JP3834631B2 - Method for producing photocatalyst comprising titania-based crystal formed on substrate - Google Patents
Method for producing photocatalyst comprising titania-based crystal formed on substrate Download PDFInfo
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- JP3834631B2 JP3834631B2 JP2002295668A JP2002295668A JP3834631B2 JP 3834631 B2 JP3834631 B2 JP 3834631B2 JP 2002295668 A JP2002295668 A JP 2002295668A JP 2002295668 A JP2002295668 A JP 2002295668A JP 3834631 B2 JP3834631 B2 JP 3834631B2
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- titania
- sol
- anatase
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims description 175
- 239000000758 substrate Substances 0.000 title claims description 42
- 239000013078 crystal Substances 0.000 title claims description 31
- 238000004519 manufacturing process Methods 0.000 title claims description 19
- 239000011941 photocatalyst Substances 0.000 title claims description 18
- 239000011148 porous material Substances 0.000 claims description 63
- 239000002131 composite material Substances 0.000 claims description 39
- 238000000034 method Methods 0.000 claims description 26
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 23
- 238000010438 heat treatment Methods 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 9
- 230000003647 oxidation Effects 0.000 claims description 8
- 238000007254 oxidation reaction Methods 0.000 claims description 8
- 239000007788 liquid Substances 0.000 claims description 6
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 4
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 3
- 229910052714 tellurium Inorganic materials 0.000 claims description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 2
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 2
- 229910006404 SnO 2 Inorganic materials 0.000 claims description 2
- GEIAQOFPUVMAGM-UHFFFAOYSA-N ZrO Inorganic materials [Zr]=O GEIAQOFPUVMAGM-UHFFFAOYSA-N 0.000 claims description 2
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims description 2
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 claims description 2
- 239000002086 nanomaterial Substances 0.000 description 41
- 239000000126 substance Substances 0.000 description 29
- 239000000499 gel Substances 0.000 description 25
- 239000000523 sample Substances 0.000 description 21
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 20
- 230000001699 photocatalysis Effects 0.000 description 19
- 239000002071 nanotube Substances 0.000 description 16
- 239000000243 solution Substances 0.000 description 15
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 12
- 239000000463 material Substances 0.000 description 12
- 229910052751 metal Inorganic materials 0.000 description 12
- 239000002184 metal Substances 0.000 description 12
- 239000011521 glass Substances 0.000 description 11
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- 238000000576 coating method Methods 0.000 description 10
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- 239000011248 coating agent Substances 0.000 description 7
- 238000005868 electrolysis reaction Methods 0.000 description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 7
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 7
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 6
- 239000010407 anodic oxide Substances 0.000 description 6
- 238000002048 anodisation reaction Methods 0.000 description 6
- 238000011161 development Methods 0.000 description 6
- 239000007789 gas Substances 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 238000003980 solgel method Methods 0.000 description 6
- 239000000377 silicon dioxide Substances 0.000 description 5
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 229910003069 TeO2 Inorganic materials 0.000 description 4
- 229910052681 coesite Inorganic materials 0.000 description 4
- 229910052906 cristobalite Inorganic materials 0.000 description 4
- 238000004090 dissolution Methods 0.000 description 4
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- 235000006408 oxalic acid Nutrition 0.000 description 4
- 238000005240 physical vapour deposition Methods 0.000 description 4
- 229910052682 stishovite Inorganic materials 0.000 description 4
- 229910052905 tridymite Inorganic materials 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
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- 239000002073 nanorod Substances 0.000 description 3
- 238000004544 sputter deposition Methods 0.000 description 3
- KVGZZAHHUNAVKZ-UHFFFAOYSA-N 1,4-Dioxin Chemical compound O1C=COC=C1 KVGZZAHHUNAVKZ-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 229910003077 Ti−O Inorganic materials 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 230000003373 anti-fouling effect Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
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- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000004332 deodorization Methods 0.000 description 2
- 238000001784 detoxification Methods 0.000 description 2
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- 150000002013 dioxins Chemical class 0.000 description 2
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- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 2
- 238000001764 infiltration Methods 0.000 description 2
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- 150000002739 metals Chemical class 0.000 description 2
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- 229910052757 nitrogen Inorganic materials 0.000 description 2
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 238000006303 photolysis reaction Methods 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000001552 radio frequency sputter deposition Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000013074 reference sample Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(IV) oxide Inorganic materials O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- 239000012780 transparent material Substances 0.000 description 2
- 238000001771 vacuum deposition Methods 0.000 description 2
- 238000007740 vapor deposition Methods 0.000 description 2
- 239000012855 volatile organic compound Substances 0.000 description 2
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 241000588724 Escherichia coli Species 0.000 description 1
- FUJCRWPEOMXPAD-UHFFFAOYSA-N Li2O Inorganic materials [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 1
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 1
- 229910019714 Nb2O3 Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910052581 Si3N4 Inorganic materials 0.000 description 1
- 229910004481 Ta2O3 Inorganic materials 0.000 description 1
- 229910004160 TaO2 Inorganic materials 0.000 description 1
- 229910052770 Uranium Inorganic materials 0.000 description 1
- 241000700605 Viruses Species 0.000 description 1
- 230000032900 absorption of visible light Effects 0.000 description 1
- IKHGUXGNUITLKF-XPULMUKRSA-N acetaldehyde Chemical compound [14CH]([14CH3])=O IKHGUXGNUITLKF-XPULMUKRSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 238000007743 anodising Methods 0.000 description 1
- 230000000844 anti-bacterial effect Effects 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
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- 238000013461 design Methods 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- XUCJHNOBJLKZNU-UHFFFAOYSA-M dilithium;hydroxide Chemical compound [Li+].[Li+].[OH-] XUCJHNOBJLKZNU-UHFFFAOYSA-M 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 238000011978 dissolution method Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 239000002659 electrodeposit Substances 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 239000003673 groundwater Substances 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum oxide Inorganic materials [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 1
- YEXPOXQUZXUXJW-UHFFFAOYSA-N lead(II) oxide Inorganic materials [Pb]=O YEXPOXQUZXUXJW-UHFFFAOYSA-N 0.000 description 1
- 239000002923 metal particle Substances 0.000 description 1
- 239000002070 nanowire Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 235000019645 odor Nutrition 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- KTUFCUMIWABKDW-UHFFFAOYSA-N oxo(oxolanthaniooxy)lanthanum Chemical compound O=[La]O[La]=O KTUFCUMIWABKDW-UHFFFAOYSA-N 0.000 description 1
- 238000007146 photocatalysis Methods 0.000 description 1
- 238000013032 photocatalytic reaction Methods 0.000 description 1
- 238000001782 photodegradation Methods 0.000 description 1
- 208000017983 photosensitivity disease Diseases 0.000 description 1
- 231100000434 photosensitization Toxicity 0.000 description 1
- 230000015843 photosynthesis, light reaction Effects 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 229910001925 ruthenium oxide Inorganic materials 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 229910010271 silicon carbide Inorganic materials 0.000 description 1
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- IATRAKWUXMZMIY-UHFFFAOYSA-N strontium oxide Inorganic materials [O-2].[Sr+2] IATRAKWUXMZMIY-UHFFFAOYSA-N 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- LAJZODKXOMJMPK-UHFFFAOYSA-N tellurium dioxide Chemical compound O=[Te]=O LAJZODKXOMJMPK-UHFFFAOYSA-N 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- 229910052726 zirconium Inorganic materials 0.000 description 1
Images
Description
【０００１】
【発明の属する技術分野】
本発明は、基体上に形成されたチタニア系結晶体からなるナノ構造体、特に、ガラス等の透明基体上に直接接合して規則配列した、高い比表面積を持ち、有害有機化合物等を高効率で分解除去できるセルディメンション（セルの大きさ）及び化学組成からなる耐久性と強度に優れた光触媒特性を有するナノ構造体を利用したナターゼ型チタニア系結晶体からなる光触媒の製造方法に関する。
【０００２】
【従来の技術】
光触媒特性を持つアナターゼ型酸化チタンは既に良く知られている。この結晶は、一般的には、例えば、原料の酸化チタン粉末を約７００〜８００℃で焼成したりして作成するが、およそ１０００℃以上の加熱では徐々に安定なルチル型に転移し、これに伴い光触媒特性も徐々に低下する。
【０００３】
これに対して、溶液法のゾル−ゲル法では、約４００〜５００℃程度の低温加熱処理で容易にアナターゼ型となり、６００℃以上ではルチル型に転移する利点をもつ。また、このとき、ゾル−ゲル法により形成したチタニア膜は、粒子が小さく、ＰＶＤ、ＣＶＤ等の蒸着法で形成した膜よりも比表面積が大きいことも知られている。
【０００４】
今日、市販されている光触媒用チタニアの作成は湿式法が多く、粒状原料を用いて焼成して得た平滑な基板や表面凹凸のある基板等が多く用いられている。一方、これらの触媒体の形状は、用途によって異なるが、通常はナノチューブ、ナノロッド等のナノ構造体が配列したほどには微細ではなく、大きなディメンションの構造体である。
