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가시광 광촉매 연구의 최근 동향

가시광 광촉매 연구의 최근 동향. 최 원 용 포항공과대학교 환경공학부. Common Strategies for Developing Visible Light Photocatalysts. Impurity Doping in Wide Band-gap Oxide Semiconductors - transition metal ions (cations) - nitrogen, carbon (anions) Sensitization of Wide Band-gap Oxide Semiconductors

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가시광 광촉매 연구의 최근 동향

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  1. 가시광 광촉매 연구의 최근 동향 최 원 용 포항공과대학교 환경공학부

  2. Common Strategies for Developing Visible Light Photocatalysts • Impurity Doping in Wide Band-gap Oxide Semiconductors • - transition metal ions (cations) • - nitrogen, carbon (anions) • Sensitization of Wide Band-gap Oxide Semiconductors • - organometallic complexes (e.g., ruthenium bipyridyl derivatives) • - organic dyes • - inorganic quantum dots (e.g., CdS) • Surface Complexation • Sensitized Zeolites • 5.Combined Systems

  3. Band Gap Positions in Various Semiconductors eV E vs. NHE Vacuum level 0 -3.0 -1.0 -4.0 1.1 -4.5 H+/H2 0 3.0 2.3 -5.0 1.7 2.5 Si +1.0 -6.0 2.8 3.4 3.2 2.7 3.4 2.2 3.0 3.2 3.8 5.0 3.2 2.8 3.2 GaP CdSe +2.0 SiC -7.0 CdS Fe2O3 +3.0 SrTiO3 -8.0 MnTiO3 TiO2 Rutile TiO2 Anatase ZnO2 KTaO3 FeTiO3 BaTiO3 Nb2O5 WO3 ZrO2 SnO2 @ pH = 0

  4. 2.1 eV Doping TiO2 with transition metal ions Charge transfer between the metal ion d electron and the TiO2 CB or VB Red shift of the light absorption

  5. V-doped TiO2 ( Zhao, et al., Thin Solid Films, 1999, 123 ) Cr3+-doped Pt/TiO2 ( Borgarello, et al., J. Am. Chem. Soc.,1982, 2996 ) Doping TiO2 with transition metal ions Cr3+/TiO2/Pt

  6. Ru3+-doped TiO2 at 0, 0.5, 1, 2and 3 % Ru3+ concentrations (from bottom to up) Separate absorption band centered at 437 nm : donor transition of Ru3+ into CB Ru3+→ Ru4+ + ecb- ( Choi, et al., J. Phys. Chem.,1994, 98, 13669 ) Ru-doped TiO2 hv Ti0.97Ru0.03O2 crystal (——) TiO2 single crystal (­ ­ ­) Two-photon excitation process Ru4+→ Ru5+ + ecb- Ru5+→ Ru4+ + hvb+ hv hv ( Gutierrez and Salvador, J. Electroanal. Chem.,1985, 139 )

  7. Doped TiO2 for Visible Light Activity V-doped TiO2 & its visible light photooxidation of ethanol UV-visible absorption spectra of blank PVG and three TiO2-based catalysts: (a) PVG, (b) TiO2/PVG, (c) TiO2/V/PVG, and (d) V/TiO2/PVG. PVG : transparent porous Vycor 7930 borosilicate glass. Bloch decay spectra of ethanol over V/TiO2/PVG before (a) and after 1 h irradiation with visible (b) and UV/visible (c) light. (Klosek, et al., J. Phys. Chem. B,2001, 105, 2815.)

  8. Doped TiO2 for Visible Light Activity Au/Au3+-TiO2 photocatalysts (a) The UV-visible absorption spectra of the TiO2 modified with gold; (b) the UV-visible absorption spectra of the TiO2 modified with gold ion. (Li, et al., Environ. Sci. Technol.,2001, 35, 2381)

  9. Doped TiO2 for Visible Light Activity Au/Au3+-TiO2 photocatalysts toward visible photooxidation for water and wastewater treatment The TOC removal and MB decolorization during MB photodegradation with initial MB concentration of 12 mg L-1 and pH 5.98. ( > 400 nm) MB : methylene blue

  10. Doped TiO2 for Visible Light Activity Visible light activity of Ni-doped InTaO4 (In1-xNixTaO4) for water spltting Optical properties of the photocatalyst. The main panel shows the ultraviolet–visible diffuse reflectance spectra of In1-xNixTaO4 (x = 0 and 0.1) at room temperature. (QY for H2 production = 0.66%) (Zou, et al., Nature, 2001,414, 625)

