Polyphosphate-enhanced production of reactive oxidants by nanoparticulate zero-valent iron and ferrous ion in the presence of oxygen: Yield and nature of oxidants

Activation of Hydrogen Peroxide by a Titanium Oxide-Supported Iron Catalyst: Evidence for Surface Fe(IV) and Its Selectivity

“…AAP, phenol, BA, and CBZ were used as the target contaminant to identify the nature of the oxidants produced from H 2 O 2 activation. These compounds selectively react with • OH (BA and CBZ) or with both • OH and Fe­(IV) (AAP and phenol). ,− In a separate set of experiments, phenylmethyl sulfoxide (PMSO, 100 mM) was used as the target compound, since PMSO is known to selectively react with Fe­(IV) , and also because the oxidation product of this reaction, phenylmethyl sulfodioxide (PMSO 2 ), can be readily quantified. In some experiments, the reaction solution also contained either 10 mM Cl – , 10 mM HCO 3 – , or 5.9 mg C/L SRHA to investigate the effect of these solutes on the rate of contaminant oxidation.…”

“… − These pathways are thought to be predominant over the one-electron transfer pathway through which • OH is generated (reactions and ). ,,, Studies in the past two decades have suggested that the oxidant yield can be increased by immobilizing iron (Fe) on a support with low redox reactivity, such as silica, aluminum oxide, titanium oxide, or zeolites. − Using this strategy, several iron-containing catalysts with enhanced H 2 O 2 activation ability have been synthesized and used for contaminant degradation. − Despite these efforts, progress toward developing more effective catalysts for H 2 O 2 activation has been hampered by the lack of a mechanistic understanding of how the support influences the reactivity of Fe. It has been hypothesized that the dispersion of Fe on the support created isolated reactive sites, thereby facilitating the production of • OH. ,, It has also been hypothesized that the support can affect the coordination environment of Fe, analogous to the way in which ligands, such as oxalate, nitrilotriacetate (NTA), ethylenediaminetetraacetate (EDTA), and polyphosphate, influence the coordination environment of dissolved iron ions and enhance the oxidant yield in the homogeneous Fenton reaction (i.e., the reaction between dissolved Fe and H 2 O 2 ). ,,− Additionally, the adsorption of H 2 O 2 by the support has also been invoked to explain the change in the H 2 O 2 decomposition rate and oxidant yield . This hypothesis was based on the theoretical calculations and spectroscopic data that show the chemisorption of H 2 O 2 on the surface of amorphous silica and titanium oxide. − To date, however, the above hypotheses remain largely speculative.…”

Abiotic Transformation of Nitrobenzene by Zero Valent Iron under Aerobic Conditions: Relative Contributions of Reduction and Oxidation in the Presence of Ethylene Diamine Tetraacetic Acid

“…Subsequently, the produced H 2 O 2 and Fe 2+ would react to give •OH. In addition, EDTA could inhibit the formation of oxide and precipitate on the surface of ZVI by complexing with Fe­(III), and the complexation also inhibited the coprecipitation of Fe­(II) and Fe­(III), resulting in the enhanced utilization rate of Fe­(II). ,, It is worth noting that although some studies have reported that the possible ROS generated by the ZVI/O 2 system under neutral conditions is Fe­(IV) rather than ·OH, there is still a lack of recognized detection methods for Fe­(IV). Therefore, in this study, we attributed the oxidative degradation of contaminants in the system to ·OH.…”

“…However, the yields of ROS in the ZVI/O 2 system are low, which limits the application of this process in full-scale remediation technologies. , In order to improve the yield of ROS in ZVI/O 2 systems, various ligands that complex with Fe­(II) have been used. , …”

“…14,16 In order to improve the yield of ROS in ZVI/O 2 systems, various ligands that complex with Fe(II) have been used. 17,18 The combination of contaminant reduction and oxidation pathways described above could result in these processes operating in parallel, or in series, which could create synergistic benefits to treatments using ZVI/O 2 . To explore this possibility, we choose nitrobenzene (NB) as a model contaminant and probe compound (Figure 1), and its reaction rate constant with •OH is 2.2 × 10 8 M −1 S −1 .…”