Peroxide Species Research Articles

Removal of Rhodamine 6G in the absence of UV radiation using ceria nanoparticles (CeO2-NPs)

In this work, the capacity to removal rhodamine 6 G (R6 G), in the absence of UV radiation, using cerium dioxide nanoparticles (CeO2-NP) was determined. The synthesized NPs were characterized by X-ray powder diffraction (XRD) and X-ray photoelectron (XPS), Raman and photoluminiscence spectroscopies. The results indicated that CeO2 powders had a crystallite size between ∼ 12 and ∼ 14 nm. The presence of the peroxide species (O22-) η2, superoxide (O2-) η1, adsorbed species O2δ (0 < δ < 1) over the surface of the ceria nanoparticles was demonstrated in the Raman spectra. Additionally, the ability of the CeO2-NPs synthesized to interact with organic molecules was determined by evaluating the removal of the R6 G dye. The results of these tests showed substantial dye removal by the as-synthesized CeO2-NPs at pH∼9.1 (∼87 % within 120 min). The kinetic adsorption of the R6 G by these NPs was suitably described by a pseudo-second-order equation.

A boronic acid based intramolecular charge transfer probe for colorimetric detection of hydrogen peroxide

Many oxidative stress related diseases and adverse health conditions have been associated with the negative effects of hydrogen peroxide and other similar reactive oxygen species in human body. Therefore, increasing attention has been attracted to the detection and monitoring of hydrogen peroxide in living organisms and food items. In this work, a simple, inexpensive colorimetric method for the quantitative determination of hydrogen peroxide in aqueous sample is described. This method utilizes the de-protection of aryl boronic acid to yield a strongly colored water-soluble dye, which is capable of absorbing and emitting in the red region of the spectrum. The mechanism is faster in alkaline condition and utilizes the intramolecular charge transfer between strong phenolate donor and TCF acceptor, thus allowing a naked eye detection of hydrogen peroxide within seconds. The method is unaffected by the presence of various salts, metal ions, and other interfering species, and it can provide a limit of detection as low as ~1 ppm in aqueous samples. This unique way of generating a fluorogenic donor-acceptor pair holds a potential of this dye and other related derivatives for understanding the role of hydrogen peroxide in physiology and pathology.

CeO2–Nb2O5 photocatalysts for degradation of organic pollutants in water

The photocatalytic properties of CeO2–Nb2O5 photocatalysts in heterogeneous photocatalysis (under ultraviolet and visible radiation) and in Fenton-like process were reported. Methylene blue dye (MB) and phenol (Ph) were used as models of pollutant molecules for these reactions, and the photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and thermally stimulated luminescence (TL). The results indicated that the addition of CeO2 (0.3 wt%, 1.0 wt% and 2.0 wt%) to Nb2O5 sensitized the resultant materials, increasing light absorption in the visible region. However, there is a suitable formulation of CeO2–Nb2O5 photocatalysts to improve each photocatalytic process. In heterogeneous photocatalysis, the addition of small CeO2 quantities to Nb2O5 was enough to improve the photocatalytic activity of CeO2–Nb2O5 photocatalysts (The best composition reported was CeO2 0.3 wt%.). The effectiveness of the catalyst was explained by the decrease in the number of trapping and luminescence centers in the conduction band of the material after the addition of CeO2 to Nb2O5, but a large amount of CeO2 decreased the number of trapping, luminescent and active centers to a large extent. Contrarily, in a Fenton-like process, the addition of CeO2 to Nb2O5 was favorable in all the proportions studied. (The best composition was 2.0 wt% CeO2.) In this case, the effectiveness was explained by the influence of the adsorption process (adsorption-triggered process), and the interactions between H2O2 and Ce3+ of the CeO2 in each photocatalyst thus formed surface peroxide species O22−, which induced the removal of the organic molecules under visible light.

(Battery Division Postdoctoral Associate Research Award sponsored by MTI Corporation and the Jiang Family Foundation) Toward the Stable and Reversible Lattice Oxygen Redox in Li-Rich Layered Oxides

