A New Method To Determine the Generation of Hydroxyl Radicals in Illuminated TiO₂Suspensions

Abstract

The generation of hydroxyl ( • OH) radicals produced by irradiation of aqueous TiO 2 suspensions was investigated by electron paramagnetic resonance (EPR) and product analysis employing a stable free nitroxide radical (3-carboxyproxyl) as a spin trap of • OH. Product analysis demonstrated that the attack of • OH on 3-carboxyproxyl produces a diamagnetic product (proxyl-NH) with a trapping efficiency of ca. 80%. It could also be shown that a small amount of the nitroxides is reduced by conducting band electrons. The rate of formation of • OH could be determined by monitoring the time dependence of the decrease in the concentration of 3-carboxyproxyl monitored by EPR spectroscopy or the time dependence of the increase in the concentration of proxyl-NH monitored by gas chromatography analysis. The rate of formation of • OH serves as a mechanistic parameter to investigate the mechanism of formation of this reactive species by the photoexcitation of TiO 2 . The dependence of the rate of formation of • OH was shown to be a linear function of light intensity at low intensities. It was observed that molecular oxygen, a good scavenger of conduction band electrons, only slightly influences the rate of formation of • OH and supports the production of • OH from photogenerated holes. Addition of selected anions to the photolysis mixtures results in a diminished rate of disappearance of the spin trap as the result of a competition between the spin trap and the anion for • OH. From a SternVolmer analysis of the data, the rate constant for the reaction of hydroxyl radicals with the anions was determined.

DCFH2 interactions with hydroxyl radicals and other oxidants – Influence of organic solvents

“…From DMPO it is known that its trapping efficiency amounts to 33 % (Schwarz et al, 1997). A corresponding trapping efficiency for DCFH 2 is not known.…”

Modulation of the electron transfer processes in Au–ZnO nanostructures

“…32,33 It is apparent that the heights of the peaks decrease at higher fields, a fact that is characteristic of anisotropic motion about the axis of the N-O bond, due to solvent viscosity. 33,34 As observed in the inset of Fig. 2, each line is widened by the contribution of the hydrogen hyperfine coupling constants, a H , mainly arising from the equatorial methyl and methylene protons.…”

Study of Oxidation of Thin Ti Film Controlled by Reduction Processes in Water Vapor Plasma

“…3 and 6, respectively). Irradiation of the surface area covered by monomolecular water layer by particles arriving from plasma leads to the split of water molecules into their atomic components of hydrogen and oxygen [12,13]. It results that the metallic titanium beneath the water island layer is oxidized much faster than the titanium uncovered by water layer (Fig.…”