H2O2-based Oxidation Research Articles

Degradation of diethyl phthalate by photolysis of hydrogen peroxide electrogenerated using a Printex L6 carbon modified with Benzophenone cathode in an improved tangential flow cell

In this work, a gas diffusion electrode (GDE) made of Printex L6 carbon modified with 2.0% w/w of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (PL6C/BTDA 2%) was employed as cathode in a new 3D printed electrochemical cell with tangential flow. With this configuration, the performance of the technology was evaluated for hydrogen peroxide (H2O2) electrogeneration and remediation of aqueous wastes contaminated with diethyl phthalate (DEP) using different H2O2-based advanced oxidation processes (AOPs). The electrogeneration study was carried out varying the current density applied to the system, and it was found that 50 mA cm-2 was the best performing value, resulting in remarkable Faradaic efficiencies of nearly 100%. This led to the production of higher amounts of H2O2 (442.5 mg L-1) in 90 minutes at an acceptable energy consumption (8.5 kWh kg-1) compared to values reported in the literature. Based on these findings, H2O2-based AOPs were employed to investigate the removal of DEP in cathodic compartment, including mediated electrochemical degradation with electrogenerated H2O2 (e-H2O2) and the integration of this technology with ultraviolet-C (UVC) photolysis (e-H2O2/UVC). The integrated e-H2O2/UVC obtained the best performance compared to single photolysis and e-H2O2, leading to the total elimination of DEP (90 μmol L-1) within only 30 min of treatment, reaching the highest kinetic rate constant (0.3 min-1). Fifteen by-products, generated through oxidation processes studied, were successfully identified by LC-MS/MS, enabling the proposal of the degradation mechanism of DEP.

Photocatalytic coproduction of hydrogen peroxide and Aldehydic/Keto acid on carbon nitride

Photocatalytic H2O2 production is emerging as an alternative technology to contribute H2O2-based advanced oxidation applications. However, the present reaction systems rarely consider the selective oxidation of sacrificial agent along with oxygen reduction reaction. Herein, we design a reaction system by using hydroxycarboxylic acids as additives to boost photocatalytic H2O2 production. More importantly, hydroxycarboxylic acids could simultaneously be dehydrogenated into aldehydic/keto acids with high selectivity. Lactic acid as one of the typical hydroxycarboxylic acids reveals the feasibility of this hypothesis, delivering 6.56 mM/h of H2O2 generation along with > 70 % pyruvic acid selectivity. The universality of this reaction system is demonstrated by using other hydroxycarboxylic acids. This works sheds new light on coupling H2O2 generation with value-added chemicals production by mild photocatalytic approach.

Quenching residual H2O2 from UV/H2O2 with granular activated carbon: A significant impact of bicarbonate

UV/H2O2 has been used as an advanced oxidation process to remove organic micropollutants from drinking water. It is essential to quench residual H2O2 to prevent increased chlorine demand during chlorination/chloramination and within distribution systems. Granular activated carbon (GAC) filter can quench the residual oxidant and eliminate some of the dissolved organic matter. However, knowledge on the kinetics and governing factors of GAC quenching of residual H2O2 from UV/H2O2 and the mechanism underlying the enhancement of the process by HCO3− is limited. Therefore, this study aimed to analyse the kinetics and influential factors, particularly the significant impact of bicarbonate (HCO3−). H2O2 decomposition by GAC followed first-order kinetics, and the rate constants normalised by the GAC dosage (kn) were steady (1.6 × 10−3 L g−1 min−1) with variations in the GAC dosage and initial H2O2 concentration. Alkaline conditions favour H2O2 quenching. The content of basic groups exhibited a stronger correlation with the efficiency of GAC in quenching H₂O₂ than did the acidic groups， with their specific kn values being 8.9 and 2.4 min−1 M−1, respectively. The presence of chloride, sulfate, nitrate, and dissolved organic matter inhibited H2O2 quenching, while HCO3− promoted it. The interfacial hydroxyl radical (HO•) zones were visualised on the GAC surface, and HCO3− addition increased the HO• concentration. HCO3− increased the concentration of persistent free radicals (PFRs) on the GAC surface, which mainly contributed to HO• generation. A significant enhancement of HCO3− on H2O2 quenching by GAC was also verified in real water. This study revealed the synergistic mechanism of HCO3− and GAC on H2O2 quenching and presents the potential applications of residual H2O2 in the H2O2-based oxidation processes.