【０００５】
従来品のチタニア基板は、表面のクラックや大きな粒子の界面を利用したり、表面にスタンパー等で押印した大きな凹凸模様による表面を利用したりするものであり、比表面積は一般的にあまり大きくはない。これらの微細構造はμｍ〜サブμｍ程度である。また、従来のゾル−ゲル法では、基板上のゲル表面積の凹凸や膜内の大小様々なクラックを利用し比表面積を高めているものもあるが、比表面積はあまり大きくならず限界がある。他の方法として、陽極酸化皮膜の細孔内にチタニア等の光触媒粒子を充填するものがある（特許文献１〜５）。
【０００６】
最近、急激にナノマテリアルの分野が注目され、新たな視点からのナノ構造体の見直しが始まっている。現在は、ナノ構造体としての多孔質皮膜のみならず、皮膜細孔中の電析物や浸入物質等を含めたナノ構造体に関する多くの知見が見られる。特に、最近では、皮膜をテンプレートとして応用する研究が盛んで、皮膜の細孔中にＣＶＤ法、ＰＶＤ法、ゾル−ゲル法、めっき法、及び有機膜法等により、種々の金属、無機物、有機物を浸入させて、ナノドット、ナノロッド、ナノチューブ及びナノファイバ等が配列したナノ構造体の作製例がある（特許文献６〜１１、非特許文献１〜４）。
【０００７】
上記のような背景を踏まえ、本発明者らは、導電層付き基体の利用展開を目指して、特に、この基体表面と金属の陽極酸化皮膜層との密着性と成膜形態に注目しつつ、陽極酸化法とゾル−ゲル法を組み合わせたチタニアナノチューブ等のナノ構造体の作製上の様々な利点に着目し、これらの技術の総合統一化を図ること、そして、実用化を視野に入れつつ先端技術への展開と地球環境保全のための新たな材料開発手段を開発した（非特許文献５）。
【０００８】
【特許文献１】
特開平９−７１８９７号公報
【特許文献２】
特開平１０−２４９２１２号公報
【特許文献３】
特開平１１−２６７５１４号公報
【特許文献４】
特開２００１−２０５１０１号公報
【特許文献５】
特開２００１−３０３２９６号公報
【特許文献６】
特開平１１−２０００９０号公報
【特許文献７】
特開２０００−３１４６２号公報
【特許文献８】
特開２０００−３１４７１４号公報
【特許文献９】
特開２００１−１６２６００号公報
【特許文献１０】
特開２００１−２７８７００号公報
【特許文献１１】
特開２００２−１７５６２１号公報
【０００９】
【非特許文献１】
Ｍａｓｕｄａ，Ｈ．， Ｔａｎａｋａ， Ｈ．， Ｂａｂａ， Ｎ．， Ｂｕｌｌ． Ｃｈｅｍ． Ｓｏｃ． Ｊｐｎ．， １９９３， ６６， ３０５．
【非特許文献２】
Ｍａｒｔｉｎ， Ｃ． Ｒ．， Ｓｃｉｅｎｃｅ， １９９４， ２６６， １９６１．
【非特許文献３】
Ｌａｋｓｈｉｍｉ，Ｂ． Ｂ．， Ｐａｔｒｉｓｓｉ， Ｃ． Ｊ．， Ｍａｒｔｉｎ， Ｃ． Ｒ．， Ｃｈｅｍ． Ｍａｔｅｒ．， １９９７， ９， ２５４４．
【非特許文献４】
Ｋｙｏｔａｎｉ，Ｔ．， Ｐａｒａｄｈａｎ， Ｂ． Ｋ．， Ｔｏｍｉｔａ， Ａ．， Ｂｕｌｌ． Ｃｈｅｍ． Ｓｏｃ． Ｊｐｎ．， １９９９， ７２， １９５７．
【非特許文献５】
社団法人 表面技術協会「第１０３回講演大会講演要旨集」、２０５〜２０６頁、２００１年３月５日発行
【００１０】
【発明が解決しようとする課題】
チタニアの中でもアナターゼ型の酸化チタンが紫外光によって光触媒特性を有し、抗菌、脱臭、防汚作用、浄化作用等の効果を示し、有機物を分解することは既によく知られている。そして、最近は、ガス、汚泥、粉塵等の汚染の激しい環境では、省エネルギーやメンテナンスフリー用のパネル（外装材）や空気清浄機用フィルター、土壌や地下水中の揮発性有機化合物（ＶＯＣ）の除去材等として広く利用され、環境保全材料として今後ますますの発展が期待され、開発研究が活発に行われている。
【００１１】
さらなる開発課題としては、チタニアの結晶度及び活性度の向上、耐汚染性、耐久性、リユース性、物理的強度の向上、比表面積の増大、及び太陽光波長域での応用拡大等が挙げられる。特に、チタニアの触媒活性度の向上はアナターゼの結晶性の向上及び比表面積の増大とともに重要な因子である。
【００１２】
ナノレベルで制御された多孔質型及びナノチューブ配列型を含むナノ構造体は、（１）高効率の光触媒体、（２）太陽電池用の高効率フォトセル、（３）ナノレベルの多機能フォトニックス材料、（４）ナノレベルの高性能垂直磁気記録媒体、（５）ナノレベルハイブリッド化による回路実装分野等への展開が図れ、極めて興味深い材料である。
【００１３】
そこで、本発明は、ガラス等の基体上へのアナターゼ型チタニア系ナノ構造体の構築とその配列化により、比表面積を増大させ、また、例えば、開放表面孔を持つ中空型ナノ構造体を形成し、特に光触媒活性のいっそうの効率化を図った、製造容易なアナターゼ型チタニア系結晶体からなる光触媒の製造方法の提供を課題とする。
【００１４】
【課題を解決するための手段】
アルミニウム陽極酸化皮膜は、高密度の多孔質構造であるため、高い比表面積を持つことが知られている。本発明は、多孔質アルミナ皮膜とゾル−ゲル法とを組み合わせることによりさらに優れた特性を有するアナターゼ型チタニア系ナノ構造体を開発した。
【００１５】
すなわち、本発明は、下記のとおりである。
（１）基体の表面に２〜２００ｎｍの深さの微細凹凸構造を有する透明導電層を形成し、該導電層上にアルミニウムを蒸着し、陽極酸化により基体上に多孔質アルミナ皮膜からなる規則化配列した、径が８０ｎｍ以上２５０ｎｍ以下である細孔を形成して、該細孔にチタニアゾル液を浸入させてゲル化させ、これを加熱してアナターゼ型チタニア系結晶体を形成する方法において、粘度が２．４ｃＳｔ−２０℃のチタニアゾル中に粘度が２．１ｃＳｔ−２０℃以下の酸化物ゾルを１〜２０重量％添加することによって粘度を低くした複合ゾル液中に該細孔を形成した基体を浸漬して複合ゾル液を該細孔内に浸入させ、続いて、乾燥して複合ゾルを複合ゲル化した後、５００〜６００℃で加熱して該細孔壁と密着した開放表面孔を持つアナターゼ型チタニア系結晶の中空構造を形成することを特徴とするアナターゼ型チタニア系結晶体からなる光触媒の製造方法。
【００１６】
（２）前記酸化物ゾルが、Ａｌ ２ Ｏ ３ 、ＴｉＯ ２ 、ＳｉＯ ２ 、ＺｒＯ ２ 、ＳｎＯ ２ 、またはＴａＯ ２ あることを特徴とする上記（１）のアナターゼ型チタニア系結晶体からなる光触媒の製造方法。
【００１８】
（３）前記酸化物ゾルがシリカゾルと酸化テルルゾルの混合物であることを特徴とする上
記（１）のアナターゼ型チタニア系結晶体からなる光触媒の製造方法。
【００１９】
（４）上記１ないし３のいずれかに記載の方法によりアナターゼ型チタニア結晶体を形成した後、多孔質アルミナ皮膜を溶解除去することを特徴とするアナターゼ型チタニア系結晶体からなる光触媒の製造方法。
【００２０】
本発明は、アナターゼ型チタニア系ナノ構造体の光触媒デバイス分野への実用化に向けて、優れた耐化学性、物理的強度、機械加工性等を得るために、チタニアゾルへの種々の特性を持つ物質を添加した複合ゾルを用いることを特徴とする。
【００２１】
チタニアゾルへシリカ（ＳｉＯ２ ）や酸化テルル（ＴｅＯ２ ）等の低温加熱でガラス化する酸化物を添加すると、ゾルと細孔壁との濡れ性の改善、ゲルの緻密化による高強度化及び耐化学性等の向上化が図れ、チタニア単独では得られない様々な相乗効果が生まれ、実用化に向けての光触媒体の特性改善が図れる。また、例えば、ＲｕＯ２のような可視光及び紫外光の吸収を強める化合物を含めることができ、さらに光触媒特性を高めることもできる。
【００２２】
多孔質アルミナ皮膜体を利用して、ＣＶＤ法やＰＶＤ法のような乾式（ドライ）法等により細孔の内壁部に金属や無機物等を吸着及び浸入させてナノ構造体を作成する方法は知られている。しかし、こうした研究では、一般的にナノ多孔体内に種々の物質をいかに制御して浸入させるかが重要であり、通常はゾルと壁との濡れ性、ゾルの粘度、細孔径及び細孔のアスペクト比（アスペクト比＝細孔の長さ／細孔の孔径）が重要な問題となる。また、細孔表面の孔径が小さくなるほど、物質の浸入は難しくなる。
【００２３】
特に、細孔が小さい場合には、アスペクト比が大きくなるほど必然的に細孔の奥（深部）への物質の浸入は容易でなくなる。一般的にＰＶＤ等のドライなプロセスでは、多孔質ナノ構造体の奥に浸入できるアスペクト比はおよそ１〜２程度であり、限界値は１０を超すことはない。これに対して、ゾル−ゲル法のような溶液法による方法では、ゾルが浸入できるアスペクト比がおよそ３０００程度までは可能である。
【００２４】
例えば、ダイオキシンやアセトアルデヒドのような有害物質を効率的に分解するには、ある程度以上の大きさの細孔径とアスペクト比が必要である。つまり、細孔中へのガスの出入りが容易な微細構造を設計し、作成することが必要となる。
【００２５】
有害気体等の一分子のみを出入りさせるには、細孔径は最小およそ４ｎｍ以上必要である。したがって、実用化を目指して有害物質を効率的に分解させるために、開放表面孔を持つナノ構造体が望ましい。そのためには、ゾルの浸入のしやすさ及びゲル層を結晶化させるに必要な厚さを考えると、アルミナ多孔質皮膜の細孔径はおよそ８０ｎｍ〜２５０ｎｍの範囲が適切である。勿論、２５０ｎｍ以上でもよいが、その場合には比表面積が低下することもある。
【００２６】
また、チタニア結晶粒子の大きさから考えると、チタニアゲル層を結晶化させるに適切な厚さは、チタニア結晶粒子の大きさのおよそ２倍以上必要である。このため、酸化チタン等の光触媒効率を高め、かつゾル−ゲル液が細孔壁に沿って浸入しやすくするために、適度な孔径のアルミナ多孔質構造を作成する必要があり、そのために主として電解液の種類、電解電圧、化学溶解等の条件やプロセスを適切に制御する。
【００２７】
しかし、こうして作成したアルミナ多孔体へのチタニアゲル単独コーティングにおいても限界があり、ゾルの粘性、ゲル粒子の大きさ、加熱温度によるゲルと細孔壁との密着性や結晶化度等の基本的な問題、及び光触媒体としての実用化に向けたチタニア改質多孔質ナノ構造体の耐化学性、物理的強度、リユース性等のさらなる改善が求められる。
【００２８】
本発明はこうした問題解決のために、チタニア単独ではなく、チタニアの本来の光触媒特性を活かしつつ実用化に向けた諸特性の改善のために、目的に応じた各種化合物を添加した複合ゾルを用い、アルミナ多孔質ナノ構造体の細孔壁をゾル−ゲルコーティングにより改質し、複合強化を図った。
【００２９】
こうして得られた複合ナノ多孔質構造体を『多孔質複合ナノ構造体』と定義する。そして更に、この多孔質複合ナノ構造体を化学溶解法でアルミナ皮膜のみを除去したアナターゼ型チタニアを主成分とする結晶体からなり、その構造がチューブ状のナノ構造体を『ナノチューブ配列構造体』と定義する。このような、『多孔質複合ナノ構造体』又は『ナノチューブ配列構造体』が、本発明の製造方法で得られるアナターゼ型チタニア系結晶体からなる光触媒の特有の構造である。
【００３０】
本発明の方法で製造する多孔質複合ナノ構造体は、細孔がナノオーダであることに加え、さらに細孔中のチタニア結晶粒子が小さいため（約４〜８ｎｍ）、比表面積は従来品に比べて格段に大きく、従来品の平面型酸化チタン基板に比較して、およそ２００倍以上となる。
【００３１】
また、本発明の方法で製造する多孔質複合ナノ構造体は、ナノチューブ、ナノドット、ナノロッド、ナノファイバ、又はナノワイア（アスペクト比：５〜３０００）から選ばれた少なくとも１種類からなる形状を有するが、特に、ナノチューブ配列構造体は、分解物質の出入りが容易な中空型であるため、チューブの内壁又はチューブの内壁と外壁の全ての表面を有効に利用でき、光照射により有害化学物質を効率的に分解することができる。
