Fenton-like Reaction Mechanism Research Articles

Multi-channel electron transfer induced by polyvanadate in metal-organic framework for boosted peroxymonosulfate activation

Catalytic peroxymonosulfate (PMS) activation processes don’t solely rely on electron transfer from dominant metal centers due to the complicated composition and interface environment of catalysts. Herein the synthesis of a cobalt based metal-organic framework containing polyvanadate [V4O12]4− cluster, Co2(V4O12)(bpy)2 (bpy = 4,4’-bipyridine), is presented. The catalyst demonstrates superior degradation activity toward various micropollutants, with higher highest occupied molecular orbital (HOMO), via nonradical attack. The X-ray absorption spectroscopy and density functional theory (DFT) calculations demonstrate that Co sites act as both PMS trapper and electron donor. In situ spectral characterizations and DFT calculations reveal that the terminal oxygen atoms in the [V4O12]4− electron sponge could interact with the terminal hydrogen atoms in PMS to form hydrogen bonds, promoting the generation of SO5* intermediate via both dynamic pull and direct electron transfer process. Further, Co2(V4O12)(bpy)2 exhibits long-term water purification ability, up to 40 h, towards actual wastewater discharged from an ofloxacin production factory. This work not only presents an efficient catalyst with an electron sponge for water environmental remediation via nonradical pathway, but also provides fundamental insights into the Fenton-like reaction mechanism.

Activation Mechanism of a Peroxymonosulfate-based Fenton-like System with Birnessite and Cu2+ Modified Birnessite.

The peroxymonosulfate (PMS) activation mechanism is closely related to the structure/configuration of the "active site" of the Fenton-like catalysts. In this paper, it is shown that Cu2+ chemically bonds the surface of birnessite at the Mn vacancy site to form triple-corner-sharing inner-sphere surface complexes (Cu-Bir), which regulates the PMS activation mechanism. Birnessite/PMS Fenton-like system degrades phenol via a non-radical mechanism, which involves high valent Mn(V)=O generated from the surface reaction of Mn(III) with adsorbed PMS. While Cu-Bir initiates an additional radical mechanism that involves reactive oxygen species of ⋅O2 - and 1 O2 , and the k value of 5Cu-Bir is 1.9 times higher than that of Bir. The Fenton-like reaction mechanism of the Cu-Bir/PMS system is thus proposed as a radical and non-radical cooccurrence mechanism, which involves a synergistic effect that the radical pathway accelerates the regeneration of Mn(III) for the non-radical pathway, and the non-radical pathway assists to produce 1 O2 for the radical pathway.

New Insight into a Fenton-like Reaction Mechanism over Sulfidated β-FeOOH: Key Role of Sulfidation in Efficient Iron(III) Reduction and Sulfate Radical Generation.

Sulfidation can greatly improve the efficiency of utilization of reducing equivalents for contaminant removal; however, whether this method benefits Fenton-like reactions or not and the possible mechanism are not well understood. In this study, we revealed that surface sulfidation can greatly promote the heterogeneous Fenton activity of β-FeOOH (Fe3S4@β-FeOOH) by 40 times, in which not only the •OH formation was enhanced but also SO4•- as a new oxidation species was generated. Moreover, their contribution to metronidazole (MTZ) degradation was 52.5 and 37.1%, respectively. In comparison, almost no HO2•/O2•- was detected in the Fe3S4@β-FeOOH/H2O2 system. These results were different from some previously reported Fenton counterparts. Based on the characterization and probe experiments, sulfur species, including S2-, S0, and Sn2-, as an electron donor and electron shuttle were responsible for efficient conversion of Fe(III) into Fe(II) other than via the Haber-Weiss mechanism, leading to excellent •OH generation via a Fenton-like mechanism. Most importantly, HSO5- can be generated from SO32- oxidized by •OH, and its scission into SO4•- was not dependent on the extra electric potential or Fe-O2-S(IV) intermediate. These findings provided new insight for utilizing sulfidation to improve the activity of iron-based Fenton catalysts.