Conventional wisdom on utilizing cation redox in intercalation materials for energy storage has been challenged by a new class of cathode materials where oxygen anions actively participate in the reversible electrochemical reaction. This type of Li-rich layered oxides (LRLO) have captured great interests in the field of energy storage materials as they are considered as one of the most promising cathode materials for future high energy density lithium-ion and lithium metal batteries. However, the activation of solid-state oxygen redox reaction usually causes some detrimental effects on the electrochemical performance (e.g., O2 loss, voltage fade) preventing the practical application of LRLO (Y. S. Meng et al., Nature Energy, 2018, 3, 641-647; X. Yu et al., Nature Energy, 2018, 3, 690-698). Till now, the charge-compensation mechanism associated with oxygen reduction/oxidation is still under fierce debate. For instance, J.M. Tarascon et al. proposed the presence of peroxo-like species (O2 n-, O-O: 2.45 Å) in lattice oxygen redox based on the research results of 4d/5d-TM LRLO (Science, 2015, 350, 1516-1521; Nature Materials, 2017, 16, 580-586). In contrast, P. Bruce et al. clearly demonstrated that there is no peroxide species formed in 3d-TM LRLO (Nature Chemistry, 2016, 8, 684-691). The controversial viewpoints regarding oxygen reduction/oxidation at solid state may be originated from the intrinsic complexity of this class of materials and the limitations of the characterization techniques. Our work reveals the origin of stable and reversible lattice oxygen redox in 3d TM LRLO, specifically, the localized structure distortion (i.e., short O-O pairs) accompanying the oxygen redox is favorable for the stability of the average layered lattice structure, maintaining the high-voltage character and topotactic structure-reversibility of LRLO. With a model compound (Li1.2Mn0.54Co0.13Ni0.13O2), we for the first time observe a local occurrence of short O-O pair (~2.39 Å) concomitant with the lattice oxygen redox via neutron pair distribution function. It was found that the distance of this short O-O pair is very similar to that of O-O dimer in peroxo-like species, but our quantum mechanical calculation results suggest that the bonding nature of this short O-O pair (in which potential π-type overlap dominated) is quite different from that of peroxo-like O-O dimer (in which σ-type bond formed). Based on these understandings in our work, an optimization guidance for LRLO is unambiguously presented: designing a robust layered structure with high-covalency TMs while constructing a flexible local structure (e.g., honeycomb structure) with high-ionicity TMs to accommodate the local distortion induced by oxygen redox, thus achieving the reversible high energy density in LRLO. Figure 1

Characterization of different ozonized sunflower oils I. Chemical changes during ozonization

Vegetable oils are usually rich in unsaturated fatty acids which are susceptible to oxidation. The oxidation of vegetable oils has been one of the most widely studied fields within lipid chemistry, because it alters their properties and nutritive value, inducing the formation of harmful compounds and off-flavors. Moreover, oxidized vegetable oils display altered physical and chemical properties which are conferred by the newer oxygenated compounds they contain. This is the case of ozonized oils. Ozone is a powerful oxidizing agent that mainly acts on olefinic compounds which generate ozonides and other peroxidic species that can decompose into carbonilic fragments. The action of the oxidant and the later reactions depend on the chemical environment of the reaction as well as the carbonyl termination products resulting from peroxide cleavage. In recent years, sunflower oils with different fatty acid compositions have been developed by breeding and mutagenesis. They displayed higher contents of oleic, stearic or palmitic acids, which mainly alters their triacylglycerol composition. Therefore, four different sunflower oils, common, high oleic, high stearic-high oleic and high palmitic-high oleic, were oxidized with ozone and the progress of the reaction was monitored by measuring the level of oil peroxygenation and the changes in the oils’ fatty acid compositions. The peroxidated species formed during ozonation were studied by FT-IR spectroscopy. The main conclusions of this work were that ozonation caused linear oxidation rates that were similar in all the oils assayed. The addition of water accelerated oxidation, which tended to occur in linoleic polyunsaturated fatty acid The FT-IR pointed to the presence of ozonide-derived peroxides as the major oxygenated species.

Oxygen Reduction at Pt{Hkl} Electrodes in an Alkali Metal Ion Containing Aprotic Solvent

Metal-oxygen battery cathodes utilise the reversible redox species of oxygen in the presence of metal ions. However the oxygen reduction and evolution reaction mechanisms are yet to be conclusively determined. In order to elucidate the effect of surface structure on the oxygen reduction reaction (ORR) a method of preparing clean, well-defined Pt{hkl} electrodes for adsorption studies in non-aqueous solvents is described. The ORR in MClO4 (M = Li+, Na+, K+) containing dimethyl sulfoxide (DMSO) as the electrolyte highlights the structural sensitivity of the ORR under these conditions. Using cyclic voltammetry (CV) and in situ electrochemical Shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS), the various stages of oxygen reduction as a function of i) potential, ii) metal ion concentration and iii) sweep rate are investigated. In the sodium system it is found that on Pt{111} and Pt{110}-(1x1) terraces, a long lived surface sodium peroxide species is formed reversibly, whereas on Pt{100} and polycrystalline electrodes, this species is unstable and dissolves into the bulk electrolyte. On all surfaces studied, the initial reduction pathway corresponds to the formation of a surface sodium superoxide phase. In the absence of sodium ions, superoxide formation takes place exclusively followed by superoxide formation into the bulk of the electrolyte with no evidence of peroxide formation. The discovery that Pt surfaces can control the reaction pathway between superoxide and peroxide species opens up the development of practical electrocatalysts capable of controlling the desired reaction pathway towards Na2O2 to deliver Na-O2 batteries with higher theoretical specific energies.

