Amplification effects of magnetic field on hydroxylamine-promoted ZVI/H2O2 near-neutral Fenton like system

This study has demonstrated an interesting amplification effect of magnetic field（MF） on the hydroxylamine（HA）-promoted zero valent iron（ZVI）/H2 O₂ Fenton-like system.Sulfamethoxazole（SMX） could be efficiently degraded at near neutral pH.Conditional parameters affecting the SMX degradation in the ZVI/H₂ O₂/HA/MF system,e.g.,pH and the dosages of ZVI,HA and H₂ O₂,were investigated.Unlike the acid-favorable ZVI/H₂ O₂ and ...     

Study on catalytic mechanisms of Fe3O4-rGOx in three typical advanced oxidation processes for tetracycline hydrochloride degradation

This study explored the catalytic mechanism and performance impacted by the materials ratio of Fe₃O₄-GO_x composites in three typical advanced oxidation processes (AOPs) of O₃, peroxodisulfate (PDS) and photo-Fenton processes for tetracycline hydrochloride (TCH) degradation. The ratio of GO in the Fe₃O₄-GO_x composites exhibited different trends of degradation capacity in each AOPs based on different mechanisms. Fe₃O₄-rGO_20wt% exhibited the optimum catalytic performance which enhanced the ozone decomposition efficiency from 33.48% (ozone alone) to 51.83% with the major reactive oxygen species (ROS) of O₂^??. In PDS and photo-Fenton processes, Fe₃O₄-rGO_5wt% had the highest catalytic performance in PDS and H₂O₂ decomposition for SO₄^??, and ^?OH generation, respectively. Compared with using PDS alone, PDS decomposition rate and TCH degradation rate could be increased by 5.97 and 1.73 times under Fe₃O₄-rGO_5wt% catalysis. In the photo-Fenton system, Fe₃O₄-rGO_5wt% with the best catalyst performance in H₂O₂ decomposition, and TCH degradation rate increased by 2.02 times compared with blank group. Meantime, the catalytic mechanisms in those systems of that the ROS produced by conversion between Fe²⁺/Fe³⁺ were also analyzed.     

Effect of various oxidants in a photocatalysis/filtration system for the treatment of contaminants

This study was conducted to investigate the effect of a photocatalysis/oxidant system for the treatment of humic acid and hazardous heavy metals in aqueous solutions. Hydrogen peroxide, ozone, and potassium peroxodisulfate were tested as oxidants. The effect of oxidant concentration was conducted with a pH of 7, a UV intensity of 64 W, and a TiO₂ dosage of 0.3 g L⁻¹. The oxidant addition in the UV/TiO₂ system enhanced the degradation efficiency of humic acid and hazardous heavy metals compared to no addition of an oxidant. The addition of oxidants over the amounts of H₂O₂ 50 mg L⁻¹, O₃ 20 g m⁻³, and K₂S₂O₈ 50 mg L⁻¹ inhibits the system efficiency. The negative effect of higher oxidant concentrations likely results from OH radical quenching caused by the excess oxidant. Therefore, the optimal dosages of oxidants such as a hydrogen peroxide, ozone, and potassium peroxodisulfate were found to be 50 mg L⁻¹, 20 g m⁻³, and 50 mg L⁻¹, respectively. The degradation efficiency of UV/TiO₂/oxidant systems for the removal of humic acid and hazardous heavy metals was much greater in the UV/TiO₂/H₂O₂ system using H₂O₂ as an oxidant.     

The carbon nanotubes-based materials and their applications for organic pollutant removal:A critical review

The carbon nanotubes(CNTs) as the emerging materials for organic pollutant removal have gradually become a burgeoning research field.Herein,a mini-review of CNTs-based materials curre ntly studies for organic pollutant elimination is presented.This review summarizes the preparation methods of CNTsbased materials.CNTs-based materials can be used as adsorbents to remove organic pollutants in wastewater.The adsorption mechanisms mainly include surface diffusio n,pore diffusion and adsorption reaction.Most importantly,an in-depth overview of CNTs-based materials currently available in advanced oxidation processes(AOPs) applications for wastewater treatment is proposed.CNTs-based materials can catalyze different oxidants(e.g.,hydrogen peroxide(H_2 O_2),persulfates(PMS/PDS),ozone(O_3) and ferrate/permanganate(Fe(Ⅵ)/Mn(Ⅶ)) to generate more reactive oxygen species(ROS) for organic pollutant elimination.Moreover,the possible reaction mechanisms of removing organic pollutants by CNTs-based materials are summarized systematically and discussed in detail.Finally,application potential and future research directions of CNTs-based materials in the environmental remediation field are proposed.     

Current trends in the use of zero-valent iron (Fe0) for degradation of pharmaceuticals present in different water matrices

Zero-valent iron (Fe⁰) has recently been proposed as a potential candidate for the degradation of pharmaceuticals, because Fe⁰ can release dissolved iron species, activate molecular oxygen, and react with oxidant species. Additionally, due to its small particle size and large surface area, this catalyst can provide better degradation results, compared to traditional processes. This work focuses on the elimination of pharmaceuticals present in different water matrices, considering the potential harm that these substances can cause in the environment. The mechanisms of pharmaceutical removal using Fe⁰ particles include reduction, adsorption, precipitation, and oxidation processes. Most studies have focused on oxidation processes in the presence of Fe⁰ and radicals derived from oxidants such as hydrogen peroxide (H₂O₂), ozone (O₃), peroxysulfate (SO₅²⁻), peroxodisulfate (S₂O₈²⁻), and oxygen (O₂). Most of the results have shown that high percentages of pharmaceuticals can be removed, degraded, and mineralized. The mechanisms of oxidation and the parameters that influence the degradation of pharmaceuticals, as well as the possible degradation pathways, are discussed here. This review provides information on trends of different processes that use Fe⁰, considering aspects such as particle size, type of matrix, the pharmaceuticals studied, and the results obtained that can improve understanding of new advances in the field of advanced oxidation processes (AOPs) for the degradation and elimination of pharmaceuticals.     

Kinetics and mechanism of oxidation of excited state Tris-(2,2′-bipyridyl)-ruthenium (II) complex by peroxomonosulfate,peroxodisulfate, and peroxodiphosphate

Excitation of Ru(bipy)₃²⁺ ion by visible radiation of wavelength λ = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy)₃³⁺. The kinetics of this photochemical oxidation of Ru(bipy)₃²⁺ by each peroxide was followed spectrophotometrically and found to obey a total second-order, first-order each in [Ru(bipy)₃²⁺] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy)₃²⁺ occurred but only when at 1.0 M [H⁺] and > 10^?2M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy)₃³⁺ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy)₃²⁺] on the visible light induced oxidation of Ru(bipy)₃²⁺ by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.     

The Direct Partial Oxidation of Methane to Dimethyl Ether over Pt/Y2O3 Catalysts Using an NO/O2 Shuttle

Using a mixture of NO + O₂ as the oxidant enabled the direct selective oxidation of methane to dimethyl ether (DME) over Pt/Y₂O₃. The reaction was carried out in a fixed bed reactor at 0.1 MPa over a temperature range of 275–375 °C. During the activity tests, the only carbon‐containing products were DME and CO₂. The DME productivity (μmol g_cat^?1 h^?1) was comparable to oxygenate productivities reported in the literature for strong oxidants (N₂O, H₂O₂, O₃). The NO + O₂ mixture formed NO₂, which acted as the oxygen atom carrier for the ultimate oxidant O₂. During the methane partial oxidation reaction, NO and NO₂ were not reduced to N₂. In situ FTIR showed the formation of surface nitrate species, which are considered to be key intermediate species for the selective oxidation.     