Facile synthesis of copper-based bimetallic oxides for efficient removal of bisphenol a via Fenton-like degradation

• A series of copper-based bimetallic oxides are synthesized. • Cu-Al 2 O 3 exhibits excellent Fenton-like catalytic activity and stability. • Selective H 2 O 2 conversion to OH · radicals is obviously enhanced. • The possible Fenton-like reaction mechanism is discussed. In this study, three copper-based bimetallic oxides (Cu-M, M: Al, Fe, and Zn) were prepared via a facile hydrothermal method and used as the catalyst for the Fenton-like process to degrade bisphenol A (BPA). Compared to other bimetallic oxides, Cu-Al bimetallic oxide exhibited excellent catalytic activity. The results of XRD, TEM, SEM, and EDS illustrated that Cu-Al was synthesized as CuAlO 2 /Al 2 O 3 (named Cu-Al 2 O 3 ) with a sponge-like structure. Nitrogen sorption isotherm showed that the Cu-Al 2 O 3 was consists of mesoporous with a high specific surface area and a narrow pore size distribution. FTIR spectra indicated the formation of a Cu − ligand complex between BPA and the surface Cu of the catalyst. 90% of BPA could be degraded within 90 min when adding 0.75 g/L (Cu-7.8 wt%) Cu-Al 2 O 3 catalyst and 12.5 mM H 2 O 2 . Furthermore, it still kept over 70% removal efficiency after ten consecutive cycles, suggesting the superior stability of the catalyst. Based on the XPS and radical quenching experiments results, the Cu-Al 2 O 3 catalyst can not only improve the reduction of Cu 2+ to Cu + but also inhibit the oxidization of H 2 O 2 to generate O 2 - · radicals via the σ - C u l i g a n d c o m p l e x associated mechanism. Overall, this study indicates that Cu-Al 2 O 3 is a promising catalyst for the Fenton-like process. In addition, the strategy of the construction of the electron-rich catalytic site is an effective method to address the drawbacks of the classical Fenton process.

Nanoscale Fe0/Cu0 bimetallic catalysts for Fenton-like oxidation of the mixture of nuclear-grade cationic and anionic exchange resins

Spent resins generated from the nuclear industrial processes are still difficult to be treated and disposed. Fenton-like processes have great application potential in the treatment of spent resins, but the Fenton reaction mechanisms and resin degradation pathways remain challenging. In this study, nanoscale Fe0/Cu0 bimetallic catalysts were prepared and characterized for the Fenton-like degradation of the mixture of cationic and anionic resins. High catalytic property of Fe0/Cu0 bimetallic nanoparticles activated by H2O2 was evaluated, according to the effects of various nanoparticles, temperature, catalyst amount, H2O2 concentration and the mixing ratio of cationic and anionic resins. Combined the shape and color changes of mixed resins with the experimental and calculated characterization results, different degradation difficulty of cationic and anionic resins and their degradation mechanisms were studied. According to the density functional theory calculations of the optimized resin molecules with the Fe0/Cu0 catalyst, the mechanisms of Fenton-like reactions and the degradation of mixed resins through the synergistic effect of Fe and Cu species were proposed. The comprehensive Fenton-like reactions and degradation mechanisms provide new insights to advance the treatment of spent resins and organic polymers by Fenton-like processes.

Building block and rapid synthesis of catecholamines-inorganic nanoflowers with their peroxidase-mimicking and antimicrobial activities

Protein incorporated flower-shaped hybrid nanostructures have received highly considerable attention due to their greatly enhanced catalytic activities and stabilities. Up to date, proteins, enzymes (mostly considered as proteins), and amino acids (as the building blocks of peptides and proteins) have been used as organic components of the hybrid nanoflowers. Herein, we present a rational strategy to rapidly form catecholamines (dopamine, epinephrine and norepinephrine)-copper ion (Cu2+) incorporated nanoflowers (cNFs) mostly in 3 hours and show their peroxidase-mimic catalytic, dye degradation and antimicrobial activities through Fenton-like reaction mechanism. We systematically studied effects of experimental parameters including catecholamine concentrations, reaction time and reaction pH values, on formation of the cNFs. We also explained that norepinephrine nanoflower (neNF) with its porous structure, high surface area, polar surface property behaves as an efficient Fenton agent by exhibiting highly much catalytic activities compared to dopamine nanoflower (dNF) and epinephrine nanoflower (epNF). We claim that the NFs formed using nonprotein molecules can be used in designing new generation nanobiocatalytics, antimicrobial agents, nanobiosensors and pharmaceutical products.

