Photoinduced hole transfer from TiO[sub 2] to methanol molecules in aqueous solution studied by electron paramagnetic resonance
- Argonne National Lab., IL (United States)
An electron paramagnetic resonance (EPR) study is reported on the paramagnetic species formed on irradiation of aqueous TiO[sub 2] colloids in the presence of methanol. In laser (308 nm) irradiated aqueous solution of methanol at 1.9 K, the observed EPR signals are centered around g = 2 and have a line shape characteristic of the CH[sub 2]OH radical. The appearance of these radicals at the very low temperature of 1.9 K implicates charge transfer from the oxygen lattice holes to methanol molecules within a few monolayers of the surface of the TiO[sub 2] particles. Different radicals are formed when CH[sub 3]OH is chemisorbed on TiO[sub 2]. The EPR signals detected in TiO[sub 2] colloidal solution prepared in methanol and then evaporated and dissolved in water also show the formation of the CH[sub 2]OH radical due to oxidation of chemisorbed methanol on the TiO[sub 2] surface. These particles, with high laser pulse intensities, oxidize the chemisorbed methanol further to give the CHO radical. In addition, the CH[sub 3] radical is formed from reducing processes and observed at 6-50 K. In the absence of methanol, holes are trapped by surface hydroxide groups forming TI[sup IV]-O-Ti[sup IV]-O[sup [sm bullet]]. At higher temperature (150 K) in aqueous methanol solution, the CH[sub 2]OH radical transfers an electron to TiO[sub 2], doubling the yield of formation of surface Ti[sup III] ions which are stable in air-free solution. When an electron scavenger such as Hg[sup 2+] is present in solution, the EPR signal of Ti[sup III] disappears since mercury ions are reduced. 44 refs., 7 figs.
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 5114883
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 97:50; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
661300 -- Other Aspects of Physical Science-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALCOHOLS
AQUEOUS SOLUTIONS
CHALCOGENIDES
CHARGE TRANSPORT
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
COLLOIDS
DISPERSIONS
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
ELECTRON TRANSFER
HOLE MOBILITY
HYDROXY COMPOUNDS
KINETICS
LASER RADIATION
MAGNETIC RESONANCE
METHANOL
MIXTURES
MOBILITY
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
RADIATION EFFECTS
RADIATIONS
RADICALS
REACTION KINETICS
RESONANCE
SEPARATION PROCESSES
SOLUTIONS
SORPTION
SURFACE PROPERTIES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRAPS