Numerous studies have reported that pollutant reduction rates by ferrous iron (Fe) are substantially enhanced in the presence of an iron (oxyhydr)oxide mineral. Developing a thermodynamic framework to explain this phenomenon has been historically difficult due to challenges in quantifying reduction potential ( E) values for oxide-bound Fe species. Recently, our group demonstrated that E values for hematite- and goethite-bound Fe can be accurately calculated using Gibbs free energy of formation values. Here, we tested if calculated E values for oxide-bound Fe could be used to develop a free energy relationship capable of describing variations in reduction rate constants of substituted nitrobenzenes, a class of model pollutants that contain reducible aromatic nitro groups, using data collected here and compiled from the literature. All the data could be described by a single linear relationship between the logarithms of the surface-area-normalized rate constant ( k) values and E and pH values [log( k) = - E/0.059 V - pH + 3.42]. This framework provides mechanistic insights into how the thermodynamic favorability of electron transfer from oxide-bound Fe relates to redox reaction kinetics.
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http://dx.doi.org/10.1021/acs.est.8b00481 | DOI Listing |
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