REDUCTIVE ACTIVITY OF ADSORBED Fe(II) ON IRON (OXYHYDR)OXIDES FOR 2-NITROPHENOL TRANSFORMATION

Much attention has been paid to the adsorption of Fe(II) onto mineral surfaces as it is a crucial step in enhancing the reductive activity of Fe(II) species. The present study elucidates the role of Fe(II) adsorbed on Fe (oxyhydr)oxides (gamma-FeOOH, alpha-FeOOH, and alpha-Fe2O3) for the reductive transformation of 2-nitrophenol (2-NP), using cyclic voltammetry (CV). Studies of Fe(II) adsorption and 2-NP reduction kinetics showed that an increase in pH gave rise to an elevated density of adsorbed Fe(II) on mineral surfaces, which further resulted in an enhanced reaction rate of 2-NP reduction. In addition, CV tests showed that the enhanced activity of Fe(II) species is attributed to the negative shift of peak oxidation potential (E-P) of the Fe(III)/Fe(II) couple. The dependence of adsorbed Fe(II) reactivity on pH values was proven by the three linear correlations obtained (In k vs. pH, E-P vs. pH, and In k vs. E-P). The present study demonstrated that the reductive activity of adsorbed Fe(II) species can be indicated by the E-P value of active Fe(II) species. Moreover, the electrochemical approach can be used as an effective tool to study the reductive activity of adsorbed Fe(II) species in subsurface environments.