Oxygen Deficient TiO2−x with Dual Reaction Sites for Activation of H2O2 to Degrade Organic Pollutants

The present study reports the development of a novel defective TiO2−x catalyst with oxygen vacancy (OV) which carries dual types of reaction sites for H2O2 activation. The performance of this catalyst on the degradation of organic pollutants was evaluated using organic dyes [such as methyl orange, methylene blue, and rhodamine B (RhB)] as model pollutants. The defects in TiO2−x exhibited a wide pH working window (pH 2–9) for RhB degradation which is wider than that of traditional Fenton systems. Furthermore, this catalyst retained its high catalytic activity even after five cycles. It was confirmed that the surface OV and Ti3+ of TiO2−x served as the active sites for H2O2 activation while the oxygen vacancy promoted adsorption of the organic pollutants, thus enhancing the Fenton-like catalytic performance. The results are applicable to Fenton catalysts via surface engineering and can stimulate new opportunities for the optimization of defect-type Fenton catalysts. This study, reports the defect of TiO2−x oxygen vacancy (OV) catalyst with oxygen vacancy (OV) which carries dual types of reaction sites for H2O2 activation. The performance of this catalyst on the degradation of organic pollutants was evaluated using organic dyes [such as methyl orange, methylene blue, and rhodamine B (RhB)] as model pollutants. The defects in TiO2−x exhibited a wide pH working window (pH 2–9) for RhB degradation which is wider than that of traditional Fenton systems. Figure shows the schematic of the reaction mechanism. First, H2O2 adsorbs on the TiO2−x surfaces; consequently, the OV and Ti3+ serve as the “Fenton-catalytic” center for H2O2 activation to produce ·OH radicals on the TiO2−x surface. Meanwhile, OV on TiO2−x surface is beneficial for the adsorbed organic pollutants. Because of the generated hydroxyl radical on the TiO2−x surface is very close to the adsorbed pollutant. As a result, the rapid reaction of in situ generated hydroxyl radical with the adsorbed organic pollutants on the TiO2−x surface giving rise to excellent Fenton-like catalytic performance. The proposed overall Fenton-like reaction mechanism on oxygen deficient TiO2−x catalyst.

High-flux efficient catalytic membranes incorporated with iron-based Fenton-like catalysts for degradation of organic pollutants

A novel composite catalytic membrane is developed by blending silicon oxide coated ferroferric oxide (Fe3O4@SiO2) nanoparticles in polyether sulfone (PES) membrane as Fenton-like catalysts via liquid-induced phase separation (LIPS) method. By introducing Fe3O4@SiO2 nanoparticles in PES membrane matrix, the surface hydrophilicity, porosity and mean pore diameter of as-prepared composite catalytic membranes are improved due to the hydrophilic nature of the SiO2 coating layer on the Fe3O4@SiO2 nanoparticles. The as-fabricated catalytic membrane can filter large particles above ~100 nm and shows a high water flux of 2084 kg m−2 h−1 under 0.1 MPa. Importantly, the composite catalytic membrane shows efficient catalytic performance and satisfactory stability in the degradation of organic pollutants based on the Fenton-like reaction mechanism. The proposed strategy for membrane fabrication and the experimental results in this study provide valuable guidance for developing high-flux catalytic membranes with efficient catalytic performances for treatment of industrial and municipal wastewater.

