JP4018161B2 - Method for producing titanium oxide for photocatalyst and method for removing harmful substances using the same - Google Patents
Method for producing titanium oxide for photocatalyst and method for removing harmful substances using the same Download PDFInfo
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- JP4018161B2 JP4018161B2 JP02902294A JP2902294A JP4018161B2 JP 4018161 B2 JP4018161 B2 JP 4018161B2 JP 02902294 A JP02902294 A JP 02902294A JP 2902294 A JP2902294 A JP 2902294A JP 4018161 B2 JP4018161 B2 JP 4018161B2
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- Prior art keywords
- titanium oxide
- rutile
- suspension
- light
- sample
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Links
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims description 148
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 title claims description 117
- 239000000126 substance Substances 0.000 title claims description 18
- 238000000034 method Methods 0.000 title claims description 9
- 239000011941 photocatalyst Substances 0.000 title claims description 9
- 238000004519 manufacturing process Methods 0.000 title claims description 5
- 239000000725 suspension Substances 0.000 claims description 25
- 239000013078 crystal Substances 0.000 claims description 21
- 239000002245 particle Substances 0.000 claims description 16
- 239000003513 alkali Substances 0.000 claims description 9
- 238000002441 X-ray diffraction Methods 0.000 claims description 8
- 150000003071 polychlorinated biphenyls Chemical group 0.000 claims description 8
- 239000002253 acid Substances 0.000 claims description 6
- 150000004820 halides Chemical class 0.000 claims description 5
- 230000001678 irradiating effect Effects 0.000 claims description 2
- 239000003054 catalyst Substances 0.000 description 28
- 238000010438 heat treatment Methods 0.000 description 17
- 230000003197 catalytic effect Effects 0.000 description 16
- 239000010419 fine particle Substances 0.000 description 13
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 9
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 9
- 239000000047 product Substances 0.000 description 9
- KBPLFHHGFOOTCA-UHFFFAOYSA-N 1-Octanol Chemical compound CCCCCCCCO KBPLFHHGFOOTCA-UHFFFAOYSA-N 0.000 description 8
- 229910010413 TiO 2 Inorganic materials 0.000 description 8
- 238000006555 catalytic reaction Methods 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 7
- 238000000354 decomposition reaction Methods 0.000 description 7
- CYTYCFOTNPOANT-UHFFFAOYSA-N Perchloroethylene Chemical group ClC(Cl)=C(Cl)Cl CYTYCFOTNPOANT-UHFFFAOYSA-N 0.000 description 6
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 6
- 230000007547 defect Effects 0.000 description 6
- 230000001699 photocatalysis Effects 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 229950011008 tetrachloroethylene Drugs 0.000 description 6
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 6
- 238000013032 photocatalytic reaction Methods 0.000 description 5
- -1 titanium oxide Chemical class 0.000 description 5
- 241000195493 Cryptophyta Species 0.000 description 4
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000010335 hydrothermal treatment Methods 0.000 description 4
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 4
- 229910017604 nitric acid Inorganic materials 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 229920006395 saturated elastomer Polymers 0.000 description 4
- 229910000349 titanium oxysulfate Inorganic materials 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 241000894006 Bacteria Species 0.000 description 3
- 241000233866 Fungi Species 0.000 description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 150000001412 amines Chemical class 0.000 description 3
- 229910021529 ammonia Inorganic materials 0.000 description 3
- 150000007522 mineralic acids Chemical class 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000001935 peptisation Methods 0.000 description 3
