Interfacial electron-transfer equilibria and flat-band potentials of. cap alpha. -Fe/sub 2/O/sub 3/ and TiO/sub 2/ colloids studied by pulse radiolysis

Journal Article · Thu Sep 13 04:00:00 EDT 1984 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j150663a018· OSTI ID:6222590

Dimitrijevic, N M; Savic, D; Micic, O I; Nozik, A J

The kinetics and equilibria of electron transfer between methylviologen cation radicals and ..cap alpha..-Fe/sub 2/O/sub 3/ or TiO/sub 2/ colloidal particles were studied with the pulse-radiolysis technique. The rates of electron transfer to both colloids are lower than those predicted for a diffusion-controlled reaction. For higher pHs (TiO/sub 2/, pH > 2; ..cap alpha..-Fe/sub 2/O/sub 3/, pH > 9) the established equilibrium MV/sup +/ in equilibrium MV/sup 2 +/ + (e/sup -/)/sub coll/ is strongly influenced by the MV/sup 2 +/ concentration and pH. The MV/sup +/ equilibrium concentration can be exploited to derive the flat-band potential of the semiconductor colloids. The method for determining the flat-band potential of the particles is independent of whether the injected electrons are free or trapped, and whether the electrons raise the bulk Fermi level toward the conduction band or just produce a space charge. The flat-band potentials for both colloids appear to be somewhat more negative (-0.1 to -0.2 V) than the corresponding single-crystal electrodes. Also, the flat-band potentials become slightly more negative with increasing radiation dose (initial MV/sup +/ concentration). The effect of absorbed radiation dose is explained by the corresponding changes in the ratio of oxidized to reduced forms of the redox couple, which in turn changes the adsorbed ionic charge on the semiconductor surface. For colloidal particles of TiO/sub 2/ stabilized by poly(vinyl alcohol) (PVA), the flat-band potentials were almost the same as those for PVA-free TiO/sub 2/ sols. The decrease of particle diameter from 800 to 70 A does not affect the value of the flat-band potentials for TiO/sub 2/ and ..cap alpha..-Fe/sub 2/O/sub 3/ colloids. 28 references, 9 figures.

• Research Organization: Boris Kidric Inst. of Nuclear Sciences, Beograd, Yugoslavia
• OSTI ID: 6222590
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 88:19; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600* -- Radiation Chemistry
ABSORPTION SPECTRA
AZINES
BIPYRIDINES
CHALCOGENIDES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTION KINETICS
CHEMISTRY
COLLOIDS
DATA
DATA ANALYSIS
DISPERSIONS
DOSE RATES
ELECTRON TRANSFER
EQUILIBRIUM
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
IRON COMPOUNDS
IRON OXIDES
IRRADIATION
KINETICS
MATERIALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
PULSED IRRADIATION
PYRIDINES
RADIATION CHEMISTRY
RADIATION EFFECTS
REACTION KINETICS
SEMICONDUCTOR MATERIALS
SPECTRA
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS