Probing defect sites on TiO2 with [Re3(CO)12H3]: spectroscopic characterization of the surface species.
Samples of the anatase phase of titania were treated under vacuum to create Ti(3+) surface-defect sites and surface O(-) and O(2) (-) species (indicated by electron paramagnetic resonance (EPR) spectra), accompanied by the disappearance of bridging surface OH groups and the formation of terminal Ti(3+)-OH groups (indicated by IR spectra). EPR spectra showed that the probe molecule [Re(3)(CO)(12)H(3)] reacted preferentially with the Ti(3+) sites, forming Ti(4+) sites with OH groups as the [Re(3)(CO)(12)H(3)] was adsorbed. Extended X-ray absorption fine structure (EXAFS) spectra showed that these clusters were deprotonated upon adsorption, with the triangular metal frame remaining intact; EPR spectra demonstrated the simultaneous removal of surface O(-) and O(2) (-) species. The data determined by the three complementary techniques form the basis of a schematic representation of the surface chemistry. According to this picture, during evacuation at 773 K, defect sites are formed on hydroxylated titania as a bridging OH group is removed, forming two neighboring Ti(3+) sites, or, when a Ti(4+)-O bond is cleaved, forming a Ti(3+) site and an O(-) species, with the Ti(4+)-OH group being converted into a Ti(3+)-OH group. When the probe molecule [Re(3)(CO)(12)H(3)] is adsorbed on a titania surface with Ti(3+) defect sites, it reacts preferentially with these sites, becoming deprotonated, removing most of the oxygen radicals, and healing the defect sites.
Suriye
Kongkiat
K
Department of Chemical Engineering and Materials Science, University of California, One Shields Ave., Davis, CA 95616, USA.
Lobo-Lapidus
Rodrigo J
RJ
Yeagle
Gregory J
GJ
Praserthdam
Piyasan
P
Britt
R David
RD
Gates
Bruce C
BC
D000327:Adsorption; D004578:Electron Spin Resonance Spectroscopy; D006859:Hydrogen / Q000737:chemistry; D006878:Hydroxides / Q000737:chemistry; D007659:Ketones / Q000737:chemistry; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000032:analysis* / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011522:Protons; D012211:Rhenium / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D014025:Titanium / Q000032:analysis* / Q000737:chemistry*
D006878:Hydroxides; D007659:Ketones; D009942:Organometallic Compounds; D010087:Oxides; D011522:Protons; C009495:titanium dioxide; D012211:Rhenium; D006859:Hydrogen; D014025:Titanium; D010100:Oxygen