Electron transfer reactions from different electron donors, such as (CH3)2ĊOH, ĊOO-, MV+, Eu2+, and HȮ2 radicals, to WO3 colloidal particles were studied by pulse radiolysis techniques. The optical properties of excess electrons in WO3 colloids show an increase in absorption at wavelengths above 700 nm, which is consistent with free carrier absorption. The same absorption spectrum was also obtained after steady-state γ-irradiation and after illumination of WO3 colloidal sols with visible light. Electrons injected into WO3 colloids are stable in an argon atmosphere but disappear rapidly upon addition of Fe3+, O2, or Fe(CN)63-. In the presence of Cu2+ ions and PVA, the equilibrium Cu+ ⇄ Cu2+ + (e-)WO3 is established. The equilibrium concentration of excess electrons in the presence of Cu2+ can be exploited to derive the flat-band potential of semiconductor colloids; the values are about 150 mV more negative than those for compact electrodes. The flat-band potential of WO3 sols becomes slightly more negative with increasing radiation dose or intensity of light. These results are explained by the corresponding changes in the surface charge on the colloids.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry