pH Dependence of Hydroxyl Radical, Ferryl, and/or Ferric Peroxo Species Generation in the Heterogeneous Fenton Process

Abstract

The heterogeneous Fenton process in the presence of Fe-containing minerals is ubiquitous in nature and widely deployed in wastewater treatment. While there have been extensive relevant studies, the dependence on pH of the nature and extent of oxidant generation and key reaction pathways remain unclear. Herein, the adsorption and decomposition of formate and H2O2 were quantified in the presence of ferrihydrite within the pH range of 3.0–6.0, and experiments with methyl phenyl sulfoxide were conducted to distinguish between HO• and weaker oxidant(s) which react via oxygen atom transfer including ferryl ion ([FeIVO]2+) and/or ferric hydroperoxo intermediates (FeIII(O2H)). Both HO• and [FeIVO]2+/FeIII(O2H) are concurrently produced on the surface over the acidic to near-neutral pH range. Despite the simultaneous formation of both oxidants, HO• is the major oxidant responsible for substrate oxidation in the interfacial boundary layer with [FeIVO]2+/FeIII(O2H) exhibiting limited exposure to substrates. With an increase of pH, the yield of both oxidants is inhibited by the decreasing availability of surface sites due to ferrihydrite particle aggregation. Increasing pH also favors the nonradical decay of H2O2 as evident from the consistent oxidant production rate relative to the surface area (SSA) despite an accelerated H2O2 decay rate relative to SSA with pH increase.

Mn(II) Acceleration of the Picolinic Acid-Assisted Fenton Reaction: New Insight into the Role of Manganese in Homogeneous Fenton AOPs

“…Besides HO • and iron peroxo species, reactive ferryl species (Fe IV O or Fe V O) can also be generated in Fenton reactions, depending on ligands and pH. − Ferryl characteristically oxidizes sulfoxides to sulfones. However, no phenyl methyl sulfone (PMSO 2 ) was detected after adding phenyl methyl sulfoxide (PMSO) to Fe­(III)/PICA/H 2 O 2 with or without Mn­(II) at pH 3.0–6.0 (Figure S5).…”

Comparative Experimental and Computational Studies of Hydroxyl and Sulfate Radical-Mediated Degradation of Simple and Complex Organic Substrates

“…Experiments were conducted in magnetically stirred glass bottles covered with aluminum foils to shield the reaction solutions from light. The performance of the PS/Fe­(II) process in comparison with that of the H 2 O 2 /Fe­(II) process was first evaluated using radiolabeled formate as the target compound, with only the oxidation of formate quantified through the dissolution method developed previously − (details provided in Section S2 of the Supporting Information). When examining the oxidation of the NF concentrate, simultaneous quantification of the adsorptive removal and mineralization of TOC was conducted by comparison of the filtered and unfiltered samples using a method developed previously (details provided in Section S2 of the Supporting Information).…”

“…When examining the oxidation of the NF concentrate, simultaneous quantification of the adsorptive removal and mineralization of TOC was conducted by comparison of the filtered and unfiltered samples using a method developed previously (details provided in Section S2 of the Supporting Information). − Briefly, one set of samples was filtered prior to TOC measurement, with the changes in the organic content considered to be due to both mineralization and adsorption of any organic compounds present. A second set of samples was dissolved prior to filtration to release the adsorbed organics to solution, with any decrease in the TOC measured considered to be due to the mineralization of organics only.…”

“…The Fenton process (H 2 O 2 /Fe­(II)), which involves the catalytic decomposition of H 2 O 2 by Fe­(II) to generate HO • (eq ), is one of the most popular traditional AOPs for the oxidation of refractory organics in wastewater treatment due to its low cost and simple operation. ,, As such, the H 2 O 2 /Fe­(II) process was chosen as the benchmark with which the PS/Fe­(II) process (eq ) is compared in this study. With a view to attaining both mechanistic insight and performance comparison, formate was used as a target compound in view of its straightforward oxidation to CO 2 , − while the concentrate from the nanofiltration treatment of domestic wastewater was used as a representative complex organic substrate . The performance of the PS/Fe­(II) and H 2 O 2 /Fe­(II) processes was compared on the basis of the oxidant yield, reagent consumption, transformation of target compounds, and the potential occurrence of undesirable side reactions.…”

Advance Oxidation Process (AOP) of Bisphenol A Using a Novel Surface-Functionalised Polyacrylonitrile (PAN) Fibre Catalyst

“…Based on the theoretical oxidation condition for the Fenton process, the best pH range for the homogeneous Fenton process is from 2.5 to 4 [32] Wadley, whereas for the heterogenous Fenton process it could be higher at near-neutral [33,34].…”