Heterogeneous H2O2-based selective oxidations over zirconium tungstate α-ZrW2O8.

Catalytic properties of a crystalline zirconium tungstate, ZrW2O8, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrW2O8 were prepared by hydrothermal synthesis and characterised by N2 adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl3) revealed the presence of Brønsted acidic and basic sites on the surface of ZrW2O8. It was demonstrated that ZrW2O8 is able to activate H2O2 under mild conditions and accomplish the epoxidation of CC bonds in alkenes and unsaturated ketones, oxidation of thioethers to sulfoxides and sulfones, along with the oxidation of alcoholic functions to produce ketones and aldehydes. The oxidation of tetramethylethylene and α-terpinene over ZrW2O8 revealed the formation of peroxidation products, 2,3-dimethyl-3-butene-2-hydroperoxide and endoperoxide ascaridole, respectively, indicating the involvement of singlet oxygen in the oxidation process. The ZrW2O8 catalyst preserves its structure and morphology under the turnover conditions and does not suffer from metal leaching. It can be easily recovered, regenerated by calcination, and reused without the loss of activity and selectivity.

What factors determine activity of UiO-66 in H2O2-based oxidation of thioethers? The role of basic sites

Zr-based metal–organic frameworks (Zr-MOFs) have attracted significant attention as selective oxidation catalysts due to their stability in aqueous and oxidative media and high activity in H2O2 activation. Oxidation of thioethers with aqueous H2O2 over Zr-MOFs reveals extremely high selectivity toward the formation of sulfones even at low conversions. Herein, the main factors determining activity of Zr-MOF in the thioether oxidation have been investigated using zirconium terephthalate UiO-66 as a model catalyst and methyl phenyl sulfide (MPS) as a model substrate. Samples of UiO-66 differing in the particle size, number of defects, and composition have been synthesized. The particle size was evaluated based on high resolution transmission electron microscopy images. Thermogravimetric analysis (TGA), proton nuclear magnetic resonance spectroscopy (1H NMR), and inductively coupled plasma atomic emission spectroscopy (ICP-OES) were employed for quantification of defects and determination of the composition of the UiO-66 samples. The number of basic sites was determined by liquid-phase adsorption of isobutyric acid. It was demonstrated that this characteristic depends on both the number of defects and specific composition of UiO-66 and can be affected by dehydration/hydration procedures. The number of basic sites turned out close to the number of terminal Zr–OH2/OH groups in the Zr-MOF defects determined by combinations of 1H NMR/TGA and 1H NMR/ICP-OES, suggesting that the basic sites are represented by Zr-OH groups at open Zr sites. Kinetic studies implicated that catalytic activity of UiO–66 in MPS oxidation is proportional to the number of basic sites provided that the particle size of the Zr-MOF does not exceed 10–20 nm. Acid additives suppress both the thioether oxidation and H2O2 dismutation, pointing to the key role of basic Zr–OH groups in these two catalytic reactions.

A single-atom Fe-N-C catalyst with superior Fenton-like reaction performance prepared facilely using microalgae: Key roles of oxygen and interactions between Fe-Nx and Fe/Fe compounds

A single-atom Fe-N-C catalysts (Fe-N-C) was successfully prepared through a facile synthesis route using microalgae to drive hydrogen peroxide (H2O2)-based Fenton-like reactions. The detailed characterization analyses confirmed the simultaneous presence of Fe/Fe compounds and Fe-Nx coordination sites in the optimal catalyst (Fe-N @ MBC) obtained through the pyrolysis of FeCl3·6 H2O and Chlorella vulgaris. Surprisingly, when applied in H2O2-based advanced oxidation processes (AOPs), Fe-N @ MBC demonstrated excellent proficiency for both H2O2 and O2 activation, with the contribution of the original dissolved oxygen for sulfamethoxazole removal reaching up to 47.59%. The experiment and density functional theory (DFT) calculation results indicated that the Fe/Fe compounds significantly boosted the activity of Fe-Nx by lowering the energy barrier of the reactive oxygen species formation and promoting the electron transfer between Fe-Nx and the oxidants (H2O2 and O2). These findings provide new insights into the facile synthesis, rational design, and catalytic mechanisms of Fe-N-C used in H2O2-based AOPs.