【００３２】
本発明の方法で製造する多孔質複合ナノ構造体及びナノチューブ配列構造体は、光触媒作用によりダイオキシン類、アセトアルデヒド、窒素酸化物、悪臭のような有害気体、及び大腸菌、ウイールス等の有害物質の分解による無害化、防汚、脱臭に利用することができる。
【００３３】
【発明の実施の形態】
本発明の製造方法において、基体上へのチタニア系複合ナノ構造体の作製工程を図に基づいて説明する。図１のａ）に示すように、基体１の表面に導電層２、例えば、ＩＴＯ、ＳｎＯ２、ＺｎＯ、又はＳｒＣｕ２Ｏ２及びこれらの物質へのドープ元素（例えば、Ｓｎ、Ｓｂ、Ｆ、Ａｌ、Ｇａ）を含む化合物のうちのいずれかのような透明導電層を形成する。基体１はガラス、アルミナ、ダイヤモンド、又は有機膜等の透明材料や炭化ケイ素、窒化ケイ素等の耐熱性に優れた半透明及び不透明材料を使用できる。
【００３４】
導電層２が存在しない場合は、蒸着金属層３を完全に酸化させることができず、陽極酸化によって形成されるバリヤー層／基体界面に金属が一部残留して透明性が劣るものとなり、透明材料を基体として用いても基体の透明度が低くダイオキシン類の分解用途には利用できない。
【００３５】
また、導電層は、表面が平坦過ぎると蒸着する金属との密着性が悪く、完全に陽極酸化した後、又は加熱処理時に剥離が起こり利用できない。したがって、導電層表面には、蒸着する金属及びその陽極酸化皮膜との密着性を高めるためのアンカー効果を発現する微細凹凸構造が存在するものを用いるほどよい。このアンカー効果を発現する微細凹凸構造は、２〜２００ｎｍの深さが必要で、これにより種々の大きさの蒸着金属粒子との密着性が高まる。
【００３６】
導電層の形成方法は真空蒸着法、イオンプレーティング法及びスパッタリング法等で行うことができる。導電層の膜厚や表面の微細凹凸構造の深さは、目的により該形成方法の使い分けや成膜速度及び基体温度等を制御することによって調整する。
【００３７】
次に、導電層２上に蒸着金属層３を形成する。金属の蒸着は、真空蒸着法、イオンプレーティング法及びスパッタリング法等で成膜されたものを使用できるが、その成膜条件及び膜質等は、次の工程の陽極酸化により細孔がシリンダー状に整然と配列するようにすることが重要である。例えば、通常は成膜速度は０．２ｎｍ／秒程度であるが、本発明のスパッタリング法では少なくともこの条件を１〜２ｎｍ／秒の範囲で制御し、蒸着粒子が小さく、柱状配向性のない緻密な膜とし、かつ表面の平滑性も可能な限り均一で平らになるように配慮する。
【００３８】
次に、図１のｂ）に示すように、蒸着金属層３を陽極酸化する。蒸着金属の陽極酸化では、ダイオキシン類等の有機物が浸入し易い多孔質アルミナ皮膜４の構造を作ることが重要である。ところが、伝統的かつＪＩＳやＩＳＯに規定された標準的な電解条件で行うと、電圧が上げられないだけでなく、細孔径Ａも、例えば、硫酸皮膜１０〜１５ｎｍ、シュウ酸皮膜２０〜５０ｎｍ、リン酸皮膜３０〜６０ｎｍ程度であるため、有機物等の浸入は不十分である。
【００３９】
このため、例えば、分解のための有機物の大きさとその浸入及び酸化物ゾルの大きさ（ＴｉＯ２ゾルでは粒子の大きさは約３〜２０ｎｍである）等を考慮して、これらの物質が浸入できるのに容易な多孔質アルミナ皮膜４の構造として、細孔径Ａがおよそ８０ｎｍ〜２５０ｎｍになるような電解液、電解条件、製造プロセスを総合的に選択する。つまり、電解液は化学溶解性の高いリン酸溶液、シュウ酸溶液を選択し、電解電圧はセル径（のｂのＣで示す孔壁の中心と中心間の距離）が３００〜６００ｎｍと大きくなるように高電圧をかけ、液温度も高電圧がかけられるようにできるだけ低温、好ましくはおよそ１０℃以下とする。
【００４０】
多孔質陽極酸化皮膜４と導電層２との密着性が優れた金属蒸着基体１は、９０〜２００Ｖもの高電圧電解でも多孔質アルミナ皮膜４の構造が破壊されることもなく、導電層２からの剥離もなくなり、シリンダー状細孔の配列した強固な皮膜が形成する。つまり、この密着性が考慮されない一般的な陽極酸化では、例えば、シュウ酸皮膜では電圧をおよそ４０Ｖ以上にすることができず、また、リン酸皮膜でもおよそ６０Ｖ以上での電解は困難である。この電圧を超えると、大電流が流れて皮膜溶解と皮膜破壊が同時に起こり、また導電層からの皮膜剥離も起こり、電解処理できない。
【００４１】
次に、該細孔中にチタニア系複合ナノ構造体物質をゾル−ゲルコーティング法により充填する。ゾル−ゲルコーティング法により、ゾルが孔壁を伝って浸入し、さらに、細孔底部の微細凹凸構造を有する導電体層まで浸入して導電体層と強固に直接接合する。さらに、ゾルは、上記のとおり、蒸着時に形成された孔壁の隙間状の境界領域の隙間にも浸入してゲル化する。これにより、ゾル溶液は、基体上に形成された多孔質陽極酸化皮膜の細孔内壁及び細孔中に充填される。
【００４２】
さらに、化学溶解により、アルミナ細孔壁を選択溶解し、ナノチューブ配列構造体を作製して、ナノチューブの外壁の利用も可能である。従って、これらの複合ナノ構造体は比表面積が高く、有害物質と有効に接触できるため高い光触媒特性が得られる。
【００４３】
本発明の方法では、ゾル−ゲルコーティングを以下の方法により行い、光触媒特性及び実用化に向けたその他の諸特性の高性能化を図る。
（１）チタニアゾル中に粘度の低い酸化物ゾルを添加する。
チタニアゾルの粘度は約２．４ｃＳｔ−２０℃であり、これに粘度の低い酸化物ゾルとして、粘度が２．１ｃＳｔ−２０℃以下のＡｌ２Ｏ３、ＴｉＯ２、ＳｉＯ２、ＺｒＯ２、ＳｎＯ２、ＴａＯ２等のゾルを添加する。粘度がこれより高いものでは効果が乏しくなる。特にＳｉＯ２は粘度が低く、チタニアの光触媒特性に及ぼす影響が少なく、アルミナ多孔体の細孔壁とチタニアゾルとの濡れ性を改善する効果も大きい。酸化物ゾルを添加して混合ゾルの粘度を低くするほど濡れ性は改善されるが、過剰な添加はかえって光触媒効果を減ずるので、添加量は１〜２０重量％の範囲内で調整する。なお、粘度は、ＡＳＴＭ及びＪＩＳに準拠して製作されたガラス製毛管式粘度計（ウベローデ）を用いて、規定の条件において、一定量の液体が毛細管を流れる時間を２０℃で測定し、流出時間（秒）に粘度計定数を乗じて求めた動粘度（ｃＳｔ：センチストークス）である。
【００４４】
これにより、乾燥中にゲルの収縮によって起こる細孔壁からの剥離やゲル体の割れを防止できる。またチタニア粒子の凝集を抑制でき、チタニアゾルの細孔中への浸入を容易にする。つまり、改質層の緻密化による高強度化及び耐久性の向上化及び改質層と細孔底部とのアンカー効果による高密着性化ができる。よって、その後の加熱処理によるアルミナ細孔壁との密着性が高まり、開放表面孔を持つ中空構造（図１−ｄの６）を形成できる。また、ゲルの成膜性も高め、ゲル粒子及びチタニア結晶間を埋め、ゲル層の強度、緻密性や接着性等も高めることができる。
【００４５】
（２）チタニアゾル中への３００〜４００℃の低温加熱でガラス化できる酸化物は、ＴｅＯ２、Ｌｉ２Ｏ、Ｎａ２Ｏ、Ｎｂ２Ｏ３ 、Ａｌ２Ｏ３ 、ＴｉＯ２ 、ＰｂＯ、ＷＯ３ 、ＳｒＯ、Ｌａ２Ｏ３、Ｔａ２Ｏ３、ＢａＯ、ＺｎＯ、ＭｇＯ等であり、その添加量は０．５〜１０重量％の範囲内で調整する。過剰な添加は光触媒効果を減少させる。例えば、ＴｅＯ２のようなゾルの添加によりゲル粒子同士の接合性の強化を図ることによりチタニアと基体及びアルミナ細孔壁との密着性がさらに強化される。また、ＳｉＯ２と同様にゲルの成膜性、ゲル層の強度、緻密性や接着性等も高めることができる。これにより、チタニア系複合ナノ構造体の耐久性等の実用化上重要な特性の向上が図れる。
【００４６】
（３）チタニアゾル中へ可視光吸収特性を有する酸化物ゾルを添加する。
可視光吸収特性を有する酸化物は、現在ＲｕＯ２がその代表であるが、この他にも、Ｎｄ、Ｚｒ、Ｈｆ、Ｌａ、Ｃｅ、Ｕ等の酸化物は有効である。これらの添加量は一般的には微量でも効果がある。本発明では０．１〜５重量％の範囲内で調整するが、特に過剰な添加はかえってその効果を失う。例えば、Ｒｕ錯体は、酸化ルテニウムとしての導電性を利用する太陽光、特に、可視光領域の波長の吸収による光増感効果が見込めるため、光触媒効果の利用に留まらず、複合機能の展開を可能にし、例えば、太陽電池分野へも応用できる。
【００４７】
（４）チタニアゾルにＴｉ−Ｏの結合のバンドギャップを狭める物質を添加して、紫外光及び可視光の両方の吸収特性を併せ持つ光触媒体とする。
現在、これに該当する添加元素として、窒素のみが知られる。本発明では窒素を含み、比較的作業性の良好なものとして、硝酸又はアンモニア溶液を選択し、これらの添加量を０．１〜１０重量％の範囲内で調整する。こうして形成した窒素を含む物質は、酸化チタンのＴｉ−Ｏ結合のバンド幅を狭くする効果を生じ、光触媒反応に必要とするエネルギーが減少するため、紫外光領域の光触媒効果が増加し、さらに可視光領域への利用も可能となる。
【００４８】
このようにして形成された多孔質複合酸化物ナノ構造体（図１−ｄの６参照）は、さらに、図１−ｅに示すように、例えば、５重量％リン酸と２重量％クロム酸との混酸等の酸溶液、又は２重量％〜５重量％濃度の水酸化ナトリウム等のアルカリ溶液による化学溶解工程でエッチングすると、アルミニウムの陽極酸化皮膜のみが溶解して、チタニア系ナノチューブ配列構造体７が導電層２を介して基体１上に直接接合して基体面と垂直方向に伸びて基体面に規則的に配列させることができる。
【００４９】
すなわち、これによって、基体１及び導電層２として共に透明材料を用いた場合は、
に示すように、透明基体１及び透明導電層２上に光触媒特性を有し、比表面積の大きな透明で密着性に優れたチタニア系ナノチューブ配列構造体７の規則化配列体を形成できる。
【００５０】
【実施例】
以下、実施例により本発明を具体的に示すが、本発明はこれに限定されるものではなく、適宜、本発明の範囲内で変更できるものである。
実施例１
表面に１２０ｎｍの厚さのＩＴＯ層をスパッタコーティングした透明ガラス基板を用いて、この上にさらにＡｌを２μｍほどＲＦスパッタリングした基板を用い、前処理としてアセトン中で１０分間超音波洗浄した試料を陽極酸化に供した。陽極酸化は、１０容量％リン酸溶液中で１３０Ｖにて定電位電解によった。次に、陽極酸化により形成されたアルミナ多孔質膜の孔径を拡大するため、試料を３０℃の５容量％リン酸溶液中に浸漬して孔径をおよそ１８０ｎｍに調整した。
【００５１】
その後、ＴｉＯ２ゾルに２．５重量％ＳｉＯ２ゾルと２．５重量％ＴｅＯ２ゾルを添加した組成の複合ゾル液中に試料を浸漬して、ディップコーティングによりアルミナ多孔質膜の孔内に複合ゾルを浸入させて充填した。続いて、長時間（１２時間以上）乾燥して複合ゾルを複合ゲル化した後、５００℃で２時間の加熱処理により複合ゲルをアナターゼ型チタニア結晶を主とする構造体とした。最後に、５容量％リン酸と２容量％クロム酸との混酸溶液（７０℃）中で陽極酸化皮膜のみを化学溶解除去し、透明ガラス基板上に基板面と垂直方向に伸びたナノチューブを基板面に規則的に配列したチタニア系複合ナノ構造体（図１の７）の試料１を製造した。
【００５２】
実施例２
実施例１と同じＩＴＯ及びＡｌスパッタリングした透明ガラス基板を用いて、前処理、陽極酸化、細孔拡大及びゾル−ゲル処理まで、実施例１と全く同様のプロセスで試料を作成した。次に、このディップコーティングした複合型の試料を陽極酸化皮膜を化学溶解せずに、最後に５００℃で２時間加熱処理してアナターゼ型チタニア結晶を主とする多孔質チタニア系複合ナノ構造体（図１の６）の試料２を製造した。
