Oxidation of Benzene by Persulfate in the Presence of Fe(III)- and Mn(IV)-Containing Oxides: Stoichiometric Efficiency and Transformation Products

Abstract

Sulfate radical (SO4(•-)) is a strong, short-lived oxidant that is produced when persulfate (S2O8(2-)) reacts with transition metal oxides during in situ chemical oxidation (ISCO) of contaminated groundwater. Although engineers are aware of the ability of transition metal oxides to activate persulfate, the operation of ISCO remediation systems is hampered by an inadequate understanding of the factors that control SO4(•-) production and the overall efficiency of the process. To address these shortcomings, we assessed the stoichiometric efficiency and products of transition metal-catalyzed persulfate oxidation of benzene with pure iron- and manganese-containing minerals, clays, and aquifer solids. For most metal-containing solids, the stoichiometric efficiency, as determined by the loss of benzene relative to the loss of persulfate, approached the theoretical maximum. Rates of production of SO4(•-) or hydroxyl radical (HO(•)) generated from radical chain reactions were affected by the concentration of benzene, with rates of S2O8(2-) decomposition increasing as the benzene concentration increased. Under conditions selected to minimize the loss of initial transformation products through reaction with radicals, the production of phenol only accounted for 30%-60% of the benzene lost in the presence of O2. The remaining products included a ring-cleavage product that appeared to contain an α,β-unsaturated aldehyde functional group. In the absence of O2, the concentration of the ring-cleavage product increased relative to phenol. The formation of the ring-cleavage product warrants further studies of its toxicity and persistence in the subsurface.

Activation performance and mechanism of a novel heterogeneous persulfate catalyst: metal–organic framework MIL-53(Fe) with FeII/FeIII mixed-valence coordinatively unsaturated iron center

“…At the same time, Fe III CUS in the framework was also able to initiate the decomposition of PS to generate oxidative persulfate radical (S 2 O 8 − ·) as Fe III CUS was reduced to Fe II CUS (Eq. (2)), which could be supported by several previous studies [52, 53, 54]. Under this circumstance, Fe II CUS together with Fe III CUS embedded in the framework transferred to each other continuously.…”

“…Simultaneously, SO 4 − · could be directly converted into OH· via hydrolysis reaction with water (at all pHs) (Eq. (3)) [54], this could explain why OH· existed in this system (solution pH was acidic). Besides, SO 4 − · and OH· could react with persulfate anion to generate additional S 2 O 8 − · (Eq.…”

Carbon and Hydrogen Isotope Fractionation of Benzene, Toluene, and o‐Xylene during Chemical Oxidation by Persulfate

“…Such absence or minor enrichment has also been observed for biological degradation of benzene (Gibson et al ; Wilkins et al ; Fischer et al ). It has been suggested that in the initial step of benzene oxidation by persulfate an electron is abstracted from benzene to produce a short‐lived cation radical (Norman et al ; Huie and Neta ; Aravindakumar et al ; Anipsitakis et al ; Liu et al ). In contrast to benzene, the hydrogen presents a greater tendency to get enriched relative to carbon during chemical oxidation of toluene and o ‐xylene by persulfate.…”

Sulfate Radical Technologies as Tertiary Treatment for the Removal of Emerging Contaminants from Wastewater

“…Between these methods, the addition of transition metals is recognized to be a viable way to enact the homogenous activation of (persulfate/peroxymonosulfate) PS/PMS [17].…”