Degradation of 4-chlorophenol by mixed Fe⁰/Fe₃O₄ nanoparticles: from the perspective of mechanisms

Fe⁰ nanoparticles have been widely studied for pollution abatement in recent years; however, regarding the mechanism for pollutant degradation, studies have mainly focused on the reductive dechlorination by Fe⁰, and the dynamic process has not been clarified completely. As reported, some organics could be degraded during the oxidation of Fe⁰ by O₂, and hydrogen peroxide was supposed to be produced. In this study, Fe₃O₄, an oxidation product of Fe⁰, was used to treat the pollutant combining with Fe⁰ nanoparticles, and 4-chlorophenol (4-CP) was used as the model pollutant. The results showed that the addition of Fe₃O₄ nanoparticles hindered the removal of 4-CP by Fe⁰ nanoparticles under anoxic conditions. However, the dechlorination efficiency was improved in the initial 6 h. Under aerobic conditions, the reused Fe₃O₄ nanoparticles would improve the removal and dechlorination of 4-CP. Especially, the dechlorination efficiency was obviously increased. It is proposed that the removal of 4-CP was due to the effects of both nanosized Fe⁰ and Fe₃O₄ – reducing action of Fe⁰ and catalytic oxidation action of Fe₃O₄. The reducing action of Fe⁰ was the major factor under anoxic conditions. And the catalytic oxidation action of Fe₃O₄ became an important reason under aerobic conditions.