Environmental Science and Pollution Research

, Volume 26, Issue 9, pp 8640–8649 | Cite as

Photogeneration of hydroxyl radical in Fe(III)-citrate-oxalate system for the degradation of fluconazole: mechanism and products

  • Dong Wan
  • Guofei Zhang
  • Yong ChenEmail author
  • Xiye Lu
  • Yuegang Zuo
Research Article


The photochemical role of Fe(III)-citrate complex is significant in natural waters due to its ubiquitous existence and excellent photoreactivity at near neutral pH. Although there are many reports on the photoinduced degradation of pollutants in the Fe(III)-citrate system, the optimum pH for its photoreactivity is yet not clearly understood. Here, for the first time, we demonstrated that the optimum pH was 5.5 for the photoproduction of OH in the Fe(III)-citrate system via kinetics modeling based on the steady-state approximation. According to the experimental results, the OH photoproduction increased with increasing pH until 5.5 and then decreased in Fe(III)-citrate solution, which agreed well with the prediction trend of kinetic modeling. The effect of the common ligand oxalate on the photoreactivity of Fe(III)-citrate system was also investigated. The addition of oxalate promoted the photoproduction of OH in Fe(III)-citrate solutions, and the measured [OH]ss increased with oxalate concentration under a fixed Fe(III)-to-citrate ratio. Little synergistic effect exists in Fe(III)-citrate-oxalate system at pH 4.0–5.5. In contrast, an appreciable synergistic effect was observed at near neutral pH (6.0–8.0). Higher oxalate-to-citrate ratio facilitated the synergistic effect. Furthermore, antifungal drug fluconazole could be removed efficiently in the Fe(III)-citrate-oxalate system. The photodegradation kinetics also verified the optimum pH of Fe(III)-citrate system and synergistic effect of oxalate. By LC-ESI-MS/MS analyses, the photoproducts of fluconazole in the Fe(III)-citrate-oxalate system were identified and the reaction mechanism involving hydroxylation substitution and subsequent cleavage of heterocyclic amine was proposed. These findings suggest that Fe(III)-citrate exhibits best photoreactivity at pH 5.5, and the coexistence of reactive ligands will enhance its photoreactivity at circumneutral pH, indicating potential application in wastewater treatment via addition of appropriate citrate and co-ligands.


Fe(III)-citrate-oxalate  Optimum pH Synergistic effect Fluconazole Mechanism 


Funding information

This work was financially supported by the National Natural Science Foundation of China (Nos. 21677054 and 21377043) and project funded by China Postdoctoral Science Foundation (No. 2018 M630865).

Supplementary material

11356_2019_4348_MOESM1_ESM.doc (3.4 mb)
ESM 1 (DOC 3.37 mb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Dong Wan
    • 1
  • Guofei Zhang
    • 1
  • Yong Chen
    • 1
    Email author
  • Xiye Lu
    • 1
  • Yuegang Zuo
    • 2
  1. 1.School of Environmental Science and EngineeringHuazhong University of Science and TechnologyWuhanChina
  2. 2.University of Massachusetts DartmouthNorth DartmouthUSA

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