Formation and decay of N,N, N′, N′-tetraethyl-p-phenylenediamine radical cation in aqueous solution. A kinetic study by stopped-flow technique

A kinetic study has been carried out on the oxidation of N, N, N′, N′,-tetraethyl-p-phenylenediamine (TEPD) by metal ion like Ce⁴⁺, oxoanions viz., MnO₄^? and Cr₂O₇^2?; peroxides such as peroxomonosulphate (PMS), peroxodisulphate (PDS), and H₂O₂; and halogens namely Cl₂, Br₂, and I₂. The fast kinetics of the formation and decay of the radical cation TEPD^˙+ have been analyzed at 565 nm by the stopped-flow technique under pseudo-first-order conditions. From the kinetic data, it has been inferred that the reactions were found to be of first-order with respect to [TEPD] and [oxidant] but over all it has been of second-order. The observed second-order rate constants in both the formation and decay of TEPD^˙+ has been correlated with the oxidation potentials of the various oxidants employed in this study. The effect of pH on the oxidation has been investigated in the formation and decay of TEPD^˙+ as well as reduction studies have also been carried out using dithionite which has been found to regenerate the TEPD from the TEPD^˙+ and the corresponding rate constant has also been determined. Besides these, this article also explains how the TEPD, which forms TEPD^˙+ acts as a better electron relay than TMPD(N, N, N′, N′-tetramethyl-p-phenylenediamine) which forms TMPD^˙+, even though both of them undergo one-electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have good correlation. © 1995 John Wiley & Sons, Inc.     

Simple and efficient treatment of high-strength industrial waste water using commercial zero-valent iron

The zero-valent iron (ZVI)/H₂O₂ Fenton system can be considered as an effective solution for the removal of many of the organic pollutants present in the waste waters generated by the drug manufacturing industry. The hydrogen peroxide concentration and dosage rate were studied in order to improve the efficiency of the oxidant in the TOC reduction and, thereby enhance the overall catalytic performance of the ZVI/H₂O₂ Fenton system. TOC reductions of up to 80 % and BOD₅/COD ratios of up to 0.6 were achieved in the waste water as received without dilution (TOC_O approximately 5 g L^?1) using hydrogen peroxide dose-staggering. This showed that the ZVI/H₂O₂ process led not only to a decrease in TOC removal but also to an increase in the biodegradability of the by-products formed. The hydrogen peroxide was consumed more efficiently and very low concentrations of iron dissolved (7 mg L^?1) were obtained in the final effluents. The final values of COD, BOD₅, the suspended solids’ content and the conductivity of the treated waste water met the limits of the Spanish legal industrial discharge, Decree 57/2005 (Ministry of Environment, Local Government and Planning, Community of Madrid, 2005). In addition, the composite thus formed, consisting of zero-valent iron and iron oxide-oxyhydroxides, can be readily removed from the treated effluent, avoiding any post-treatment step.     

Oxidation of captopril by hydrogen peroxide and peroxomonosulfate ion catalyzed by a ruthenium(III) complex: kinetic and mechanistic studies

The complex [Ru^III(edta)(H₂O)]^? (edta^4? = ethylenediaminetetraacetate) catalyzes the oxidation of captopril (CapSH) using primary oxidants, hydrogen peroxide (H₂O₂) and peroxomonosulfate (\( {\text{HSO}}_{5}^{ - } \)). The kinetics of the oxidation reaction were studied as a function of both oxidant (H₂O₂, \( {\text{HSO}}_{5}^{ - } \)) and substrate (CapSH) concentrations using stopped-flow and rapid scan stopped-flow techniques. Spectral and kinetic data are suggestive of a pathway involving rapid formation of the intermediate complex [Ru^III(edta)(CapS)]^2? followed by direct attack of the oxidant (H₂O₂ or \( {\text{HSO}}_{5}^{ - } \)) at the S atom of the coordinated CapS^?. ESI–MS and HPLC analysis of the reaction products showed that captopril disulfide (CapSSCap) is the major oxidation product. A probable mechanism in agreement with the spectral and kinetic data is presented.     