H2O2-Based Selective Oxidations Catalyzed by Supported Polyoxometalates: Recent Advances

Polyoxometalates (POMs) are transition metal oxygen anionic clusters that are oxidatively and thermally robust due to their inorganic, metal oxide-like nature. The versatility of their structures and compositions ensures tunable acid and redox properties, solubility, and functionality. The potential of POMs as homogeneous catalysts and building blocks for the construction of heterogeneous selective oxidations catalysts is being intensively investigated. POM catalysts immobilized on solid supports have the clear advantages of easy separation and reuse and, thus, better meet the requests of sustainable chemistry, provided that they are leaching-resistant under the reaction conditions. Here, we give a brief overview of recent advances in the field of liquid-phase selective oxidation of organic compounds using supported POMs and the green oxidant–hydrogen peroxide, with a focus on the critical issues of the catalyst stability and reusability. The scope and limitations of various approaches to POM immobilization are discussed.

Performance and mechanism of the pyrite-kerogen complexes oxidation with H2O2 at low temperature during shale stimulation: An experimental and modeling study

Pyrite and organic matter (OM) paly important role during rock chemical weathering and shale gas exploitation, the oxidation of which by O2 is widely recognized. But the performance and mechanism of pyrite and kerogen oxidizing with H2O2 during shale gas production are not well understood, and the impact of carbonates and clays on the oxidation process is still not known. In this study, the performance of the gas bearing carbonate-rich shale oxidation with 15 wt% H2O2 at low temperature was firstly explored. The total oxidation-dissolution capacity of the studied shale with H2O2 at room temperature was less than 5%, which is significantly poorer than shale richness in silicates. To unravel the underlying mechanisms leading to the divergent oxidation dissolution of shale with different compositions, pyrite-kerogen complexes were isolated from shale and batch experiments between individual key components including pyrite/kerogen/carbonates/clays and H2O2 were performed. On the basis of mechanistic understanding, kinetic models of the pure components reaction with H2O2 were also developed. Results show that pyrite is preferentially oxidized by H2O2 when compared to kerogen, and possesses a reaction rate 1–3 orders of magnitude larger than kerogen at different pyrite/kerogen mass ratio. Pyrite can induce the Fenton-like reactions to promote kerogen oxidation. The contribution of hydroxyl radicals on the oxidation of kerogen was about 22% for pyrite-kerogen complex with a pyrite/kerogen mass ratio of 1.65. Existence of calcite can buffer the solution pH to a circumneutral condition and induce the precipitation of Fe(III)-(oxy)hydroxides and anhydrite on the surface of the pyrite-kerogen complexes, thus to limit the generation of hydroxyl radicals and encapsulate the pyrite-kerogen complex, so as to inhibit the oxidation of these reduced components. This finding presents new insight into the mechanisms of H2O2-based oxidation stimulation of shale and provides guidance for the optimization of fracturing recipe.

Recent advances in H2O2-based advanced oxidation processes for removal of antibiotics from wastewater

As important emerging contaminants, antibiotics have caused potential hazards to the ecological environment and human health due to their extensive production and consumption. Among various techniques for removing antibiotics from wastewater, H2O2-based advanced oxidation processes (AOPs) have received increasing attention due to their fast reaction rate and strong oxidation capability. Hence this review critically discusses: (i) Recent research progress of AOPs with the addition of H2O2 for antibiotics removal through different methods of H2O2 activation; (ii) recent advances in AOPs that can in-situ generate and activate H2O2 for antibiotics removal; (iii) H2O2-based AOPs as a combination with other techniques for the degradation and mineralization of antibiotics in wastewater. Future perspectives about H2O2-based AOPs are also presented to grasp the future research trend in the area.

