Inhibitory effects and mechanisms of low-molecular-mass organic acids (LMMOAs) toward Cr(III) oxidation

Kim Hoong Ng, Yu Ting Liu, Chung Tse Chang, Po Neng Chiang, Heng Yi Teah, Po Hsiang Chang, Yu Min Tzou*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Photo-reduction of Cr(VI) into Cr(III) has been extensively studied for the alleviation of Cr(VI) hazards. However, knowledge in regard to the Cr(III) oxidation back into Cr(VI), which serves an equally important role in controlling Cr pollution, is limited. To this end, inhibitory effects and related mechanisms of low-molecular-mass organic acids (LMMOAs), including citric acid, oxalic acid and acetic acid, toward Cr(III) oxidation in the presence of Fe(III) under UV-irradiation were determined in this study. Results showed that the most prominent Cr(III) oxidation (~4 μM out of 300 μM Cr(III)) occurred at pH 3.0 in the presence of 400 μM Fe(III) and 12 h of UV-irradiation, yet such Cr(III) oxidation could be entirely or partially suppressed upon the addition of LMMOAs. Both citric and oxalic acids triggered a nearly complete inhibition of Cr(III) oxidation, even with the lowest dosage of 50 μM, ascribed to promoted generation of Fe(II) that scavenged OH• radicals. Regarding acetic acid, the addition of 50 μM only yielded 75% inhibitory efficiency, and further decreased to 50% as its amount increased to 400 μM. In contrast with citric/oxalic acids, acetic acid tended not to complex with Fe(III). While such free acetic acid reacted with OH• radicals generated from photolysis of Fe(OH)2+, additional OH• radicals were produced. Furthermore, the Fe(II) generation in the acetic acid system was about 28–35% of that in the citric/oxalic acid systems. In the case of supplementary OH• radicals and insufficient Fe(II), less OH• radicals could be consumed, and thereby the amendment of acetic acid showed a relatively weak inhibitory effect toward Cr(III) oxidation. This study evidenced that all three LMMOAs are effective toward the inhibition of Cr(III) oxidation in the presence of Fe(III). This feasible, practical, and environmental friendly approach is promising to prevent the secondary pollution caused by Cr(III) oxidation.

Original languageEnglish
Article number127726
JournalJournal of Cleaner Production
Publication statusPublished - 2021 Sept 1


  • Chromium
  • Ferric ion
  • Inhibitory mechanism
  • Low-molecular-mass organic acids
  • Oxidation

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Environmental Science(all)
  • Strategy and Management
  • Industrial and Manufacturing Engineering


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