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

Abstract

Nano-dispersed Fe⁰ and Fe₃O₄ on reduced graphene oxide (Fe⁰/Fe₃O₄-RGO) was prepared and characterized. The prepared Fe⁰/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 Fe⁰/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 ˙OH rather than Fe^IV. High resolution TEM results revealed that nanoscale Fe⁰ 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 Fe²⁺ by nano-dispersed iron/graphene. RGO served as an effective mediator to facilitate the electron transfer from Fe⁰ to Fe³⁺ for the regeneration of Fe²⁺, which was critical in the catalytic process. This electron transfer-facilitated regeneration of active Fe²⁺ resulted in a reusable catalyst with high catalytic activity for the removal of phenol. The nano-dispersed Fe⁰/Fe₃O₄-RGO could be easily separated and recovered by magnetic field. The Fe⁰/Fe₃O₄-RGO catalyst was reusable and the removal efficiency of phenol after 5 catalytic cycles was as high as 93%. The Fe⁰/Fe₃O₄-RGO could be an effective Fenton-like catalyst for the treatment of waste water containing refractory phenol and phenol type pollutants.