JP3749641B2 - Photocatalyst powder and method for producing photocatalyst film - Google Patents
Photocatalyst powder and method for producing photocatalyst film Download PDFInfo
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- JP3749641B2 JP3749641B2 JP32145999A JP32145999A JP3749641B2 JP 3749641 B2 JP3749641 B2 JP 3749641B2 JP 32145999 A JP32145999 A JP 32145999A JP 32145999 A JP32145999 A JP 32145999A JP 3749641 B2 JP3749641 B2 JP 3749641B2
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- 239000011941 photocatalyst Substances 0.000 title claims description 113
- 239000000843 powder Substances 0.000 title claims description 58
- 238000004519 manufacturing process Methods 0.000 title claims description 35
- 229910052719 titanium Inorganic materials 0.000 claims description 67
- 239000010936 titanium Substances 0.000 claims description 67
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 65
- 239000002244 precipitate Substances 0.000 claims description 42
- 230000001699 photocatalysis Effects 0.000 claims description 38
- 238000000034 method Methods 0.000 claims description 36
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 32
- 150000003609 titanium compounds Chemical class 0.000 claims description 32
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 31
- 239000002243 precursor Substances 0.000 claims description 30
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 28
- 238000001035 drying Methods 0.000 claims description 21
- 150000001875 compounds Chemical class 0.000 claims description 20
- 239000011248 coating agent Substances 0.000 claims description 19
- 238000000576 coating method Methods 0.000 claims description 19
- 239000010703 silicon Substances 0.000 claims description 18
- 229910052710 silicon Inorganic materials 0.000 claims description 18
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 16
- 229910017604 nitric acid Inorganic materials 0.000 claims description 16
- 239000003513 alkali Substances 0.000 claims description 15
- 239000002131 composite material Substances 0.000 claims description 15
- 150000003377 silicon compounds Chemical class 0.000 claims description 15
- 238000010438 heat treatment Methods 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 14
- LLZRNZOLAXHGLL-UHFFFAOYSA-J titanic acid Chemical compound O[Ti](O)(O)O LLZRNZOLAXHGLL-UHFFFAOYSA-J 0.000 claims description 12
- 229910021529 ammonia Inorganic materials 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 9
- 239000002585 base Substances 0.000 claims description 7
- 239000012528 membrane Substances 0.000 claims description 4
- 239000010408 film Substances 0.000 description 36
- 239000000243 solution Substances 0.000 description 31
- 239000000758 substrate Substances 0.000 description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 17
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 16
- 230000000052 comparative effect Effects 0.000 description 15
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 8
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 8
- 238000001179 sorption measurement Methods 0.000 description 8
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 7
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 7
- 235000011114 ammonium hydroxide Nutrition 0.000 description 7
- 239000011230 binding agent Substances 0.000 description 7
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-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
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 238000000354 decomposition reaction Methods 0.000 description 6
- 238000001914 filtration Methods 0.000 description 6
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 6
- 238000003756 stirring Methods 0.000 description 6
- 239000000725 suspension Substances 0.000 description 6
- 240000008415 Lactuca sativa Species 0.000 description 5
- 239000007864 aqueous solution Substances 0.000 description 5
- 238000001354 calcination Methods 0.000 description 5
- 239000003921 oil Substances 0.000 description 5
- 235000012045 salad Nutrition 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 229910000349 titanium oxysulfate Inorganic materials 0.000 description 5
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 229910010413 TiO 2 Inorganic materials 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 4
- IYVLHQRADFNKAU-UHFFFAOYSA-N oxygen(2-);titanium(4+);hydrate Chemical compound O.[O-2].[O-2].[Ti+4] IYVLHQRADFNKAU-UHFFFAOYSA-N 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 4
- 239000003463 adsorbent Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- 239000000123 paper Substances 0.000 description 3
- 239000004033 plastic Substances 0.000 description 3
- 239000011164 primary particle Substances 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 description 3
- -1 titanium alkoxide Chemical class 0.000 description 3