【００５３】
実施例３
実施例１と同じＩＴＯ及びＡｌスパッタリングした透明ガラス基板を用いて、前処理、陽極酸化、細孔拡大及びゾル−ゲル処理までも実施例１と全く同様のプロセスで試料を作成した。次に、このディップコーティングした複合型の試料を陽極酸化皮膜を化学溶解せずに、最後に６００℃で２時間加熱処理してルチル型とアナターゼ型の混ざったチタニア結晶を主とする多孔質チタニア系複合ナノ構造体の試料３を製造した。
【００５４】
実施例４
表面に厚さおよそ１２０ｎｍのＩＴＯ層をスパッタリングした透明ガラス基板を用いて、この上に、さらに２μｍほどのＡｌをＲＦスパッタリングした基板を用い、前処理としてアセトン中で１０分間超音波洗浄した試料を陽極酸化に供した。陽極酸化は、３重量％のシュウ酸溶液中で４０Ｖの定電位電解した。陽極酸化により形成されたアルミナ多孔質膜の孔径拡大は、試料を３０℃の５容量％リン酸溶液中に浸漬して孔径をおよそ８０ｎｍに調整した。
【００５５】
その後、実施例１と同じ組成、濃度のゾル中に試料を浸漬して、ディップコーティングした。最後に５００℃にて２時間加熱処理してアナターゼ型チタニア結晶を主とする多孔質チタニア系複合ナノ構造体の試料４を製造した。
【００５６】
実施例５
実施例４までと同じＡｌスパッタリングしたガラス基板を用いて、前処理、陽極酸化、孔径拡大処理までは実施例１と全く同じプロセス、組成、条件により処理した孔径約１８０ｎｍのリン酸陽極酸化皮膜を作成した。次いで、ＴｉＯ２ゾルに５重量％ＳｉＯ２ゾルと５重量％ＴｅＯ２ゾルを添加した組成のゾル中に試料を浸漬してディップコーティングし、最後に６００℃で２時間加熱処理してアナターゼ型チタニア結晶を主とする多孔質チタニア系複合ナノ構造体の試料５を製造した。
【００５７】
実施例６
実施例５までと同じＡｌスパッタリングしたガラス基板を用いて、続く前処理から孔径拡大処理までは実施例１と全く同じプロセス、組成、条件により処理した孔径約１８０ｎｍのリン酸陽極酸化皮膜を作成した。次いで、ＴｉＯ２ゾルに２重量％ＲｕＯ２ゾルを添加した組成のゾル中に試料を浸漬し、最後に５００℃で２時間加熱処理してアナターゼ型チタニア結晶を主とする多孔質チタニア系複合ナノ構造体の試料６を製造した。
【００５８】
本発明のチタニア系複合ナノ構造体の光触媒特性の評価のために、有害化学物質の代表として、アセトアルデヒドガスを用いてＵＶ光照射により、ＣＯ２と水とする無害化のための光分解実験を行った。表１は、上記の実施例１〜６の６種類のチタニア系複合ナノ構造体（ナノチューブ配列型及び多孔質型）の試料１〜６と参考試料、標準試料からなるチタニア系ナノ構造体の合計８種類の試料を用いて、紫外線照射下における照射時間の経過に伴うアセトアルデヒドガスの光分解反応初速度の比較としてまとめたものである。
【００５９】
【表１】
光触媒特性の比較のために、標準試料として、市販品のＤｅｇｕｓｓａ Ｐ２５ 純チタニア粉末を用いた。参考試料は、ゾル−ゲルコーティング時のゾル組成がＴｉＯ２単独ゾルであることを除き、作成プロセス及び条件等は、全て実施例２と同一とした多孔質チタニア系ナノ構造体である。
【００６１】
アセトアルデヒドの光分解反応の初速度は、表１から明らかなように、標準試料が０．３７であるのに対して、本発明の６種類の試料は全て５倍以上の値であり、特に、試料１〜４については９倍以上で、最高値はナノチューブの配列した試料１の１７．６倍であり、極めて優れた性能を持つことが明らかになった。
【図面の簡単な説明】
【図１】図１は、本発明の『多孔質複合ナノ構造体』の製造工程を示す概念図である。
【図２】図２は、本発明の『ナノチューブ配列構造体』の構造を示す概念図である。[0001]
BACKGROUND OF THE INVENTION
The present invention is a nanostructure comprising a titania-based crystal formed on a substrate, particularly a high specific surface area that is directly bonded and arranged on a transparent substrate such as glass and has high efficiency for harmful organic compounds. Cell dimensions that can be disassembled and removed with(Cell size)And a nanostructure having chemical properties and photocatalytic properties with excellent durability and strengthOf photocatalysts consisting of natase-type titania crystalsIt relates to the manufacturing method.
[0002]
[Prior art]
Anatase-type titanium oxide having photocatalytic properties is already well known. This crystal is generally prepared by, for example, firing a raw material titanium oxide powder at about 700 to 800 ° C., but when it is heated to about 1000 ° C. or more, it gradually changes to a stable rutile type. Along with this, the photocatalytic properties gradually decrease.
[0003]
On the other hand, the sol-gel method of the solution method has an advantage that it easily becomes anatase type by low-temperature heat treatment at about 400 to 500 ° C., and transitions to the rutile type at 600 ° C. or higher. At this time, it is also known that the titania film formed by the sol-gel method has small particles and has a larger specific surface area than a film formed by a vapor deposition method such as PVD or CVD.
[0004]
Today, many commercially available titania for photocatalysts are prepared by a wet method, and a smooth substrate obtained by firing using a granular raw material or a substrate having surface irregularities is often used. On the other hand, although the shapes of these catalyst bodies differ depending on the application, they are usually not as fine as the arrangement of nanostructures such as nanotubes and nanorods, but are large dimension structures.
[0005]
Conventional titania substrates use cracks on the surface and the interface of large particles, or use a surface with a large concavo-convex pattern stamped on the surface with a stamper etc., and the specific surface area is generally too large Absent. These microstructures are about μm to sub-μm. In addition, some conventional sol-gel methods increase the specific surface area by utilizing unevenness of the gel surface area on the substrate and various cracks in the film, but the specific surface area is not so large and has a limit. Another method is to fill photocatalyst particles such as titania into the pores of the anodized film (Patent Documents 1 to 5).
[0006]
Recently, the field of nanomaterials has attracted attention, and the review of nanostructures from a new perspective has begun. At present, not only a porous film as a nanostructure but also a lot of knowledge about nanostructures including electrodeposits and infiltrating substances in the pores of the film can be seen. In particular, research on application of a film as a template has recently been actively conducted, and various metals, inorganic substances, and organic substances are formed in the pores of the film by CVD, PVD, sol-gel, plating, and organic film methods. There are examples of manufacturing nanostructures in which nanodots, nanorods, nanotubes, nanofibers, and the like are arranged (Patent Documents 6 to 11 and Non-Patent Documents 1 to 4).
