The reduction of nitrobenzene by Fe(II)-goethite-hematite heterogeneous systems: Insight from thermodynamic parameters of reduction potential.

Determining the contaminants reduction rate by dissolved ferrous iron (Fe(II)) bound to iron oxides is curial for evaluating the abiotic attenuation of contaminants in aquifers. However, few studies have assessed the contaminants reduction rate controlled by thermodynamic parameters in heterogeneous systems with different iron oxides. In this study, a linear free energy relationship (LFER) was established between the nitrobenzene reduction rate and the thermodynamic driving force (reduction potential (E) and pH) in Fe(II)-goethite-hematite co-existing systems. Results showed that the reduction rate of nitrobenzene correlated with the E of the heterogeneous system. The standard reduction potential (E) of the mixed iron oxides could be obtained by a proportionate linear combination of the single iron oxide system E. Based on this, the E of the heterogeneous systems could be calculated theoretically by combining E and the Nernst equation. Furthermore, a parallel LFER with the slope of 1 was established to associate the nitrobenzene reduction rate with E and pH. The intercept term was related to the adsorption capacity of different iron oxides towards Fe(II). The Fe(II) saturation adsorption capacity of hematite was 1.5 times higher than that of goethite. After normalizing the nitrobenzene reduction rate to the Fe(II) saturation adsorption capacity, the maximum difference in intercept terms was reduced from 37% to 15%. These findings would provide an important and feasible methodological support for the quantitative evaluation of abiotic attenuation of contaminants in groundwater.