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Heterogeneous Fenton reactions : oxidation of adsorbing and non-adsorbing probe molecules via H2O2-promoted reduction of iron oxides

Zhang, Bowen LU orcid ; Op De Beeck, Michiel LU orcid ; Troein, Carl LU orcid ; Tunlid, Anders LU and Persson, Per LU (2026) In Journal of Colloid and Interface Science 716.
Abstract

Hydroxyl radicals (HO•), produced through reactions between H2O2 and iron oxides, drive biogeochemical transformations, mediate organism toxicity, and facilitate advanced oxidation processes. The effectiveness of these processes depends on the spatial proximity between HO• generation and target substrates. Consequently, the oxidation mechanisms should be governed by interfacial interactions among H2O2, substrates, and iron oxide surfaces. Substrate oxidation by iron oxide/H2O2 systems were studied using two probes simultaneously: terephthalate (TPA), forming outer-sphere surface complexes, and coumarin, exhibiting no surface interactions. The... (More)

Hydroxyl radicals (HO•), produced through reactions between H2O2 and iron oxides, drive biogeochemical transformations, mediate organism toxicity, and facilitate advanced oxidation processes. The effectiveness of these processes depends on the spatial proximity between HO• generation and target substrates. Consequently, the oxidation mechanisms should be governed by interfacial interactions among H2O2, substrates, and iron oxide surfaces. Substrate oxidation by iron oxide/H2O2 systems were studied using two probes simultaneously: terephthalate (TPA), forming outer-sphere surface complexes, and coumarin, exhibiting no surface interactions. The reactions were followed as a function of pH, time and H2O2 concentration. Complementary experiments were performed with oxalate inner-sphere surface complexes. Both ferrihydrite and goethite were studied, representing differences in reduction potential. Solution analyses were combined with in-situ infrared spectroscopy probing the interfacial reactions. Both probes were oxidized by ferrihydrite/H2O2. Between pH 5.5–6.5, substantial amounts of TPA outer-sphere surface complexes were oxidized, while coumarin was mainly oxidized at pH ≤ 4.5, coinciding with a decrease in TPA oxidation. At all investigated pH values, H2O2 reduced ferrihydrite, and the partitioning of Fe(II) controlled the location of HO• generation. At low pH, Fe(II) diffused into solution triggering homogeneous Fenton reactions, while adsorption and re-oxidation at higher pH confined radical generation to the near-surface region. Oxalate inner-sphere complexes resisted oxidation. Oxidation by the goethite/H2O2 system was low compared to ferrihydrite, consistent with the lower reduction potential of goethite. This work demonstrates that H2O2-promoted reduction of iron oxides is a key reaction leading to HO• oxidation of organic outer-sphere surface complexes.

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author
; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Coumarin, Fe(II) dissolution, Ferrihydrite, Goethite, Inner-sphere surface complexes, Outer-sphere surface complexes, Terephthalate
in
Journal of Colloid and Interface Science
volume
716
article number
140342
publisher
Academic Press
external identifiers
  • pmid:41875603
  • scopus:105033421389
ISSN
0021-9797
DOI
10.1016/j.jcis.2026.140342
language
English
LU publication?
yes
id
676ad679-6fad-4a60-80f5-7b3edf1556be
date added to LUP
2026-04-20 12:15:17
date last changed
2026-05-18 15:30:43
@article{676ad679-6fad-4a60-80f5-7b3edf1556be,
  abstract     = {{<p>Hydroxyl radicals (HO<sup>•</sup>), produced through reactions between H<sub>2</sub>O<sub>2</sub> and iron oxides, drive biogeochemical transformations, mediate organism toxicity, and facilitate advanced oxidation processes. The effectiveness of these processes depends on the spatial proximity between HO<sup>•</sup> generation and target substrates. Consequently, the oxidation mechanisms should be governed by interfacial interactions among H<sub>2</sub>O<sub>2</sub>, substrates, and iron oxide surfaces. Substrate oxidation by iron oxide/H<sub>2</sub>O<sub>2</sub> systems were studied using two probes simultaneously: terephthalate (TPA), forming outer-sphere surface complexes, and coumarin, exhibiting no surface interactions. The reactions were followed as a function of pH, time and H<sub>2</sub>O<sub>2</sub> concentration. Complementary experiments were performed with oxalate inner-sphere surface complexes. Both ferrihydrite and goethite were studied, representing differences in reduction potential. Solution analyses were combined with in-situ infrared spectroscopy probing the interfacial reactions. Both probes were oxidized by ferrihydrite/H<sub>2</sub>O<sub>2</sub>. Between pH 5.5–6.5, substantial amounts of TPA outer-sphere surface complexes were oxidized, while coumarin was mainly oxidized at pH ≤ 4.5, coinciding with a decrease in TPA oxidation. At all investigated pH values, H<sub>2</sub>O<sub>2</sub> reduced ferrihydrite, and the partitioning of Fe(II) controlled the location of HO<sup>•</sup> generation. At low pH, Fe(II) diffused into solution triggering homogeneous Fenton reactions, while adsorption and re-oxidation at higher pH confined radical generation to the near-surface region. Oxalate inner-sphere complexes resisted oxidation. Oxidation by the goethite/H<sub>2</sub>O<sub>2</sub> system was low compared to ferrihydrite, consistent with the lower reduction potential of goethite. This work demonstrates that H<sub>2</sub>O<sub>2</sub>-promoted reduction of iron oxides is a key reaction leading to HO<sup>•</sup> oxidation of organic outer-sphere surface complexes.</p>}},
  author       = {{Zhang, Bowen and Op De Beeck, Michiel and Troein, Carl and Tunlid, Anders and Persson, Per}},
  issn         = {{0021-9797}},
  keywords     = {{Coumarin; Fe(II) dissolution; Ferrihydrite; Goethite; Inner-sphere surface complexes; Outer-sphere surface complexes; Terephthalate}},
  language     = {{eng}},
  publisher    = {{Academic Press}},
  series       = {{Journal of Colloid and Interface Science}},
  title        = {{Heterogeneous Fenton reactions : oxidation of adsorbing and non-adsorbing probe molecules via H<sub>2</sub>O<sub>2</sub>-promoted reduction of iron oxides}},
  url          = {{http://dx.doi.org/10.1016/j.jcis.2026.140342}},
  doi          = {{10.1016/j.jcis.2026.140342}},
  volume       = {{716}},
  year         = {{2026}},
}