]
FIG. 1 XRD patterns with different aging times; (a) 1.5 hours, (b) 2 hours, (c) 3 hours, (d) 6 hours, (e) 8 hours, (f) 12 hours FIG. 2 is a diffuse reflection spectrum of BiVO 4 ; a continuous line is produced using urea, and a dotted line is obtained by solid phase reaction. FIG. 3 is a wavelength of visible light from 420 nm of BiVO 4 produced in the present invention. Oxygen Generation Photocatalytic Activity from Sacrificial Reagent AgNO 3 Aqueous Solution (300W Xenon Lamp)
4 is a photodegradation characteristic of NP by sunlight irradiation using the visible light responsive photocatalyst BiVO 4 powder of Example 2 (October 15, 2001, Kanazawa, Hare, 21-23 ° C.). FIG. 11 Decomposition characteristics of NP dissolved in NaOH aqueous solution (pH = 13.0) using sunlight simulator; photocatalyst BiVO 4 (◆), photocatalyst TiO 2 (◇) when air saturated (oxygen partial pressure 0.2 atm) ), Photocatalyst BiVO 4 (▲), photocatalyst TiO 2 (Δ) when oxygen is saturated (oxygen
FIG. 6 shows the effect of visible light irradiation on NP decomposition of photocatalytic BiVO 4 fine powder. FIG. 7 shows the effect of oxygen in the water to be purified on NP decomposition of photocatalytic BiVO 4 fine powder by visible light irradiation. Photodegradation characteristics of bisphenol A as a photocatalyst BiVO 4 fine powder in a solution of 1.0 × 10 −4 M dissolved in water or NaOH (pH 12.8) aqueous solution of bisphenol A FIG. 9 shows visible light of Example 4 Decomposition characteristics of estrogen (176-estradiol, estrone, estriol) by visible light using responsive photocatalyst BiVO 4 fine powder [Fig. 10] Under fine weather (October 30, 2001, Kanazawa, Haruharu, 16-21 ° C) decomposition characteristics of 176- estradiol photocatalytic BiVO 4 fine powder in) [11] photocatalytic TiO 2 powder (dotted line) and a photocatalyst BiVO 4 powder Diffuse reflection spectrum of the continuous line) [12] synchrotron radiation spectrum of sunlight simulator
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