[0007]
Based on the background as described above, the present inventors aimed at the utilization development of the substrate with a conductive layer, and in particular, paying attention to the adhesion between the surface of the substrate and the metal anodized film layer and the film formation mode, Focusing on various advantages in the production of nanostructures such as titania nanotubes that combine anodizing and sol-gel methods, we aim to unify these technologies and to put them to practical use A new material development means for technology development and global environmental conservation was developed (Non-patent Document 5).
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-71897
[Patent Document 2]
JP-A-10-249212
[Patent Document 3]
JP-A-11-267514
[Patent Document 4]
JP 2001-205101 A
[Patent Document 5]
JP 2001-303296 A
[Patent Document 6]
Japanese Patent Laid-Open No. 11-200090
[Patent Document 7]
JP 2000-31462 A
[Patent Document 8]
JP 2000-314714 A
[Patent Document 9]
JP 2001-162600 A
[Patent Document 10]
JP 2001-278700 A
[Patent Document 11]
JP 2002-175621 A
[0009]
[Non-Patent Document 1]
Masuda, H .; , Tanaka, H .; Baba, N .; , Bull. Chem. Soc. Jpn. 1993, 66, 305.
[Non-Patent Document 2]
Martin, C.I. R. , Science, 1994, 266, 1961.
[Non-Patent Document 3]
Lakshimi, B.H. B. Patrissi, C.I. J. et al. Martin, C .; R. Chem. Mater. , 1997, 9, 2544.
[Non-Patent Document 4]
Kyotani, T .; Paradhan, B .; K. Tomita, A. , Bull. Chem. Soc. Jpn. 1999, 72, 1957.
[Non-Patent Document 5]
The Surface Technology Association of Japan “Abstracts of the 103rd Lecture Meeting”, pp. 205-206, published on March 5, 2001
[0010]
[Problems to be solved by the invention]
Among titania, anatase-type titanium oxide has photocatalytic properties by ultraviolet light, exhibits effects such as antibacterial effect, deodorization, antifouling action and purification action, and is already well known to decompose organic substances. And recently, in environments where gas, sludge, dust, etc. are heavily polluted, energy-saving and maintenance-free panels (exterior materials), filters for air purifiers, removal of volatile organic compounds (VOC) in soil and groundwater It is widely used as a material, etc., and further development is expected as an environmental conservation material, and development research is actively conducted.
[0011]
Further development issues include improvements in titania crystallinity and activity, stain resistance, durability, reusability, physical strength, specific surface area, and application expansion in the solar wavelength range. . In particular, improvement of the catalytic activity of titania is an important factor along with improvement of anatase crystallinity and specific surface area.
[0012]
Nanostructures, including nano-level controlled porous and nanotube array types, are (1) high-efficiency photocatalysts, (2) high-efficiency photocells for solar cells, and (3) nano-level multifunctional photo It is a very interesting material because it can be developed in the field of nicks materials, (4) nano-level high-performance perpendicular magnetic recording media, and (5) nano-level hybrid circuit mounting.
[0013]
Therefore, the present invention increases the specific surface area by constructing and arranging anatase-type titania-based nanostructures on a substrate such as glass and forms a hollow nanostructure having, for example, open surface pores. Especially photocatalytic activityMoreIncrease efficiencyWas,Made of anatase-type titania crystals that are easy to manufacturephotocatalystOf manufacturing methodIs an issue.
[0014]
[Means for Solving the Problems]
Since an aluminum anodic oxide film has a high-density porous structure, it is known to have a high specific surface area. The present invention has developed an anatase titania-based nanostructure having further excellent characteristics by combining a porous alumina film and a sol-gel method.
[0015]
That is, the present invention is as follows.
(1)SubstrateA transparent conductive layer having a fine concavo-convex structure with a depth of 2 to 200 nm is formed on the surface of the conductive layer;Aluminum was vapor-deposited on it, and anodized and ordered arrangement of porous alumina film on the substrate.The diameter is not less than 80 nm and not more than 250 nmIn a method of forming pores, allowing a titania sol solution to enter into the pores to be gelled, and heating this to form anatase-type titania-based crystal,Viscosity is 2.4 cSt-20 ° CAdd 1 to 20% by weight of oxide sol with a viscosity of 2.1cSt-20 ° C or less in titania solAfter immersing the substrate in which the pores are formed in the composite sol liquid having a reduced viscosity to allow the composite sol liquid to enter the pores, and subsequently drying to form a composite gel of the composite sol, Forming a hollow structure of anatase-type titania crystal with open surface pores in close contact with the pore walls by heating at 500-600 ° CIt is characterized byAnatase typeMade of titania crystalphotocatalystManufacturing method.
[0016]
(2) The oxide sol is Al 2 O 3 TiO 2 , SiO 2 , ZrO 2 , SnO 2 Or TaO 2 A method for producing a photocatalyst comprising the anatase-type titania crystal of (1) above,
[0018]
(3) The oxide sol is a mixture of silica sol and tellurium oxide sol.
A method for producing a photocatalyst comprising the anatase-type titania crystal of (1).
[0019]
(41) to 1 above3A method for producing a photocatalyst comprising an anatase-type titania crystal, comprising forming an anatase-type titania crystal by the method according to any one of the methods and then dissolving and removing the porous alumina film.
[0020]
The present invention has various characteristics to titania sol in order to obtain excellent chemical resistance, physical strength, machinability and the like for practical application of anatase-type titania-based nanostructures to the field of photocatalytic devices. A composite sol to which a substance is added is used.
[0021]
To titania solsilica(SiO2 )AndTellurium oxide (TeO2 )Addition of an oxide that vitrifies by low-temperature heating, such as improving the wettability between the sol and pore walls, increasing the strength by densifying the gel, and improving the chemical resistance, etc. Various synergistic effects are born, and the characteristics of the photocatalyst can be improved for practical use. For example, RuO2Such a compound that enhances absorption of visible light and ultraviolet light can be included, and photocatalytic properties can be further enhanced.
[0022]
There is a known method for making nanostructures by using porous alumina coatings to adsorb and infiltrate metals and inorganic substances into the inner wall of pores by dry methods such as CVD and PVD. It has been. However, in these studies, it is generally important to control and infiltrate various substances into the nanoporous body, and usually the wettability between sol and wall, sol viscosity, pore diameter and pore aspect. The ratio (aspect ratio = pore length / pore diameter) is an important issue. Further, the smaller the pore diameter on the pore surface, the more difficult the substance enters.
[0023]
In particular, when the pores are small, the larger the aspect ratio, the more inevitably the substance enters the back (depth) of the pores. Generally, in a dry process such as PVD, the aspect ratio that can penetrate into the interior of the porous nanostructure is about 1 to 2, and the limit value does not exceed 10. On the other hand, in a method using a solution method such as a sol-gel method, the aspect ratio into which the sol can enter can be up to about 3000.
[0024]
For example, in order to efficiently decompose harmful substances such as dioxin and acetaldehyde, a pore size and an aspect ratio larger than a certain size are required. That is, it is necessary to design and create a fine structure in which gas can easily enter and exit the pores.
[0025]
In order to allow only one molecule such as harmful gas to enter and exit, the minimum pore size is about 4 nm or more. Therefore, nanostructures with open surface pores are desirable in order to efficiently decompose harmful substances for practical use. For this purpose, considering the ease of sol penetration and the thickness required to crystallize the gel layer, the pore diameter of the alumina porous film is suitably in the range of about 80 nm to 250 nm. Of course, it may be 250 nm or more, but in that case, the specific surface area may decrease.
[0026]
Considering the size of the titania crystal particles, the thickness appropriate for crystallizing the titania gel layer needs to be about twice or more the size of the titania crystal particles. For this reason, it is necessary to create an alumina porous structure with an appropriate pore size in order to increase the photocatalytic efficiency of titanium oxide and the like and to make the sol-gel solution easily enter along the pore walls. Appropriately control conditions and processes such as liquid type, electrolysis voltage, and chemical dissolution.
[0027]
However, there is a limit to the titania gel single coating on the alumina porous body thus prepared, and there are fundamental limitations such as the viscosity of the sol, the size of the gel particles, the adhesion between the gel and the pore wall depending on the heating temperature, and the degree of crystallinity. There is a need for further improvements in the chemical resistance, physical strength, reusability, etc. of the titania-modified porous nanostructure for practical application as a photocatalyst.
