Electrochemical evidences for promoted interfacial reactions: the role of Fe(II) adsorbed onto gamma-Al2O3 and TiO2 in reductive transformation of 2-nitrophenol.

This study was aimed at elucidating the role of adsorbed Fe(II) on minerals in the reductive transformation of 2-nitrophenol (2-NP) by using electrochemical methods. The studies of Fe(ll) adsorption and 2-NP reduction kinetics showed that the identity of minerals such as gamma-Al2O3 and TiO and the solution pH were crucial factors to determine the Fe(ll) adsorption behavior and to influence the rate constant (k) of 2-NP reduction. Furthermore, two electrochemical methods, cyclic voltammetry (CV) and electrochemical impedance spectrometry (EIS), were applied to characterize the Fe(II) reactivity with both the mineral-coated and mineral-free electrodes. The electrochemical evidence confirmed that the peak oxidation potential (Ep) of complex Fe(II) can be significantly affected by the solution pH;the enhanced reductive transformation of 2-NP can be related to the reduced Ep of surface-complex Fe(II) and the reduced charge transfer resistance (R(CT)) of the Fe(III)/Fe(II) couple. All these relationships were studied quantitatively. At pH 6.7, the measured Ep and R(CT) decreased in the order TiO2/GC < gamma-Al2O3/ GC < GC (Ep, 0.140 < 0.190 < 0.242 V; R(CT), 0.30 < 0.41 < 0.78 komega), while the 2-NP reduction on different minerals were in the order TiO2 > gamma-Al2O3 > nonmineral (k x 10-2, 7.91 > 0.64 > 0.077 min(-l)).