A mechanism study of light-induced Cr(VI) reduction in an acidic solution

Shan Li Wang, Chung Chi Chen, Yu Min Tzou*, Chia Lian Hsu, Jen Hshuan Chen, Chen Fang Lin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


The mechanisms of photo-catalytic reduction of Cr(VI) were investigated in acidic solutions with and without Fe(III). In a system without Fe(III), no Cr(VI) reduction was observed in dark conditions; conversely, under light conditions, the reduction reaction rate increased to 0.011 and 0.020 μM min-1 at pH 2 and pH 1, respectively, indicating the occurrence of Cr(VI) photo-reduction. The Cr(VI) photo-reduction reaction was induced by the photolysis of water molecules, leading to O2 production. Upon the addition of Fe(III), the photo-reduction rate of Cr(VI) was significantly enhanced due to the formation of Fe(II), which is the photolytic product of FeCl2+ and the electron donor for Cr(VI) reduction. However, with the same concentration of FeCl complexes, a strong inhibition of Cr(VI) reduction at pH 2 was observed, compared with pH 1. A possible explanation is that FeOH2+ becomes predominant with increasing pH and that its photolytic product, the OH free radical, is an oxidant for Fe(II) and Cr(III) and can compromise Cr(VI) reduction. The kinetic result of each photo-reduction reaction pathway shows zero-order kinetics, suggesting that the photolysis reaction of H2O or FeCl2+ is the rate-determining step in each pathway. The results also show the potential of developing a homogeneous photo-catalytic method to treat Cr(VI)-containing water.

Original languageEnglish
Pages (from-to)223-228
Number of pages6
JournalJournal of Hazardous Materials
Issue number1
Publication statusPublished - 2009 May 15


  • Chromium
  • Photo-reduction
  • Photolysis
  • Reaction rate

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution
  • Health, Toxicology and Mutagenesis


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