Jeffrey M. Hudson, George W. Luther, III, Yu-Ping Chin
{"title":"Assessing Iron Complexation by Dissolved Organic Matter Using Mediated Electrochemical Oxidation","authors":"Jeffrey M. Hudson, George W. Luther, III, Yu-Ping Chin","doi":"10.1021/acsearthspacechem.4c00131","DOIUrl":null,"url":null,"abstract":"Fe<sup>II</sup> is an abundant reductant in the environment that participates in numerous biogeochemical cycles and pollutant attenuation. Fe<sup>II</sup> in aquatic environments can exist as a complex with dissolved organic matter (DOM), where organic ligands in DOM can modulate iron’s redox potential (<i>E</i><sub>H</sub>) and henceforth reactivity as a reductant. Previous studies have assessed the reactivity of Fe<sup>II</sup>-complexes using probe compounds, although these compounds are limited in their ability to profile Fe<sup>II</sup> oxidation across multiple thermodynamic conditions (i.e., both pH and <i>E</i><sub>H</sub>) and fail to validate the <i>E</i><sub>H</sub> of Fe(II)-complexes via their direct measurement. This study elucidated the redox potentials of Fe<sup>II</sup>-DOM complexes via mediated electrochemical oxidation (MEO) and assessed the extent of Fe<sup>II</sup> oxidation at two different applied <i>E</i><sub>H</sub> and pH regimes. Furthermore, we used a Nernstian-based model calibrated with a training set between known iron-ligand thermodynamic stability constants and their respective measured potentials to indirectly determine the stability constants of both Fe<sup>II</sup> and Fe<sup>III</sup>-DOM complexes as a function of <i>E</i><sub>H</sub> and pH. This work highlights the versatility of MEO as an electrochemical technique and is the first to assess stability constants of Fe-complexes with aquatic DOM isolates. We also discuss linkages between speciation modeling and redox reactivity of Fe<sup>II</sup>.","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":null,"pages":null},"PeriodicalIF":2.9000,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Earth and Space Chemistry","FirstCategoryId":"92","ListUrlMain":"https://doi.org/10.1021/acsearthspacechem.4c00131","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
FeII is an abundant reductant in the environment that participates in numerous biogeochemical cycles and pollutant attenuation. FeII in aquatic environments can exist as a complex with dissolved organic matter (DOM), where organic ligands in DOM can modulate iron’s redox potential (EH) and henceforth reactivity as a reductant. Previous studies have assessed the reactivity of FeII-complexes using probe compounds, although these compounds are limited in their ability to profile FeII oxidation across multiple thermodynamic conditions (i.e., both pH and EH) and fail to validate the EH of Fe(II)-complexes via their direct measurement. This study elucidated the redox potentials of FeII-DOM complexes via mediated electrochemical oxidation (MEO) and assessed the extent of FeII oxidation at two different applied EH and pH regimes. Furthermore, we used a Nernstian-based model calibrated with a training set between known iron-ligand thermodynamic stability constants and their respective measured potentials to indirectly determine the stability constants of both FeII and FeIII-DOM complexes as a function of EH and pH. This work highlights the versatility of MEO as an electrochemical technique and is the first to assess stability constants of Fe-complexes with aquatic DOM isolates. We also discuss linkages between speciation modeling and redox reactivity of FeII.
期刊介绍:
The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.