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 description 2
- 229910021536 Zeolite Inorganic materials 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000003373 anti-fouling effect Effects 0.000 description 2
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 239000003779 heat-resistant material Substances 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 230000003472 neutralizing effect Effects 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 235000019353 potassium silicate Nutrition 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 239000001632 sodium acetate Substances 0.000 description 2
- 235000017281 sodium acetate Nutrition 0.000 description 2
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 150000003608 titanium Chemical class 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 239000010457 zeolite Substances 0.000 description 2
- 239000004925 Acrylic resin Substances 0.000 description 1
- 229920000178 Acrylic resin Polymers 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 1
- UGACIEPFGXRWCH-UHFFFAOYSA-N [Si].[Ti] Chemical compound [Si].[Ti] UGACIEPFGXRWCH-UHFFFAOYSA-N 0.000 description 1
- 230000000844 anti-bacterial effect Effects 0.000 description 1
- 239000004202 carbamide Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000004332 deodorization Methods 0.000 description 1
- 230000001877 deodorizing effect Effects 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 229910021331 inorganic silicon compound Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000012452 mother liquor Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- DCKVFVYPWDKYDN-UHFFFAOYSA-L oxygen(2-);titanium(4+);sulfate Chemical compound [O-2].[Ti+4].[O-]S([O-])(=O)=O DCKVFVYPWDKYDN-UHFFFAOYSA-L 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000013032 photocatalytic reaction Methods 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- FDNAPBUWERUEDA-UHFFFAOYSA-N silicon tetrachloride Chemical compound Cl[Si](Cl)(Cl)Cl FDNAPBUWERUEDA-UHFFFAOYSA-N 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 230000001954 sterilising effect Effects 0.000 description 1
- 238000004659 sterilization and disinfection Methods 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910000348 titanium sulfate Inorganic materials 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 239000012808 vapor phase Substances 0.000 description 1
- 230000004580 weight loss Effects 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
Description
【０００１】
【発明の属する技術分野】
本発明は高温で加熱処理を施さなくても光触媒活性を有する光触媒粉体又は光触媒膜を製造できる方法に関するものである。
【０００２】
【従来の技術及び発明が解決しようとする課題】
酸化チタン等の半導体物質にバンドギャップ以上のエネルギーを有する波長の光を照射すると強力な酸化力が発現し、その半導体物質に吸着接触した有害物質や臭気成分を分解して、脱臭、自己浄化作用等の光触媒作用を発揮する。
【０００３】
酸化チタンの工業的製造方法としては塩化チタンを高温で分解酸化して酸化チタンとする気相法と、硫酸チタニルや塩化チタンを加水分解または中和して得られた沈殿物を焼成して酸化チタンとする液相法が採用されている。液相法には、無機チタン塩を用いる場合のほか、チタンアルコキシドを用いる方法もある。
【０００４】
気相法で製造された酸化チタンは光触媒活性の高いアナターゼ形結晶と光触媒活性の低いルチル形結晶の混合物となるため、光触媒用酸化チタンの製造方法としては好ましくない。
【０００５】
液相法の場合、得られる酸化チタンの結晶形は焼成温度に依存するので、焼成温度をコントロールすることにより、実質的にアナターゼ形からなる酸化チタンを製造することができる。例えば、特許２８０５２０２号では、コロイド粒子の一つ一つが互いに強固に結合することなく粉体として得ることができる方法として、チタン塩の加水分解により得られる水酸化チタンを有機溶媒中に分散させた後、共沸温度以上で蒸留し、得られた水和酸化チタンを母液から分離した後、乾燥、仮焼する方法が開示されている。この方法の仮焼温度は、アナターゼ形結晶を得るために、３００〜８００℃としている。つまり、焼成温度を低くすると一次粒子径が小さく高比表面積の酸化チタンを得ることができ、比表面積が高くなると気相中の有害物質や臭気成分と光触媒とが接触しやすくなるので好ましい。しかしながら、３００℃以下の低温で焼成すると、酸化チタンの結晶化が不十分となり、高い光触媒活性が得られない。また低温で焼成した場合、得られた光触媒には不純物が残っている場合が多く、これらの不純物は光照射により生成した電子と正孔の再結合に寄与するため、結果として光触媒反応の量子効率が低下するという問題がある。
【０００６】
また、基材に光触媒体が含有された膜を形成して、基材に抗菌や防汚機能を付与することが試みられている。光触媒膜は、一般に、酸化チタンの前駆体ゾル等のコーティング液を基材に塗布し加熱処理することにより形成される。しかしながら酸化チタンの前駆体ゾルを用いて光触媒活性を有する酸化チタン膜を形成するためには、４００〜５００℃程度で前駆体を加熱する必要がある。このため、このような方法は、プラスチック、紙、繊維等の耐熱性に問題がある基材には適用できなかった。
【０００７】
プラスチック、木材、紙などの非耐熱性基材の表面に酸化チタン膜を形成する方法としては、特開平１１−２１１２７号に、酸化チタンゾルをコーティングした後、マイクロ波を照射する方法が提案されている。しかしながら、マイクロ波の照射は大規模な設備を要するため、生産コストが高くなる。また大型の基材表面にコーティングした膜の硬化方法としては、不適当である。
【０００８】
尚、光触媒粉体（酸化チタン粉末）を樹脂等の有機バインダーやシリカゾル、アルミナゾル等の無機バインダーに分散させてなる液をコーティング液として、基材に塗布し乾燥して固定化する方法であれば、高温の加熱工程を経ることなく、光触媒膜を非耐熱性基材の表面に形成することが可能である。しかしながら、２００ｍ2／ｇ以上の高い比表面積を有し、かつ微粒子の光触媒粉体を高分散させることは難しく、良好な塗膜を得ることは困難である。また比表面積が１００ｍ2／ｇ以下のものを使用すれば分散は可能となるが、酸化チタンは隠蔽用顔料として用いられることから明らかなように、光触媒粉体を分散させてなるコーティング液の乾燥硬化による方法からは透明な膜を形成することはできない。
【０００９】
本発明はこのような事情に鑑みてなされたものであり、その目的とするところは、高温での加熱処理を施さなくても優れた光触媒活性を有する光触媒粉体を容易に製造する方法及び非耐熱性基材の表面であっても光触媒膜を作製できる方法を提供することにある。
【００１０】
【課題を解決するための手段】
本発明の光触媒粉体の製造方法は、チタン化合物含有溶液を加熱又はアルカリで処理することによりチタン含有沈殿物を生成する第１工程；該チタン含有沈殿物を硝酸水溶液に分散させて、光触媒前駆体ゾルを得る第２工程；該光触媒前駆体ゾルにアルカリ性化合物を添加して得られたゲル状物を２００℃以下で乾燥する第３工程を含むことを特徴とする。
【００１１】
前記第１工程に代えて、水酸化チタン又は酸化チタンの水和物を使用して、第２工程以降を行なってもよい。
【００１２】
また、前記チタン化合物含有溶液として、チタン化合物及びケイ素化合物を含有する溶液を使用してもよい。この場合、第１工程で生成されるチタン含有沈殿物がチタンとケイ素の複合系共沈物であって、第３工程で得られる光触媒粉体のチタン含有率は２０モル％以上である。
【００１３】
上記本発明の光触媒粉体の製造方法において、前記アルカリ性化合物として、アンモニアを使用することが好ましい。また、製造される光触媒粉体は、比表面積が３００ｍ2／ｇ以上であることが好ましい。ここでいう比表面積は、ＢＥＴ法で測定した値をいう。
【００１４】
