environmental application of photocatalysis

Transcription

1 environmental application of photocatalysis Special Lecture on Environmental Science II Bunsho OHTANI, Professor Catalysis Research Center/Graduate School of Environmental Science ce Hokkaido University Ohtani Lab Hokkaido search 2009/12/09 Environmental Application of Photocatalysis 1

2 Catalysis Research Center, Hokkaido University Only one research institute of research concentrating to CATALYSIS Restructured from Institute for Catalysis, Hokkaido University (from 1943) Moved to the "North Campus" in November 2003 Seven laboratories Nanotechnology Research Center Catalysis Research Center (CRC) Research Initiative "SOSEI" 2009/12/09 Environmental Application of Photocatalysis 2

3 titania-coated glass of our building all glass plates are coated with titania to reduce infrared radiation (with expectation to keep the surfaces clean). coated on site; not construction with pre-coated glass plates expected photocatalytic self-cleaning effect CRC /12/09 Environmental Application of Photocatalysis 3

4 Ohtani Laboratory for photocatalysis research evaluation of of photocatalytic activities opened for for researchers in in academics and and industries education for for young young people people collaboration work work using using advanced instruments designed for for photocatalysis research 2009/12/09 Environmental Application of Photocatalysis 4

5 photocatalysis: two major phenomena photocatalytic decomposition target: organic compounds steins (oil) microorganisms photoinduced (super) hydrophilicity washable with running water anti-fogging 2009/12/09 Environmental Application of Photocatalysis 5

6 exterior materials coated with titania substrate: steal plates JFE Building Materials application /12/09 Environmental Application of Photocatalysis 6

7 tent material coated with titania photocatalyst after exposure outdoor for 5 months regular PVC showing change in color Teflon-coated titania-coated PVC must contain organic additives, which go out to the surface slowly, to be elastic. Taiyo Kogyo application /12/09 Environmental Application of Photocatalysis 7

8 titania photocatalytic painting paints requiring no heating: : room-temperature coating without painting procedure: spraying with without with with without painting procedure with brush or roller application /12/09 Environmental Application of Photocatalysis 8

9 photocatalyst coated glass inside: outside: anti-fogging effect to give water droplet-free surface photocatalytic decomposition and (super) hydrophilicity to keep the surface clean titania- coated glass regular glass on-site coating > pre-coating Japan Hydrotect Coatings application /12/09 Environmental Application of Photocatalysis 9

10 titania photocatalyst-including paint titania coatings with heating = pre-coating window blinds No effect of photo- induced hydrophilicity is expected for indoor use. application /12/09 Nippon Soda soda.co.jp/photo/report.html 2009/12/09 Environmental Application of Photocatalysis 10

11 titania-coatings for anti-fogging no water droplets due to the (super) hydrophilicity of photocatalytic titania surface titania coated part regular part TOTO application /12/09 Environmental Application of Photocatalysis 11

12 road-side sound barriers coated with titania polycarbonate plates covered with titania photocatalyst on both sides titania 1.5 year regular 1.5 year regular 3.5 year Sekisui Plastics application /12/09 Environmental Application of Photocatalysis 12

13 pavements containing titania photocatalyst "Photoroad" Nitrogen oxides (NO x ) are oxidized by photocatalyst Resulting nitrate (NO - 3 ) ions are captured by calcium ions Calcium nitrate (Ca(NO 3 ) 2 ) is washed out by rain water Fujita application /12/09 Environmental Application of Photocatalysis 13

14 lighting device with titania photocatalyst a covering window glass coated with titania lights for outdoor use regular fluorescent lamp Toshiba Lightec application /12/09 Environmental Application of Photocatalysis 14

15 photocatalytic air purifier unit active air purification: decontamination and deodorization of circulating air air conditioner Hitachi Home and Life Solution hl.com/ Daikin Ltd. air purifier application /12/09 Environmental Application of Photocatalysis 15

16 photocatalytic treatment of water Contaminated ground water is treated to remove volatile organic compounds. separator flow dryer neutra- lizer photocata- lyst exhaust decontaminated apparatus water air polluted gas soil ground water pump aeration unit drain polluted gas black light Sumitomo Metal Industries application /12/09 Environmental Application of Photocatalysis 16

