Unveiling the mechanism of electron transfer facilitated regeneration of active Fe2+ by nano-dispersed iron/graphene catalyst for phenol removal

Nano-dispersed Fe and Fe3O4 on reduced graphene oxide (Fe /Fe3O4-RGO) was prepared and characterized. The prepared Fe/Fe3O4-RGO was used as a magnetically separable Fenton-like catalyst and showed superior catalytic activity compared to Fe3O4-RGO and Fe3O4 as well as other Fenton-like catalysts for the removal of phenol. The Fe/Fe3O4-RGO achieved 100% removal efficiency for phenol within 30 min. Free radical inhibition experiments and Electron Paramagnetic Resonance (EPR) showed that the main reactive species was cOH rather than Fe. High resolution TEM results revealed that nanoscale Fe and Fe3O4 were uniformly dispersed and distributed on RGO without agglomeration, furnishing more active sites. The catalyst featured a unique mechanism of electron transfer-facilitated regeneration of active Fe by nano-dispersed iron/graphene. RGO served as an effective mediator to facilitate the electron transfer from Fe to ^Fe for the regeneration of ^Fe, which was critical in the catalytic process. This electron transfer-facilitated regeneration of active Fe resulted in a reusable catalyst with high catalytic activity for the removal of phenol. The nano-dispersed Fe/Fe3O4-RGO could be easily separated and recovered by magnetic field. The Fe/Fe3O4-RGO catalyst was reusable and the removal efficiency of phenol after 5 catalytic cycles was as high as 93%. The Fe/Fe3O4-RGO could be an effective Fenton-like catalyst for the treatment of waste water containing refractory phenol and phenol type pollutants.