本発明の光触媒膜の製造方法は、チタン化合物含有溶液を加熱又はアルカリで処理することによりチタン含有沈殿物を生成する第１工程；該チタン含有沈殿物を硝酸水溶液に分散せしめて光触媒前駆体ゾルを得る第２工程；該光触媒前駆体ゾルを含むコーティング液を基材に塗布する第３工程；第３工程で得られた塗膜にアルカリ性化合物処理を施した後、２００℃以下で乾燥する第４工程を含むことを特徴とする。
【００１５】
光触媒粉体の製造方法の場合と同様に、本発明の光触媒膜の製造方法においても、第１工程で得られるチタン含有沈殿物に代えて、水酸化チタン又は酸化チタンの水和物を使用してもよい。また、前記チタン化合物含有溶液として、チタン化合物及びケイ素化合物を含有する溶液を用いてもよい。この場合、第１工程で生成される沈殿物がチタンとケイ素の複合系共沈物であり、得られる光触媒膜のチタン含有率が２０モル％以上である。
【００１６】
前記アルカリ性化合物処理は、前記塗膜をアンモニアガス雰囲気に曝すことにより行なってもよい。また、第４工程の乾燥は、１２０℃以下で行なってもよい。
【００１７】
【発明の実施の形態】
〔光触媒粉体の製造方法〕
まず、本発明の光触媒粉体及びその製造方法について説明する。
【００１８】
本発明の光触媒粉体の製造方法は、チタン化合物含有溶液を加熱又はアルカリで処理することによりチタン含有沈殿物を生成する第１工程；該チタン含有沈殿物を硝酸水溶液に分散させて、光触媒前駆体ゾルを得る第２工程；該光触媒前駆体ゾルにアルカリ性化合物を添加して得られたゲル状物を２００℃以下で乾燥する第３工程を含む。以下、第１工程から順に説明する。
【００１９】
第１工程で用いられるチタン化合物としては、塩化チタン、硫酸チタン、硫酸チタニル等の無機系チタン化合物やチタンのアルコキシド、アルキルアルコキシド等の有機系チタン化合物が挙げられる。これらのうち、取り扱いやコストの観点より硫酸チタニルが好ましい。チタン化合物含有溶液の溶媒としては水を用いることが好ましい。
【００２０】
チタン化合物含有溶液を加熱する場合、その加熱温度は、８０〜１００℃が好ましい。この程度の温度で加熱すれば、上記チタン化合物の加水分解が達成できるからである。
【００２１】
アルカリ処理する場合、アルカリとしては、アンモニア、炭酸ナトリウム、尿素などを用いることができる。これらのアルカリを添加することにより、上記チタン化合物を加水分解することができる。
【００２２】
以上のように、加熱又はアルカリ処理によりチタン化合物を加水分解すると、チタン含有沈殿物が得られるので、この沈殿物を濾過等により分離採取すればよい。チタン含有沈殿物は、主として、水酸化チタンあるいは水和酸化チタンである。従って、第１工程に代えて、他の方法により製造された水酸化チタン又は水和酸化チタン、あるいは購入した水酸化チタン又は水和酸化チタンを用いてもよい。
【００２３】
チタン含有沈殿物の分離採取に際しては、必要に応じてアンモニア等のアルカリによって中和処理してから濾別してもよい。また、第２工程に供する前に、十分に水洗することが好ましい。
【００２４】
このようにして、分離採取したチタン含有沈殿物を、硝酸水溶液に分散させて、光触媒前駆体ゾルを得る（第２工程）。
【００２５】
チタン含有沈殿物を分散させる硝酸溶液の量は、チタン含有沈殿物に含まれるチタンに対して０．５〜１０倍当量の硝酸であり、分散液の濃度が酸化物換算で３〜１０質量％となるように調整することが好ましい。硝酸に分散すると、チタン含有沈殿物は解膠され無色透明あるいは乳白色のゾル状の分散液（光触媒前駆体ゾル）となる。
【００２６】
次に、この光触媒前駆体ゾルにアルカリ性化合物を添加し、得られたゲル状物を２００℃以下にて乾燥する（第３工程）。
【００２７】
光触媒前駆体ゾルに添加するアルカリ性化合物としては、アンモニア、炭酸ナトリウム、酢酸ナトリウム等の弱アルカリ性化合物；水酸化ナトリウムなどの強アルカリ性化合物などが挙げられる。これらのうち、弱アルカリ性化合物が好ましく、特にアンモニアを用いると、光触媒活性の高い光触媒粉体が得られる。
【００２８】
アルカリ性化合物の添加量は、分散液の硝酸を中和できる程度の量が好ましく、具体的には、１〜１．５倍当量が好ましい。
【００２９】
アルカリ性化合物の添加によりゲル状物が生成されるので、このゲル状物を濾過により採取する。採取したゲル状物をそのまま乾燥してもよいが、十分に水洗してから乾燥することが好ましい。
【００３０】
ゲル状物の乾燥は、２００℃以下で行なう。好ましくは１５０℃以下、より好ましくは１２０℃以下である。一方、乾燥温度の下限は５０℃以上とすることが好ましい。５０℃以下で乾燥しても光触媒粉体を得ることは可能であるが、水分を除去するための乾燥時間が長くなり好ましくない。
【００３１】
乾燥により得られたチタン化合物は、そのままで本発明の光触媒粉体として用いてもよいし、必要に応じてハンマーミル等により更に微粉化してもよい。
【００３２】
以上のようにして、比表面積が３００ｍ2／ｇ以上である本発明の光触媒粉体を製造することができる。
【００３３】
上記本発明の製造方法において、第１工程で、チタン化合物とともにケイ素化合物を含有する溶液を使用し、得られたチタンとケイ素の複合系共沈物を用いて、第２工程に供してもよい。当該複合系共沈物を用いても、第２工程以降を同様に行なうことにより、光触媒活性を有し、且つ比表面積が３００ｍ2／ｇ以上の光触媒粉体が得られる。チタンとケイ素の複合系共沈物を用いて得られるチタンとケイ素の複合系光触媒粉体は、チタン単独の光触媒粉体よりも光触媒活性を高くて好ましい。
【００３４】
ケイ素化合物としては、シリカゾル、コロイド状シリカ、水ガラス、塩化ケイ素等の無機系ケイ素化合物やアルコキシシラン等の有機系ケイ素化合物を用いることができる。
【００３５】
チタン化合物及びケイ素化合物を含有する溶液におけるチタン化合物とケイ素化合物の含有比率は、得ようとする光触媒粉体のチタンとケイ素の含有比率に応じて選択すればよい。従って、光触媒活性の観点から、チタン化合物及びケイ素化合物を含有する溶液中のチタン含有率が２０モル％以上となるようにすることが好ましい。
【００３６】
このように、チタンとケイ素の複合系共沈物を用いて同様の操作を行なうことにより、得られた光触媒体におけるチタンの含有率は２０モル％以上であり、好ましくは５０モル％以上である。チタン含有率が５０モル％未満からは、チタン含有率が下がるに従って、光触媒活性が徐々に低くなり、２０モル％未満となると、チタン単独の酸化物と同等以下の性能となって複合化の効果がなくなり、且つ第３工程で行なうゲル状物の採取作業が困難となるからである。
【００３７】
以上説明したように、本発明の方法により得られる光触媒粉体は比表面積が高いので、有害ガス成分の吸着が大きく、優れた脱臭性能、有害成分の除去性能を示すことができる。この点、従来の光触媒では、アナターゼ形酸化チタンの比表面積が小さいことをカバーするために、活性炭やゼオライト等の吸着材を併用するケースが多かったが、本発明の光触媒粉体を用いれば、吸着材を併用することなく、単独で優れた吸着性能を示すことができる。また、活性炭やゼオライトによる吸着効果は、有害成分が活性炭等の表面を覆いつくすように吸着される飽和状態に達すると、それ以上の有害成分を吸着することはできないが、光触媒への吸着は光触媒作用による分解除去が並行して進行するので、吸着飽和状態にならずに済む。従って、本発明の光触媒を用いれば、従来の光触媒を用いる場合と比べて、有害成分の分解量の増大、光触媒粉体量あたりの有害成分の分解速度の増大、効果の持続性を期待できる。
【００３８】
〔光触媒膜の製造方法〕
次に、本発明の光触媒膜の製造方法について説明する。
【００３９】
まず、チタン化合物含有溶液を加熱又はアルカリで処理することによりチタン含有沈殿物を得る。この第１工程は、光触媒粉体の製造方法の第１工程と共通である。すなわち、上記光触媒粉体の製造方法で用いたチタン化合物と同様のチタン含有化合物を使用でき、チタン含有沈殿物を得るための加熱条件、使用できるアルカリも同様である。
【００４０】
第１工程により得られるチタン含有沈殿物は、光触媒粉体の製造方法の第１工程で得られるチタン含有沈殿物と同じで、主成分が酸化チタンの水和物又は水酸化チタンである。従って、第１工程に代えて他の方法により生成した酸化チタンの水和物又は水酸化チタン、あるいは市販されている酸化チタンの水和物又は水酸化チタンを用いて、第２工程に供しても良い。
【００４１】
第１工程において、チタン化合物含有溶液に、必要に応じて、ケイ素化合物を含有した溶液を用いてもよい。ケイ素化合物を併存させた場合、チタンとケイ素の複合系共沈物が得られるので、これをチタン含有沈殿物として第２工程に供すればよい。尚、併存させるケイ素化合物としては、上記光触媒粉体の製造方法で用いたものを使用することができ、チタン化合物とケイ素化合物の含有比率も、上記光触媒粉体の製造方法と同様にすることが好ましい。
【００４２】
次に、第１工程で得られたチタン含有沈殿物（ケイ素化合物を添加した場合にはチタンとケイ素の複合系共沈物）あるいは他の方法により入手した酸化チタンの水和物若しくは水酸化チタン（以下、これらを特に区別しないときは、単に「チタン含有沈殿物」と総称する）を硝酸水溶液に分散させて、光触媒前駆体ゾルを得る（第２工程）。チタン含有沈殿物を硝酸水溶液に分散させて光触媒前駆体ゾルを得る操作（硝酸濃度など）は、上記光触媒粉体の製造方法と同様にすればよい。
【００４３】
第３工程は、第２工程で得られた光触媒前駆体ゾルを含むコーティング液を基材に塗布する工程である。
【００４４】
光触媒前駆体ゾルは、そのままコーティング液として用いることも可能であるが、必要に応じて溶剤やバインダーを添加してもよい。基材と形成される光触媒膜との親和性が低い場合、基材との密着性に優れたバインダーを添加することにより、光触媒膜と基材との密着性を確保することができる。使用できるバインダーとしては、基材の種類により適宜選択すればよいが、具体的には、シリカゾル、アルミナゾル、水ガラス等の無機系バインダー；フッ素系樹脂、シリコン系樹脂、アクリル樹脂等の有機系バインダーなどが挙げられる。
【００４５】
本発明の方法で用いられる基材は特に限定しない。金属、セラミックスなどの耐熱性材は勿論、プラスチック、フィルム、紙、繊維、木材等の非耐熱性材に分類される基材であってもよい。本発明の方法は、全工程のうち最も高温で行われる工程が後述する２００℃以下で行なう乾燥工程（第４工程）であることから、乾燥工程に耐え得る程度の耐熱性を有するものであればよい。
【００４６】
コーティングにより基材表面に薄膜を形成した後、アルカリ処理を施し、２００℃以下で乾燥する（第４工程）。
【００４７】
第４工程で用いられるアルカリ性化合物は、光触媒粉体の製造の第３工程で用いたアルカリ性化合物と同様のものを用いることができる。すなわち、アンモニア、炭酸ナトリウム、酢酸ナトリウム、水酸化ナトリウムなどを用いることができ、これらのうちアンモニアが好ましく用いられる。
【００４８】