  11. Metal Ion Implanted TiO2 Metal-ion doped TiO2 prepared by an ion implantation method Systematic diagram of metal ion implantation The depth profiles of V ions content for the V ion-implanted TiO2 wafer. Ion acceleration energy: 150 keV. Amounts of implanted V ions (×10.7 mol/g-cat.): (a) 2.2; (b) 6.6; (c) 13.2; (d) 22.0. • no presence of metal ions at the TiO2 surface • highly dispersed within the deep bulk • modify the bulk electronic property • no formation of defect sites within the band gap (not working as a recombination center)

  12. Metal Ion Implanted TiO2 V ion-implanted TiO2 photocatalyst The diffuse reflectance UV–VIS spectra of TiO2 (a) and V ion-implanted TiO2 photocatalysts (b)–(e). Amounts of implanted V ions (x10-7 mol/g-cat.): (b) 2.2; (c) 6.6; (d) 13.2; (e) 22.0. The reaction time profiles of the photocatalytic oxidative degradation of 2-propanol diluted in water on the V ion-implanted TiO2 photocatalysts under visible light irradiation ( >450 nm). (Yamashita, et al., J. Photochem. Photobiol. A,2002, 148, 257)

  13. Metal Ion Implanted TiO2 Cr ion-implanted TiO2 Effects of Cr ion-implantation on the UV-VIS diffuse reflectance spectra of the TiO2 catalyst. Number of implanted Cr ions (N/cm2): (a) 0.0 (original TiO2), (b) 1x1016, (c) 6x1016, (d) 12x1016. Time profiles of the photocatalytic decomposition of NO on the Cr ion-impanted TiO2 catalyst (a), and non-implanted original TiO2 catalyst (b) under visible light irradiation (>450nm). (Anpo, Catalysis Surveys from Japan, 1997, 1, 169)

  14. Doped TiO2 for Visible Light Activity Nitrogen-doped TiO2 (TiO2-xNx): O2- N3- Experimental optical absorption spectra of TiO2-xNx and TiO2 films. Photocatalytic properties of TiO2-xNx samples (solid circles) compared with TiO2 samples (open squares). CO2 evolution as a function of irradiation time (light on at zero) during the photodegradation of acetaldehyde gas. (QY = 0.42% @436 nm) (Asahi, et al., Science,2001, 293, 269-271)

  15. Doped TiO2 for Visible Light Activity Carbon-doped TiO2 (TiO2-xCx: x ~ 0.15) by flame pyrolysis At Eapp = 0.3 V, carbon-doped TiO2 performs water splittingwith a total conversion efficiency of 11%. UV-visible spectra of CM-n-TiO2 and reference n-TiO2. The flame-made sample shows threshold wavelengths of 535 nm (band gap of 2.32 eV) and440 nm (band gap of 2.82 eV) Photocurrent density jp as a function of applied potential Eapp at CM-n-TiO2 and the reference n-TiO2 photoelectrodes under xenon lamp illumination at an intensity of 40 mW/cm2. (Khan, et al., Science,2002, 297, 2243)

  16. Combinatorial approach in doping semiconductor photocatalysts 9x5 flask matrix. Doped photocatalysts synthesized and tested within the flasks 4-CP conversions X for TiO2-based mixed oxides after 2.5 h of irradiation. Each library member is identified by its position in the library, given by a column (A-E) and a row (1-13). The table contains the doping salts (1 mol % with respect to TiO2). The library members showing 4-CP conversions >5 % are shaded grey in the table. (Lettmann, et al., Angew. Chem. Int. Ed.,2001, 40, 3160)

  17. Absorption of light: • Ru2+-complexsurface *Ru2+-complexsurface • (2) Sensitization: • *Ru2+-complexsurface + TiO2 Ru3+-complexsurface+ TiO2(e-CB) • Regeneration of complex: • 2Ru3+-complexsurface+ H2O  2 Ru2+-complexsurface + 1/2O2 + 2H+ • Hydrogen formation: • TiO2(e- CB) + Pt  TiO2 + Pt(e-), Pt(e-) + H3O+  Pt + 1/2H2 Sensitized Pt/TiO2 for Hydrogen Production A mechanism of the sensitizer [Ru(dcbpy)2(dpq)]2+ leading to efficient water reduction A feasible mechanism for the photocatalytic hydrogen evolution, S= [Ru(dcbpy)2(dpq)]2+ (Dhanalakshmi, et al., Int. J. Hydrogen Energy, 2001, 26, 669 – 674)

  18. Sensitized Pt/TiO2 for Hydrogen Production Hydrogen evolution from water using Eosin Y-fixed TiO2 under visible light Dye-sensitized photocatalyst for H2 evolution system in two-steps water splitting. (Abe et al., J. Photochem. Photobiol. A, 2000,137, 63-69) Fig. 7. H2 evolution from TEOA aq. on the Eosin Y fixed TiO2-ST-01 under visible light irradiation (460 nm). H2PtCl6 aq. (0.5 wt.%) was added into TEOA aq. before first run. The catalyst was collected by centrifugation after 7 h of irradiation, added into new TEOA aq. and irradiated.

