Iron-catalyzed photochemical transformation of benzoic acid in atmospheric liquids: Product identification and reaction mechanisms

Yiwei Deng, Kai Zhang, Hao Chen, Taixing Wu, Metthew Krzyaniak, Amina Wellons, Dawn Bolla, Kenneth Douglas, Yuegang Zuo

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This study investigated iron-catalyzed photochemical oxidation of benzoic acid (BA), one of the major photodegradation products of petroleum hydrocarbons, under sunlight or monochromatic light irradiation in a wavelength range of 254-419 nm. The photochemical degradation of BA in the absence of iron (III) occurred at irradiation wavelengths below 300 nm. The photochemical transformation of BA in the presence Fe(III) was observed at both 254, 350, 419 nm and under solar irradiation. The half-life for the photodegradation of BA (100 μM) was 160±20 min in the presence of 20 μM Fe(III) at pH 3.20 on sunny August days at noon time. The degradation rate increased with increasing concentration of Fe(III). The reaction products were separated and identified using capillary electrophoresis (CE), gas chromatography/mass spectrometry (GC/MS) and UV-Visible spectrophotometry. The major reaction products were 2-hydroxybenzoic, 3-hydroxybenzoic and 4-hydroxybenzoic acids. Hydrogen peroxide (H2O2) and Fe(II) species were also formed during the photochemical reactions. The proposed reaction mechanisms include the photoexcitation of Fe(III) hydroxide complexes to form Fe(II) ions and hydroxyl radicals (OH{radical dot}) that attack ortho, meta and para positions of BA to form corresponding monohydroxybenzoic acids and H2O2. The monohydroxybenzoic acids formed further react with hydroxyl and surperoxide radicals (HO2-{radical dot}/O2-{radical dot}) to yield dihydroxybenzoic acids in atmospheric water droplets.

Original languageEnglish (US)
Pages (from-to)3665-3676
Number of pages12
JournalAtmospheric Environment
Issue number20
StatePublished - Jun 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Environmental Science
  • Atmospheric Science


  • Aquatic chemistry
  • Atmosphere
  • Benzoic acid
  • Capillary electrophoresis
  • Fe(III)/Fe(II) redox cycling
  • GC-MS
  • Hydroxybenzoic acid
  • Photochemical degradation
  • Sunlight


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