アルカリ処理方法としては、当該アルカリガスの雰囲気（例えばアンモニア雰囲気）に曝す方法、アルカリ性化合物の水溶液を噴霧する方法、基材をアルカリ水溶液中に浸漬する方法などが挙げられる。特にアルカリ性化合物としてアンモニアを用い、コーティングした基材をアンモニアガス雰囲気に曝す方法が簡便であり、かつ良好な膜性状が得られるため好ましい。
【００４９】
乾燥温度は、２００℃以下、好ましくは１５０℃以下、より好ましくは１２０℃以下である。このような温度で乾燥しても光触媒活性を有する光触媒膜が得られるので、基材の耐熱性に応じて乾燥温度を適宜選択すればよい。但し、５０℃未満では乾燥時間が長くなり、かつ基材との密着性も低くなるので、基材の耐熱性に問題がない限り、１００℃以上で乾燥することが好ましい。また乾燥により光触媒膜が基材に固定されてから水洗により残留イオンを除去することが好ましい。
【００５０】
上記本発明の製造方法によって光触媒膜を形成することにより、臭気成分や有害成分の浄化、殺菌、防汚等の光触媒機能を基材に付与することが可能となる。本発明の製造方法によれば、耐熱性を有する基材は勿論のこと、耐熱性に乏しい基材についても適用することができる。
【００５１】
【実施例】
〔光触媒粉体の製造〕
実施例１：
硫酸チタニルの硫酸水溶液１００ｃｍ3（ＴｉＯ2濃度２５０ｇ／ｌ，全硫酸濃度１１００ｇ／ｌ）を純水で２倍に希釈した。この希釈液に、攪拌しながら１０質量％のアンモニア水溶液４００ｇを徐々に滴下してチタン含有沈殿物を得た。この沈殿物を濾過水洗した後、純水を加えて２００ｇの懸濁液とした。この懸濁液に、６５質量％の硝酸１００ｇを添加し、２時間ホモミキサーで攪拌して光触媒前駆体ゾルを得た。次にこの光触媒前駆体ゾルに、攪拌しながら１０質量％のアンモニア水溶液２００ｇを徐々に滴下してゲル状物を得た。濾過によりこのゲル状物を採取し、水洗した後、１２０℃で１晩乾燥した。乾燥後、ハンマーミルにて粉砕し光触媒粉体を得た。得られた光触媒粉体の比表面積は３８０ｍ2／ｇであった。
【００５２】
実施例２：
四塩化チタンの塩酸水溶液１００ｇ（ＴｉＯ2濃度２７．５％，全塩酸量３６０ｇ／ｋｇ）を純水で３倍に希釈した。希釈液に、攪拌しながら１０質量％のアンモニア水溶液２００ｇを徐々に滴下して沈殿物を得た。濾過して沈殿物を採取し、水洗後、純水を加えて３５０ｇの懸濁液とした。この懸濁液に６５質量％の硝酸５０ｇを加えて２時間ホモミキサーで攪拌して光触媒前駆体ゾルを得た。次にこの光触媒前駆体ゾルに、攪拌しながら１０質量％のアンモニア水溶液１００ｇを徐々に滴下してゲル状物を沈殿させた。このゲル状物を濾過により採取し、水洗した後、１２０℃で１晩乾燥した。乾燥後、ハンマーミルにて粉砕し光触媒粉体を得た。得られた光触媒粉体の比表面積は４１０ｍ2／ｇであった。
【００５３】
実施例３：
シリカゾル１０ｇ（日産化学製ＮＣＳ−３０）に１０質量％アンモニア水溶液３５０ｇを添加してケイ素含有溶液を得た。次に硫酸チタニルの硫酸水溶液９０ｃｍ3（ＴｉＯ2濃度２５０ｇ／ｌ，全硫酸濃度１１００ｇ／ｌ）に水１２５ｇを加えて、チタン化合物溶液を得た。このチタン化合物溶液を、先に調製したケイ素含有溶液に、攪拌しながら徐々に滴下してチタンとケイ素の複合系化合物を共沈させた。この共沈物を濾過により採取した後、水洗し、さらに純水を加えて１５０ｇの懸濁液とした。この懸濁液に、６５質量％の硝酸１５０ｇを添加し、２時間ホモミキサーで攪拌することにより光触媒前駆体ゾルを得た。次に、この光触媒前駆体ゾルに、攪拌しながら１０質量％のアンモニア水溶液３００ｇを徐々に滴下してゲル状共沈物を得た。この共沈物を濾過水洗した後、１２０℃で１晩乾燥した。乾燥後、ハンマーミルにて粉砕し光触媒粉体を得た。得られた光触媒粉体におけるチタン含有率は８５モル％であり、比表面積は４００ｍ2／ｇであった。
【００５４】
実施例４：
実施例３においてチタンとケイ素の配合比を変えた以外は実施例３と同様にしてチタン及びケイ素の複合系光触媒粉体を得た。得られた光触媒粉体のチタン含有率は５０モル％であり、比表面積は４３０ｍ2／ｇであった。
【００５５】
比較例１〜４：
実施例１及び２においてチタン化合物含有溶液にアンモニアを加えてチタン含有沈殿物を得、これを濾過水洗した後、１２０℃で１晩乾燥したものを夫々比較例１及び２とした。また比較例１及び２の乾燥品を更に５００℃で２時間焼成したものを比較例３及び４とした。
【００５６】
比較例５，６：
これらは、いずれも光触媒用酸化チタンとして市販されているものであり比較例５は一次粒子径が７ｎｍで比表面積が３００ｍ2／ｇ、比較例６は一次粒子径が２０ｎｍで比表面積が５０ｍ2／ｇある酸化チタン単独である。
【００５７】
〔光触媒粉体の評価〕
実施例１〜４および比較例１〜６にて得られた光触媒粉体について、アセトアルデヒドの分解性能を下記試験方法に基づいて調べた。
【００５８】
光透過性のある１０ｌ試験容器に光触媒粉体１ｇ及び３００ｐｐｍのアセトアルデヒド３００ｐｐｍを入れて密閉した。かかる状態で、ブラックライト照射下（０．３ｍＷ／ｃｍ2）における経時的なガス濃度の減衰を測定し、分解速度定数をもとめた。同様の実験を暗所でも行なった。
【００５９】
尚、初期の吸着による影響を避けるため、３０分経過後以降に一次反応的に濃度減衰が進んでいることを確認してから速度定数を求めた。結果を表１に示す。
【００６０】
【表１】
比較例１および比較例２の粉体では光照射の有無による性能差は認められず、単に第１工程の沈殿物を乾燥しただけでは光触媒性能は得られないことがわかる。これら沈殿物を活性化するためには高温での加熱処理が必要であり、比較例３及び比較例４に示すように５００℃で焼成することによって光触媒性能を発現している。
【００６２】
一方、実施例の光触媒粉体は、高温で焼成した比較例３，４及び市販の光触媒用酸化チタンと同程度以上に、光触媒活性を示した。特に実施例３及び実施例４のチタンにケイ素を複合せしめた光触媒粉体は光触媒活性を有していることがわかる。
【００６３】
〔光触媒膜を有する複合材の製造〕
実施例５：
実施例１の方法に基づいて光触媒前駆体ゾルを調製し、得られた光触媒前駆体ゾル３００ｇと２０質量％のシリカゾル１５０ｇを混合してゾル状のコーティング液を調製した。調製したコーティング液を、アクリル板の表面に、ディップコーティング法にて塗布した。
【００６４】
デシケーターに１０質量％のアンモニア水１００ｇが入った３００ｃｍ3のビーカーを静置し、このデシケータの中に、コーティングしたアクリル板を入れて、蓋を閉めた。
【００６５】
５分後に、デシケータからアクリル板を取り出して、１００℃の乾燥機に入れて１０分間乾燥することにより、光触媒膜が固定化されたアクリル板を得た。
【００６６】
実施例６：
実施例３と同様にして得られたチタンとケイ素の複合系光触媒前駆体ゾル３００ｇを使用した以外は、実施例５と同様にして、チタン含有率が８５モル％の光触媒膜をアクリル板に形成した。
【００６７】
比較例７：
市販の光触媒用チタニアゾル（ＴｉＯ2：１０質量％）３００ｇとシリカゾル１５０ｇを混合してゾル状のコーティング液を調製した。調製したコーティング液を実施例５と同様にしてアクリル板をコーティングした後、１００℃の乾燥機に入れて１０分間乾燥することによりチタン含有膜を形成した。
【００６８】
〔光触媒膜の評価〕
実施例５，６及び比較例７で得た光触媒膜が形成されたアクリル板について、下記方法に基づいて光触媒活性を調べた。
【００６９】
光触媒膜上にサラダ油を滴下して、光触媒表面に薄く広げた後、ブラックライトにより３ｍＷ／ｃｍ2の紫外線を１２時間照射した。照射後のサラダ油付着重量を測定した。重量減少量が多いほど、光触媒膜のサラダ油分解能力が強いこと、すなわち光触媒活性が高いことを示している。
【００７０】
測定結果を表２に示す。
【００７１】
【表２】
表２より、実施例の光触媒膜は、サラダ油分解率が高く、光触媒活性を示すことがわかる。一方、市販の光触媒用ゾルを用いた比較例の光触媒膜は、サラダ油の分解能力が小さく、光触媒活性をほとんど有していないことがわかる。
【００７３】
【発明の効果】
本発明の光触媒粉体の製造方法によれば、安価な原料を使用して高い比表面積を有する光触媒粉体を製造できる。これにより各種有害成分に対する吸着能力を高めることが可能となる。光触媒粉体に高い吸着能を持たせることにより、活性炭等の吸着材を併用しないくても優れた除去効果が得られる。
【００７４】
本発明の光触媒膜の製造方法によれば、高温で焼成しなくても優れた光触媒活性を有する膜を製造できる。従って、耐熱性に乏しい基材に対しても、優れた光触媒活性を有する膜を形成することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method capable of producing a photocatalyst powder or photocatalyst film having photocatalytic activity without performing a heat treatment at a high temperature.
[0002]
[Prior art and problems to be solved by the invention]
When a semiconductor material such as titanium oxide is irradiated with light having a wavelength greater than the band gap, a strong oxidizing power is developed, decomposing harmful substances and odorous components adsorbed on the semiconductor material, and deodorizing and self-purifying action. Demonstrates photocatalytic action.
[0003]
Titanium oxide is industrially produced by a vapor phase method in which titanium chloride is decomposed and oxidized at high temperature to form titanium oxide, and a precipitate obtained by hydrolyzing or neutralizing titanyl sulfate or titanium chloride is calcined and oxidized. A liquid phase method using titanium is adopted. The liquid phase method includes a method using a titanium alkoxide in addition to using an inorganic titanium salt.
[0004]