  19. Sensitized TiO2 for CCl4 Destruction TiO2 sensitized with tris(4,4'-dicarboxy-2,2'-bipyridyl)ruthenium(II) complex under visible light to degrade CCl4 Production of Cl- from the photosensitized degradation of CCl4 as a function of irradiation time. The suspensions were sparged with O2, N2, or air before photolysis. The experimental conditions were: [TiO2] = 0.5 g/L, [RuIIL3]i = 3 M, [CCl4] = 1.0 mM, pHi = 3, Ii (420 < λ< 550 nm) 6 × 10-3 Einstein L-1 min-1. (Cho, et al., Environ. Sci. Technol.,2001, 35, 966 -970)

  20. Sensitized Pt/TiO2 for CCl4 Destruction Highly enhanced photoreactivity of dye-sensitized Pt/TiO2 under visible light Time-dependent chloride production from CCl4 degradation on TiO2/RuIIL3 and Pt/TiO2/RuIIL3 under visible light. The effects of adding 0.1 M isopropyl alcohol (IPA) on the chloride production are compared as well. The experimental conditions were as follows: [TiO2] = 0.5 g/L, pHi= 3, [RuIIL3]i= 10 mM, [CCl4] = 1 mM, l> 420 nm, and initially N2-saturated. (Bae and Choi, Environ. Sci. Technol.,2003, 37, 147)

  21. Quantum Dot Sensitization of TiO2 e- hν CB e- CdS TiO2 VB Normalized photocurrent excitation spectra showing the incident photon to current conversion efficiency (IPCE) of TiO2 electrodes sensitized by CdS Q-particles. The size of the CdS particles estimated from the photocurrent onset wavelengths are (a) 2.9 and (b) 1.9 nm. CdS quantum dots can be self-assembled on high surface area nanocrystalline TiO2 electrodes. (Peter, et al., Chem. Commun., 2002, 1030)

  22. Surface Complex of H2O2 on TiO2 surface Diffuse reflectance spectra of TiO2 powder in the absence (spectrum 1) or presence (spectrum 2) of H2O2 (5 × 10-3 mol/L). Inset: differential diffuse reflectance spectrum. (Li, et al., Langmuir,2001, 17, 4118)

  23. Surface Complex of H2O2 on TiO2 surface A possible mechanism Photoinduced Electron Transfer and Interface Photoreaction of the Surface Complex of H2O2 on the TiO2 Surface.

  24. Sensitized Zeolite Photocatalyst 2,4,6-triphenylpyrylium ion (TP+) encapsulated in Y zeolite TP+, MG+(malachite green): a well-known single electron transfer photosensitizer Encapsulated inside the voids of a microporous Y zeolite  TPY and MGY Normalized diffuse reflectance spectra of (a) TiO2, (b) TPY, and (c) MGY. (Sanjuan, et al., Applied Catalysis B: Environmental, 1998, 15, 247)

  25. 210 420 Time (min) Sensitized Zeolite Photocatalyst 2,4,6-triphenylpyrylium ion (TP+) encapsulated in Y zeolite (1) Adsorption of CPA into the pores of the Y zeolite; (2) irradiation with UV, visible or solar light promotes TP+ to its excited state; and (3) 4-chlorophenol is the primary product. Time-conversion plot for the TP+ photosensitized irradiation of CPA with solar light. (a) TPY or (b) TP/SiO2.

  26. Sensitized Zeolite Photocatalyst Representation of a zeolite consisting of dye molecules (p-N,N’-dimethylamionobenzoic acid (DMABA) acting as sensitizer and TiO2 acting as an electron acceptor. (Kim and Yoon, J. Mol. Catal. A: Chem.2001, 168, 257)

  27. Heteropoly acid(HPA) combined with TiO2 Photoinduced electron transfer at the heterojunction of HPA/TiO2 colloids in the presence of 0.1% PVA as an electron donor Photocatalytic action spectrum of HPA/TiO2 in 0.1% PVA aqueous solutions upon two-beam irradiation. One beam is 300 nm and the other is a variable from 300 to 700 nm. (Yoon, et al., J. Phys. Chem. B,2001, 105, 2539)

  28. Perspectives for Visible Light Photocatalysts “Nature preserves this world by not activating various metal oxides with visible light that would have destroyed organic matter.” (Hiskia et al., Chem. Soc. Rev.,2001, 30, 62) We are challenging what the Creator has forbidden: the visible light activation of metal oxides in a controlled manner! The development of visible light photocatalysts has been progressed very slowly and will continue to proceed at a slow pace. Be patient but… Can we ever succeed???

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