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles as efficient micro-electrolysis-promoted Fenton-like catalysts for metronidazole removal

Three-dimensional macroporous graphene-wrapped zero-valent copper nanoparticles (3D-GN@Cu0) were synthesized using a self-assembly process of liquid-phase reduction and characterized by field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, X-ray diffraction, Raman spectrum analysis, and X-ray photoelectron spectroscopy. The catalytic activity of 3D-GN@Cu0 was evaluated in view of the effects of various systems, the pH value, catalyst dosage, initial metronidazole concentration and temperature, and it showed a high efficiency for removing metronidazole with saturated dissolved oxygen (without adding extra H2O2) in a wide range of pH value from 3.2 to 9.8. Combined with the results of dissolved oxygen activation, determination of reactive oxidizing species, and X-ray photoelectron spectroscopy (XPS) analysis, the surface-bounded ·OHads formed by the reaction of the in situ generation H2O2 with 3D-GN@Cu0 was mainly responsible for the removal of metronidazole. The charge distribution and electrostatic potential (ESP) of 3D-GN@Cu0 further illustrated the distribution and transfer of electrons on the catalyst surface, which predicted a micro-electrolysis-promoted Fenton-like reaction mechanism.

Oxygen Vacancy Promoted Heterogeneous Fenton-like Degradation of Ofloxacin at pH 3.2-9.0 by Cu Substituted Magnetic Fe3O4@FeOOH Nanocomposite.

To develop an ultraefficient and reusable heterogeneous Fenton-like catalyst at a wide working pH range is a great challenge for its application in practical water treatment. We report an oxygen vacancy promoted heterogeneous Fenton-like reaction mechanism and an unprecedented ofloxacin (OFX) degradation efficiency of Cu doped Fe3O4@FeOOH magnetic nanocomposite. Without the aid of external energy, OFX was always completely removed within 30 min at pH 3.2-9.0. Compared with Fe3O4@FeOOH, the pseudo-first-order reaction constant was enhanced by 10 times due to Cu substitution (9.04/h vs 0.94/h). Based on the X-ray photoelectron spectroscopy (XPS), Raman analysis, and the investigation of H2O2 decomposition, •OH generation, pH effect on OFX removal and H2O2 utilization efficiency, the new formed oxygen vacancy from in situ Fe substitution by Cu rather than promoted Fe3+/Fe2+ cycle was responsible for the ultraefficiency of Cu doped Fe3O4@FeOOH at neutral and even alkaline pHs. Moreover, the catalyst had an excellent long-term stability and could be easily recovered by magnetic separation, which would not cause secondary pollution to treated water.

Kinetic Modelling of the catalytic oxidation of 2-(methylmercapto)-benzothiazole under mild conditions

2-(Methylmercapto)-benzothiazole oxidation was performed over Copper modified zeolites. The microporous materials were synthesized by the hydrothermal crystallization method and later modified with metal incorporation by wet impregnation. The solid catalysts were characterized by means of X-ray diffraction, surface area determinations, inductively coupled plasma emission spectrophotometry, temperature programmed reduction and Fourier transformed infrared spectroscopy. Reaction parameters (Copper content, nature of the solvent, hydrogen peroxide concentration, reaction time, catalyst mass and reaction temperature) were evaluated to reach the optimum reaction conditions. Kinetic modelling and kinetic parameter estimation based on experimental kinetic data were included. Cu(II) species were confirmed as the active sites of the catalysts, being Y zeolite the optimal support. Thus, Fenton-like reaction mechanism with reactive oxygen species as hydroxyl and hydroperoxyl radicals (HO, HO2) was confirmed. Reactions rates constants values and activation energy were determined by non-linear least-square parameter estimation. Also, homogeneous catalytic system was evaluated in order to discard diffusional limitations.

Hydrothermal Carbon-Mediated Fenton-Like Reaction Mechanism in the Degradation of Alachlor: Direct Electron Transfer from Hydrothermal Carbon to Fe(III).

