Enhanced Formation of Oxidants from Bimetallic Nickel-Iron Nanoparticles in the Presence of Oxygen

Nanoparticulate zero-valent iron (nZVI) rapidly reacts with oxygen to produce strong oxidants capable of transforming organic contaminants in water. However, the low yield of oxidants with respect to the iron added normally limits the application of this system. Bimetallic nickel-iron nanoparticles (nNi-Fe; i.e., Ni-Fe alloy and Ni-coated Fe nanoparticles) exhibited enhanced yields of oxidants compared to nZVI. nNi-Fe (Ni-Fe alloy nanoparticles with [Ni]/[Fe] = 0.28 and Ni-coated Fe nanoparticles with [Ni]/[Fe] = 0.035) produced approximately 40% and 85% higher yields of formaldehyde from the oxidation of methanol relative to nZVI at pH 4 and 7, respectively. Ni-coated Fe nanoparticles showed a higher efficiency for oxidant production relative to Ni-Fe alloy nanoparticles based on Ni content. Addition of Ni did not increase the oxidation of 2-propanol or benzoic acid, indicating that Ni addition did not enhance hydroxyl radical formation. The enhancement in oxidant yield was observed over a pH range of 4-9. The enhanced production of oxidant by nNi-Fe appears to be attributable to two factors. First, the nNi-Fe surface is less reactive toward hydrogen peroxide (H2O2) than the nZVI surface, which favors the reaction of H2O2 with dissolved Fe(II) (the Fenton reaction). Second, the nNi-Fe surface promotes oxidant production from the oxidation of ferrous ion by oxygen at neutral pH values.close453

A novel homogeneous Fenton-like system with Fe(III)-phosphotungstate for oxidation of organic compounds at neutral pH values

Ferric ion (Fe[III]) catalyzes the decomposition of hydrogen peroxide (H(2)O(2)) into strong oxidants such as hydroxyl radical ((center dot)OH) and ferryl ion (Fe[IV]) through the redox cycling of the iron Couple (Fe[II]/Fe[III]). The use of these reactions for the catalytic oxidation of organic compounds is usually limited to the acidic pH region due to the low solubility of Fe(III) and the low efficiency of oxidant production at neutral pH values. The addition of phosphotungstate (PW(12)O(40)(3-)). a polyoxometalate, extends the working pH range of the Fe(III)/H(2)O(2) system up to pH 8.5. PW(12)O(40)(3-) forms a soluble complex with iron that converts H(2)O(2) into oxidants. The coordination of Fe(II) by PW(12)O(40)(3-) also alters the mechanism of the reaction of Fe(II) with H(2)O(2) at neutral pH, resulting in formation of an oxidant capable of oxidizing aromatic compounds. The base-catalyzed hydrolysis of PW(12)O(40)(3-) gradually results in inactivation of the catalyst. In the absence of Fe(III), PW(12)O(40)(3-) was completely hydrolyzed after 1 day at pH 7.5, whereas the Fe(III)-PW(12)O(40)(3-) complex was active for at least 4 days under the same conditions.close242

Polyoxometalate-enhanced oxidation of organic compounds by nanoparticulate zero-valent iron and ferrous ion in the presence of oxygen

The oxidation of N-nitrosodimethylamine (NDMA) precursors during water treatment was investigated using ozone and chlorine dioxide (CIO2). Second-order rate constants for the reactions of model NDMA precursors (dimethylamine (DMA) and 7 tertiary amines) with ozone (kapp at pH 7 = 2.4 ?? 10-1 to 2.3 ?? 109 M-1 s-1), CIO2 (kapp at pH 7 = 6.7 ?? 10 -3 to 3.0 ?? 107 M-1 s-1), and hydroxyl radical (̇OH) (kapp at pH 7 = 6.2 ?? 107 to 1.4 ?? 1010 M-1 s-1) were determined, which showed that the selected NDMA precursors, with the exception of dimethylformamide (DMFA) can be completely transformed via their direct reaction with ozone. During ozonation, DMFA may be partially transformed through oxidation by the secondary oxidant ̇OH. CIO2 was also shown to effectively transform most of the precursors, with the exceptions of DMA and DMFA. In the second part of the study, the NDMA formation potentials (NDMA-FP) in synthetic and natural waters were measured with and without pre-oxidation with ozone and CIO2. A significant reduction in the NDMA-FPs was observed after complete transformation of the model NDMA precursors. Ozonation generally led to more effective reduction of the NDMA-FP than CIO2. For most of the precursors, the formation of DMA could account for the NDMA-FPs remaining after complete transformation of the model NDMA precursors. In contrast, dimethylethanolamine and dimethyldithio-carbamate yielded other NDMA precursors (not DMA) as their oxidation products. Pre-oxidation by ozone and CIO2 of several natural waters showed behavior similar to that of the oxidation of model NDMA precursors with a reduction of the NDMA-FP by 32-94% for various natural water sources.close514

Response to Comment on "Polyoxometalate-Enhanced Oxidation of Organic Compounds by Nanoparticulate Zero-Valent Iron and Ferrous Ion in the Presence of Oxygen"