Titanium oxide produced by the gas phase method is a mixture of anatase-type crystals with high photocatalytic activity and rutile-type crystals with low photocatalytic activity, and is not preferable as a method for producing titanium oxide for photocatalyst.
[0005]
In the case of the liquid phase method, the crystal form of the obtained titanium oxide depends on the calcination temperature, so that the titanium oxide substantially having the anatase form can be produced by controlling the calcination temperature. For example, in Japanese Patent No. 2805202, titanium hydroxide obtained by hydrolysis of a titanium salt is dispersed in an organic solvent as a method in which each of the colloidal particles can be obtained as a powder without being firmly bonded to each other. Thereafter, a method is disclosed in which distillation is performed at an azeotropic temperature or higher, and the obtained hydrated titanium oxide is separated from the mother liquor, followed by drying and calcining. The calcining temperature of this method is set to 300 to 800 ° C. in order to obtain anatase type crystals. That is, lowering the calcination temperature is preferable because titanium oxide having a small primary particle diameter and a high specific surface area can be obtained, and increasing the specific surface area is preferable because the harmful substances and odor components in the gas phase easily come into contact with the photocatalyst. However, when firing at a low temperature of 300 ° C. or lower, crystallization of titanium oxide becomes insufficient, and high photocatalytic activity cannot be obtained. In addition, when calcined at a low temperature, impurities often remain in the obtained photocatalyst, and these impurities contribute to the recombination of electrons and holes generated by light irradiation, resulting in the quantum efficiency of the photocatalytic reaction. There is a problem that decreases.
[0006]
In addition, an attempt has been made to form an antibacterial or antifouling function on a substrate by forming a film containing a photocatalyst on the substrate. The photocatalyst film is generally formed by applying a coating liquid such as a titanium oxide precursor sol to a substrate and heat-treating it. However, in order to form a titanium oxide film having photocatalytic activity using a precursor sol of titanium oxide, it is necessary to heat the precursor at about 400 to 500 ° C. For this reason, such a method could not be applied to a substrate having a problem in heat resistance such as plastic, paper, and fiber.
[0007]
As a method of forming a titanium oxide film on the surface of a non-heat-resistant substrate such as plastic, wood, paper, etc., JP-A-11-21127 proposes a method of irradiating microwaves after coating a titanium oxide sol. Yes. However, since microwave irradiation requires a large-scale facility, the production cost becomes high. Further, it is not suitable as a method for curing a film coated on the surface of a large substrate.
[0008]
If the photocatalyst powder (titanium oxide powder) is dispersed in an organic binder such as a resin or an inorganic binder such as silica sol or alumina sol as a coating liquid, it can be applied to a substrate, dried and fixed. The photocatalytic film can be formed on the surface of the non-heat-resistant substrate without going through a high-temperature heating step. However, it is difficult to highly disperse fine photocatalyst powder having a high specific surface area of 200 m 2 / g or more, and it is difficult to obtain a good coating film. Dispersion is possible if a specific surface area of 100 m 2 / g or less is used, but as is apparent from the fact that titanium oxide is used as a concealing pigment, drying of the coating liquid in which the photocatalyst powder is dispersed is performed. A transparent film cannot be formed from the method by curing.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for easily producing a photocatalyst powder having excellent photocatalytic activity without performing heat treatment at a high temperature and The object is to provide a method capable of producing a photocatalytic film even on the surface of a heat-resistant substrate.
[0010]
[Means for Solving the Problems]
The method for producing a photocatalyst powder of the present invention comprises a first step of producing a titanium-containing precipitate by heating or treating a titanium compound-containing solution with an alkali; the titanium-containing precipitate is dispersed in a nitric acid aqueous solution, and a photocatalyst precursor A second step of obtaining a body sol; a third step of drying a gel-like product obtained by adding an alkaline compound to the photocatalyst precursor sol at 200 ° C. or lower.
[0011]
Instead of the first step, titanium hydroxide or a hydrate of titanium oxide may be used to perform the second and subsequent steps.