Revisiting the contribution of FeIVO2+ in Fe(II)/peroxydisulfate system

Recent studies have proposed that the high-valent iron species (such as Fe^IVO²⁺) rather than sulfate radical (SO₄^??) and hydroxyl radical (^?OH) are the main reactive oxidant species (ROS) in Fe(II)/peroxydisulfate (PDS) system with the methyl phenyl sulfoxide (PMSO) as the Fe^IVO²⁺ probe. However, many operational factors may interfere with the accuracy of this method, so the contribution of Fe^IVO²⁺ calculated by this method is controversial. In this study, the possible effect of Fe(II) concentration, pollutant type, reducing agent, or coexisted anions on Fe^IVO²⁺ production and its corresponding contribution to the removal of target pollutants in the Fe(II)/PDS system were investigated in detail, and the intrinsic mechanisms involved were also explored. This study shows that ROS generation is a complex process in the Fe(II)/PDS system, and multiple combinatorial approaches are urgently required to deeply explore the contribution of ROS to the elimination of target contaminants.     

Photo-Fenton and photo-Fenton-like processes for the degradation of methyl orange in aqueous medium: Influence of oxidation states of iron

Degradation of methyl orange (MO) was carried out by the photo-Fenton process (Fe²⁺/H₂O₂/UV) and photo-Fenton-like processes (Fe³⁺/H₂O₂/UV, Fe²⁺/S₂O₈²⁻/UV, and Fe³⁺/S₂O₈²⁻/UV) at the acidic pH of 3 using hydrogen peroxide and ammonium persulfate (APS) as oxidants. Oxidation state of iron had a significant influence on the efficiency of photo-Fenton/photo-Fenton-like processes. It was found that a process with a source of Fe³⁺ ions as the catalyst showed higher efficiency compared to a process with the Fe²⁺ ion as the catalyst. H₂O₂ served as a better oxidant for both oxidation states of iron compared to APS. The lower efficiency of APS is attributed to the generation of excess protons which scavenges the hydroxyl radicals necessary for degradation. Further, the sulfate ions produced from S₂O₈²⁻ form a complex with Fe²⁺/Fe³⁺ ions thereby reducing the concentration of free iron ions in the solution. This process can also reduce the concentration of hydroxyl radicals in the solution. Efficiency of the various MO degradation processes follows the order: Fe³⁺/H₂O₂/UV, Fe³⁺/APS/UV, Fe²⁺/H₂O₂/UV, Fe²⁺/APS/UV.     

Analysis of oxidation process of cholecystokinin octapeptide with reactive oxygen species by high‐performance liquid chromatography and subsequent electrospray ionization mass spectrometry

The C‐terminal octapeptide of cholecystokinin (CCK8) includes some easily oxidizable amino acids. The oxidation of CCK8 by reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) and hydroxyl radicals (OH^?) was investigated using reversed‐phase high performance liquid chromatography (RP‐HPLC) and subsequent electrospray ionization mass spectrometry. The mechanism of oxidation of CCK8 in the H₂O₂ system differed from that of CCK8 in the Fenton system, in which OH^? are produced. In the H₂O₂ system, ²⁸Met and ³¹Met were oxidized to methionine sulfoxide, and no further oxidation or degradation/hydrolysis occurred. On the other hand, in the Fenton system, ²⁸Met and ³¹Met residues were oxidized to methionine sulfone via the formation of methionine sulfoxide. In addition, the oxidized product was observed at the Trp residue but not at the Tyr residue, and small peptide fragments from CCK8 were observed in the Fenton system. From these results, it was concluded that ²⁸Met and ³¹Met residues of CCK8 are susceptible to oxidation by ROS. Copyright © 2009 John Wiley & Sons, Ltd.     

Controllable Release and High‐Efficiency Collection of Hydrogen Peroxide: Application on the Quantitative Investigation of Biomolecule Oxidation Induced by Reactive Oxygen Species