[0028]
In order to solve such problems, the present invention uses not a titania alone but a composite sol to which various compounds according to the purpose are added in order to improve various properties for practical use while utilizing the original photocatalytic properties of titania. The pore walls of the alumina porous nanostructure were modified by sol-gel coating to strengthen the composite.
[0029]
The composite nanoporous structure thus obtained is defined as “porous composite nanostructure”. Furthermore, this porous composite nanostructure is composed of a crystal composed mainly of anatase-type titania from which only the alumina film is removed by a chemical dissolution method. It is defined asSuch “porous composite nanostructure” or “nanotube array structure” is a unique structure of a photocatalyst composed of anatase-type titania crystal obtained by the production method of the present invention.
[0030]
Of the present inventionManufactured by the methodSince the porous composite nanostructure has nanopores in the pores and the titania crystal particles in the pores are small (about 4 to 8 nm), the specific surface area is much larger than the conventional products. Compared to the planar type titanium oxide substrate, it is about 200 times or more.
[0031]
In addition, the present inventionManufactured by the methodThe porous composite nanostructure has at least one shape selected from nanotubes, nanodots, nanorods, nanofibers, or nanowires (aspect ratio: 5 to 3000). In particular, the nanotube array structure is decomposed. Since it is a hollow type in which a substance can easily enter and exit, all the surfaces of the inner wall of the tube or the inner wall and the outer wall of the tube can be used effectively, and harmful chemical substances can be efficiently decomposed by light irradiation.
[0032]
Of the present inventionPorous composite produced by the methodNanostructureAnd nanotube array structureCan be used for detoxification, antifouling, and deodorization by decomposition of harmful gases such as dioxins, acetaldehyde, nitrogen oxides, offensive odors, and harmful substances such as Escherichia coli and viruses by photocatalysis.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Of the present inventionIn the manufacturing method,A process for producing a titania-based composite nanostructure on a substrate will be described with reference to the drawings. As shown in FIG. 1 a), a
[0034]
When the
[0035]
Further, when the surface of the conductive layer is too flat, the adhesion with the metal to be deposited is poor, and peeling occurs during complete anodic oxidation or during heat treatment. Therefore, it is better to use a conductive layer having a fine uneven structure that exhibits an anchor effect for enhancing the adhesion between the deposited metal and its anodized film. The fine concavo-convex structure that expresses the anchor effect needs to have a depth of 2 to 200 nm, thereby improving the adhesion with various sizes of deposited metal particles.
[0036]
The conductive layer can be formed by vacuum deposition, ion plating, sputtering, or the like. The film thickness of the conductive layer and the depth of the fine concavo-convex structure on the surface are adjusted by controlling the proper use of the forming method, the film forming speed, the substrate temperature, and the like according to the purpose.
[0037]
Next, the deposited metal layer 3 is formed on the
[0038]
Next, as shown in FIG. 1 b), the deposited metal layer 3 is anodized. In the anodic oxidation of vapor-deposited metal, it is important to create a porous alumina coating 4 structure into which organic substances such as dioxins can easily enter. However, when the standard electrolysis conditions specified in JIS and ISO are used, not only the voltage cannot be increased, but also the pore diameter A is, for example, a sulfuric acid film 10 to 15 nm, an oxalic acid film 20 to 50 nm, Since the phosphoric acid film has a thickness of about 30 to 60 nm, infiltration of organic substances and the like is insufficient.
[0039]
For this reason, for example, the size of organic matter for decomposition and its penetration and the size of oxide sol (TiO 2)2In the sol, the size of the particles is about 3 to 20 nm), and the pore diameter A is about 80 nm to 250 nm as the structure of the porous alumina film 4 that can easily enter these materials. Comprehensively select the appropriate electrolyte, electrolysis conditions, and manufacturing process. In other words, a phosphoric acid solution or an oxalic acid solution having high chemical solubility is selected as the electrolytic solution, and the electrolysis voltage has a cell diameter (distance between the center of the hole wall indicated by C of b) of 300 to 600 nm. In order to apply a high voltage, the liquid temperature is set as low as possible, preferably about 10 ° C. or less.
[0040]
The metal vapor-deposited substrate 1 having excellent adhesion between the porous anodic oxide coating 4 and the
[0041]
Next, the titania-based composite nanostructure material is filled into the pores by a sol-gel coating method. By the sol-gel coating method, the sol penetrates through the pore wall, and further penetrates to the conductor layer having a fine uneven structure at the bottom of the pore and is firmly bonded directly to the conductor layer. Furthermore, as described above, the sol enters the gap in the gap-like boundary region of the hole wall formed during vapor deposition and gels. Thereby, the sol solution is filled in the pore inner walls and pores of the porous anodic oxide film formed on the substrate.
[0042]
Furthermore, the alumina pore wall can be selectively dissolved by chemical dissolution to produce a nanotube array structure, and the outer wall of the nanotube can be used. Therefore, these composite nanostructures have a high specific surface area and can effectively contact harmful substances, so that high photocatalytic properties can be obtained.
[0043]
In the method of the present invention, sol-gel coating is performed by the following method to improve the performance of photocatalytic properties and other properties for practical use.
(1) An oxide sol having a low viscosity is added to the titania sol.
The titania sol has a viscosity of about 2.4 cSt-20 ° C. As an oxide sol having a low viscosity, Al has a viscosity of 2.1 cSt-20 ° C. or less.2O3TiO2, SiO2, ZrO2, SnO2, TaO2And so on. If the viscosity is higher than this, the effect becomes poor. Especially SiO2Has a low viscosity, has little influence on the photocatalytic properties of titania, and has a great effect of improving the wettability between the pore walls of the porous alumina and the titania sol. The wettability improves as the viscosity of the mixed sol is reduced by adding the oxide sol, but excessive addition reduces the photocatalytic effect on the contrary, so the addition amount is adjusted within the range of 1 to 20% by weight. Viscosity is measured at 20 ° C. for a specified amount of liquid flowing through the capillary tube under specified conditions using a glass capillary viscometer (Ubbelohde) manufactured according to ASTM and JIS. It is a kinematic viscosity (cSt: centistokes) obtained by multiplying the outflow time (seconds) by a viscometer constant.
[0044]
Thereby, peeling from the pore wall and cracking of the gel body caused by gel contraction during drying can be prevented. Further, aggregation of titania particles can be suppressed, and the infiltration of titania sol into the pores is facilitated. That is, it is possible to increase the strength and the durability by densifying the modified layer, and to increase the adhesion by the anchor effect between the modified layer and the bottom of the pore. Therefore, adhesiveness with the alumina pore wall by the subsequent heat treatment is enhanced, and a hollow structure (6 in FIG. 1-d) having an open surface hole can be formed. Moreover, the film-forming property of the gel can be improved, the space between the gel particles and the titania crystal can be filled, and the strength, denseness, adhesiveness and the like of the gel layer can be improved.
[0045]
(2) An oxide that can be vitrified by heating at a low temperature of 300 to 400 ° C. in a titania sol is TeO.2, Li2O, Na2O, Nb2O3, Al2O3TiO2, PbO, WO3, SrO, La2O3, Ta2O3BaO, ZnO, MgO, etc., and the amount of addition is adjusted within the range of 0.5 to 10% by weight. Excessive addition reduces the photocatalytic effect. For example, TeO2By adding the sol as described above, the adhesion between the gel particles is enhanced, whereby the adhesion between the titania, the substrate and the alumina pore walls is further enhanced. In addition, SiO2Similarly to the above, the film formability of the gel, the strength of the gel layer, the denseness and the adhesiveness can be improved. As a result, it is possible to improve characteristics important for practical use such as durability of the titania-based composite nanostructure.
[0046]
(3) An oxide sol having visible light absorption characteristics is added to the titania sol.
Oxides having visible light absorption properties are currently RuO.2In addition to these, oxides such as Nd, Zr, Hf, La, Ce, and U are also effective. These addition amounts are generally effective even in trace amounts. In the present invention, the content is adjusted within the range of 0.1 to 5% by weight, but particularly excessive addition loses its effect. For example, the Ru complex can be expected to have a photosensitization effect due to absorption of sunlight as a ruthenium oxide, particularly absorption of wavelengths in the visible light region. For example, it can be applied to the solar cell field.
[0047]
(4) A substance that narrows the band gap of the Ti—O bond is added to the titania sol to obtain a photocatalyst having both absorption characteristics of ultraviolet light and visible light.
