TY - JOUR
T1 - Citrate Controls Fe(II)-Catalyzed Transformation of Ferrihydrite by Complexation of the Labile Fe(III) Intermediate
AU - Sheng, Anxu
AU - Li, Xiaoxu
AU - Arai, Yuji
AU - Ding, Yuefei
AU - Rosso, Kevin M.
AU - Liu, Juan
N1 - Funding Information:
This work is supported by National Natural Science Foundation of China (91751105, 41820104003, and 41972318). We acknowledge SLAC National Accelerator Laboratory at Stanford Synchrotron Radiation Light Source that is supported by Office of Basic Energy Sciences, the U.S. Department of Energy under Contract No. DE-AC02-76SF00515 for the provision of synchrotron radiation facilities. This research used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We also acknowlege support from the beamline 14W1 at Shanghai Synchrotron Radiation Facility (SSRF).
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/6/16
Y1 - 2020/6/16
N2 - Ferrihydrite (Fh) is generally associated with dissolved organic matter (DOM) in natural environments due to a strong sorption affinity at circumneutral pH and its high specific surface area. In suboxic conditions, aqueous Fe(II) (Fe(II)aq) can catalyze transformation of Fh into more stable crystalline Fe(III) phases, but how DOM influences the transformation kinetics and pathway is still unclear. Using citrate as a surrogate, we have examined Fh transformation with 1 mM Fe(II)aq and 0-60 μM citrate at pH 7.2. We focus on quantifying the time-dependent concentrations of sorbed Fe(II), structural Fe(II), and a key intermediate species, labile Fe(III) (Fe(III)labile), resulting from interfacial electron transfer (IET), and how these species correlate with the evolution of lepidocrocite (Lp), magnetite (Mt), and goethite (Gt) products. Low concentrations of citrate significantly impact the proportions of Lp/Gt, and the collective results reveal that its effect is primarily through its ability to complex labile Fe(III) and thereby disrupt polymerization into product crystallites, as opposed to modifying the surface properties of Fh or inhibiting IET. The emergence of a Mt coprecipitate is observed in the transformation experiments with 5-10 μM citrate, when the Fe(II)/Fe(III)labile ratio on/near the Fh surface is close to 0.5, the stoichiometric Fe(II)/Fe(III) ratio in Mt. At the molecular level, the findings suggest that citrate, and by extension DOM, can modify the relative rates of olation and oxolation reactions that assemble labile Fe(III) into various product minerals.
AB - Ferrihydrite (Fh) is generally associated with dissolved organic matter (DOM) in natural environments due to a strong sorption affinity at circumneutral pH and its high specific surface area. In suboxic conditions, aqueous Fe(II) (Fe(II)aq) can catalyze transformation of Fh into more stable crystalline Fe(III) phases, but how DOM influences the transformation kinetics and pathway is still unclear. Using citrate as a surrogate, we have examined Fh transformation with 1 mM Fe(II)aq and 0-60 μM citrate at pH 7.2. We focus on quantifying the time-dependent concentrations of sorbed Fe(II), structural Fe(II), and a key intermediate species, labile Fe(III) (Fe(III)labile), resulting from interfacial electron transfer (IET), and how these species correlate with the evolution of lepidocrocite (Lp), magnetite (Mt), and goethite (Gt) products. Low concentrations of citrate significantly impact the proportions of Lp/Gt, and the collective results reveal that its effect is primarily through its ability to complex labile Fe(III) and thereby disrupt polymerization into product crystallites, as opposed to modifying the surface properties of Fh or inhibiting IET. The emergence of a Mt coprecipitate is observed in the transformation experiments with 5-10 μM citrate, when the Fe(II)/Fe(III)labile ratio on/near the Fh surface is close to 0.5, the stoichiometric Fe(II)/Fe(III) ratio in Mt. At the molecular level, the findings suggest that citrate, and by extension DOM, can modify the relative rates of olation and oxolation reactions that assemble labile Fe(III) into various product minerals.
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U2 - 10.1021/acs.est.0c00996
DO - 10.1021/acs.est.0c00996
M3 - Article
C2 - 32421322
AN - SCOPUS:85086524889
SN - 0013-936X
VL - 54
SP - 7309
EP - 7319
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 12
ER -