Hydrogen peroxide and hydroxyl radical, both important members of the reactive oxygen species (ROS) family, can cause serious oxidative damages in biological systems. In order to proclaim and prevent oxidation stress, researches on the biomolecule oxidation induced by H₂O₂ or OH^. are in crucial need. However, due to the high reactivity of ROS, traditional methods are difficult to achieve the in situ quantitative investigations on those reactions involving ROS. In this work, using scanning electrochemical microscopy technique (SECM) in a tip generation‐substrate collection mode (TG‐SC), the controllable release and the high‐efficiency collection of electrogenerated H₂O₂ were achieved. Compared to ex situ fluorescence method, SECM improved the collection efficiency approximately two times larger. Based on it, SECM combined with surface plasmon resonance (SPR) was employed to in situ monitor the protein oxidation (taking Cu₁₂⁺? MT as a model) induced by H₂O₂. OH^., which was generated from the interaction between H₂O₂ and Cu₁₂⁺? MT, can attack the peptide chain and induced the unrepairable protein oxidation damage. The whole process was quantitatively characterized by SPR, and the linear relationship between SPR dip shift and the amounts of released H₂O₂ was successfully built. Our work proves that the combined SECM‐SPR technique can realize the in situ quantitative determinations of the biomolecule oxidation induced by ROS, which affords an avenue for further elucidation on the mechanisms of oxidation stress in organisms.     

Different non-radical oxidation processes of persulfate and peroxymonosulfate activation by nitrogen-doped mesoporous carbon

Activated persulfate oxidation is an emerging advanced oxidation process for organic pollutant degradation. Own to different molecular structures and oxidation potentials, persulfate (PDS) and peroxymonosulfate (PMS) may show different degradation performances due to various catalytic mechanisms even by the same catalysts. In this study, the nitrogen-doped mesoporous carbon (N-OMC) was applied to activate PDS and PMS for degrading a model organic pollutant phenol to reveal their activation mechanisms. Results show that both PDS and PMS could be efficiently activated by N-OMC. The degradation of phenol fitted well with pseudo-first-order kinetics, whose kinetic constants increased with the increase of pH, PDS/PMS dosage, and N-OMC dosage. Based on quenching experiments and electron spin resonance spin-trapping technique, the N-OMC was found to activate PDS and PMS via non-radical process of electron transfer and singlet oxygen formation, respectively, instead of the commonly observed radical process. This work will be useful to understand the activation processes of PDS and PMS, and benefit for the development of catalysts for pollutant degradation.     

Effective E. coli inactivation of core-shell ZnO@ZIF-8 photocatalysis under visible light synergize with peroxymonosulfate: Efficiency and mechanism

How to utilize inexhaustible solar light as a means of disinfection technology for its cheap and green remains a challenge. In this work, core-shell ZnO@ZIF-8 was synthesized and used for bacterial inactivation synergizing with peroxymonosulfate（PMS） under visible light irradiation. It took 50 min to achieve thorough sterilization for 7.5-log Escherichia coli（E. coli） cells in vis/PMS/ZnO@ZIF-8 system, compared with that 4.5-log reduction completed in vis/PMS/Zn O system under the same condition...     

A Review on the Degradation of Pollutants by Fenton-Like Systems Based on Zero-Valent Iron and Persulfate: Effects of Reduction Potentials,pH, and Anions Occurring in Waste Waters

Among the advanced oxidation processes (AOPs), the Fenton reaction has attracted much attention in recent years for the treatment of water and wastewater. This review provides insight into a particular variant of the process, where soluble Fe(II) salts are replaced by zero-valent iron (ZVI), and hydrogen peroxide (H₂O₂) is replaced by persulfate (S₂O₈²⁻). Heterogeneous Fenton with ZVI has the advantage of minimizing a major problem found with homogeneous Fenton. Indeed, the precipitation of Fe(III) at pH > 4 interferes with the recycling of Fe species and inhibits oxidation in homogeneous Fenton; in contrast, suspended ZVI as iron source is less sensitive to the increase of pH. Moreover, persulfate favors the production of sulfate radicals (SO₄^•−) that are more selective towards pollutant degradation, compared to the hydroxyl radicals (^•OH) produced in classic, H₂O₂-based Fenton. Higher selectivity means that degradation of SO₄^•−-reactive contaminants is less affected by interfering agents typically found in wastewater; however, the ability of SO₄^•− to oxidize H₂O/OH⁻ to ^•OH makes it difficult to obtain conditions where SO₄^•− is the only reactive species. Research results have shown that ZVI-Fenton with persulfate works best at acidic pH, but it is often possible to get reasonable degradation at pH values that are not too far from neutrality. Moreover, inorganic ions that are very common in water and wastewater (Cl⁻, HCO₃⁻, CO₃²⁻, NO₃⁻, NO₂⁻) can sometimes inhibit degradation by scavenging SO₄^•− and/or ^•OH, but in other cases they even enhance the process. Therefore, ZVI-Fenton with persulfate might perform unexpectedly well in some saline waters, although the possible formation of harmful by-products upon oxidation of the anions cannot be ruled out.     

