Considerable Fenton and photo-Fenton reactivity of passivated zero-valent iron

Abstract

International audienceThe vulnerability of Zero-Valent Iron (ZVI) to passivation, which significantly decreases its surface reactivity, limits its use as a reducing agent in environmental remediation applications (e.g., permeable reactive barriers). Passivation of ZVI occurs rapidly in ambient environments due to the presence of oxygen and water, as well as during the reduction of contaminants (e.g. chlorinated and nitrated organic compounds) even in anoxic conditions. Passivated zero-valent iron (pZVI) particles are typically covered by an iron (hydr)oxide layer that entails a loss of the typical properties of this material, prevents the reductive activity to take place, and could made pZVI a waste to be disposed of. This work shows that pZVI has considerable Fenton (oxidizing) reactivity in the presence of H2O2 at acidic pH. The pZVI-Fenton process likely involves reaction between H2O2 and the pZVI surface or near-surface species, because the detected levels of leached Fe in the solution bulk were insufficient to account for the observed degradation processes. Still, leached Fe in the solution at pH 2 and 3 would be too concentrated for some possible applications (e.g. wastewater treatment, which would require an additional precipitation step to remove excess Fe). In such a case, operation at pH 4 would be preferred to maintain reasonable reactivity without measurable Fe leaching. The pZVI-Fenton process was inactive above pH 4, but reactivity could be extended up to pH 5 by UVA irradiation. Surprisingly, a pZVI sample that underwent an additional 78 day aging in aqueous solution exhibited a considerable ability to photochemically remove phenol despite a slower initial stage. These properties account for the possible use of a potential waste in decontamination reactions. © 2016 The Royal Society of Chemistry

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

“…Model of photo-Fenton mechanism using iron-based catalysts. Reproduced with permission from Reference [104]. …”

Coupling of Nanofiltration and Thermal Fenton Reaction for the Abatement of Carbamazepine in Wastewater

“…26 Possible solutions to tackle these drawbacks are as follows:The immobilization of the iron centers on solid supports 27,28 or the use of iron-based solid materials as sources of iron, such as magnetite, 29−31 hematite, 32,33 as well as zero-valent iron. 29,34,35 These solid materials can be recovered at the end of the process, for example, through their magnetic properties and reused;The implementation of Fenton-like reactions based on the production of reactive transients that are more selective toward the pollutant to be degraded, such as the sulfate radicals SO 4 •– . These transients are generated from S 2 O 8 2– instead of H 2 O 2 .…”

Degradation of ibuprofen and phenol with a Fenton-like process triggered by zero-valent iron (ZVI-Fenton)

“…In contrast, metallic Fe (or zero-valent iron, ZVI) is Fenton-active and, although easily oxidized, it gets covered by a Fe (II) layer that takes part in the Fenton process as well (Litter and Slodowicz 2017;Rezaei and Vione 2018). Indeed, the Fenton reactivity of ZVI undergoes limited influence by weathering, corrosion and surface passivation (Minella et al 2016). ZVI is better known as a reducing agent that can be used in the reductive (not oxidative) treatment of pollutants occurring in, e.g., groundwater, such as for instance chlorinated compounds, nitroaromatics, CrO 4 2− , As(III), As(V), NO 3 − , U(VI) (Fu et al 2014).…”

“…However, in the presence of O 2 or especially H 2 O 2 , ZVI is able to take part to the Fenton reaction (Fu et al 2014;Ling et al 2018). In heterogeneous Fenton processes the reaction between Fe(II) and H 2 O 2 may either take place in solution, with Fe 2+ leached from the solid surface, or involve surface Fe(II) and dissolved H 2 O 2 (Minella et al 2016;Nidheesh 2015). In the case of ZVI, Fe(II) leaching is too limited to account for the observed reaction and the solid surface plays a major role (Minella et al 2016;Ling et al 2018).…”