17 smoke cleaner/refrigerator deodorization decomposition of ethylene (CH 2 =CH 2 ) from vegetables/fruits to keep freshness TOSHIBA TOSHIBA 光触媒実例 /12/09 Environmental Application of Photocatalysis 17

18 photocatalytic water treatment photocatalytic fiber cartridge for decomposition of dioxin sterilization チタニアが有機物を酸化分解する光触媒機能に着目して 接触面積が大きく 丈夫な繊維状にしたのが 光触媒繊維 既存の光触媒製品と差別化した製品の特色を活かして市場開発を進めています この新素材はダイオキシンの分解にも期待されています UBE Industries 光触媒実例 /12/09 Environmental Application of Photocatalysis 18

19 photocatalysis industries in Japan industries related to photocatalysis almost 300 million USD after 2005 (Photocatalysis Industry Association of Japan) 400 million USD others livingware cleanup road interior exterior 光触媒統計 /12/09 Environmental Application of Photocatalysis 19

20 photocatalysis industries in Japan 2008 (2007): ca. 320 million USD others livingware cleanup exterior road interior 光触媒統計 /12/09 Environmental Application of Photocatalysis 20

21 photocatalysis: two major phenomena superhydrophilicity: the surface of photocatalytic (titania) coatings becomes super hydrophilic, i.e., contact angle to be almost zero. left: left: photocatalytic/right: ordinary photocatalytic oxidation: organic and inorganic compounds are oxidized under air to be inorganic materials, i.e, mineralization. 2009/12/09 Environmental Application of Photocatalysis 21

22 hydrogen evolution by GaN:ZnO photocatalyst Domen's group (The University of Tokyo) 2009/12/09 Environmental Application of Photocatalysis 22

23 principle of photocatalytic reaction electronic structure of semiconductors and insulators conduction & valence bands separated by bandgap photoexcitation beyond the bandgap photoexcitation electron and hole relaxation reduction & oxidation recombination conduction band e - relaxation e - excitation h + h + recombination relaxation reduction photo- absorption oxidation valence band photocatalysis /12/09 Environmental Application of Photocatalysis 23

24 roles of oxygen in photocatalysis reaction with (capture of) photoexcited electron reacts with photoexcited electron to yield superoxide anion radical (O 2 + e - = O 2 - ) unknown fate of superoxide anion radical accelerates the reaction with holes (oxidation) participation in radical chain mechanism reacts with radical species, which is liberated by positive hole reaction, to give peroxy species radical chain reaction to give higher efficiency = one photon produces several products RH + h + = R + H + (H 2 O) RH + HO = R + H 2 O R + O 2 = RO 2 RO 2 + RH = RO 2 H + R RO 2 H (decomposition) (RH + R = R + RH) 光触媒 /12/09 Environmental Application of Photocatalysis 24

25 final photocatalytic oxidation products acid liberation except for H 2 O not volatile except for H 2 O and CO 2 need to neutralize the washings (rain water) spontaneously neutralized by basic components in soil, e.g., CaO for outdoor use H =C= =N S X (Cl, Br,...) H 2 O CO 2 HNO 3 H 2 SO 4 HX 光触媒 /12/09 Environmental Application of Photocatalysis 25

26 super hydrophilicity induced on titania surface proposed mechanism of photoinduced super hydrophilicity (still unknown in details) looses hydrophilicity slowly in the dark 光触媒 /12/09 Environmental Application of Photocatalysis 26

27 titanium(iv) oxide (titania) as a photocatalyst no change after reaction = "catalyst" especially strong oxidizing power when irradiated high photo- stability superior redox ability titanium(iv) oxide TiO 2 titania not poisonous & natural availability no reaction in the dark = "safe" and environmentally benign very popular and cheap material white or colorless = no effect on appearance but, requires ultraviolet irradiation photocatalysis /12/09 Environmental Application of Photocatalysis 27

28 photocatalytic activity efficiency of photocatalytic reaction depending on the photocatalyst recombi- nation photo- irradiation electron-hole pair efficient excitation to to give electron-hole pair faster surface reaction with electron-hole fewer (slower) recombination redox (chemical) reaction photocatalysis /12/09 Environmental Application of Photocatalysis 28