- 238000001834 photoacoustic spectrum Methods 0.000 description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 description 3
- 229910052724 xenon Inorganic materials 0.000 description 3
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 3
- 241000186361 Actinobacteria <class> Species 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- XSTXAVWGXDQKEL-UHFFFAOYSA-N Trichloroethylene Chemical group ClC=C(Cl)Cl XSTXAVWGXDQKEL-UHFFFAOYSA-N 0.000 description 2
- 150000001299 aldehydes Chemical class 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 230000007062 hydrolysis Effects 0.000 description 2
- 238000006460 hydrolysis reaction Methods 0.000 description 2
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 description 2
- 230000031700 light absorption Effects 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 230000003472 neutralizing effect Effects 0.000 description 2
- 229910017464 nitrogen compound Inorganic materials 0.000 description 2
- 150000002830 nitrogen compounds Chemical class 0.000 description 2
- 239000003921 oil Substances 0.000 description 2
- 150000007524 organic acids Chemical class 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical class [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 2
- 230000001443 photoexcitation Effects 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 230000008707 rearrangement Effects 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- LLZRNZOLAXHGLL-UHFFFAOYSA-J titanic acid Chemical compound O[Ti](O)(O)O LLZRNZOLAXHGLL-UHFFFAOYSA-J 0.000 description 2
- 229910052723 transition metal Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- UBOXGVDOUJQMTN-UHFFFAOYSA-N trichloroethylene Natural products ClCC(Cl)Cl UBOXGVDOUJQMTN-UHFFFAOYSA-N 0.000 description 2
- BJEPYKJPYRNKOW-REOHCLBHSA-N (S)-malic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O BJEPYKJPYRNKOW-REOHCLBHSA-N 0.000 description 1
- 229910002012 Aerosil® Inorganic materials 0.000 description 1
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 208000035985 Body Odor Diseases 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical class S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- 206010040904 Skin odour abnormal Diseases 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 235000011054 acetic acid Nutrition 0.000 description 1
- INNSZZHSFSFSGS-UHFFFAOYSA-N acetic acid;titanium Chemical compound [Ti].CC(O)=O.CC(O)=O.CC(O)=O.CC(O)=O INNSZZHSFSFSGS-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- BJEPYKJPYRNKOW-UHFFFAOYSA-N alpha-hydroxysuccinic acid Natural products OC(=O)C(O)CC(O)=O BJEPYKJPYRNKOW-UHFFFAOYSA-N 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000001099 ammonium carbonate Substances 0.000 description 1
- 235000012501 ammonium carbonate Nutrition 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- KYKAJFCTULSVSH-UHFFFAOYSA-N chloro(fluoro)methane Chemical compound F[C]Cl KYKAJFCTULSVSH-UHFFFAOYSA-N 0.000 description 1
- 150000001845 chromium compounds Chemical class 0.000 description 1
- 235000019504 cigarettes Nutrition 0.000 description 1
- 235000015165 citric acid Nutrition 0.000 description 1
- 238000010411 cooking Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 239000002781 deodorant agent Substances 0.000 description 1
- 238000004332 deodorization Methods 0.000 description 1
- 230000001877 deodorizing effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000000417 fungicide Substances 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 239000000383 hazardous chemical Substances 0.000 description 1
- 239000004009 herbicide Substances 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 150000002484 inorganic compounds Chemical class 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000002917 insecticide Substances 0.000 description 1
- 239000004310 lactic acid Substances 0.000 description 1
