Application of coumarin and coumarin-3-carboxylic acid for the determination of hydroxyl radicals during different advanced oxidation processes

Máté Náfrádi, Luca Farkas, Tünde Alapi, Klára Hernádi, Krisztina Kovács, László Wojnárovits, Erzsébet Takács

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Transformation of coumarin (COU) and coumarin-3-carboxylic acid (3-CCA), the formation of their fluorescent hydroxylated products, (7-hydroxy-coumarin (7-HO-COU) and 7-hydroxy-3-carboxycoumarinic acid (7-HO-3-CCA)) were investigated and compared using three different advanced oxidation processes: gamma radiolysis, VUV (172 nm) photolysis and heterogeneous photocatalysis (TiO2/UV (300–400 nm)). Beside OH (hydroxyl radical), other reactive species: H (H-atom, in VUV irradiated aqueous solution and in gamma radiolysis with low yield) and eaq (hydrated electron, in gamma radiolysis) also contributed to the degradation. The reaction rate constants of COU and 3-CCA with each reactive species were determined via pulse radiolysis. The values obtained were: 6.88 × 109 and 4.9 × 109 with OH; 2.5 × 109 and 1.3 × 109 with H; 11.4 × 109 and 14.3 × 1010 mol−1 dm3 s−1 with eaq , in the case of COU and 3-CCA, respectively. Based on the results of radiolysis it was suggested, that the formation of fluorescent products are initiated only by OH. The effects of dissolved O2 and OH scavengers (MeOH and t-BuOH) were also investigated. In radiolysis dissolved O2 increased the formation rate of fluorescent products. In VUV photolysis of COU and 3-CCA solutions the inhibition effect of alcohols was more pronounced in the presence of O2 than in its absence. In heterogeneous photocatalysis both MeOH and t-BuOH decreased the transformation rate of COU, while they had no observable effect on that of 3-CCA, which is well adsorbed on TiO2 surface.

Original languageEnglish
Article number108610
JournalRadiation Physics and Chemistry
Publication statusPublished - May 2020



  • 172 nm VUV photolysis
  • Adsorption
  • Heterogeneous photocatalysis
  • Hydroxyl radical
  • Radiolysis

ASJC Scopus subject areas

  • Radiation

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