An insight in magnetic field enhanced zero-valent iron/H2O2 Fenton-like systems: Critical role and evolution of the pristine iron oxides layer

Abstract

This study demonstrated the synergistic degradation of 4-chlorophenol (4-CP) achieved in a magnetic field (MF) enhanced zero-valent iron (ZVI)/H2O2 Fenton-like (FL) system and revealed an interesting correlative dependence relationship between MF and the pristine iron oxides layer (FexOy) on ZVI particles. First, a comparative investigation between the FL and MF-FL systems was conducted under different experimental conditions. The MF-FL system could suppress the duration of initial lag degradation phase one order of magnitude in addition of the significant enhancement in overall 4-CP degradation. Monitoring of intermediates/products indicated that MF would just accelerate the Fenton reactions to produce hydroxyl radical more rapidly. Evolutions of simultaneously released dissolved iron species suggested that MF would not only improve mass-transfer of the initial heterogeneous reactions, but also modify the pristine ZVI surface. Characterizations of the specific prepared ZVI samples evidenced that MF would induce a special evolution mechanism of the ZVI particles surface depending on the existence of FexOy layer. It comprised of an initial rapid point dissolution of FexOy and a following pitting corrosion of the exposed Fe0 reactive sites, finally leading to appearance of a particular rugged surface topography with numerous adjacent Fe0 pits and FexOy tubercles.

Effect of pH on Zero Valent Iron Performance in Heterogeneous Fenton and Fenton-Like Processes: A Review

“…They reported that acidic conditions were more favorable to contaminant removal, but the MF/ZVI/EDTA system could effectively decompose diclofenac in the pH range of 4 to 7 [96]. Different studies have shown that application of magnetic field together with EDTA could accelerate pitting corrosion on the disclosed fresh Fe 0 sites, in neutral or even alkaline systems [96,97]. The mechanism of contaminant removal by ZVI/EDTA at acidic pH involves the formation of complexes between EDTA and Fe ions (Equation (8)), together with the reaction of the Fe II EDTA complex with soluble oxygen (Equation (9)) to yield O 2 ●− .…”

“…Additionally, reductive adsorption of contaminants could directly occur on the Fe 0 surface. Some studies have reported that in MF/ZVI systems, ● OH radicals could be generated at anodic sites upon oxidation of water even at neutral and alkaline pH values [97,99,100].…”

“…The pH decrease could further increase the ZVI corrosion, thereby amplifying the influence of the magnetic field [100]. Several studies have in fact demonstrated that the main synergistic role of the magnetic field in the system operates through increased surface dissolution and corrosion of ZVI, which occurs together with a decrease in solution pH [97,99,101]. Due to enhanced dissolution, the MF-ZVI-Fenton system can still be operational at neutral and alkaline pH values.…”

“…( a ): Slow Fe x O y dissolution in the ZVI-Fenton system; ( b ): rapid point dissolution of Fe x O y in the presence of magnetic field followed by ( c ): pitting corrosion of the exposed Fe 0 sites and ( d ): uniform corrosion of the ZVI surface. Reproduced with permission from Reference [97].…”

Fe Oxides Loaded on Carbon Cloth by Hydrothermal Process as an Effective and Reusable Heterogenous Fenton Catalyst

“…In this work, the rate constant k 1 decreased from 0.0516 min −1 to 0.0266 min −1 when the pH value was increased from 1.54 to 3.01. In addition, the reaction rate decreased clearly at pH 3.48. considering the reaction rate and acidification of the solution, the pH value for most of the iron-based heterogeneous Fenton-like reactions were set around 2.0-3.0 [29,31], therefore, the pH value was set at 2.50 for further study in this work.…”