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Reactions between ferric oxyhydroxide mineral coatings and a dimethoxyhydroquinone : A source of hydroxyl radicals

Lyngsie, Gry LU ; Herzog, Simon D. ; Hansen, Hans Christian Bruun and Persson, Per LU (2024) In Science of the Total Environment 949.
Abstract

Quinones are organic molecules that facilitate electron-transfer reactions in terrestrial environments. The reduced forms, hydroquinones, are powerful reductants that can trigger non-enzymatic radical-based decomposition of organic matter and contaminants by simultaneous reduction of iron and oxygen. Iron oxides often occur as coatings on other minerals, thus our study investigated the reactions between the ferric oxyhydroxide (FeO(OH)) surface coatings on gibbsite (Al(OH)3) and 2,6-dimethoxy-1,4-hydroquinone (2,6-DMHQ). The main aim was to investigate the oxidation of 2,6-DMHQ and the generation ∙OH in the presence of O2 at low Fe concentrations in a novel setup that allows local structural characterization. The... (More)

Quinones are organic molecules that facilitate electron-transfer reactions in terrestrial environments. The reduced forms, hydroquinones, are powerful reductants that can trigger non-enzymatic radical-based decomposition of organic matter and contaminants by simultaneous reduction of iron and oxygen. Iron oxides often occur as coatings on other minerals, thus our study investigated the reactions between the ferric oxyhydroxide (FeO(OH)) surface coatings on gibbsite (Al(OH)3) and 2,6-dimethoxy-1,4-hydroquinone (2,6-DMHQ). The main aim was to investigate the oxidation of 2,6-DMHQ and the generation ∙OH in the presence of O2 at low Fe concentrations in a novel setup that allows local structural characterization. The heterogeneous redox reactions between 2,6-DMHQ and the FeO(OH) coatings were studied at pH 5.0 as a function of the amount of Fe present on the gibbsite surfaces, including the effect of aging of the FeO(OH) coatings. The results showed that reactions between 2,6-DMHQ and FeO(OH) coated gibbsite under ambient conditions can generate substantial amounts of ·OH, comparable with amounts generated on pure ferrihydrite surfaces. The ·OH is the product of two sequential reactions: hydroquinone oxidation by O2 and degradation of the formed H2O2. The calculated rate constant of the former reaction is the same regardless of amount of FeO(OH) coating suggesting a surface catalytic process where 2,6-DMHQ is oxidized by O2 resulting in formation of H2O2. Subsequently, the observed induction period, the low Fe2+ (aq) concentrations in solution and the dependency of FeO(OH) coating amount influencing ·OH formation suggest that the pathway for ∙OH is through H2O2 decomposition by the surface sites on the FeO(OH) coating. Overall, this study shows that co-existence of oxygen, FeO(OH) and organic reductants, possibly secreted by soil microorganisms, creates favorable conditions for generation of ·OH contributing to decomposition of organic matter and organic pollutants in soil environments.

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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Fungal metabolites, Heterogeneous Fenton, Iron reduction, Mineral coatings, Quinone, Redox reactions
in
Science of the Total Environment
volume
949
article number
175065
publisher
Elsevier
external identifiers
  • pmid:39067593
  • scopus:85200121008
ISSN
0048-9697
DOI
10.1016/j.scitotenv.2024.175065
language
English
LU publication?
yes
id
a9e66e1c-2213-43f6-aa75-e247262b2bb5
date added to LUP
2024-09-05 15:07:01
date last changed
2024-09-05 15:08:27
@article{a9e66e1c-2213-43f6-aa75-e247262b2bb5,
  abstract     = {{<p>Quinones are organic molecules that facilitate electron-transfer reactions in terrestrial environments. The reduced forms, hydroquinones, are powerful reductants that can trigger non-enzymatic radical-based decomposition of organic matter and contaminants by simultaneous reduction of iron and oxygen. Iron oxides often occur as coatings on other minerals, thus our study investigated the reactions between the ferric oxyhydroxide (FeO(OH)) surface coatings on gibbsite (Al(OH)<sub>3</sub>) and 2,6-dimethoxy-1,4-hydroquinone (2,6-DMHQ). The main aim was to investigate the oxidation of 2,6-DMHQ and the generation ∙OH in the presence of O<sub>2</sub> at low Fe concentrations in a novel setup that allows local structural characterization. The heterogeneous redox reactions between 2,6-DMHQ and the FeO(OH) coatings were studied at pH 5.0 as a function of the amount of Fe present on the gibbsite surfaces, including the effect of aging of the FeO(OH) coatings. The results showed that reactions between 2,6-DMHQ and FeO(OH) coated gibbsite under ambient conditions can generate substantial amounts of ·OH, comparable with amounts generated on pure ferrihydrite surfaces. The ·OH is the product of two sequential reactions: hydroquinone oxidation by O<sub>2</sub> and degradation of the formed H<sub>2</sub>O<sub>2</sub>. The calculated rate constant of the former reaction is the same regardless of amount of FeO(OH) coating suggesting a surface catalytic process where 2,6-DMHQ is oxidized by O<sub>2</sub> resulting in formation of H<sub>2</sub>O<sub>2</sub>. Subsequently, the observed induction period, the low Fe<sup>2+</sup> (aq) concentrations in solution and the dependency of FeO(OH) coating amount influencing ·OH formation suggest that the pathway for ∙OH is through H<sub>2</sub>O<sub>2</sub> decomposition by the surface sites on the FeO(OH) coating. Overall, this study shows that co-existence of oxygen, FeO(OH) and organic reductants, possibly secreted by soil microorganisms, creates favorable conditions for generation of ·OH contributing to decomposition of organic matter and organic pollutants in soil environments.</p>}},
  author       = {{Lyngsie, Gry and Herzog, Simon D. and Hansen, Hans Christian Bruun and Persson, Per}},
  issn         = {{0048-9697}},
  keywords     = {{Fungal metabolites; Heterogeneous Fenton; Iron reduction; Mineral coatings; Quinone; Redox reactions}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Science of the Total Environment}},
  title        = {{Reactions between ferric oxyhydroxide mineral coatings and a dimethoxyhydroquinone : A source of hydroxyl radicals}},
  url          = {{http://dx.doi.org/10.1016/j.scitotenv.2024.175065}},
  doi          = {{10.1016/j.scitotenv.2024.175065}},
  volume       = {{949}},
  year         = {{2024}},
}