Alternating Magnetic Field Accelerates the Transformation between Fe(II) and Fe(III) of Fe@NiFe2O4 in a Fenton-Like Process

Promoting the Fe(II)/Fe(III) cycle efficiency is of wide interest for the broader applications of the Fenton process in water treatment sector. In this study, the alternating magnetic field (AMF) was employed to accelerate the reduction from Fe(III) to Fe(II). To achieve this purpose, a composite of nano-zero valence iron and NiFe2O4 was fabricated (denoted as Fe@NiFe2O4). Under the optimal reaction conditions, bisphenol A (BPA) was removed completely within 15 min by the Fe@NiFe2O4/H2O2 system in the presence of AMF, while only ∼60% was removed in the absence of AMF. The faster removal rate in the presence of AMF was ascribed to the elevated temperature caused by the inductive heating of Fe@NiFe2O4 (∼41°C according to the simulation). The simulator of the Fenton process was considered to be the leaked Fe(II) from the Fe part of the composite, as an equal concentration of Fe(II) (∼5.7 mg/L) resulted into a similar removal kinetic. However, the system with Fe@NiFe2O4 as the catalyst consumed less H2O2 in this process, indicating its different activation pathway from the conventional Fenton process. Electrochemical analysis confirmed that the AMF can generate the internal electric field within the composite particle. This field may facilitate the reduction from Fe(III) to Fe(II), which further benefitted the Fenton reactions.