Effect of chloride ions on the oxidation of aniline by Fentonʹs reagent

The objective of this study was to experimentally probe the mechanism of chloride ions specifically affecting aniline oxidation by Fentonʹs reagent. Batch experiments were carried out to investigate the effects of pH, Fe2+, H2O2 and chloride concentration on the oxidation reaction. Results show that the inhibition caused by chloride ions can be overcome by extending the reaction time if the concentration of chloride ions is low. At a high concentration of chloride ions, however, the oxidation of aniline was inhibited, and actually ceased due to the complexation of Fe–Cl. In this study, the chloride ion concentration was kept at 0.2 M in the experiments when studying the effect of ferrous ion concentration on the Fenton reaction. If the ratio of [Cl−]/[Fe2+] was ≤200, the inhibition effect was very significant. In other words, adding more ferrous ions rather than hydrogen peroxide can break the inhibition originating from the chloride ions at an initial stage of pH 3. The inhibition effect of chloride ions on the aniline reaction depended on the reaction pH; the extent of inhibition decreased with increasing the initial pH as long as the pH was less than 5. Consequently, the inhibition effect by chloride ions was primarily due to the complexation of iron species and chloride ions. The influence of chloride ions on aniline oxidation due to the competition of hydroxyl radicals was not significant.