[0012]
Moreover, you may use the solution containing a titanium compound and a silicon compound as said titanium compound containing solution. In this case, the titanium-containing precipitate produced in the first step is a composite coprecipitate of titanium and silicon, and the titanium content of the photocatalyst powder obtained in the third step is 20 mol% or more.
[0013]
In the method for producing the photocatalyst powder of the present invention, it is preferable to use ammonia as the alkaline compound. The photocatalyst powder to be produced preferably has a specific surface area of 300 m 2 / g or more. Here, the specific surface area is a value measured by the BET method.
[0014]
The method for producing a photocatalyst film of the present invention comprises a first step of producing a titanium-containing precipitate by heating or treating a titanium compound-containing solution with an alkali; the titanium-containing precipitate is dispersed in an aqueous nitric acid solution to form a photocatalyst precursor sol A second step of applying a coating liquid containing the photocatalyst precursor sol to a substrate; a coating obtained in the third step is treated with an alkaline compound, and then dried at 200 ° C. or lower. 4 steps are included.
[0015]
As with the photocatalyst powder production method, the photocatalyst film production method of the present invention uses titanium hydroxide or titanium oxide hydrate instead of the titanium-containing precipitate obtained in the first step. May be. Moreover, you may use the solution containing a titanium compound and a silicon compound as said titanium compound containing solution. In this case, the precipitate produced in the first step is a composite coprecipitate of titanium and silicon, and the titanium content of the resulting photocatalytic film is 20 mol% or more.
[0016]
The alkaline compound treatment may be performed by exposing the coating film to an ammonia gas atmosphere. The drying in the fourth step may be performed at 120 ° C. or lower.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
[Method for producing photocatalyst powder]
First, the photocatalyst powder of the present invention and the production method thereof will be described.
[0018]
The method for producing a photocatalyst powder of the present invention comprises a first step of producing a titanium-containing precipitate by heating or treating a titanium compound-containing solution with an alkali; the titanium-containing precipitate is dispersed in a nitric acid aqueous solution, and a photocatalyst precursor A second step of obtaining a body sol; a third step of drying a gel-like material obtained by adding an alkaline compound to the photocatalyst precursor sol at 200 ° C. or lower. Hereinafter, it demonstrates sequentially from a 1st process.
[0019]
Examples of the titanium compound used in the first step include inorganic titanium compounds such as titanium chloride, titanium sulfate, and titanyl sulfate, and organic titanium compounds such as titanium alkoxides and alkyl alkoxides. Of these, titanyl sulfate is preferable from the viewpoint of handling and cost. Water is preferably used as the solvent for the titanium compound-containing solution.
[0020]
When heating a titanium compound containing solution, the heating temperature has preferable 80-100 degreeC. This is because the titanium compound can be hydrolyzed by heating at such a temperature.
[0021]
In the case of alkali treatment, ammonia, sodium carbonate, urea or the like can be used as the alkali. The titanium compound can be hydrolyzed by adding these alkalis.
[0022]
As described above, when the titanium compound is hydrolyzed by heating or alkali treatment, a titanium-containing precipitate is obtained. Therefore, the precipitate may be separated and collected by filtration or the like. The titanium-containing precipitate is mainly titanium hydroxide or hydrated titanium oxide. Therefore, instead of the first step, titanium hydroxide or hydrated titanium oxide manufactured by another method, or purchased titanium hydroxide or hydrated titanium oxide may be used.
[0023]
When separating and collecting the titanium-containing precipitate, if necessary, it may be filtered after being neutralized with an alkali such as ammonia. Moreover, it is preferable to wash with water sufficiently before using for a 2nd process.
[0024]
In this way, the separated titanium-containing precipitate is dispersed in an aqueous nitric acid solution to obtain a photocatalyst precursor sol (second step).
[0025]
The amount of the nitric acid solution in which the titanium-containing precipitate is dispersed is nitric acid equivalent to 0.5 to 10 times the titanium contained in the titanium-containing precipitate, and the concentration of the dispersion is 3 to 10% by mass in terms of oxide. It is preferable to adjust so that. When dispersed in nitric acid, the titanium-containing precipitate is peptized to form a colorless transparent or milky white sol dispersion (photocatalyst precursor sol).
[0026]
Next, an alkaline compound is added to the photocatalyst precursor sol, and the resulting gel is dried at 200 ° C. or lower (third step).
[0027]
Examples of the alkaline compound added to the photocatalyst precursor sol include weak alkaline compounds such as ammonia, sodium carbonate and sodium acetate; strong alkaline compounds such as sodium hydroxide. Of these, weakly alkaline compounds are preferred, and in particular, when ammonia is used, a photocatalytic powder having high photocatalytic activity can be obtained.
[0028]
The addition amount of the alkaline compound is preferably an amount capable of neutralizing nitric acid in the dispersion, and specifically, 1 to 1.5 times equivalent is preferable.
[0029]
Since a gel-like substance is generated by adding the alkaline compound, the gel-like substance is collected by filtration. The collected gel-like material may be dried as it is, but it is preferable to dry it after sufficiently washing with water.
[0030]
The gel-like product is dried at 200 ° C. or lower. Preferably it is 150 degrees C or less, More preferably, it is 120 degrees C or less. On the other hand, the lower limit of the drying temperature is preferably 50 ° C. or higher. Although it is possible to obtain a photocatalyst powder even if it is dried at 50 ° C. or lower, the drying time for removing moisture is prolonged, which is not preferable.
[0031]
The titanium compound obtained by drying may be used as it is as the photocatalyst powder of the present invention, or may be further pulverized by a hammer mill or the like as necessary.
[0032]
As described above, the photocatalyst powder of the present invention having a specific surface area of 300 m 2 / g or more can be produced.
[0033]
In the production method of the present invention, in the first step, a solution containing a silicon compound together with the titanium compound may be used, and the resulting composite coprecipitate of titanium and silicon may be used for the second step. . Even if the composite coprecipitate is used, a photocatalyst powder having photocatalytic activity and a specific surface area of 300 m 2 / g or more can be obtained by carrying out the second and subsequent steps in the same manner. A composite photocatalyst powder of titanium and silicon obtained using a composite coprecipitate of titanium and silicon is preferable because it has a higher photocatalytic activity than a photocatalyst powder of titanium alone.
[0034]
As the silicon compound, inorganic silicon compounds such as silica sol, colloidal silica, water glass and silicon chloride, and organic silicon compounds such as alkoxysilane can be used.
[0035]
What is necessary is just to select the content ratio of the titanium compound and silicon compound in the solution containing a titanium compound and a silicon compound according to the content ratio of titanium and silicon of the photocatalyst powder to be obtained. Therefore, from the viewpoint of photocatalytic activity, it is preferable that the titanium content in the solution containing the titanium compound and the silicon compound is 20 mol% or more.
[0036]
Thus, by performing the same operation using the composite coprecipitate of titanium and silicon, the content of titanium in the obtained photocatalyst is 20 mol% or more, preferably 50 mol% or more. . When the titanium content is less than 50 mol%, the photocatalytic activity gradually decreases as the titanium content decreases. When the titanium content is less than 20 mol%, the performance becomes equal to or less than that of an oxide of titanium alone. This is because the collection of the gel-like material performed in the third step becomes difficult.