Immobilization of Polyoxometalates on Carbon Nanotubes: Tuning Catalyst Activity, Selectivity and Stability in H2O2-Based Oxidations

In recent years, carbon nanotubes (CNTs), including N-doped ones (N-CNTs), have received significant attention as supports for the construction of heterogeneous catalysts. In this work, we summarize our progress in the application of (N)-CNTs for immobilization of anionic metal-oxygen clusters or polyoxometalates (POMs) and use of (N)-CNTs-supported POM as catalysts for liquid-phase selective oxidation of organic compounds with the green oxidant–aqueous hydrogen peroxide. We discuss here the main factors, which favor adsorption of POMs on (N)-CNTs and ensure a quasi-molecular dispersion of POM on the surface and their strong attachment to the support. The effects of the POM nature, N-doping of CNTs, acid additives, and other factors on the POM immobilization process and catalytic activity/selectivity of the (N)-CNTs-immobilized POMs are analyzed. Particular attention is drawn to the critical issue of the catalyst stability and reusability. The scope and limitations of the POM/(N)-CNTs catalysts in H2O2-based selective oxidations are discussed.

Biodegradation of petroleum hydrocarbons in a weathered, unsaturated soil is inhibited by peroxide oxidants

Field-weathered crude oil-containing soils have a residual concentration of hydrocarbons with complex chemical structure, low solubility, and high viscosity, often poorly amenable to microbial degradation. Hydrogen peroxide (H2O2)-based oxidation can generate oxygenated compounds that are smaller and/or more soluble and thus increase petroleum hydrocarbon biodegradability. In this study, we assessed the efficacy of H2O2-based oxidation under unsaturated soil conditions to promote biodegradation in a field-contaminated and weathered soil containing high concentrations of total petroleum hydrocarbons (25200 mg TPH kg−1) and total organic carbon (80900 mg TOC kg−1). Microcosms amended with three doses of 48 g H2O2 kg−1 soil (unactivated or Fe2+-activated) or 24 g sodium percarbonate kg−1 soil and nutrients did not show substantial TPH changes during the experiment. However, 7.6–41.8% of the TOC concentration was removed. Furthermore, production of DOC was enhanced and highest in the microcosms with oxidants, with approximately 20–40-fold DOC increase by the end of incubation. In the absence of oxidants, biostimulation led to > 50% TPH removal in 42 days. Oxidants limited TPH biodegradation by diminishing the viable concentration of microorganisms, altering the composition of the soil microbial communities, and/or creating inhibitory conditions in soil. Study’s findings underscore the importance of soil characteristics and petroleum hydrocarbon properties and inform on potential limitations of combined H2O2 oxidation and biodegradation in weathered soils.

Intensification strategies for thermal H2O2-based advanced oxidation processes: Current trends and future perspectives

H2O2-based advanced oxidation technologies, commonly Fenton process or Catalytic Wet Peroxide Oxidation (CWPO), have been widely studied and applied over the past decades for wastewater treatment due to their ability to generate highly oxidizing species, HO• and HOO• radicals, along with a low selectivity which allow the degradation of a wide range of pollutants . Nonetheless, these technologies present some limitations. In the case of Fenton, the requirement of acidic media (pH: 3), the loss of catalyst at the end of reaction because it is dissolved, and the catalyst inactivation caused by certain reaction intermediates (i.e. oxalic acid) that forms complexes compromising its efficiency. For CWPO, the main drawbacks in this heterogeneous process are mainly associated to the relative low activity and stability of the catalysts employed. All these shortcomings can be solved through process intensification, which generally involves in Fenton and CWPO increasing the temperature or the application of an external radiation, being the most interesting ones UV–vis radiation (photo-assisted technologies), and microwave radiation, which inherently presents the advantages of working at high temperature. This paper gathers the most recent advances explored in thermal-intensified H2O2–based advanced oxidation technologies, summarizing the main results obtained for each intensification strategy and outlining where future efforts should be focused.