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Comment on "Oxidation of Sulfoxides and Arsenic(III) in Corrosion of Nanoscale Zero Valent Iron by Oxygen: Evidence against Ferryl Ions (Fe(IV)) as Active Intermediates in Fenton Reaction"

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pH-Dependent reactivity of oxidants formed by iron and copper-catalyzed decomposition of hydrogen peroxide

The decomposition of hydrogen peroxide catalyzed by iron and copper leads to the generation of reactive oxidants capable of oxidizing various organic compounds. However, the specific nature of the reactive oxidants is still unclear, with evidence suggesting the production of hydroxyl radical or high-valent metal species. To identify the reactive species in the Fenton system, the oxidation of a series of different compounds (phenol, benzoic acid, methanol, Reactive Black 5 and arsenite) was studied for iron- and copper-catalyzed reactions at varying pH values. At lower pH values, more reactive oxidants appear to be formed in both iron and copper-catalyzed systems. The aromatic compounds, phenol and benzoic acid, were not oxidized under neutral or alkaline pH conditions, whereas methanol, Reactive Black 5, and arsenite were oxidized to a different degree, depending on the catalytic system. The oxidants responsible for the oxidation of compounds at neutral and alkaline pH values are likely to be high-valent metal complexes of iron and copper (i.e., ferryl and cupryl ions).close11

Inactivation of MS2 coliphage by Fenton's reagent

Fenton's reagent (i.e., Fe[II]/H(2)O(2)) is known to generate strong oxidants capable of oxidizing a broad spectrum of organic compounds in aqueous solution. This study demonstrates the successful inactivation of MS2 coliphage (MS2) by the oxidants produced from Fenton's reagent. The inactivation process of MS2 by Fenton's reagent was found to proceed in two distinct stages. The first stage inactivation, which took place rapidly within 1 min reaction time, was mainly achieved by the reaction of Fe(II) with H(2)O(2) (i.e., the Fenton reaction). The second stage, which occurred by the catalytic reactions of Fe(III) with H(2)O(2), exhibited much slower inactivation than the first stage. The rate of MS2 inactivation increased as pH decreased from 8.0 to 6.0. The addition of oxalate and humic acids significantly inhibited the MS2 inactivation, whereas 1,10-phenanthroline and bipyridine resulted in a gradual and steady inactivation of MS2. These observations on the effects of pH and iron-chelating agents indicate that oxidants formed on the surface or inside MS2 are responsible for the inactivation.close121

Inactivation of Escherichia coli by Nanoparticulate Zerovalent Iron and Ferrous Ion▿ †

The mechanism of Escherichia coli inactivation by nanoparticulate zerovalent iron (nZVI) and Fe(II) was investigated using reactive oxygen species (ROS) quenchers and probes, an oxidative stress assay, and microscopic observations. Disruption of cell membrane integrity and respiratory activity was observed under deaerated conditions [more disruption by nZVI than Fe(II)], and OH or Fe(IV) appears to play a role

Bactericidal effect of zero-valent iron nanoparticles on Escherichia coli

Zero-valent iron nanoparticles (nano-Fe0) in aqueous solution rapidly inactivated Escherichia coli. A strong bactericidal effect of nano-Fe0 was found under deaerated conditions, with a linear correlation between log inactivation and nano-Fe0 dose (0.82 log inactivation/mg/L nano-Fe0??h). The inactivation of E. coli under air saturation required much higher nano-Fe0 doses due to the corrosion and surface oxidation of nano-Fe0 by dissolved oxygen. Significant physical disruption of the cell membranes was observed in E. coli exposed to nano-Fe0, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron. The reaction of Fe(II) with intracellular oxygen or hydrogen peroxide also may have induced oxidative stress by producing reactive oxygen species. The bactericidal effect of nano-Fe 0 was a unique property of nano-Fe0, which was not observed in other types of iron-based compounds.close14213

Inactivation of MS2 Coliphage by Ferrous Ion and Zero-Valent Iron Nanoparticles

This study demonstrates the inactivation of MS2 coliphage (MS2) by nano particulate zerovalent iron (nZVI) and ferrous ion (Fe[II]) in aqueous solution. For nZVI, the inactivation efficiency of MS2 under air-saturated conditions was greater than that observed under deaerated conditions, indicating that reactions associated with the oxidation of nZVI were mainly responsible for the MS2 inactivation. Under air-saturated conditions, the inactivation efficiency increased with decreasing pH for both nZVI and Fe(II), associated with the pH-dependent stability of Fe(II). Although the Fe(II) released from nZVI appeared to contribute significantly to the virucidal activity of nZVI, several findings suggest that the nZVI surfaces interacted directly with the MS2 phages, leading to their inactivation. First, the addition of 1,10-phenanthroline (a strong Fe(II)-chelating agent) failed to completely block the inactivation of MS2 by nZVI Second, under deaerated conditions, a linear dose log inactivation curve was still observed for nZVI. Finally, ELISA analysis indicated that nZVI caused more capsid damage than Fe(II).close2