photocatalysison tio2 surfaces
TRANSCRIPT
Photocatalysis onTiO2 Surfaces
KiraWyckoffJune6,2016
Introduction
ElectronicExcitation
TiO2Properties
PhotocatalyticApplications
Light
VB
CBelectron
hole
-
+
Bandgap
Introduction
ElectronicExcitation
TiO2Properties
PhotocatalyticApplications
Light
VB
CBelectron
hole
-
+
Bandgap
Generationofelectron-holepairsinsemiconductorparticles
electronfromdonor cancombinewithholetooxidizedonor
ExcitationofelectronfromVBtoCBbylightwithenergyequaltobandgap
donateelectronstoreduceanelectronacceptor
HoleandelectroncanrecombineonSurfaceorinvolume
Linsebigler,Lu&Yates. Chem.Rev.Vol95,No3,735–58(1995).
QuantumYieldhasidealvalueof1forthephotocatalyticprocess
∅ ∝𝑘$%
𝑘$% + 𝑘'
• Idealization• Recombinationdoesoccur• Concentrationofelectrons(ns)andholes(ps)atthesurfaceisnotequal
• Chargecarriertrapsusedtopromotetrappingofelectronsandholesatsurface
• ForTiO2,ns>psbecauseelectrontransfertoO2 isslow
Chargetransferrate
Electron-holerecombination rate
QuantumYieldorEfficiency
Linsebigler,Lu&Yates. Chem.Rev.Vol95,No3,735–58(1995).
IncreaseinBandGapforDecreasingParticleSize
• Quantumsizeeffectsoccurforsemiconductorparticlesonorderof10-100A
• ArisewhensizeofparticleiscomparabletodeBrogliewave-length
• Confinementproducesquantizationofdiscreteelectronicstates
• Increaseseffectivebandgap
Linsebigler,Lu&Yates. Chem.Rev.Vol95,No3,735–58(1995).
Outline
ElectronicExcitation
TiO2Properties
PhotocatalyticApplications
Light
VB
CBelectron
hole
-
+
Bandgap
TiO2 Anatase showshigherphotocatalyticactivity
• ChainsofTiO6 octahedra• EachTi4+issurroundedbysixO2- ions
• Octahedrondistortedtolowersymmetrythanorthorhombic
• Eachoctahedronincontactwitheightneighbors
• Latticestructurecausesdifferentelectronicbandstructure
Linsebigler,Lu&Yates. Chem.Rev.Vol95,No3,735–58(1995).
DOSshowslargebandgap
O2porbitals
Energy
Ti 3dorbitals
Ti 4s,4porbitals
EFBandGap=3.3eV
Outline
ElectronicExcitation
TiO2Properties
PhotocatalyticApplications
Light
VB
CBelectron
hole
-
+
Bandgap
Application:environmentalcleanup
Light
VB
CBelectron
hole
-
+
Bandgap
Degradationoforganicmolecules:• Depollutionofsmoke• Killbacteria• Decontaminatewater
O2
O2.-
Reduction
Oxidation
P
P+H++OH.-
H2O
Manydifferentnovelcommercialapplications
Clothing
Selfcleaningwindows
Wenxi Guo,etal. JournaloftheAmericanChemicalSociety.
Researchtowardsacatalystsensitivetovisiblelight
• GaN andZnO• Rh-Crmixedoxideco-catalyst• Canabsorbinvisiblelight• Watersplittingtoformhydrogen
andwaterusingsolarenergy
• TiO2 doesnotabsorblightinthevisibleregion
Maeda&Domen. J.Phys.Chem.C.Vol111,No22,2007.Linsebigler,Lu&Yates. Chem.Rev.Vol95,No3,735–58(1995).
Questions?
Extra
Anatase [TiO2]Structure TetragonalSpaceGroup : I 41/amd (No.141)a=3.7845Å, c=9.5143Åa=b=g=90.00Z=4AtomicPositionalParametersTi 4a0.00000.00000.0000O 8e0.00000.00000.2081
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