- 235000014655 lactic acid Nutrition 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000001630 malic acid Substances 0.000 description 1
- 235000011090 malic acid Nutrition 0.000 description 1
- 244000005700 microbiome Species 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 239000005645 nematicide Substances 0.000 description 1
- 150000002825 nitriles Chemical class 0.000 description 1
- 235000005985 organic acids Nutrition 0.000 description 1
- 150000002896 organic halogen compounds Chemical class 0.000 description 1
- 150000002903 organophosphorus compounds Chemical class 0.000 description 1
- 239000000575 pesticide Substances 0.000 description 1
- 238000004867 photoacoustic spectroscopy Methods 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000012306 spectroscopic technique Methods 0.000 description 1
- 150000003464 sulfur compounds Chemical class 0.000 description 1
- 239000013076 target substance Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 150000003609 titanium compounds Chemical class 0.000 description 1
- 239000004408 titanium dioxide Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Landscapes
- Inorganic Compounds Of Heavy Metals (AREA)
- Catalysts (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
Description
【０００１】
【産業上の利用分野】
本発明は優れた光触媒機能を有する酸化チタンの製造方法に関する。さらに、その酸化チタンを用いて有害物質を除去する方法に関する。
【０００２】
【従来の技術】
酸化チタンは、有機物質を合成する反応や有害物質などを除去する反応の触媒として利用されている。この触媒反応は、酸化チタンを加熱したり、あるいは酸化チタンにそのバンドギャップ以上のエネルギーを持つ波長の光を照射しながら、処理対象物質を酸化チタンに接触させて行われる。後者の反応は光触媒反応といわれ、近年、盛んに研究開発が行われている。この光触媒反応に使用される酸化チタンを光触媒と称している。酸化チタンに光を照射すると、酸化チタンが光励起して、伝導帯に電子を、価電子帯に正孔を生じる。この光励起により生じた電子の持つ強い還元力や正孔の持つ強い酸化力は、有害物質の除去・浄化、アンモニア、アルデヒド類、アミン類などの悪臭ガスの脱臭のほか、水の分解、細菌、放線菌、菌類、藻類などの殺菌・殺藻などに利用されている。たとえば、特公平２−９８５０号公報には、酸化チタンなどの光触媒を用いて廃棄物中の有害物質を除去し、浄化することが記載されている。また、特公平４−７８３２６号公報には、酸化チタンなどの光触媒を用いてトイレのし尿臭、ペットの臭い、たばこの臭い、調理臭、体臭などを脱臭することが記載されている。さらに、特公平４−２９３９３号公報には、光照射により酸化チタンなどの光触媒に生起した所定電圧を細胞に接触印可して細胞を殺すことが記載されている。
【０００３】
【発明が解決しようとする課題】
種々の触媒反応に用いられる酸化チタンは、たとえば、硫酸チタニルをアルカリで中和したり、加熱して加水分解したり、あるいは塩化チタンを気相で熱分解酸化したりして得られる。しかしながら、触媒反応の時間を短縮したり、触媒反応に用いる装置を小型化するため、一層優れた触媒機能を有する酸化チタンが嘱望されている。
【０００４】
【課題を解決するための手段】
本発明者らは、優れた触媒機能を有する酸化チタン触媒を得るべく研究した結果、▲１▼ルチル転位促進シードなどのルチル型酸化チタン微粒子を含有した特定の酸化チタンが高い触媒機能を有すること、▲２▼前記▲１▼の特定の酸化チタンを懸濁した液を加熱処理して得られた酸化チタンがより高い触媒機能を有すること、▲３▼前記▲１▼の特定の酸化チタンを解膠した後、加熱処理して得られた酸化チタンがさらに高い触媒機能を有すること、▲４▼前記▲１▼〜▲３▼の酸化チタンは特に光触媒として有用であり、ポリ塩化ビフェニルなどの有害物質を極めて効率よく除去できることなどを見出し、本発明を完成した。
すなわち、本発明は優れた触媒機能を有する酸化チタンを提供することにある。さらに、本発明の酸化チタン触媒を用いて、有害物質を迅速、かつ、効率よく除去する方法を提供することにある。
【０００５】
本発明の酸化チタン光触媒は、実質的にルチル型結晶構造を有し、その平均粒子径が１〜１００ｎｍである酸化チタンであって、Ｘ線回折像においてルチル型結晶と同定しうる酸化チタンを０．１〜５０重量％含有し、そのルチル型酸化チタンの平均粒子径が１〜１００ｎｍであり、しかも、残部が非晶質であり、アナタース型結晶を実質的に含有しない酸化チタンと、酸あるいはアルカリとを混合してｐＨが４以下あるいは９以上の懸濁液とし、次いで、該懸濁液を１００℃以上の温度で水熱処理して製造する。本発明において、酸化チタンとは、酸化チタン、メタチタン酸、オルソチタン酸などの各種の酸化チタンあるいは水酸化チタン、含水酸化チタンを意味する。また、ルチル型酸化チタン微粒子を含有した酸化チタンとは、Ｘ線回折像においてルチル型結晶と同定しうる微細な酸化チタンを好ましくは０．１〜５０重量％、より好ましくは０．５〜５０重量％、さらに好ましくは１．０〜３０重量％含有し、残部のほとんどが非晶質であり、アナタース型結晶を実質的に含有しない酸化チタンをいう。これに相当するものには、二酸化チタン顔料を製造する際に使われるルチル転位促進シードが挙げられる。このルチル型酸化チタン微粒子を含有した酸化チタンは、たとえば、（１）硫酸チタニル、酢酸チタン、四塩化チタンなどのチタン化合物を必要に応じて核晶の存在下、アルカリで中和したり、加水分解したりして沈殿物を得、次いで該沈殿物を、必要に応じてアルカリを添加し加熱した後、塩酸、硝酸などの無機酸またはクエン酸などの有機酸を添加し５０℃以上沸点以下の温度で熟成したり、（２）塩化チタンを用いる場合には特に、ｐＨが４〜７の範囲で炭酸ナトリウムなどのアルカリで中和したり、塩酸濃度が１１％以上の条件下で加熱して加水分解しても得られる。このようにして得られたルチル型酸化チタン微粒子を含有した酸化チタンを、分別し、洗浄して、硫酸根、塩素根、アルカリなどの不純物を除去したり、必要に応じて乾燥したりすることができる。乾燥は任意の温度で行うことができるが、１００〜５００℃の温度が適当である。ルチル型酸化チタン微粒子の平均粒子径は１〜１００ｎｍが適当であり、好ましくは１〜５０ｎｍ、より好ましくは１〜４０ｎｍ、さらに好ましくは１〜３０ｎｍ、もっとも好ましくは５〜３０ｎｍである。
【０００６】
本発明においては、前記のルチル型酸化チタン微粒子を含有した酸化チタンを通常の方法によって溶媒に懸濁し、得られた懸濁液を加熱処理するのが好ましい。加熱処理の温度は、６０℃以上、好ましくは７０〜４５０℃、より好ましくは８０〜４５０℃、さらに好ましくは９０〜３５０℃である。本発明においては、１００℃以上の水系での加熱処理を水熱処理と呼んでいる。加熱処理の温度が６０℃より低いと得られる酸化チタンの触媒機能が改善され難い。前記の加熱処理の圧力は通常飽和蒸気圧程度で行うのが好ましいが、飽和蒸気圧以上に加圧したり、大気圧程度の圧力で行ってもよい。本発明の水熱処理は、通常、工業的に用いられる耐熱耐圧装置で行うことができる。加熱処理時間は適宜設定できるが、１〜４８時間程度が適当である。また、懸濁液中の酸化チタン濃度は適宜設定できるが、ＴｉＯ2 に換算して１０〜１２００ｇ／ｌの濃度が適当である。このようにして得られた酸化チタンを懸濁液の状態で触媒反応に用いることができる。また、必要に応じて、加熱処理後の懸濁液から分別し、洗浄し、乾燥して得られた乾燥粉末をそのままの状態、あるいは乾燥粉末を粉砕した状態、さらには、成形した状態で触媒反応に用いることもできる。乾燥は任意の温度で行うことができるが、１００〜５００℃の温度が適当である。
