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1、John T Yates Jr John T Yates Jr Department of ChemistryDepartment of Chemistry University of University of VirginiaVirginia Charlottesville VA 22904Charlottesville VA 22904 johnt virginia edujohnt virginia edu Photochemistry on TiOPhotochemistry on TiO 2 2 Semiconductor SurfacesSemiconductor Surface
2、s 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 0 200 400 600 800 1000 1200 1400 1600 1800 Number of Publications Year A A FujishimaFujishima and K Honda Nature 238 1972 37 and K Honda Nature 238 1972 37 1972 Water Splitting at n1972 Water Splitting at n TiOTiO 2 2 Electrodes
3、Electrodes Search terms TiO2 OR titanium dioxide AND photo CB VB h 3 0 eV Upon UV excitation both electrons and holes are photochemically active towards adsorbates on the TiO2surface Donor Molecule Product Product Acceptor Molecule Semiconductor Semiconductor PhotoexcitationPhotoexcitation TiO TiO 2
4、 2 Taken from Fujishima Hashimoto Watanabe TiO2 Photocatalysis Fundamentals and Applications BKC Inc Tokyo 1999 Motivation TiO2Based Photocatalytic Technology Works Motivation TiO2Based Photocatalytic Technology Works TiO2Based Systems are Efficient Photocatalysts TiOTiO 2 2 as a Photochemical Subst
5、rateas a Photochemical Substrate 2 0nm 5 fold Ti bridging O vacancy in plane O 6 fold Ti bridging O 5 fold Ti 001 MezhenneyMezhenney et al Chemical Physics et al Chemical Physics Letters 369 2003 152 Letters 369 2003 152 Atomic Structure of TiOAtomic Structure of TiO 2 2 110 Surface 110 Surface TiOT
6、iO 2 2 110 110 1x1 surface without oxygen 1x1 surface without oxygen vacancies is vacancies is stochiometricstochiometric TiO TiO 2 2 The surface density of oxygen The surface density of oxygen vacancy sites is regulated by vacancy sites is regulated by annealing conditions annealing conditions time
7、 presence of O time presence of O 2 2 Heating TiOHeating TiO 2 2 above above 700 700 800 K 800 K OO vacancy defectsvacancy defects reduced TiO reduced TiO 2 2 Pan J M Maschhoff B L Diebold U Madey T E J Vac Sci Technol A 1992 10 2470 He Ion Scattering Spectroscopy He Ion Scattering Spectroscopy Dete
8、cts Detects 18 18O O 2 2 on Vacancy Defect Siteson Vacancy Defect Sites 8 defects in surface adsorb 18O2 TiO2Photochemistry Useful for Removal of Organics by Sequence of Reaction Events i e h CH3OH H2C O H COOH CO2 H2O O2 hO2 hO2 h Sequence of complex organic oxidation reactions makes the study of p
9、hotophysics difficult Investigate a simple photo reaction to obtain details h TiO2h e O2 a hO2 g TiO2 Detailed Studies of ODetailed Studies of O 2 2 PhotodesorptionPhotodesorption from TiOfrom TiO 2 2 110 110 Providing insight into the mechanisms Providing insight into the mechanisms of photonof pho
10、ton induced electroninduced electron hole pair hole pair production and the activation of production and the activation of adsorbed molecules by these charge adsorbed molecules by these charge carriers carriers a b Oxygen Vacancies h e c h Oxygen Photodesorption O O O O O O O O a b Oxygen Vacancies
11、h e h e c h Oxygen Photodesorption O O O O O O O O O O O O O O O O Mechanism for Oxygen Mechanism for Oxygen PhotodesorptionPhotodesorption from TiOfrom TiO 2 2 110 110 h O2 O2 de Lara Castells M P Krause J L J Chem Phys 2003 118 5098 5105 OOVAC VAC O O 2 2 OO 2 2 de Larade Lara CastellsCastells M P
12、 Krause J L M P Krause J L J J Chem Phys Chem Phys 2001 2001 115115 4798 4798 48104810 de Larade Lara CastellsCastells M P Krause J L M P Krause J L Chem Phys Chem Phys LettLett 2002 2002 354354 483 483 490 490 AnpoAnpo M M CheChe M M FubiniFubini B B GarroneGarrone E E GiamelloGiamello E Paganini M
13、 E Paganini M C C TopTop Catal 1999 8 189 198 G Lu A Linsebigler and J T Yates Jr The Adsorption and Photodesorption of Oxygen on the TiO2 110 Surface J Chem Phys 102 4657 1995 QMS Hg Lamp and Filters Photodiode Detector Quartz Reflector Fh 0 096 Fh Ta TiO2 OO 2 2 PhotodesorptionPhotodesorption from
14、 TiOfrom TiO 2 2 110 110 010203040 2 0 2 4 6 8 10 12 14 Y A x 10 9 Time s Fh 4 08 x 10 14 photons cm 2s 1 Eh 3 4 0 05 eV T 110 K O2 h on Tracy L Thompson and John T Yates Jr J Phys Chem B 109 2005 18230 OO 2 2 PhotodesorptionPhotodesorption from TiOfrom TiO 2 2 110 110 k k1 1F F h h h h TiO TiO2 2 e
15、 h e h k k2 2 h T h T T T hole capture by a hole trap hole capture by a hole trap k k3 3 e h e h heat heat on recombination sites on recombination sites k k4 4 h Oh O 2 2 a a OO 2 2 g g Rate of Rate of photodesorbingphotodesorbing oxygen scales oxygen scales proportionally with the square root of th
16、e incident proportionally with the square root of the incident light intensity light intensity 2 22 1 2 1 32 1 4Oh O F kk k k dt d 0 0 5 0 x10 6 1 0 x10 7 1 5x10 7 2 0 x10 7 0 2 4 6 8 10 12 14 h 3 4 0 05 eV T 110 K Flux 1 2 h photons 1 2cm 1sec 1 2 Y0 O Amps x 10 9 A B F 1 2 h crit 2 18O2 Initial Photodesorption Yield TiO2 110 1001020304050 2 0 2 4 6 8 10 12 14 Ion Current 36 amu Time s Fh 4 08 x 10 14 cm 2s 1 Y O2 dh Fh O2 O2 O2 O2 O2 O2 O2 O2 TiO2 Hole trap centers T and average range of photo