29 liquid-phase syntheses of titania photocatalyst in general, titanium compounds are hydrolyzed to titanic acid and then calcined to dehydrate and crystallize into titania Ti(OR) 4 alkoxide TiX 4 halide Ti(SO 4 ) 2 sulfate hydrolysis Ti(OH) 4 TiO(OH) 2 hydrated titania/titanium hydroxide amorphous titania calcination dehydration/ crystallization TiO 2 titania at higher calcination temperature smaller specific surface area higher crystallinity = smaller defects 光触媒 /12/09 Environmental Application of Photocatalysis 29

30 preparation of highly active photocatalyst HyCOM TD Hydrothermal Crystallization in Organic Media simultaneous hydrolysis and crystallization by small amount of water dissolved in organic solvent under pressure Thermal Decomposition thermal decomposition of alkoxide THyCA Transfer Hydrolytic Crystallization with Alcohols simultaneous hydrolysis and crystallization of alkoxide by water liberated by thermal decomposition of alcohols autoclave glass tube alkoxide /solvent water (HyCOM) furnace 2009/12/09 Environmental Application of Photocatalysis 30

31 examples of highly active titania particles titania particles synthesized by HyCOM method fringes corresponding to anatase lattice / nanosized single crystal Catal. Today, 84,, (2003) a 5 nm 50 nm titania particles synthesized by THyCA method Each crystallites are edge-shaped single crystal of anatase. 2009/12/09 Environmental Application of Photocatalysis 31

32 natural crystal of anatase titania square bipyramid exposing {101} facets 2009/12/09 Environmental Application of Photocatalysis 32

33 decahedral anatase titania particles gas-phase reaction of titanium(iv) chloride [collaboration work with Fujikura and Showa Titanium] particle size: nm surface area: m 2 g -1 highly crystallized exposing {101} and {001} low density of defects (001) (101) fujikura /12/09 Environmental Application of Photocatalysis 33

34 gas-phase synthesis of decahedral particles use of infrared furnace to heat up only the part covered with platinum ribbon = rapid heating and rapid cooling nm nm Ar vaporizer O 2 Pt plate 4 cm width/1473 K TiCl 4 oil bath 393 K buffle to make efficient heating 2009/12/09 Environmental Application of Photocatalysis 34

35 higher photocatalytic activity relatively high photocatalytic activity even though not so large specific surface area effective also for methanol dehydrogenation CH 3 OH = HCHO + H 2 acetaldehyde decomposition 2CH 3 CHO + 5O 2 = 4CO 2 + 4H 2 O fujikura /12/09 Environmental Application of Photocatalysis 35

36 titanium(iv) oxide and tungsten(vi) oxide Why WO 3 has not been used? ultraviolet visible fluorescent light TiO 2 WO Wavelength/nm /12/09 Environmental Application of Photocatalysis 36

37 STEM images of Pt(1wt%)-loaded WO 3 highly uniform dispersion of platinum particles (average size: 5 nm) on WO 3 20 nm 2009/12/09 Environmental Application of Photocatalysis 37

38 photocatalytic activity test (liquid phase) test reaction: decomposition of acetic acid CH 3 COOH + 2O 2 2CO 2 + 2H 2 O photocatalyst: 50 mg aqueous acetic acid solution (5 vol%, 250 ml) 300-W W xenon lamp Full arc irradiation: 300 < l < 500 nm With L-42 L cutoff filter: 400 < l < 500 nm Gas phase analysis: on-line GC 2009/12/09 Environmental Application of Photocatalysis 38

39 CO 2 generation under visible light (> 400 nm) 200 Bare WO Pt(0.5 wt%)-wo 3 amount of CO 2 /µmol ca. 7 µmol h -1 amount of CO 2 /µmol ca. 190 µmol h time/h /12/09 Environmental Application of Photocatalysis time/h rate of CO 2 generation increased remarkably with Pt loading (up to a maximum of 230 µmol h -1 at 1 wt% of Pt loading)

40 comparison with TiO 2 (P25) photocatalyst Pt(1 wt%)-wo 3 vs. TiO 2 (P25) 800 amount of CO 2 /mmol mol Pt-WO 3 full arc Pt-WO 3 vis TiO 2 P25 full arc TiO 2 P25 vis UV + Vis. (300 < l < 500) Vis. (400 < l < 500) irradiation time/min 2009/12/09 Environmental Application of Photocatalysis 40

