Degradation of 4-chlorophenol by mixed Fe(0)/Fe3O4 nanoparticles: from the perspective of mechanisms.

Fe(0) 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 Fe(0), and the dynamic process has not been clarified completely. As reported, some organics could be degraded during the oxidation of Fe(0) by O2, and hydrogen peroxide was supposed to be produced. In this study, Fe3O4, an oxidation product of Fe(0), was used to treat the pollutant combining with Fe(0) 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 Fe(0) 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 Fe(0) and Fe3O4 - reducing action of Fe(0) and catalytic oxidation action of Fe3O4. The reducing action of Fe(0) was the major factor under anoxic conditions. And the catalytic oxidation action of Fe3O4 became an important reason under aerobic conditions.