Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

Jagannath Biswakarma; Kyounglim Kang; Walter D.C. Schenkeveld; Stephan M. Kraemer; Janet G. Hering; Stephan J. Hug

doi:10.1016/j.chemosphere.2020.128188

Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

Jagannath Biswakarma, Kyounglim Kang, Walter D.C. Schenkeveld, Stephan M. Kraemer, Janet G. Hering, Stephan J. Hug^*

^*Corresponding author for this work

Research output: Contribution to journal › Article (Academic Journal) › peer-review

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Abstract

Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO₂ buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.

Original language	English
Article number	128188
Journal	Chemosphere
Volume	263
DOIs	https://doi.org/10.1016/j.chemosphere.2020.128188
Publication status	Published - Jan 2021

Bibliographical note

Funding Information:
The authors are grateful to Thomas Rüttimann (Eawag) for laboratory experiments and technical assistance. This project was financially supported by the Swiss National Science Foundation , project number 200021L_150150 ‘‘Synergistic effects of redox processes and ligand controlled dissolution of iron(hydr)oxide phases” Mathematics, Natural sciences and Engineering (division II). SK, WS and KK were supported by the Austrian Science Fund ( FWF , Grant No.: I 1528-N19 and I 2865-N34, respectively).

Publisher Copyright:
© 2020 The Authors

Keywords

Bioavailability
Carbonatebuffered
Dissolution
Iron
Photochemistry
UV-A illumination

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@article{bd55e4a4101342afbc2d2c3435d1cba7,

title = "Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB",

abstract = "Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.",

keywords = "Bioavailability, Carbonatebuffered, Dissolution, Iron, Photochemistry, UV-A illumination",

author = "Jagannath Biswakarma and Kyounglim Kang and Schenkeveld, {Walter D.C.} and Kraemer, {Stephan M.} and Hering, {Janet G.} and Hug, {Stephan J.}",

note = "Funding Information: The authors are grateful to Thomas R{\"u}ttimann (Eawag) for laboratory experiments and technical assistance. This project was financially supported by the Swiss National Science Foundation , project number 200021L_150150 {\textquoteleft}{\textquoteleft}Synergistic effects of redox processes and ligand controlled dissolution of iron(hydr)oxide phases” Mathematics, Natural sciences and Engineering (division II). SK, WS and KK were supported by the Austrian Science Fund ( FWF , Grant No.: I 1528-N19 and I 2865-N34, respectively). Publisher Copyright: {\textcopyright} 2020 The Authors",

year = "2021",

month = jan,

doi = "10.1016/j.chemosphere.2020.128188",

language = "English",

volume = "263",

journal = "Chemosphere",

issn = "0045-6535",

publisher = "Elsevier Science",

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TY - JOUR

T1 - Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

AU - Biswakarma, Jagannath

AU - Kang, Kyounglim

AU - Schenkeveld, Walter D.C.

AU - Kraemer, Stephan M.

AU - Hering, Janet G.

AU - Hug, Stephan J.

N1 - Funding Information: The authors are grateful to Thomas Rüttimann (Eawag) for laboratory experiments and technical assistance. This project was financially supported by the Swiss National Science Foundation , project number 200021L_150150 ‘‘Synergistic effects of redox processes and ligand controlled dissolution of iron(hydr)oxide phases” Mathematics, Natural sciences and Engineering (division II). SK, WS and KK were supported by the Austrian Science Fund ( FWF , Grant No.: I 1528-N19 and I 2865-N34, respectively). Publisher Copyright: © 2020 The Authors

PY - 2021/1

Y1 - 2021/1

N2 - Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.

AB - Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.

KW - Bioavailability

KW - Carbonatebuffered

KW - Dissolution

KW - Iron

KW - Photochemistry

KW - UV-A illumination

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U2 - 10.1016/j.chemosphere.2020.128188

DO - 10.1016/j.chemosphere.2020.128188

M3 - Article (Academic Journal)

C2 - 33297154

AN - SCOPUS:85090822223

SN - 0045-6535

VL - 263

JO - Chemosphere

JF - Chemosphere

M1 - 128188

ER -

Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

Abstract

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Keywords

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