Currently, only nitrogen is known as an additive element corresponding to this. In the present invention, nitric acid or an ammonia solution is selected as a material that contains nitrogen and has relatively good workability, and the amount of addition thereof is adjusted within a range of 0.1 to 10% by weight. The nitrogen-containing material thus formed has the effect of narrowing the Ti—O bond bandwidth of titanium oxide, reducing the energy required for the photocatalytic reaction, increasing the photocatalytic effect in the ultraviolet region, and making it more visible. Use in the optical region is also possible.
[0048]
The porous composite oxide nanostructure formed in this way (see 6 in FIG. 1-d) further has, for example, 5 wt% phosphoric acid and 2 wt% chromic acid, as shown in FIG. When etching in a chemical dissolution process using an acid solution such as a mixed acid or an alkali solution such as sodium hydroxide having a concentration of 2 to 5% by weight, only the anodized aluminum film is dissolved, and a titania-based
[0049]
That is, by this, when a transparent material is used for both the substrate 1 and the
As shown in FIG. 2, a regular array of titania-based
[0050]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited thereto, and can be appropriately changed within the scope of the present invention.
Example 1
Using a transparent glass substrate on which a 120 nm thick ITO layer was sputter-coated on the surface, and a substrate on which RF sputtering of about 2 μm of Al was further performed, a sample which was ultrasonically cleaned in acetone for 10 minutes as a pretreatment was used as an anode. It was subjected to oxidation. Anodization was by constant potential electrolysis at 130V in 10% by volume phosphoric acid solution. Next, in order to enlarge the pore diameter of the alumina porous membrane formed by anodic oxidation, the sample was immersed in a 5 vol% phosphoric acid solution at 30 ° C. to adjust the pore diameter to about 180 nm.
[0051]
Then TiO22.5 wt% SiO in sol2Sol and 2.5 wt% TeO2Of the composition with sol addedComposite sol solutionDip coating by immersing the sample inInfiltrate the composite sol into the pores of the alumina porous membranedid. Subsequently, after drying for a long time (12 hours or more) to form a composite sol into a composite gel, the composite gel was made into a structure mainly composed of anatase-type titania crystals by heat treatment at 500 ° C. for 2 hours. Finally, only the anodized film is chemically dissolved and removed in a mixed acid solution (70 ° C.) of 5% by volume phosphoric acid and 2% by volume chromic acid, and nanotubes extending in the direction perpendicular to the substrate surface are formed on the transparent glass substrate. A sample 1 of a titania-based composite nanostructure (7 in FIG. 1) regularly arranged on the surface was manufactured.
[0052]
Example 2
Using the same ITO and Al-sputtered transparent glass substrate as in Example 1, samples were prepared in exactly the same manner as in Example 1 up to pretreatment, anodization, pore enlargement, and sol-gel treatment. Next, this dip-coated composite sample was finally heat-treated at 500 ° C. for 2 hours without chemically dissolving the anodic oxide film, and a porous titania-based composite nanostructure mainly composed of anatase-type titania crystals (
[0053]
Example 3
Using the same ITO and Al-sputtered transparent glass substrate as in Example 1, a sample was prepared in the same process as in Example 1 up to pretreatment, anodization, pore enlargement, and sol-gel treatment. Next, the dip-coated composite sample was heated at 600 ° C. for 2 hours without chemically dissolving the anodized film, and finally porous titania mainly composed of titania crystals mixed with rutile and anatase types. Sample 3 of the composite nanostructure was manufactured.
[0054]
Example 4
Using a transparent glass substrate on which an ITO layer having a thickness of about 120 nm is sputtered on the surface, and further using a substrate on which RF sputtering of about 2 μm of Al is further performed, a sample subjected to ultrasonic cleaning in acetone for 10 minutes as a pretreatment is prepared. Anodized. Anodization was conducted at a constant potential of 40 V in a 3 wt% oxalic acid solution. To enlarge the pore size of the porous alumina membrane formed by anodization, the sample was immersed in a 5% by volume phosphoric acid solution at 30 ° C. to adjust the pore size to about 80 nm.
[0055]
Thereafter, the sample was immersed in a sol having the same composition and concentration as in Example 1 and dip-coated. Finally, a sample 4 of a porous titania-based composite nanostructure mainly composed of anatase-type titania crystals was manufactured by heat treatment at 500 ° C. for 2 hours.
[0056]
Example 5
Using the same Al-sputtered glass substrate as in Example 4, a phosphoric acid anodic oxide film having a pore diameter of about 180 nm treated by the same process, composition, and conditions as in Example 1 until pretreatment, anodization, and pore diameter expansion treatment was used. Created. Then TiO25 wt% SiO in sol2Sol and 5 wt% TeO2The sample is dipped in a sol having a composition to which the sol has been added, and finally subjected to heat treatment at 600 ° C. for 2 hours to produce a sample 5 of a porous titania-based composite nanostructure mainly composed of anatase-type titania crystals. did.
[0057]
Example 6
Using the same Al-sputtered glass substrate as in Example 5, a phosphoric acid anodic oxide film having a pore diameter of about 180 nm was prepared by the same process, composition and conditions as in Example 1 from the subsequent pretreatment to the pore diameter expansion treatment. . Then
[0058]
In order to evaluate the photocatalytic properties of the titania-based composite nanostructure of the present invention, as a representative of harmful chemical substances, acetaldehyde gas is used to irradiate CO with UV light.2And photolysis experiment for detoxification with water. Table 1 shows the total of the titania-based nanostructures composed of the six types of titania-based composite nanostructures (nanotube array type and porous type) of Examples 1 to 6, the reference sample, and the standard sample. This is a summary of the comparison of the initial photodegradation rate of acetaldehyde gas with the elapse of irradiation time under ultraviolet irradiation using eight types of samples.
[0059]
[Table 1]
For comparison of photocatalytic properties, commercially available Degussa P25 pure titania powder was used as a standard sample. The reference sample has a sol composition of TiO at the time of sol-gel coating.2A porous titania-based nanostructure having the same manufacturing process and conditions as in Example 2 except that it is a single sol.
[0061]
As can be seen from Table 1, the initial rate of the photodecomposition reaction of acetaldehyde is 0.37 for the standard sample, whereas all the six types of samples of the present invention have values of 5 times or more. Samples 1 to 4 were 9 times or more, and the maximum value was 17.6 times that of Sample 1 in which nanotubes were arranged.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a production process of a “porous composite nanostructure” of the present invention.
FIG. 2 is a conceptual diagram showing the structure of the “nanotube array structure” of the present invention.
Claims (4)
粘度が２．４ｃＳｔ−２０℃のチタニアゾル中に粘度が２．１ｃＳｔ−２０℃以下の酸化物ゾルを１〜２０重量％添加することによって粘度を低くした複合ゾル液中に該細孔を形成した基体を浸漬して複合ゾル液を該細孔内に浸入させ、続いて、乾燥して複合ゾルを複合ゲル化した後、
５００〜６００℃で加熱して該細孔壁と密着した開放表面孔を持つアナターゼ型チタニア系結晶の中空構造を形成することを特徴とするアナターゼ型チタニア系結晶体からなる光触媒の製造方法。A transparent conductive layer having a fine concavo-convex structure with a depth of 2 to 200 nm is formed on the surface of the substrate, aluminum is vapor-deposited on the conductive layer, and a regular array of porous alumina films is formed on the substrate by anodic oxidation. In a method of forming a pore having a diameter of 80 nm or more and 250 nm or less, allowing a titania sol solution to enter into the pore to be gelled, and heating this to form an anatase titania-based crystal,
The pores were formed in a composite sol liquid having a reduced viscosity by adding 1 to 20% by weight of an oxide sol having a viscosity of 2.1 cSt-20 ° C. or less in a titania sol having a viscosity of 2.4 cSt-20 ° C. After immersing the substrate and allowing the composite sol solution to enter the pores, and subsequently drying to form the composite sol into a composite gel,
A method for producing a photocatalyst comprising an anatase-type titania-based crystal, which is heated at 500 to 600 ° C. to form a hollow structure of anatase-type titania-based crystal having an open surface hole in close contact with the pore wall.
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| CN1317193C (en) * | 2005-07-07 | 2007-05-23 | 上海交通大学 | Method for microwave preparation of titania nanometer tube |
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| US8273425B2 (en) * | 2009-05-14 | 2012-09-25 | Empire Technology Development Llc | Nanotube assisted self-cleaning material |
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| CN105129846A (en) * | 2015-08-20 | 2015-12-09 | 东北大学 | Preparation method, product and application of titanium dioxide nanotube/nanoribbon composite thin film |
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