Sustainable activation of peroxymonosulfate by the Mo(IV) in MoS2 for the remediation of aromatic organic pollutants

Although MoS₂ has been proved to be a very ideal cocatalyst in advanced oxidation process (AOPs), the activation process of peroxymonosulfate (PMS) is still inseparable from metal ions which inevitably brings the risk of secondary pollution and it is not conducive to large-scale industrial application. In this study, the commercial MoS₂, as a durable and efficient catalyst, was used for directly activating PMS to degrade aromatic organic pollutant. The commercial MoS₂/PMS catalytic system demonstrated excellent removal efficiency of phenol and the total organic carbon (TOC) residual rate reach to 25%. The degradation rate was significantly reduced if the used MoS₂ was directly carried out the next cycle experiment without any post-treatment. Interestingly, the commercial MoS₂ after post-treated with H₂O₂ can exhibit good stability and recyclability for cyclic degradation of phenol. Furthermore, the mechanism for the activation of PMS had been investigated by density functional theory (DFT) calculation. The renewable Mo⁴⁺ exposed on the surface of MoS₂ was deduced as the primary active site, which realized the direct activation of PMS and avoided secondary pollution. Taking into account the reaction cost and efficient activity, the development of commercial MoS₂ catalytic system is expected to be applied in industrial wastewater.     

Olefin cis‐Dihydroxylation and Aliphatic C?H Bond Oxygenation by a Dioxygen‐Derived Electrophilic Iron–Oxygen Oxidant

Many iron‐containing enzymes involve metal–oxygen oxidants to carry out O₂‐dependent transformation reactions. However, the selective oxidation of C H and CC bonds by biomimetic complexes using O₂ remains a major challenge in bioinspired catalysis. The reactivity of iron–oxygen oxidants generated from an Fe^II–benzilate complex of a facial N₃ ligand were thus investigated. The complex reacted with O₂ to form a nucleophilic oxidant, whereas an electrophilic oxidant, intercepted by external substrates, was generated in the presence of a Lewis acid. Based on the mechanistic studies, a nucleophilic Fe^II–hydroperoxo species is proposed to form from the benzilate complex, which undergoes heterolytic O O bond cleavage in the presence of a Lewis acid to generate an Fe^IV–oxo–hydroxo oxidant. The electrophilic iron–oxygen oxidant selectively oxidizes sulfides to sulfoxides, alkenes to cis‐diols, and it hydroxylates the C H bonds of alkanes, including that of cyclohexane.     

Olefin cis‐Dihydroxylation and Aliphatic CH Bond Oxygenation by a Dioxygen‐Derived Electrophilic Iron–Oxygen Oxidant

Many iron‐containing enzymes involve metal–oxygen oxidants to carry out O₂‐dependent transformation reactions. However, the selective oxidation of C? H and C?C bonds by biomimetic complexes using O₂ remains a major challenge in bioinspired catalysis. The reactivity of iron–oxygen oxidants generated from an Fe^II–benzilate complex of a facial N₃ ligand were thus investigated. The complex reacted with O₂ to form a nucleophilic oxidant, whereas an electrophilic oxidant, intercepted by external substrates, was generated in the presence of a Lewis acid. Based on the mechanistic studies, a nucleophilic Fe^II–hydroperoxo species is proposed to form from the benzilate complex, which undergoes heterolytic O? O bond cleavage in the presence of a Lewis acid to generate an Fe^IV–oxo–hydroxo oxidant. The electrophilic iron–oxygen oxidant selectively oxidizes sulfides to sulfoxides, alkenes to cis‐diols, and it hydroxylates the C? H bonds of alkanes, including that of cyclohexane.