41 photocatalytic activity test (gas phase) test reaction: decomposition of acetaldehyde CH 3 CHO + 5/2 O 2 2CO 2 + 2H 2 O photocatalyst: 50 mg acetaldehyde (AcH): 1000ppm (ca. 15 mmol) 300-W xenon lamp Full arc irradiation: 300 < l < 500 nm With L-42 cutoff filter: 400 < l < 500 nm Gas phase analysis: on-line GC 2009/12/09 Environmental Application of Photocatalysis 41

42 mineralization of acetaldehyde Dark Light irradiation (400 < l < 500 nm) 30 ACA AcH CO 2 Amount of gas / mmol mol Pt-WO 3 TiO 2 P25 N-TiO 2 Pt-WO 3 TiO 2 P25 N-TiO 2 CO 2 generated(2000 ppm, 30 mmol) AcH injected (1000 ppm, 15 mmol) CH 3 CHO + 5/2 O 2 2CO 2 + 2H 2 O Time / min /12/09 Environmental Application of Photocatalysis 42

43 hollow core-shell photocatalyst particles TiO 2 SiO 2 /void/tio 2 SiO 2 /TiO 2 (a) acetaldehyde K obs obs / min -1 TiO 2 SiO 2 /void/tio 2 SiO 2 /TiO 2 (b) acetic acid R / μmol min nm (c) PVA TiO 2 TiO 2 /void/tio R / μmol min /12/09 Environmental Application of Photocatalysis 43

44 unique characteristic of photocatalysis no need to use oxidants and reductants for redox reaction no need to use electrolytes as used in electrolytic redox reaction no need to use additive and no emission of by- products 光触媒 /12/09 Environmental Application of Photocatalysis 44

45 redox-combined photocatalytic reaction example: photocatalytic synthesis of pipecolinic acid (PCA) from L- lysine L-lysine ($1/1 kg) PCA ($500/1 g) g 2009/12/09 Environmental Application of Photocatalysis 45

46 photocatalytic synthesis L-lysine (Lys) COOH ε α H 2 N NH 2 2h + -2H + COOH COOH oxidation of amino group by h + HN NH 2 H 2 N NH hydrolysis of imines to give aldehyde or ketone Schiff base formation by dehydration reduction by e - HOC H 2 O -NH 3 H 2 O -NH 3 COOH N 2e -, 2H + -H 2 O NH 2 COOH (Pt) H 2 N cyclic Schiff base 2e -, 2H + -H 2 O N (Pt) COOH O COOH pipecolinic acid (PCA) N COOH N COOH H H ピペコリン酸 /12/09 Environmental Application of Photocatalysis 46

47 fine chemicals from pipecolinic acid Ropivacaine N NH O 2 steps 8 steps N COOH H L-pipecolinic acid O N H N O NH 2 NH 2 local anesthetic (Astra, Sweden) inhibitor of protein kinase C Federsel, H. J.; Jaksch, P.; Sandberg, R. Acta Chem. Scand. Ser. B 1987, B41, steps several steps Perumattam, J.; Shearer, B. G.; Confer, W.; Mathew, R. M. Tetrahedron Lett. 1991, 32, O N NH Ph mycotoxic alkaloid Verruculotoxin Martens, J.; Scheunemann, M. Tetrahedron Lett. 1991, 32, Cl NH H H HN O O NH H H HN antitumor antibiotic DKP593A Gitterman, C. O.; Rickes, E. L.; Wolf, D. E.; Madas, J.; Zimmerman, S. B.; Stoudt, T. H.; Demmy, T. C. J. Antibiot. 1970, 23, 305. ピペコリン酸 /12/09 Environmental Application of Photocatalysis 47 Cl Ph HOOC N H O N H COOH angiotensin conversion enzyme inhibitor Flynn, G. A.; Giroux, E. L.; Dage, R. C. J. Am. Chem. Soc. 1987, 109,

48 mini test (1) Name and matriculation card number (2) Explain briefly Gibbs energy and activation energy. (3) What do you expect to photocatalysis? 2009/12/09 Environmental Application of Photocatalysis 48