As Fenton systems suffer from the undesirable Fe(III)/Fe(II) cycle, great efforts were made to realize the effective reduction of Fe(III) to Fe(II). The effects of hydrothermal carbon (HTC) on the Fe(III)/H2O2 Fenton-like reaction and the subsequent degradation of alachlor in water was systematically investigated, and the results indicated that HTC could enhance alachlor degradation in Fe(III)/H2O2 by promoting the Fe(III)/Fe(II) cycle via electron transfer from HTC to Fe(III) ions. The apparent alachlor degradation rate constant in the HTC-G/Fe(III)/H2O2 system (7.02 × 10-2 min-1) was about 3 times higher than that in the Fe(III)/H2O2 system (2.25 × 10-2 min-1). The electron spin resonance spectra analysis revealed that HTC consists of abundant carbon-centered persistent free radicals to act as the electron donor. Meanwhile, the hydroxyl groups on the surface of HTC also played an important role in the enhanced alachlor degradation because the decrease in the surface hydroxyl groups on HTC significantly decreased the degradation of alachlor. On the basis of these results, an Fe(III) complex with surface hydroxyl groups on HTC was proposed to favor the electron transfer from the hydroxyl groups to Fe(III), and then, the simultaneously produced Fe(II) could accelerate the catalytic decomposition of H2O2 to facilitate alachlor degradation. These findings shed new light on the possible roles of carbon materials in a natural aquatic environment and provide a new pathway for environmental pollutant control and remediation of organic contaminants by HTC.

Amino acids-incorporated nanoflowers with an intrinsic peroxidase-like activity.

Functional molecules synthesized by self-assembly between inorganic salts and amino acids have attracted much attention in recent years. A simple method is reported here for fabricating hybrid organic–inorganic nanoflowers using copper (II) ions as the inorganic component and natural amino acids as the organic component. The results indicate that the interactions between amino acid and copper ions cause the growth of the nanoflowers composed by C, N, Cu, P and O elements. The Cu ions and Cu(AA)n complexes containing Cu-O bond are present in the nanoflowers. The nanoflowers have flower-like porous structure dominated by the R groups of amino acids with high surface-to-volume ratios, which is beneficial for exerting its peroxidase-like activity depending on Fenton-like reaction mechanism with ABTS and Rhodamine B as the substrates. It is expected that the nanoflowers hold great promise as enzyme mimics for application in the field of biosensor, bioanalysis and biocatalysis.

Plausible Mechanisms of the Fenton-Like Reactions, M = Fe(II) and Co(II), in the Presence of RCO2– Substrates: Are OH• Radicals Formed in the Process?

DFT calculations concerning the plausible mechanism of Fenton-like reactions catalyzed by Fe(II) and Co(II) cations in the presence of carboxylate ligands suggest that hydroxyl radicals are not formed in these reactions. This conclusion suggests that the commonly accepted mechanisms of Fenton-like reactions induced oxidative stress and advanced oxidation processes have to be reconsidered.

New particle formation above a simulated salt lake in aerosol chamber experiments

Environmental context Deforestation in Western Australia beginning in the mid-19th century led to a considerable change of the land surface, and Western Australia is now suffering more often from droughts. Particle formation induced by salt lakes has been identified as a potential control factor for changed precipitation patterns. This study aims to determine key factors involved in the particle formation process by simulating a simplified salt lake in an aerosol chamber in the laboratory. Abstract In recent field experiments, particle formation has been observed above salt lakes in Western Australia and related to changes in regional precipitation patterns. This work investigates the particle formation potential above a simulated salt lake in aerosol chamber experiments under various conditions. The salt lake mixture comprised fixed concentrations of NaBr, NaCl and Na2SO4, and varying concentrations of FeSO4 and FeCl3. Further, an organic mixture of 1,8-cineol and limonene was added under dark and light conditions. Both the presence of organic compounds and of light were found to be essential for new particle formation in our experiments. There were clear indications for conversion of FeII to FeIII, which suggests a Fenton-like reaction mechanism in the system. Contrary to the idea that a Fenton-like reaction mechanism might intensify the oxidation of organic matter, thus facilitating secondary organic aerosol formation, the observed particle formation started later and with lower intensity under elevated FeII concentrations. The highest particle number concentrations were observed when excluding FeII from the experiments. Chemical analysis of the formed aerosol confirmed the important role of the Fenton-like reaction for particle formation in this study. Ultrahigh-resolution mass spectrometry and Raman spectroscopy provide analytical proof for the formation of organosulfates and halogenated organic compounds in the experiments presented. Even though halogens and organic precursors are abundant in these experimental simulations, halogen-induced organic aerosol formation exists but seems to play a minor overall role in particle formation.

Direct in vivo inflammatory cell-induced corrosion of CoCrMo alloy orthopedic implant surfaces.