【０００７】
前記の加熱処理して得られた酸化チタンは、Ｘ線回折像においてルチル型結晶と同定しうる酸化チタンを好ましくは０．１〜１００重量％、より好ましくは５〜１００重量％、さらに好ましくは１０〜１００重量％含有し、残部のほとんどが非晶質であり、アナタース型結晶を実質的に含有しない酸化チタンである。水熱処理を行うと、実質的にルチル型の結晶構造を示す酸化チタンが得られる。得られた酸化チタンの平均粒子径は、１〜５００ｎｍが適当であり、好ましくは１〜２５０ｎｍ、より好ましくは１〜１００ｎｍ、さらに好ましくは１〜５０ｎｍ、もっとも好ましくは５〜３０ｎｍである。酸化チタンの平均粒子径は、前記の加熱処理の温度や処理時間を適宜設定することにより、調整することができる。
【０００８】
本発明では、ルチル型酸化チタン微粒子を含有した酸化チタンを加熱処理するに先立ち、酸あるいはアルカリで解膠処理するのが好ましい。この解膠処理は、ルチル型酸化チタン微粒子を含有した酸化チタンと酸とを混合してｐＨが４以下、好ましくは２以下の懸濁液としたり、あるいはアルカリとを混合してｐＨが９以上、好ましくは１０以上の懸濁液とし、該酸化チタンを解膠させる。前記の酸としては塩酸、硝酸、リン酸、炭酸などの無機酸、クエン酸、リンゴ酸、酢酸、乳酸などの有機酸が挙げられ、少なくとも一種を適宜選択して用いることができる。前記のアルカリとしては水酸化ナトリウム、水酸化カリウム、炭酸ナトリウム、炭酸アンモニウム、アンモニア、アミン類などのアルカリが挙げられ、少なくとも一種を適宜選択して用いることができる。懸濁液のｐＨが４より高く９より低いと酸化チタンが分散しにくく、コロイド溶液とすることができないため好ましくない。この解膠処理により、この後の加熱処理の効果をより一層高めることができる。本発明においては、塩酸、硝酸などの無機酸を添加して解膠するのが特に好ましい。
【０００９】
本発明の酸化チタン触媒を光触媒反応に用いるには、有害物質の存在下、該酸化チタンにそのバンドギャップ以上のエネルギーを持つ波長の光を照射する。酸化チタン触媒は、使用場面に応じて、溶媒に懸濁した状態、支持体に担持あるいは被覆した状態、乾燥粉末をそのままの状態、あるいは乾燥粉末を粉砕した状態、さらには、成形した状態で用いることもできる。さらに、使用する触媒反応に応じて、酸化チタンの粒子表面に白金、ロジウムなどの遷移金属や該遷移金属の酸化物、水酸化物を適宜担持することもできる。酸化チタンの光触媒反応により分解あるいは酸化して除去する有害物質としては、人体や生活環境に悪影響を及ぼす物質やその可能性がある物質であり、たとえば、炭化水素、有機ハロゲン化物、有機リン化合物や除草剤、殺菌剤、殺虫剤、殺線虫剤などの種々の農薬などの有機物質、窒素化合物、硫黄化合物、シアン化合物、クロム化合物などの無機化合物、細菌、放線菌、菌類、藻類、カビ類などの微生物などが挙げられる。炭化水素としては、具体的には、アルデヒド類、アミン類、メルカプタン類、油類、アルコール類などが例示できる。有機ハロゲン化物としては、具体的には、ポリ塩化ビフェニル、フロン、トリハロメタン、トリクロロエチレン、テトラクロロエチレンが例示できる。また、窒素化合物としては、具体的には、アンモニア、窒素酸化物などが例示できる。本発明の酸化チタン触媒は、特に、ポリ塩化ビフェニル、トリハロメタン、トリクロロエチレン、テトラクロロエチレンなどの有機ハロゲン化物を効率よく分解し除去することができる。バンドギャップ以上のエネルギーを持つ波長の光としては、紫外線を含有した光が好ましく、たとえば、太陽光や蛍光灯、ブラックライト、ハロゲンランプ、キセノンフラッシュランプ、水銀灯などの光を用いることができる。特に３００〜４００ｎｍの近紫外線を含有した光が好ましい。光の照射量や照射時間などは処理対象物質の量などによって適宜設定できる。
【００１０】
【実施例】
比較例１
２２２ｇ／ｌの炭酸ナトリウムの水溶液２リットルに、攪拌下、２００ｇ／ｌの四塩化チタンの水溶液１リットルを滴下して四塩化チタンを室温で中和し、含水酸化チタン沈殿物を得た。引き続き、この中和沈殿物中のＴｉＯ2 の重量に対して５重量％のクエン酸を前記の水溶液に添加した後、７０℃に加温し、２０分間熟成した。得られた生成物を濾過し、洗浄し、乾燥して、ルチル型酸化チタン微粒子を含有した酸化チタン触媒（試料Ａ）を得た。この試料Ａは、Ｘ線回折の結果、Ｓｃｈｅｒｒｅｒの式から求めた平均粒子径が７．７ｎｍであるルチル型の結晶構造の微細な酸化チタンを１５重量％含有しており、残部は非晶質であった。この試料Ａの比表面積は２０２．１ｍ2／ｇであった。
【００１１】
比較例２
比較例１と同様に処理して生成物を得た。この生成物（ルチル型酸化チタン微粒子を含有した酸化チタン）を濾過し、洗浄した後、水に分散させ、ＴｉＯ２に換算して１００ｇ／ｌの懸濁液とした。次いで、この懸濁液に塩酸水溶液を添加してｐＨを１．０にした後、四ツ口フラスコに入れ、９５℃の温度で６時間、還流下で加熱処理を行った。この後、得られた生成物を濾過し、洗浄し、乾燥して、酸化チタン触媒（試料Ｂ）を得た。この試料Ｂは、Ｘ線回折の結果、実質的にルチル型の結晶構造を有しており、Ｓｃｈｅｒｒｅｒの式から求めた平均粒子径が１２．３ｎｍであった。この試料Ｂの比表面積は９８．２ｍ２／ｇであった。
【００１２】
比較例３
８０ｇ／ｌの硫酸チタニルの水溶液１リットルを８５℃の温度に加熱し３時間保持して、硫酸チタニルを加水分解した。このようにして得られた加水分解生成物を濾過し、洗浄し、乾燥して、酸化チタン触媒（試料Ｃ）を得た。この試料Ｃはアナタース型結晶を有しており、Ｓｃｈｅｒｒｅｒの式から求めた平均粒子径は７．６ｎｍであった。この試料Ｃの比表面積は１９３．５ｍ２／ｇであった。
【００１３】
前記で得られた試料（Ａ〜Ｃ）の触媒機能を以下のようにして調べた。各試料０．１ｇを純水に分散させ、ＴｉＯ２に換算して４ｇ／ｌの懸濁液とした。これらの懸濁液２５ｍｌにオクタノール２５μｌを添加した後、１５０Ｗのキセノンランプを２時間照射して、オクタノールの光触媒反応を行った。反応前のオクタノールの濃度と反応後のオクタノールの濃度から各々の試料による分解速度を算出した。その結果を表１に示す。この表から明らかなように、ルチル型の結晶構造を有している酸化チタン触媒は光触媒機能に優れていることがわかる。
【００１４】
【表１】
実施例１
比較例１と同様に処理して生成物を得た。この生成物（ルチル型酸化チタン微粒子を含有した酸化チタン）を濾過し、洗浄した後、水に分散させ、ＴｉＯ２に換算して２５０ｇ／ｌの懸濁液とした。次いで、この懸濁液に硝酸水溶液を添加してｐＨを１．３にした後、オートクレーブに入れ、１５０℃の温度で１３時間、飽和蒸気圧下で水熱処理を行った。この後、得られた生成物を濾過し、洗浄し、乾燥して、本発明の酸化チタン触媒（試料Ｄ）を得た。この試料Ｄは、Ｘ線回折の結果、実質的にルチル型の結晶構造を有しており、Ｓｃｈｅｒｒｅｒの式から求めた平均粒子径が１８．０ｎｍであった。また、電子顕微鏡観察の結果、ルチル型結晶の自形である立方晶形状を有していた。
【００１６】
比較例４
８０ｇ／ｌの四塩化チタンの溶液１リットルに攪拌下、アンモニア水を添加し、溶液のｐＨを７．０にしてゲルを得た。このゲルを濾過し、洗浄した後、水に分散させ、ＴｉＯ２に換算して２５０ｇ／ｌの懸濁液とした。次いで、この懸濁液をオートクレーブに入れ、１５０℃の温度で１３時間、飽和蒸気圧下で水熱処理を行った。この後、得られた生成物を濾過し、洗浄し、乾燥して、酸化チタン触媒（試料Ｅ）を得た。この試料Ｅは、Ｘ線回折の結果、アナタース型の結晶構造を有しており、Ｓｃｈｅｒｒｅｒの式から求めた平均粒子径が１０．５ｎｍであった。
【００１７】
比較例５
市販の酸化チタン触媒Ｐ−２５（日本アエロジル社製、平均粒子径２２ｎｍ、ルチル型とアナタ─ス型の混合形）を試料Ｆとした。
【００１８】
実施例および比較例で得られた試料（Ｄ〜Ｆ）の触媒機能を以下のようにして調べた。試料をそれぞれ水に分散させ、ＴｉＯ2 に換算して４ｇ／ｌの懸濁液とした。これらの懸濁液２５ｍｌにテトラクロロエチレンを１０μｌ添加した後、１５０Ｗのキセノンランプを３０分間照射して、テトラクロロエチレンの光触媒分解反応を行った。反応前のテトラクロロエチレンの濃度と反応後のテトラクロロエチレンの濃度から各々の試料による分解率を算出した。その結果を表２に示す。この表から明らかなように、本発明の酸化チタン触媒は触媒機能に優れていることがわかる。
【００１９】
【表２】