Thiol-disulphide independent in-cell trapping for the identification of peroxiredoxin 2 interactors

Hydrogen peroxide (H2O2) acts as a signalling molecule by oxidising cysteine thiols in proteins. Recent evidence has established a role for cytosolic peroxiredoxins in transmitting H2O2-based oxidation to a multitude of target proteins. Moreover, it is becoming clear that peroxiredoxins fulfil their function in organised microdomains, where not all interactors are covalently bound. However, most studies aimed at identifying peroxiredoxin interactors were based on methods that only detect covalently linked partners. Here, we explore the applicability of two thiol-disulphide independent in-cell trapping methodological approaches in combination with mass spectrometry for the identification of interaction partners of peroxiredoxin 2 (Prdx2). The first is biotin-dependent proximity-labelling (BioID) with a biotin ligase A (BirA*)-fused Prdx2, which has never been applied on redox-active proteins. The second is crosslinker co-immunoprecipitation with an N-terminally His-tagged Prdx2. During the initial characterisation of the tagged Prdx2 constructs, we found that the His-tag, but not BirA*, compromises the peroxidase and signalling activities of Prdx2. Further, the Prdx2 interactors identified with each approach showed little overlap. We therefore concluded that BioID is a more reliable method than crosslinker co-immunoprecipitation. After a stringent mass spec data filtering, BioID identified 13 interactors under elevated H2O2 conditions, including subunit five of the COP9 signalosome complex (CSN5). The Prdx2:CSN5 interaction was further confirmed in a proximity ligation assay. Taken together, our results demonstrate that BioID can be used as a method for the identification of interactors of Prdxs, and that caution should be exercised when interpreting protein-protein interaction results using tagged Prdxs.

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.

Advantages and limitations of catalytic oxidation with hydrogen peroxide: from bulk chemicals to lab scale process

ABSTRACT 21st century global market place is moving towards subtainable development and without this approach our future would be at risk. Today’s chemical industries need to give more focus for the planet through improving the environmental footprints of fuels and chemicals manufacturing processes. Oxidation and hydrogenation processes are widely used in the production of chemicals and fuels. Oxidation processes are especially important to convert petroleum-based materials to useful petrochemicals of higher oxidation state. Many existing oxidation processes, however, still rely on the use of stoichiometric oxidants, such as dichromate/sulfuric acid, permanganates, periodates, chromium oxides, osmium oxide etc., and remain a major source of environmental pollution. Therefore, oxidation processes using eco-friendly oxidizing agents such as molecular oxygen, ozone and hydrogen peroxide (H2O2) are incresingly becoming important to improve the environmental sustainability. Hydrogen peroxide is especially attractive for the liquid-phase oxidation due to the presence of high percentage of active oxygen and the production of water as only by-product. As a result, H2O2-based eco-friendly oxidation processes are gradually replacing some well-established processes such as production of propylene oxide, caprolactam, phenol etc. Moreover, recent advances in the area of oxidation catalysis is promoting H2O2-based technologies to emerge as a frontline, eco-friendly sustainable processes. H2O2 is also finding greater applications in pulp/paper industries and waste water treatment as a substitute of chlorine-based oxidizing agents. Herein, we have analyzed various reactions using H2O2 as an oxidant and their recent advancement to bring important aspects of H2O2-based oxidation processes and catalysis. Moreover, various aspects of using H2O2 toward development of sustainable oxidation processes have been analyzed with respect to factors affecting the end uses in chemical industry such as efficiency, catalyst and reaction pathways. We have reviewed manufacturing trends of H2O2 and emerging applications of H2O2 in sustainable oxidation processes. Critical discussions have also been made on the opportunities and challenges with emerging H2O2 based oxidation processes in the production of bulk as well as specialty chemicals.

Kinetics of the reaction between hydrogen peroxide and aqueous iodine: Implications for technical and natural aquatic systems

Oxidative treatment of iodide-containing waters can lead to a formation of potentially toxic iodinated disinfection byproducts (I-DBPs). Iodide (I−) is easily oxidized to HOI by various oxidation processes and its reaction with dissolved organic matter (DOM) can produce I-DBPs. Hydrogen peroxide (H2O2) plays a key role in minimizing the formation of I-DBPs by reduction of HOI during H2O2-based advanced oxidation processes or water treatment based on peracetic acid or ferrate(VI). To assess the importance of these reactions, second order rate constants for the reaction of HOI with H2O2 were determined in the pH range of 4.0–12.0. H2O2 showed considerable reactivity with HOI near neutral pH (kapp = 9.8 × 103 and 6.3 × 104 M−1s−1 at pH 7.1 and 8.0, respectively). The species-specific second order rate constants for the reactions of H2O2 with HOI, HO2− with HOI, and HO2− with OI− were determined as kH2O2+HOI = 29 ± 5.2 M−1s−1, kHO2-+HOI = (3.1 ± 0.3) × 108 M−1s−1, and kHO2-+OI− = (6.4 ± 1.4) × 107 M−1s−1, respectively. The activation energy for the reaction between HOI and H2O2 was determined to be Ea = 34 kJ mol−1. The effect of buffer types (phosphate, acetate, and borate) and their concentrations was also investigated. Phosphate and acetate buffers significantly increased the rate of the H2O2–HOI reaction at pH 7.3 and 4.7, respectively, whereas the effect of borate was moderate. It could be demonstrated, that the formation of iodophenols from phenol as a model for I-DBPs formation was significantly reduced by the addition of H2O2 to HOI- and phenol-containing solutions. During water treatment with the O3/H2O2 process or peracetic acid in the presence of I−, O3 and peracetic acid will be consumed by a catalytic oxidation of I− due to the fast reduction of HOI by H2O2. The O3 deposition on the ocean surface may also be influenced by the presence of H2O2, which leads to a catalytic consumption of O3 by I−.

Carbon Nanotubes Modified by Venturello Complex as Highly Efficient Catalysts for Alkene and Thioethers Oxidation With Hydrogen Peroxide.

In this work, we elaborated heterogeneous catalysts on the basis of the Venturello complex [PO4{WO(O2)2}4]3− (PW4) and nitrogen-free or nitrogen-doped carbon nanotubes (CNTs or N-CNTs) for epoxidation of alkenes and sulfoxidation of thioethers with aqueous hydrogen peroxide. Catalysts PW4/CNTs and PW4/N-CNTs (1.8 at. % N) containing 5–15 wt. % of PW4 and differing in acidity have been prepared and characterized by elemental analysis, N2 adsorption, IR spectroscopy, HR-TEM, and HAADF-STEM. Studies by STEM in HAADF mode revealed a quasi-molecular dispersion of PW4 on the surface of CNTs. The addition of acid during the immobilization is not obligatory to ensure site isolation and strong binding of PW4 on the surface of CNTs, but it allows one to increase the PW4 loading and affects both catalytic activity and product selectivity. Catalytic performance of the supported PW4 catalysts was evaluated in H2O2-based oxidation of two model substrates, cyclooctene and methyl phenyl sulfide, under mild conditions (25–50°C). The best results in terms of activity and selectivity were obtained using PW4 immobilized on N-free CNTs in acetonitrile or dimethyl carbonate as solvents. Catalysts PW4/CNTs can be applied for selective oxidation of a wide range of alkenes and thioethers provided a balance between activity and selectivity of the catalyst is tuned by a careful control of the amount of acid added during the immobilization of PW4. Selectivity, conversion, and turnover frequencies achieved in epoxidations over PW4/CNTs catalysts are close to those reported in the literature for homogeneous systems based on PW4. IR spectroscopy confirmed the retention of the Venturello structure after use in the catalytic reactions. The elaborated catalysts are stable to metal leaching, show a truly heterogeneous nature of the catalysis, can be easily recovered by filtration, regenerated by washing and evacuation, and then reused several times without loss of the catalytic performance.

Quenchers in advanced oxidation technologies for analysis of micropollutants by liquid chromatography coupled to mass spectrometry: Sodium sulphite or catalase?

This work aimed to investigate the possible effect of 2 quenchers commonly used in H2O2-based advanced oxidation technologies (AOTs), i.e. catalase and sodium sulphite (Na2SO3), on the analytical signal of 3 detectors coupled to liquid chromatography (LC): tandem mass spectrometry (LC-MS/MS), fluorescence detection (LC-FD) and LC-diode array detection (LC-DAD). The observation of analytical interferences for a group of compounds when studying the removal by continuous mode UV/H2O2 of 26 micropollutants (MPs) from a spiked surface water (SW), for which the residual H2O2 in the samples was quenched by Na2SO3, triggered the need of understanding these effects and thus catalase was used as comparative quencher. From the 26 MPs having a wide range of polarity and pKa, those monitored after electrospray ionization (ESI) under positive ionization (PI) mode and presenting a pKa higher than 5.9 revealed a great signal suppression, but only when using Na2SO3 as H2O2 quencher. In this sense, we further explored this effect by selecting 2 MPs, metoprolol and diclofenac, which had respectively signal suppression and no interference in the LC-MS/MS response. These MPs were analysed before and after addition of H2O2 and catalase or Na2SO3 in reaction vials, using: (i) different detectors coupled to LC, namely LC-MS/MS with ESI under PI and negative ionization (NI) modes, LC-FD and LC-DAD; (ii) different environmental matrices (SW, drinking water, wastewater) and ultrapure water; and (iii) different magnitude levels (0.1-10 mg L-1). The results demonstrated a remarkable signal suppression in LC-MS/MS analyses under PI mode for those compounds with pKa higher than 5.9, confirming the interfering effect of H2O2/Na2SO3. To the best of our knowledge, the analytical interference in the LC-MS/MS analysis, after adding Na2SO3 to quench H2O2 in AOTs experiments was never reported before and the results presented herein support the recommendation to use catalase instead of Na2SO3 as quencher in AOTs studies.

H2O2-based selective oxidations by divanadium-substituted polyoxotungstate supported on nitrogen-doped carbon nanomaterials

Abstract In this work, we present a new methodology for the preparation of highly active, selective, leaching-tolerant and recyclable catalysts on the basis of polyoxometalates (POM) and nitrogen-doped carbon nanomaterials. A divanadium-substituted γ-Keggin phosphotungstate [γ-PW10O38V2(μ-O)(μ−OH)]4− (PV2), was immobilized on two types of supports – N-doped carbon nanofibers (N-CNFs) having herring-bone packing of graphite layers and bamboo-like N-doped carbon nanotubes (N-CNTs). Two series of catalysts have been prepared and characterized by elemental analysis, N2 adsorption, TEM, XPS and FTIR techniques. Their catalytic performance was assessed in the liquid-phase selective oxidation of two representative organic substrates, 2,3,6-trimethylphenol and cyclohexene, with aqueous H2O2 as the green oxidant. The presence of nitrogen in the supports ensures strong binding and quasi-molecular dispersion of POM on the carbon surface, which is crucial for the catalytic performance and catalyst stability. The catalysts reveal truly heterogeneous nature of the catalysis and can be easily recovered and reused without loss of the catalytic performance. The morphology of the support has a significant impact on the catalytic performance: the supported PV2 catalysts prepared using N-CNTs are more active and, in general, more selective than the catalysts prepared with N-CNFs.

A sandwich-type tungstoantimonate derivative: Synthesis, characterization and catalytic in H2O2-based oxidation of cyclooctene

A Fe4-substituted sandwich-type tungstoantimonate derivative, H2(C6NO2H6)2{[Na(H2O)4]2[Fe4(H2O)10(B-β-SbW9O33)2]}∙20H2O (1), has been synthesized and characterized by IR, PXRD, UV–Vis, CV and single-crystal X-ray diffraction. This compound consists of two trivacant B-β-Keggin [SbW9O33]9− units with four FeIII cations located on the sandwich belt. Compound 1 shows an excellent catalytic activity to the reaction of H2O2-based oxidation of cyclooctene. In addition, antiferromagnetic exchange interactions have been observed among four Fe(III) centers of the sandwich-type ion.