[0037]
As described above, since the photocatalyst powder obtained by the method of the present invention has a high specific surface area, adsorption of harmful gas components is large, and excellent deodorization performance and removal performance of harmful components can be exhibited. In this regard, in the conventional photocatalyst, in order to cover that the specific surface area of anatase-type titanium oxide is small, there are many cases in which an adsorbent such as activated carbon or zeolite is used in combination, but if the photocatalyst powder of the present invention is used, Without using an adsorbent in combination, excellent adsorption performance can be shown alone. In addition, the adsorption effect by activated carbon and zeolite, when reaching a saturated state where harmful components are adsorbed so as to cover the surface of activated carbon, etc., no more harmful components can be adsorbed, but the adsorption to the photocatalyst is Since the decomposition and removal due to the action proceed in parallel, the adsorption saturation state is not required. Therefore, when the photocatalyst of the present invention is used, an increase in the decomposition amount of harmful components, an increase in the decomposition rate of harmful components per amount of the photocatalyst powder, and a sustained effect can be expected as compared with the case where a conventional photocatalyst is used.
[0038]
[Method for producing photocatalytic film]
Next, the manufacturing method of the photocatalyst film | membrane of this invention is demonstrated.
[0039]
First, a titanium-containing precipitate is obtained by treating a titanium compound-containing solution with heat or alkali. This first step is common to the first step of the method for producing the photocatalyst powder. That is, the same titanium-containing compound as the titanium compound used in the method for producing the photocatalyst powder can be used, and heating conditions for obtaining a titanium-containing precipitate and usable alkali are also the same.
[0040]
The titanium-containing precipitate obtained in the first step is the same as the titanium-containing precipitate obtained in the first step of the photocatalyst powder production method, and the main component is a hydrate of titanium oxide or titanium hydroxide. Therefore, the titanium oxide hydrate or titanium hydroxide produced by another method instead of the first step, or the commercially available titanium oxide hydrate or titanium hydroxide is used for the second step. Also good.
[0041]
In the first step, a solution containing a silicon compound may be used as the titanium compound-containing solution, if necessary. When the silicon compound coexists, a composite coprecipitate of titanium and silicon is obtained, and this may be used as the titanium-containing precipitate in the second step. In addition, as a silicon compound to coexist, what was used by the manufacturing method of the said photocatalyst powder can be used, and the content ratio of a titanium compound and a silicon compound can also be made the same as that of the manufacturing method of the said photocatalyst powder. preferable.
[0042]
Next, a titanium-containing precipitate obtained in the first step (a composite coprecipitate of titanium and silicon when a silicon compound is added) or a titanium oxide hydrate or titanium hydroxide obtained by other methods. (Hereinafter, when these are not particularly distinguished, they are simply referred to as “titanium-containing precipitates”) are dispersed in an aqueous nitric acid solution to obtain a photocatalyst precursor sol (second step). The operation (such as nitric acid concentration) for obtaining a photocatalyst precursor sol by dispersing the titanium-containing precipitate in an aqueous nitric acid solution may be performed in the same manner as in the method for producing the photocatalyst powder.
[0043]
The third step is a step of applying a coating liquid containing the photocatalyst precursor sol obtained in the second step to the substrate.
[0044]
The photocatalyst precursor sol can be used as it is as a coating solution, but a solvent or a binder may be added as necessary. When the affinity between the base material and the formed photocatalyst film is low, the adhesiveness between the photocatalyst film and the base material can be ensured by adding a binder having excellent adhesiveness with the base material. The binder that can be used may be appropriately selected depending on the type of the substrate. Specifically, inorganic binders such as silica sol, alumina sol, and water glass; organic binders such as fluorine resin, silicon resin, and acrylic resin Etc.
[0045]
The substrate used in the method of the present invention is not particularly limited. As well as heat-resistant materials such as metals and ceramics, base materials classified into non-heat-resistant materials such as plastic, film, paper, fiber, and wood may be used. The method of the present invention has a heat resistance sufficient to withstand the drying step because the step performed at the highest temperature among all the steps is a drying step (fourth step) performed at 200 ° C. or below. That's fine.
[0046]
After forming a thin film on the substrate surface by coating, it is subjected to alkali treatment and dried at 200 ° C. or lower (fourth step).
[0047]
The alkaline compound used in the fourth step can be the same as the alkaline compound used in the third step of producing the photocatalyst powder. That is, ammonia, sodium carbonate, sodium acetate, sodium hydroxide and the like can be used, and among these, ammonia is preferably used.
[0048]
Examples of the alkali treatment method include a method of exposing to an alkali gas atmosphere (for example, an ammonia atmosphere), a method of spraying an aqueous solution of an alkaline compound, and a method of immersing a substrate in an aqueous alkali solution. In particular, the method of using ammonia as the alkaline compound and exposing the coated substrate to an ammonia gas atmosphere is preferable because it is simple and provides good film properties.
[0049]
The drying temperature is 200 ° C. or lower, preferably 150 ° C. or lower, more preferably 120 ° C. or lower. Even if dried at such a temperature, a photocatalytic film having photocatalytic activity can be obtained, and therefore the drying temperature may be appropriately selected according to the heat resistance of the substrate. However, if the temperature is lower than 50 ° C., the drying time becomes longer and the adhesion to the base material becomes low. Therefore, it is preferable to dry at 100 ° C. or higher unless there is a problem with the heat resistance of the base material. Moreover, it is preferable to remove residual ions by washing with water after the photocatalyst film is fixed to the substrate by drying.
[0050]
By forming the photocatalyst film by the production method of the present invention, it becomes possible to impart a photocatalytic function such as purification, sterilization, and antifouling of odor components and harmful components to the substrate. The production method of the present invention can be applied not only to a substrate having heat resistance but also to a substrate having poor heat resistance.
[0051]
【Example】
[Production of photocatalyst powder]
Example 1:
100 cm 3 of a sulfuric acid aqueous solution of titanyl sulfate (TiO 2 concentration 250 g / l, total sulfuric acid concentration 1100 g / l) was diluted twice with pure water. While stirring, 400 g of a 10% by mass aqueous ammonia solution was gradually added dropwise to the diluted solution to obtain a titanium-containing precipitate. The precipitate was washed with filtered water, and pure water was added to make a suspension of 200 g. To this suspension, 100 g of 65% by mass nitric acid was added and stirred with a homomixer for 2 hours to obtain a photocatalyst precursor sol. Next, 200 g of a 10% by mass aqueous ammonia solution was gradually added dropwise to the photocatalyst precursor sol with stirring to obtain a gel-like product. The gel-like material was collected by filtration, washed with water, and dried at 120 ° C. overnight. After drying, it was pulverized with a hammer mill to obtain a photocatalyst powder. The specific surface area of the obtained photocatalyst powder was 380 m 2 / g.
[0052]
Example 2:
100 g of an aqueous hydrochloric acid solution of titanium tetrachloride (TiO 2 concentration 27.5%, total hydrochloric acid amount 360 g / kg) was diluted three times with pure water. While stirring, 200 g of a 10% by mass aqueous ammonia solution was gradually added dropwise to the diluted solution to obtain a precipitate. The precipitate was collected by filtration, washed with water, and pure water was added to make a suspension of 350 g. To this suspension, 50 g of 65% by mass nitric acid was added and stirred with a homomixer for 2 hours to obtain a photocatalyst precursor sol. Next, 100 g of a 10% by mass aqueous ammonia solution was gradually added dropwise to the photocatalyst precursor sol with stirring to precipitate a gel. The gel was collected by filtration, washed with water, and dried at 120 ° C. overnight. After drying, it was pulverized with a hammer mill to obtain a photocatalyst powder. The specific surface area of the obtained photocatalyst powder was 410 m 2 / g.
