Radical Intermediates in Photoinduced Reactions on TiO₂ (An EPR Spin Trapping Study)

Author： Dvoranová Dana Barbieriková Zuzana Brezová Vlasta

Publisher： MDPI

E-ISSN： 1420-3049|19|11|17279-17304

ISSN： 1420-3049

Source： Molecules, Vol.19, Iss.11, 2014-10, pp. : 17279-17304

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Abstract

The radical intermediates formed upon UVA irradiation of titanium dioxide suspensions in aqueous and non-aqueous environments were investigated applying the EPR spin trapping technique. The results showed that the generation of reactive species and their consecutive reactions are influenced by the solvent properties (e.g., polarity, solubility of molecular oxygen, rate constant for the reaction of hydroxyl radicals with the solvent). The formation of hydroxyl radicals, evidenced as the corresponding spin-adducts, dominated in the irradiated TiO₂ aqueous suspensions. The addition of ¹⁷O-enriched water caused changes in the EPR spectra reflecting the interaction of an unpaired electron with the ¹⁷O nucleus. The photoexcitation of TiO₂ in non-aqueous solvents (dimethylsulfoxide, acetonitrile, methanol and ethanol) in the presence of 5,5-dimethyl-1-pyrroline N-oxide spin trap displayed a stabilization of the superoxide radical anions generated via electron transfer reaction to molecular oxygen, and various oxygen- and carbon-centered radicals from the solvents were generated. The character and origin of the carbon-centered spin-adducts was confirmed using nitroso spin trapping agents.