実施例および比較例で得られた試料（Ｄ、Ｃ）をそれぞれ水に分散させ、ＴｉＯ2 に換算して４ｇ／ｌの懸濁液とした。これらの懸濁液５０ｍｌに、ポリ塩化ビフェニル（試薬）を溶解したｎ−ヘキサン溶液を添加した。これらの混合液に空気を吹き込みながら５０℃の温度に加熱しｎ−ヘキサンを除去した。次いで、１００Ｗの高圧水銀ランプを３０分間照射して、ポリ塩化ビフェニルの光触媒分解反応を行った。なお、光量は３７ｍＷ／ｃｍ2 であった。反応前のポリ塩化ビフェニルの濃度と反応後のポリ塩化ビフェニルの濃度をガスクロマトグラフで測定し、各々の試料による分解率を算出した。その結果を表３に示す。この表から明らかなように、本発明の酸化チタン触媒は触媒機能に優れていることがわかる。
【００２１】
【表３】
実施例および比較例で得られた試料（Ａ〜Ｆ）の結晶性を光音響分光法による分光学的手法を用いて調べた。すなわち、密閉容器に試料０．５ｇを入れ、そこへ一定波長の光を照射すると試料がその波長に応じて光を吸収するが、この吸収した光のエネルギーを無放射過程により熱として放出する場合、結晶格子の振動エネルギーの増大に伴う試料の熱膨張により、試料の周囲の大気が振動し音波を発生する。この時に発生する音波を高感度マイクロホンにより検出する。試料に照射する光の波長を３００〜１６００ｎｍに変化させて高感度マイクロホンの出力を測定して、各試料の光音響スペクトルを得た。
酸化チタンは３．０ｅＶのバンドギャップを有していると一般的に言われているが、このバンドギャップに相当するエネルギーを光エネルギーに換算すると４１３ｎｍの波長の光となる。従って、理論上は４１３ｎｍより少し短い波長の光を照射すると酸化チタンに全て吸収され、一方、４１３ｎｍより少し長い波長の光を照射すると酸化チタンには全く吸収されないことになる。しかしながら、結晶性の劣った酸化チタンでは、３．０ｅＶよりも小さなエネルギーを吸収し得る欠陥準位を有しており、このため、４１３ｎｍより少し長い波長の光でも吸収してしまう。このことから、この固有光吸収端の状態を前記の光音響スペクトルを用いて比較することにより、各試料の結晶性の優劣を判断することができる。本発明の酸化チタン触媒の光音響スペクトルは固有光吸収端の立ち上がりが鋭いことから、本発明の酸化チタン触媒は結晶性が優れていることがわかった。特に、加熱処理して得られた本発明の酸化チタン触媒は結晶性がより優れていた。
【００２３】
本発明の酸化チタン触媒は、前述のように、従来のものに比べ触媒機能が高い。この理由については明らかでないが、本発明の酸化チタン触媒は、結晶性に優れており、酸化チタンの粒子内部に存在する格子欠陥が少ないためと考えられる。従来の酸化チタンは格子欠陥が多いため、紫外線などの光照射によって発生した電子や正孔が該格子欠陥に多く留まってしまい、触媒反応に関与できる電子や正孔の量が少ない。一方、本発明の酸化チタン触媒は格子欠陥が少ないため、発生した電子や正孔が格子欠陥に留まりにくく、さらに、発生した電子と正孔との電荷分離が容易になって、触媒反応に関与できる電子や正孔の量が増えたためと推察される。また、ルチル型結晶を有していることも、本発明の酸化チタン触媒の機能が高い原因の一つと考えている。すなわち、ルチル型酸化チタンのバンドギャップは３．０ｅＶに対して、アナタース型酸化チタンのバンドギャップは３．２ｅＶである。これらのバンドギャップに相当するエネルギーを光エネルギーに換算すると、それぞれ４１３ｎｍと３８７ｎｍである。つまり、光励起には、ルチル型酸化チタンは４１３ｎｍ以下の波長の光が必要であり、アナタース型酸化チタンは３８７ｎｍ以下の波長の光が必要である。従って、ルチル型酸化チタンは４００ｎｍ程度の光でも励起するため、励起する光の波長の範囲が広く、光の利用効率が高い。このため、本発明の酸化チタン触媒は、触媒機能が高いと推察される。
【００２４】
【発明の効果】
本発明の酸化チタン触媒は、ルチル型酸化チタン微粒子を含有した酸化チタンであって、優れた触媒機能、特に、優れた光触媒機能を有するものである。さらに、前記のルチル型酸化チタン微粒子を含有した酸化チタンを加熱処理すると、より高い触媒機能を有する酸化チタンとすることができる。また、前記のルチル型酸化チタン微粒子を含有した酸化チタンを加熱処理するに先立ち、解膠処理すると、さらに高い触媒機能を有する酸化チタンとすることができる。これらの酸化チタン触媒の光触媒機能を利用して有機ハロゲン化合物、悪臭ガス、油、細菌、菌類、藻類などの有害物質を迅速、かつ、効率よく除去することができるので、工業用途ばかりでなく一般家庭用の除去剤、脱臭体、殺菌体などとして極めて有用なものである。また、本発明の酸化チタン触媒は、白色であり、安全性が高く、さらに、廃棄しても環境を汚さないため、種々の用途に用いることができる。また、本発明の酸化チタン触媒はルチル型結晶を有しているため、相転移がなく、熱に対して安定である。[0001]
[Industrial application fields]
The present invention relates to a method for producing titanium oxide having an excellent photocatalytic function. Furthermore, the present invention relates to a method for removing harmful substances using the titanium oxide.
[0002]
[Prior art]
Titanium oxide is used as a catalyst for reactions that synthesize organic substances and remove harmful substances. This catalytic reaction is carried out by contacting the titanium oxide with the target substance to be treated while heating the titanium oxide or irradiating the titanium oxide with light having a wavelength having energy greater than the band gap. The latter reaction is called a photocatalytic reaction and has been actively researched and developed in recent years. The titanium oxide used for this photocatalytic reaction is called a photocatalyst. When the titanium oxide is irradiated with light, the titanium oxide is photoexcited to generate electrons in the conduction band and holes in the valence band. The strong reducing power of electrons generated by this photoexcitation and the strong oxidizing power of holes contribute to the removal and purification of harmful substances, the deodorization of odorous gases such as ammonia, aldehydes, and amines, as well as the decomposition of water, bacteria, It is used to sterilize and kill algae such as actinomycetes, fungi and algae. For example, Japanese Patent Publication No. 2-9850 discloses that harmful substances in waste are removed and purified using a photocatalyst such as titanium oxide. Japanese Examined Patent Publication No. 4-78326 describes deodorizing toilet odor, pet odor, cigarette odor, cooking odor, body odor and the like using a photocatalyst such as titanium oxide. Further, Japanese Patent Publication No. 4-29393 describes that a predetermined voltage generated in a photocatalyst such as titanium oxide by light irradiation is applied to the cell to kill the cell.
[0003]
[Problems to be solved by the invention]
Titanium oxide used for various catalytic reactions can be obtained, for example, by neutralizing titanyl sulfate with an alkali, hydrolyzing it by heating, or thermally decomposing and oxidizing titanium chloride in a gas phase. However, in order to shorten the time for the catalytic reaction and to reduce the size of the apparatus used for the catalytic reaction, titanium oxide having a further excellent catalytic function is desired.
[0004]
[Means for Solving the Problems]
As a result of researches to obtain a titanium oxide catalyst having an excellent catalytic function, the present inventors have found that (1) a specific titanium oxide containing rutile type titanium oxide fine particles such as a rutile rearrangement promoting seed has a high catalytic function. (2) The titanium oxide obtained by heat-treating the liquid in which the specific titanium oxide of (1) is suspended has a higher catalytic function, (3) The specific titanium oxide of (1) The titanium oxide obtained by heat treatment after peptization has a higher catalytic function. (4) The titanium oxides of (1) to (3) are particularly useful as photocatalysts, such as polychlorinated biphenyl. The inventors have found that harmful substances can be removed very efficiently, and completed the present invention.
That is, the present invention is to provide a titanium oxide having an excellent catalytic function. It is another object of the present invention to provide a method for quickly and efficiently removing harmful substances using the titanium oxide catalyst of the present invention.
[0005]
The titanium oxide photocatalyst of the present invention is a titanium oxide having a rutile-type crystal structure and an average particle diameter of 1 to 100 nm, which can be identified as a rutile-type crystal in an X-ray diffraction image. A titanium oxide containing 0.1 to 50% by weight, the rutile titanium oxide having an average particle diameter of 1 to 100 nm, the balance being amorphous, and substantially free of anatase crystals ; Alternatively, alkali is mixed to form a suspension having a pH of 4 or less or 9 or more, and then the suspension is hydrothermally treated at a temperature of 100 ° C. or more . In the present invention, the titanium oxide means various titanium oxides such as titanium oxide, metatitanic acid, orthotitanic acid, titanium hydroxide, and hydrous titanium oxide. The titanium oxide containing rutile-type titanium oxide fine particles is preferably a fine titanium oxide that can be identified as a rutile-type crystal in an X-ray diffraction image, preferably 0.1 to 50% by weight, more preferably 0.5 to 50%. The titanium oxide is contained in an amount of 10% by weight, more preferably 1.0 to 30% by weight, and most of the remainder is amorphous and substantially does not contain anatase type crystals. Corresponding to this is the rutile rearrangement promoting seed used in the production of titanium dioxide pigments. The titanium oxide containing the rutile-type titanium oxide fine particles can be obtained by, for example, (1) neutralizing titanium compounds such as titanyl sulfate, titanium acetate, and titanium tetrachloride with alkali in the presence of nuclei as necessary, or adding water. After decomposition, a precipitate is obtained, and then the precipitate is heated by adding an alkali as necessary, and then an inorganic acid such as hydrochloric acid and nitric acid or an organic acid such as citric acid is added and the boiling point is 50 ° C. or higher and lower than the boiling point (2) Especially when titanium chloride is used, it is neutralized with an alkali such as sodium carbonate in a pH range of 4 to 7, or heated under a condition where the hydrochloric acid concentration is 11% or more. It can also be obtained by hydrolysis. Titanium oxide containing the rutile-type titanium oxide fine particles obtained in this way is separated and washed to remove impurities such as sulfate radicals, chlorine radicals and alkalis, or to dry as necessary. Can do. Drying can be performed at any temperature, but a temperature of 100 to 500 ° C. is suitable. The average particle size of the rutile-type titanium oxide fine particles is suitably 1 to 100 nm, preferably 1 to 50 nm, more preferably 1 to 40 nm, still more preferably 1 to 30 nm, and most preferably 5 to 30 nm.
[0006]
In the present invention, it is preferable to suspend titanium oxide containing the rutile-type titanium oxide fine particles in a solvent by an ordinary method and heat-treat the obtained suspension. The temperature of the heat treatment is 60 ° C. or higher, preferably 70 to 450 ° C., more preferably 80 to 450 ° C., and further preferably 90 to 350 ° C. In the present invention, heat treatment in an aqueous system at 100 ° C. or higher is called hydrothermal treatment. When the temperature of the heat treatment is lower than 60 ° C., it is difficult to improve the catalytic function of titanium oxide obtained. The pressure for the heat treatment is usually preferably about saturated vapor pressure, but may be increased to a pressure higher than the saturated vapor pressure or may be about atmospheric pressure. The hydrothermal treatment of the present invention can be usually carried out with a heat and pressure resistant apparatus used industrially. The heat treatment time can be set as appropriate, but about 1 to 48 hours is appropriate. Although titanium oxide concentration in the suspension can be optionally set, in terms of TiO 2 concentration of 10~1200g / l it is suitable. The titanium oxide thus obtained can be used for the catalytic reaction in the form of a suspension. If necessary, the catalyst can be separated from the suspension after the heat treatment, washed and dried, and the dried powder can be used as it is, or the dried powder can be pulverized or further molded. It can also be used for the reaction. Drying can be performed at any temperature, but a temperature of 100 to 500 ° C. is suitable.
[0007]
The titanium oxide obtained by the heat treatment is preferably 0.1 to 100% by weight, more preferably 5 to 100% by weight, and still more preferably titanium oxide that can be identified as a rutile crystal in an X-ray diffraction image. The titanium oxide is contained in an amount of 10 to 100% by weight, most of the remainder is amorphous, and substantially does not contain anatase type crystals. When hydrothermal treatment is performed, titanium oxide having a substantially rutile crystal structure is obtained. The average particle diameter of the obtained titanium oxide is suitably 1 to 500 nm, preferably 1 to 250 nm, more preferably 1 to 100 nm, still more preferably 1 to 50 nm, and most preferably 5 to 30 nm. The average particle diameter of titanium oxide can be adjusted by appropriately setting the temperature and the treatment time of the heat treatment.
[0008]
In the present invention, it is preferable that the titanium oxide containing the rutile-type titanium oxide fine particles is peptized with an acid or an alkali prior to the heat treatment. In this peptization treatment, a titanium oxide containing rutile titanium oxide fine particles and an acid are mixed to form a suspension having a pH of 4 or less, preferably 2 or less, or an alkali is mixed to a pH of 9 or more. The suspension is preferably 10 or more and the titanium oxide is peptized. Examples of the acid include inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, and carbonic acid, and organic acids such as citric acid, malic acid, acetic acid, and lactic acid, and at least one kind can be appropriately selected and used. Examples of the alkali include alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, ammonia, and amines, and at least one kind can be appropriately selected and used. If the pH of the suspension is higher than 4 and lower than 9, it is not preferable because titanium oxide is difficult to disperse and cannot be made into a colloidal solution. By this peptization treatment, the effect of the subsequent heat treatment can be further enhanced. In the present invention, it is particularly preferable to peptize by adding an inorganic acid such as hydrochloric acid or nitric acid.
[0009]
In order to use the titanium oxide catalyst of the present invention for the photocatalytic reaction, in the presence of a harmful substance, the titanium oxide is irradiated with light having a wavelength having energy greater than the band gap. The titanium oxide catalyst is used in a state of being suspended in a solvent, a state of being supported or coated on a support, a state of a dry powder as it is, a state of pulverizing a dry powder, or a state of molding, depending on the use situation. You can also. Furthermore, depending on the catalytic reaction to be used, a transition metal such as platinum or rhodium, or an oxide or hydroxide of the transition metal can be appropriately supported on the surface of the titanium oxide particles. Hazardous substances that are decomposed or oxidized and removed by photocatalytic reaction of titanium oxide are substances that may adversely affect the human body and living environment, such as hydrocarbons, organic halides, organophosphorus compounds, Organic substances such as various pesticides such as herbicides, fungicides, insecticides, nematicides, inorganic compounds such as nitrogen compounds, sulfur compounds, cyanide compounds, chromium compounds, bacteria, actinomycetes, fungi, algae, molds And other microorganisms. Specific examples of the hydrocarbon include aldehydes, amines, mercaptans, oils, alcohols and the like. Specific examples of the organic halide include polychlorinated biphenyl, chlorofluorocarbon, trihalomethane, trichloroethylene, and tetrachloroethylene. Specific examples of nitrogen compounds include ammonia and nitrogen oxides. In particular, the titanium oxide catalyst of the present invention can efficiently decompose and remove organic halides such as polychlorinated biphenyl, trihalomethane, trichloroethylene, and tetrachloroethylene. As light having a wavelength having energy greater than or equal to the band gap, light containing ultraviolet rays is preferable. For example, light such as sunlight, a fluorescent lamp, a black light, a halogen lamp, a xenon flash lamp, or a mercury lamp can be used. In particular, light containing near ultraviolet rays of 300 to 400 nm is preferable. The light irradiation amount, irradiation time, and the like can be appropriately set depending on the amount of the substance to be treated.
[0010]
【Example】
Comparative Example 1
Under stirring, 1 liter of an aqueous solution of 200 g / l titanium tetrachloride was added dropwise to 2 liter of an aqueous solution of 222 g / l sodium carbonate to neutralize the titanium tetrachloride at room temperature to obtain a hydrous titanium oxide precipitate. Subsequently, 5% by weight of citric acid based on the weight of TiO 2 in the neutralized precipitate was added to the aqueous solution, followed by heating to 70 ° C. and aging for 20 minutes. The resulting product was filtered, washed and dried to obtain a titanium oxide catalyst containing a rutile type titanium oxide particles (Sample A). As a result of X-ray diffraction, this sample A contains 15% by weight of fine titanium oxide having a rutile crystal structure with an average particle diameter of 7.7 nm obtained from the Scherrer equation, and the balance is amorphous. Met. The specific surface area of Sample A was 202.1 m 2 / g.
[0011]
Comparative Example 2
The product was obtained in the same manner as in Comparative Example 1. This product (titanium oxide containing rutile-type titanium oxide fine particles) was filtered, washed, and then dispersed in water to obtain a suspension of 100 g / l in terms of TiO 2 . Next, an aqueous hydrochloric acid solution was added to the suspension to adjust the pH to 1.0, and then the suspension was placed in a four-necked flask and subjected to heat treatment at 95 ° C. for 6 hours under reflux. Thereafter, filtration of the resulting product was washed and dried to give the acid titanium catalyst (sample B). As a result of X-ray diffraction, this sample B had a substantially rutile-type crystal structure, and the average particle size determined from the Scherrer equation was 12.3 nm. The specific surface area of this sample B was 98.2 m 2 / g.
[0012]
Comparative Example 3
One liter of an 80 g / l aqueous solution of titanyl sulfate was heated to a temperature of 85 ° C. and held for 3 hours to hydrolyze the titanyl sulfate. The hydrolysis product thus obtained was filtered, washed and dried to obtain a titanium oxide catalyst (sample C). This sample C had an anatase type crystal, and the average particle size determined from Scherrer's formula was 7.6 nm. The specific surface area of Sample C was 193.5 m 2 / g.
[0013]
The catalytic function of the samples (A to C) obtained above was examined as follows. 0.1 g of each sample was dispersed in pure water and converted to TiO 2 to give a suspension of 4 g / l. After adding 25 μl of octanol to 25 ml of these suspensions, a 150 W xenon lamp was irradiated for 2 hours to carry out a photocatalytic reaction of octanol. The decomposition rate for each sample was calculated from the concentration of octanol before the reaction and the concentration of octanol after the reaction. The results are shown in Table 1. As is apparent from this table, it can be seen that the titanium oxide catalyst having the rutile crystal structure is excellent in the photocatalytic function.
[0014]
[Table 1]
Example 1
The product was obtained in the same manner as in Comparative Example 1. This product (titanium oxide containing rutile titanium oxide fine particles) was filtered and washed, and then dispersed in water to obtain a suspension of 250 g / l in terms of TiO 2 . Next, an aqueous nitric acid solution was added to the suspension to adjust the pH to 1.3, and the suspension was placed in an autoclave and subjected to hydrothermal treatment at 150 ° C. for 13 hours under saturated vapor pressure. Thereafter, the obtained product was filtered, washed, and dried to obtain a titanium oxide catalyst (sample D) of the present invention. As a result of X-ray diffraction, this sample D had a substantially rutile crystal structure, and the average particle size determined from the Scherrer equation was 18.0 nm. Further, as a result of observation with an electron microscope, it had a cubic shape which is a self-form of a rutile crystal.
[0016]
Comparative Example 4
Aqueous ammonia was added to 1 liter of a solution of 80 g / l titanium tetrachloride with stirring to adjust the pH of the solution to 7.0 to obtain a gel. This gel was filtered and washed, and then dispersed in water to obtain a suspension of 250 g / l in terms of TiO 2 . The suspension was then placed in an autoclave and hydrothermally treated at 150 ° C. for 13 hours under saturated vapor pressure. Thereafter, the obtained product was filtered, washed, and dried to obtain a titanium oxide catalyst (sample E). As a result of X-ray diffraction, this sample E had an anatase type crystal structure, and the average particle size determined from Scherrer's equation was 10.5 nm.
[0017]
Comparative Example 5
Sample F was a commercially available titanium oxide catalyst P-25 (manufactured by Nippon Aerosil Co., Ltd., average particle size 22 nm, mixed form of rutile type and anatase type).
[0018]
The catalytic functions of the samples (DF) obtained in the examples and comparative examples were examined as follows. Each sample was dispersed in water to obtain a 4 g / l suspension in terms of TiO 2 . After adding 10 μl of tetrachlorethylene to 25 ml of these suspensions, a 150 W xenon lamp was irradiated for 30 minutes to carry out a photocatalytic decomposition reaction of tetrachloroethylene. The decomposition rate for each sample was calculated from the concentration of tetrachloroethylene before the reaction and the concentration of tetrachloroethylene after the reaction. The results are shown in Table 2. As is apparent from this table, the titanium oxide catalyst of the present invention has an excellent catalytic function.
[0019]
[Table 2]
Samples (D, C) obtained in Examples and Comparative Examples were each dispersed in water to obtain a 4 g / l suspension in terms of TiO 2 . An n-hexane solution in which polychlorinated biphenyl (reagent) was dissolved was added to 50 ml of these suspensions. The mixture was heated to a temperature of 50 ° C. while blowing air to remove n-hexane. Then, a 100 W high pressure mercury lamp was irradiated for 30 minutes to carry out photocatalytic decomposition reaction of polychlorinated biphenyl. The amount of light was 37 mW / cm 2 . The concentration of polychlorinated biphenyl before the reaction and the concentration of polychlorinated biphenyl after the reaction were measured with a gas chromatograph, and the decomposition rate of each sample was calculated. The results are shown in Table 3. As is apparent from this table, the titanium oxide catalyst of the present invention has an excellent catalytic function.
[0021]
[Table 3]
The crystallinity of the samples (A to F) obtained in Examples and Comparative Examples was examined using a spectroscopic technique based on photoacoustic spectroscopy. That is, when 0.5 g of a sample is placed in a sealed container and irradiated with light of a certain wavelength, the sample absorbs light according to the wavelength, but the energy of the absorbed light is released as heat by a non-radiative process. Due to the thermal expansion of the sample accompanying an increase in the vibration energy of the crystal lattice, the atmosphere around the sample vibrates and generates sound waves. The sound wave generated at this time is detected by a high sensitivity microphone. The output of the high-sensitivity microphone was measured while changing the wavelength of light irradiated to the sample to 300 to 1600 nm, and the photoacoustic spectrum of each sample was obtained.
Titanium oxide is generally said to have a band gap of 3.0 eV. When energy corresponding to this band gap is converted into light energy, light having a wavelength of 413 nm is obtained. Therefore, theoretically, when light having a wavelength slightly shorter than 413 nm is irradiated, all of the titanium oxide is absorbed. On the other hand, when light having a wavelength slightly longer than 413 nm is irradiated, the titanium oxide is not absorbed at all. However, titanium oxide having poor crystallinity has a defect level capable of absorbing energy smaller than 3.0 eV, and therefore absorbs light having a wavelength slightly longer than 413 nm. From this, the superiority or inferiority of the crystallinity of each sample can be determined by comparing the state of the intrinsic light absorption edge using the photoacoustic spectrum. In the photoacoustic spectrum of the titanium oxide catalyst of the present invention, the rising edge of the intrinsic light absorption edge is sharp, indicating that the titanium oxide catalyst of the present invention has excellent crystallinity. In particular, the titanium oxide catalyst of the present invention obtained by heat treatment was more excellent in crystallinity.
[0023]
As described above, the titanium oxide catalyst of the present invention has a higher catalytic function than the conventional one. Although the reason for this is not clear, it is considered that the titanium oxide catalyst of the present invention is excellent in crystallinity and has few lattice defects present inside the titanium oxide particles. Since conventional titanium oxide has many lattice defects, a large number of electrons and holes generated by irradiation with light such as ultraviolet rays remain in the lattice defects, and the amount of electrons and holes that can participate in the catalytic reaction is small. On the other hand, since the titanium oxide catalyst of the present invention has few lattice defects, it is difficult for the generated electrons and holes to stay in the lattice defects, and furthermore, the charge separation between the generated electrons and holes becomes easy and participates in the catalytic reaction. This is probably because the amount of electrons and holes that can be increased. Moreover, having a rutile type crystal | crystallization considers that the function of the titanium oxide catalyst of this invention is one of the high causes. That is, the band gap of rutile titanium oxide is 3.0 eV, whereas the band gap of anatase titanium oxide is 3.2 eV. When the energy corresponding to these band gaps is converted into light energy, they are 413 nm and 387 nm, respectively. That is, for photoexcitation, rutile titanium oxide requires light with a wavelength of 413 nm or less, and anatase titanium oxide requires light with a wavelength of 387 nm or less. Therefore, since rutile titanium oxide is excited even by light having a wavelength of about 400 nm, the wavelength range of light to be excited is wide and the light use efficiency is high. For this reason, it is speculated that the titanium oxide catalyst of the present invention has a high catalytic function.
[0024]
【The invention's effect】
The titanium oxide catalyst of the present invention is a titanium oxide containing rutile-type titanium oxide fine particles, and has an excellent catalytic function, particularly an excellent photocatalytic function. Furthermore, when the titanium oxide containing the rutile-type titanium oxide fine particles is heat-treated, titanium oxide having a higher catalytic function can be obtained. Further, when the titanium oxide containing the rutile-type titanium oxide fine particles is heat-treated before the heat treatment, titanium oxide having a higher catalytic function can be obtained. By utilizing the photocatalytic function of these titanium oxide catalysts, harmful substances such as organic halogen compounds, malodorous gases, oils, bacteria, fungi, and algae can be removed quickly and efficiently. It is extremely useful as a household remover, deodorant, sterilizer and the like. In addition, the titanium oxide catalyst of the present invention is white, has high safety, and does not pollute the environment even when discarded, so it can be used for various applications. In addition, since the titanium oxide catalyst of the present invention has rutile crystals, it has no phase transition and is stable to heat.
Claims (4)
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