[0053]
Example 3:
A silicon-containing solution was obtained by adding 350 g of a 10% by mass aqueous ammonia solution to 10 g of silica sol (NCS-30 manufactured by Nissan Chemical Industries). Next, 125 g of water was added to 90 cm 3 of a sulfuric acid aqueous solution of titanyl sulfate (TiO 2 concentration 250 g / l, total sulfuric acid concentration 1100 g / l) to obtain a titanium compound solution. This titanium compound solution was gradually added dropwise to the previously prepared silicon-containing solution with stirring to co-precipitate a titanium-silicon composite compound. The coprecipitate was collected by filtration, washed with water, and pure water was added to make a suspension of 150 g. To this suspension, 150 g of 65% by mass nitric acid was added and stirred with a homomixer for 2 hours to obtain a photocatalyst precursor sol. Next, to this photocatalyst precursor sol, 300 g of a 10% by mass aqueous ammonia solution was gradually dropped while stirring to obtain a gel-like coprecipitate. The coprecipitate was washed with filtered water and dried at 120 ° C. overnight. After drying, it was pulverized with a hammer mill to obtain a photocatalyst powder. The obtained photocatalyst powder had a titanium content of 85 mol% and a specific surface area of 400 m 2 / g.
[0054]
Example 4:
A composite photocatalyst powder of titanium and silicon was obtained in the same manner as in Example 3 except that the compounding ratio of titanium and silicon was changed in Example 3. The obtained photocatalyst powder had a titanium content of 50 mol% and a specific surface area of 430 m 2 / g.
[0055]
Comparative Examples 1-4:
In Examples 1 and 2, ammonia was added to the titanium compound-containing solution to obtain a titanium-containing precipitate, which was washed with filtered water and then dried at 120 ° C. overnight to be Comparative Examples 1 and 2, respectively. Further, the dried products of Comparative Examples 1 and 2 were further baked at 500 ° C. for 2 hours to be Comparative Examples 3 and 4.
[0056]
Comparative Examples 5 and 6:
These are all commercially available as titanium oxide for photocatalysts. Comparative Example 5 has a primary particle diameter of 7 nm and a specific surface area of 300 m 2 / g, and Comparative Example 6 has a primary particle diameter of 20 nm and a specific surface area of 50 m 2. / G Titanium oxide alone.
[0057]
[Evaluation of photocatalyst powder]
About the photocatalyst powder obtained in Examples 1-4 and Comparative Examples 1-6, the decomposition | disassembly performance of acetaldehyde was investigated based on the following test method.
[0058]
1 g of photocatalyst powder and 300 ppm of 300 ppm of acetaldehyde were put in a 10 l test vessel having light transmittance and sealed. In this state, the decay of gas concentration over time under black light irradiation (0.3 mW / cm 2 ) was measured to determine the decomposition rate constant. A similar experiment was conducted in the dark.
[0059]
In order to avoid the influence of the initial adsorption, the rate constant was obtained after confirming that the concentration decay had progressed in a first-order manner after 30 minutes had elapsed. The results are shown in Table 1.
[0060]
[Table 1]
In the powders of Comparative Example 1 and Comparative Example 2, there is no difference in performance depending on the presence or absence of light irradiation, and it can be seen that the photocatalytic performance cannot be obtained simply by drying the precipitate in the first step. In order to activate these precipitates, heat treatment at a high temperature is required, and as shown in Comparative Examples 3 and 4, photocatalytic performance is expressed by firing at 500 ° C.
[0062]
On the other hand, the photocatalyst powder of the Example showed photocatalytic activity to the same extent or more as those of Comparative Examples 3 and 4 fired at high temperature and commercially available titanium oxide for photocatalyst. In particular, it can be seen that the photocatalyst powder obtained by combining silicon with titanium in Example 3 and Example 4 has photocatalytic activity.
[0063]
[Production of composite material having photocatalytic film]
Example 5:
A photocatalyst precursor sol was prepared based on the method of Example 1, and 300 g of the obtained photocatalyst precursor sol and 150 g of 20% by mass silica sol were mixed to prepare a sol-like coating liquid. The prepared coating liquid was applied to the surface of the acrylic plate by a dip coating method.
[0064]
A 300 cm 3 beaker containing 100 g of 10% by mass ammonia water was allowed to stand in a desiccator, and a coated acrylic plate was placed in the desiccator and the lid was closed.
[0065]
After 5 minutes, the acrylic plate was taken out of the desiccator, put into a dryer at 100 ° C. and dried for 10 minutes, thereby obtaining an acrylic plate with a fixed photocatalyst film.
[0066]
Example 6:
A photocatalytic film having a titanium content of 85 mol% was formed on an acrylic plate in the same manner as in Example 5 except that 300 g of the composite photocatalyst precursor sol of titanium and silicon obtained in the same manner as in Example 3 was used. did.
[0067]
Comparative Example 7:
300 g of commercially available titania sol for photocatalyst (TiO 2 : 10% by mass) and 150 g of silica sol were mixed to prepare a sol-like coating liquid. The prepared coating solution was coated on an acrylic plate in the same manner as in Example 5, and then placed in a dryer at 100 ° C. and dried for 10 minutes to form a titanium-containing film.
[0068]
[Evaluation of photocatalytic film]
About the acrylic board in which the photocatalyst film | membrane obtained in Examples 5 and 6 and Comparative Example 7 was formed, photocatalytic activity was investigated based on the following method.
[0069]
Salad oil was dropped onto the photocatalyst film and spread thinly on the surface of the photocatalyst, and then irradiated with 3 mW / cm 2 of ultraviolet light for 12 hours with a black light. The salad oil adhesion weight after irradiation was measured. It shows that the greater the weight loss, the stronger the ability of the photocatalytic film to decompose salad oil, that is, the higher the photocatalytic activity.
[0070]
The measurement results are shown in Table 2.
[0071]
[Table 2]
Table 2 shows that the photocatalyst film | membrane of an Example has a high salad oil decomposition rate and shows photocatalytic activity. On the other hand, it can be seen that the photocatalyst film of the comparative example using a commercially available sol for photocatalyst has a small ability to decompose salad oil and has almost no photocatalytic activity.
[0073]
【The invention's effect】
According to the method for producing a photocatalyst powder of the present invention, a photocatalyst powder having a high specific surface area can be produced using an inexpensive raw material. This makes it possible to increase the adsorption capacity for various harmful components. By providing the photocatalyst powder with a high adsorption ability, an excellent removal effect can be obtained without using an adsorbent such as activated carbon.
[0074]
According to the method for producing a photocatalytic film of the present invention, a film having excellent photocatalytic activity can be produced without baking at a high temperature. Therefore, a film having excellent photocatalytic activity can be formed even on a substrate having poor heat resistance.
Claims (9)
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| JP32145999A JP3749641B2 (en) | 1999-11-11 | 1999-11-11 | Photocatalyst powder and method for producing photocatalyst film |
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| JP32145999A JP3749641B2 (en) | 1999-11-11 | 1999-11-11 | Photocatalyst powder and method for producing photocatalyst film |
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| JP2001139331A JP2001139331A (en) | 2001-05-22 |
| JP3749641B2 true JP3749641B2 (en) | 2006-03-01 |
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| JP4235741B2 (en) * | 2002-10-09 | 2009-03-11 | 株式会社Ｙｏｏコーポレーション | Volatile organic compound, NOX or SOX reducing agent, and method for producing the reducing agent |
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| DE4329129A1 (en) * | 1993-08-30 | 1995-03-02 | Merck Patent Gmbh | Photostabilisation of titanium dioxide sols |
| JP4319275B2 (en) * | 1997-11-07 | 2009-08-26 | 日本曹達株式会社 | Metal plate made by laminating a photocatalyst-carrying film |
| JP3080162B2 (en) * | 1998-01-27 | 2000-08-21 | 日本パーカライジング株式会社 | Titanium oxide sol and method for producing the same |
| JP3952238B2 (en) * | 1998-07-07 | 2007-08-01 | 石原産業株式会社 | Removal method of harmful substances by photocatalyst |
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