Cobalt-chromium-molybdenum (CoCrMo) alloy, used for over five decades in orthopedic implants, may corrode and release wear debris into the body during use. These degradation products may stimulate immune and inflammatory responses in vivo. We report here on evidence of direct inflammatory cell-induced corrosion of human implanted and retrieved CoCrMo implant surfaces. Corrosion morphology on CoCrMo implant surfaces, in unique and characteristic patterns, and the presence of cellular remnants and biological materials intimately entwined with the corrosion indicates direct cellular attack under the cell membrane region of adhered and/or migrating inflammatory cells. Evidence supports a Fenton-like reaction mechanism driving corrosion in which reactive oxygen species are the major driver of corrosion. Using in vitro tests, large increases in corrosion susceptibility of CoCrMo were seen (40-100 fold) when immersed in phosphate buffered saline solutions modified with hydrogen peroxide and hydrochloric acid to represent the chemistry under inflammatory cells. This discovery raises significant new questions about the clinical consequences of such corrosion interactions, the role of patient inflammatory reactions, and the detailed mechanisms at play.

Fabrication, characterization of β-MnO2 microrod catalysts and their performance in rapid degradation of dyes of high concentration

Under hydrothermal conditions, a series of β-MnO2 microrod catalysts were fabricated using different manganese precursors (MnSO4, (CH3COO)2Mn·4H2O, MnCl2·4H2O, Mn(NO3)2·4H2O). The as-prepared β-MnO2 microrods were characterized by powder X-ray diffraction (XRD), N2 physical adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The characterization results showed that the morphologies and crystallinity of MnO2 were mainly determined by the hydrothermal time and temperature. Suitable hydrothermal time and temperature produced well defined β-MnO2 microrods with high crystallinity. The obtained β-MnO2 microrod catalysts were applied to degrade different dyes with high concentration (methylene blue (MB), methyl orange (MO), rhodamine B (RB) and acid orange II (AOII)) in the presence of H2O2. The catalytic mechanism was discussed and a Fenton-like reaction mechanism was proposed. High crystallinity and good morphology effectively promoted the catalytic performance of β-MnO2 microrods. The efficiencies of β-MnO2 microrods in degradation of different dyes are markedly different. The dye degradation rates followed the order of MB>AOII>RB>MO. Moreover, the β-MnO2 microrods exhibited high stability in recycling degradation, which suggests promising applications in practical dye pollutant treatment.

Wet air oxidation and ultrasound for the removal of linear alkylbenzene sulfonates from wastewater: the beneficial role of catalysis

The wet air oxidation (WAO) and ultrasound irradiation of sodium dodecylbenzene sulfonate in water was investigated. Heterogeneous catalysts such as a mixed copper-zinc oxide and noble metals, namely platinum, palladium and ruthenium, generally improved the efficiency of the respective uncatalysed process. The performance of sonochemical treatment, although less effective than WAO at high organic concentrations, may improve by a Fenton-like reaction mechanism on the addition of ferrous ions.

Fe (III) supported on resin as effective catalyst for the heterogeneous oxidation of phenol in aqueous solution

Fe III supported on resin as an effective catalyst for oxidation was prepared and applied for the degradation of aqueous phenol. Phenol was selected as a model pollutant and the catalytic oxidation was carried out in a batch reactor using hydrogen peroxide as the oxidant. The influent factors on oxidation, such as catalyst dosage, H 2O 2 concentration, pH, and phenol concentration were examined by considering both phenol conversion and chemical oxygen demand (COD) removal. The Fe III-resin catalyst possesses a high oxidation activity for phenol degradation in aqueous solution. The experimental results of this study show that almost 100% phenol conversion and over 80% COD removal can be achieved with the Fe III-resin catalyst catalytic oxidation system. A series of prepared resin were investigated for improving the oxidation efficiency. It was found that the reaction temperature and initial pH in solution significantly affected both of phenol conversion and COD removal efficiency. The activity of the catalyst significantly decreased at high pH, which was similar to the Fenton-like reaction mechanism. Results in this study indicate that the Fe III-resin catalytic oxidation process is an efficient method for the treatment of phenolic wastewater.