光催化课件：专题 4-TiO2光催化材料[1].ppt

1、Fundamental and ApplicationsuAtmosphere pollutionuGreen house effect (CO2)uAcid rainuWater pollutionuSoil pollutionSmogAcid rainWaste water from textile industryContaminated soilPesticides buried with strong odor uO3/H2O2uO3/UVuO3/CATALYSTSuFenton reaction (H2O2/Fe2+)uPhoto-Fenton reaction (H2O2/Fe2

2、+/UV)uH2O2/UVuO3/H2O2/UVuUV/TiO2 (Photocatalysis)In Atmosphere:1) O3+ h( 320 nm) O2(1g) + O (1D)O (1D) + H2O 2OH2) HONO + h( 400 nm) NO + OH OHavg 106radicals cm-3 ( 0.1 ppt!)In Water:1)FeIII(OH)2+ (aq) + h( 400 nm) Fe2+ (aq) + OH 2)NO3-(aq) + h NO2+ O- O-+ H2O OH-+ OHOxidation Potentials (V vs NHE)

3、HO2.80O32.07H2O21.78HO21.70ClO21.57HOCl1.49Cl21.36uThe definition of photocatalysis is basically the acceleration of a photoreaction in the presence of a catalyst.1)Hoffmann, M. S.; Martin, T.; Choi, W.; Bahnemann, D. W. Chem. Rev. 1995, 95, 69-96. OH OHCBVB-0.5V+2.7VTiO2e- / H+H2O2O2OH-OH./OH-O2-UV

4、 light ( 387.5nm)3.2eVO2-/O2e-h+TiO2UVh+ + e-e- + O2 O2-O2- + 2H+ + e-H2O2H2O2 + O2- OH + OH- + O2h+ + H2O OH + H+uLight absorption PropertyuLight absorption spectrum and coefficientuRate of reduction and oxidation of reaction substrate by e- and h+, respectivelyuRate of e- and h+ recombinationEnhan

5、cing interfacial charge-transferImproving charge separationInhibiting charge carrier recombination uTiO2uWhy TiO2?uStrong oxidizing power of valance band holeuExcellent chemical and photochemical stabilityuAvailability: One of top 50 chemicals uBand gap: 3.2 eVuOnly active under UV light (4% of the

6、incoming solar energy)AnataseRutileBrookiteAnatase is the most active one!FTo enlarge band gap by reducing crystal sizes (quantum size effect)FTo increase surface area (mesoporous structure) FTo reduce crystal defects ( high crystallinity )FTo dope metal ionsFTo deposit noble metal nanoparticlesFTo

7、couple two kinds of semiconductorsuHow to enhance the efficiencyuPreparation of nanostructured photocatalystsuExtension of absorption of TiO2 to the visible regionuDesign of novel non-titania based visible Light photocatalystsuNanocrystalsuNanoporous materialsAThermal decomposition methodASol-gel me

8、thod AMicroemulsion method AHydrothermal (or solvothermal) method ACombustion method AOther methodsmicrowavenonhydrolyticsonochemical OHCBVB-0.5V+2.7VTiO2e- / H+H2O2O2OH-OH./OH-O2-UV light ( 387.5nm)3.2eVO2-/O2e-h+AuInhibition of the recombination of h+ and e-! OHCBVB-0.5V+2.7VTiO2CBVBe-h+Inhibition

9、 of the recombination of h+ and e-!QSensitization of TiO2 Organic dyes Metal complexes Narrow band gap semiconductors PolymersQIon-doped TiO2 Metal ionsNon-metal ionsCBVB+2.7VTiO2DyeDye*Dye+O2O2-e-Visible light OHe- / H+H2O2This is also the fundamental of dye-sensitized solar cell!CBVB-0.5V+2.7VTiO2

10、O2-/O2CBVBCdS band-gap:2.4eVh+e-OH H2O2 O2-e- / H+O2e-Visible lightWater purification (Purifics environmental technologies) UV0 min30 min60 minPhoto-Electricity ConversionLightFuelElectricityElectricityPhotovoltaicssceMPhotosynthesisFuels COSugarH OO222H OOH222scMeSemiconductor/LiquidJunctionsDye Se

11、nsitized Solar CellGratzel, Nature 414, 338 (2001)uInexpensiveu1/10 of amorphous siliconuFlexibleuEfficiency not high enoughuSolid electrolyte 200019501960197019801990510152025Efficiency (%)Yearcrystalline Siamorphous Sinano TiO2CIS/CIGSCdTeWater Splitting Utilizing Solar EnergyH2anodecathodeO2membraneMOxMSxe-H+4H+ + 4e- 2H22H2O O2 + 4H+ + 4e-