(Invited) Electrochemical Analogues of Dioxygenase and Monooxygenase Activity in Synthetic Iron Porphyrins

Dioxygen adducts of heme proteins are ubiquitous in all O2 activating/reducing heme proteins in nature. While artificial dioxygen adducts of heme are known for six decades, till date these have not been demonstrated to be able to oxidize organic substrates in sharp contrast to their non-heme analogues and naturally occurring enzymes like heme dioxygenases. To address this apparent anomaly an iron porphyrin complex is synthesized which includes a pendant quinol group. The corresponding dioxygen bound iron porphyrin species is demonstrated to perform Hydrogen atom transfer (HAT) from a quinol group appended to the porphyrin ligand. The resultant ferric peroxide, formed by the first HAT, performs a 2nd HAT generating a ferryl species (FeIV=O) and resulting in the 2e-/2H+ oxidation of the pendant hydroquinol to quinone. All the intermediate species are trapped at cryogenic temperatures and spectroscopically characterized using EPR and resonance Raman spectroscopy. DFT calculations reproduce the experimental kinetic parameters and provide insight into the nature of TS involved. These results demonstrate that artificial analogues of both heme ferric superoxide and ferric hydroperoxide species can perform HAT from an organic substrate when appropriately pre-organized to hydrogen bond to the bound superoxide and peroxide species. Siilarly, catalytic oxidation of organic substrates, using a green oxidant like O2, has been a long-term goal of the scientific community. In nature, these oxidations are performed by metalloenzymes which generate highly oxidizing species from O2 which, in turn, can oxidize inert organic substrates e.g. mono/di oxygenases. The same oxidants are produced during O2 reduction during respiration in the mitochondria but are reduced by electron transfer i.e. reductases. Iron porphyrin mimics of the active site of Cytochrome P450 (Cyt P450) are created atop self-assembled monolayer covered electrode. The rate of electron transfer from the electrode to the iron porphyrin site is attenuated to derive monooxygenase reactivity from these constructs which generally show reductase activity and catalytic hydroxylation of inert C-H bonds to alcohol and epoxidation alkenes, using molecular O2, is demonstrated with turnover numbers > 104. Mechanistic investigations suggest that a compound I analogue, formed during O2 reduction, is the primary oxidant and the selectivity is determined by the shape of the distal environment of the catalyst.

Reduction of enzymatic browning of fresh-cut guava fruit by exogenous hydrogen peroxide-activated peroxiredoxin/thioredoxin system

Abiotic stresses in plants are commonly caused by antioxidant system imbalance in their tissues. A peroxiredoxin/thioredoxin (Prx/Trx) system is a ubiquitous antioxidant system involved in sensing and detoxifying hydrogen peroxide (H2O2) and other reactive oxygen species (ROS). This study investigated exogenous H2O2 potential in reducing browning and its interaction with the Prx/Trx system in fresh-cut guava fruit during storage at 25 °C. Fresh-cut guava samples were immersed in 0 (control) and 250 mM H2O2 for 10 min, placed on a foam tray, packed inside a polyethylene bag and kept at 25 ± 1 °C for 48 h. The H2O2 treatment reduced browning and maintained fresh-cut guava fruit quality during storage. The H2O2 treatment reduced oxidative membrane damage and an accumulation of ROS, but activated the Prx/Trx system by stimulating the activities of peroxiredoxin and thioredoxin reductase, and NADPH-generating dehydrogenases including glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase as well as an increase in NADP redox state. The altered redox state and the activation of the Prx/Trx system by H2O2 was correlated with delayed browning of fresh-cut guava. Thus, the Prx/Trx system is involved in browning development, and H2O2 treatment could delay browning in fresh-cut guava by reducing oxidative membrane damage via stimulating the Prx/Trx system.

The Analysis of Zirconium (IV) Oxide (ZrO2) Nanoparticles for Peroxidase Activity

In this study, the peroxidase-like activity of zirconium (IV) oxide nanoparticles (nZr) is reported. Peroxidases catalyze the oxidation of their substrate in the presence of peroxide species. 3,3′,5,5′-tetramethylbenzidine (TMB) is a peroxidase substrate, and we have demonstrated that nZr oxidizes the TMB in the presence of hydrogen peroxide resulting in a colored (TMBox) product. The reaction was tested in various buffers, and sodium acetate with pH 4 was observed to be an ideal buffer for the enzymatic reaction and the dispersity of the nZr in the solution. The nanozyme behavior was studied systematically at three different temperatures (25, 35 and 45 °C) and a wide range of H2O2 concentrations. The dependence of the enzymatic reaction on temperature, nZr content and H2O2 concentration was observed. The enzymatic reaction was tested in different protein solutions and no noticeable interference was observed with these proteins. Overall, we demonstrate that nZr, which is often used for industrial applications, mimics peroxidase enzyme and catalyzes oxidation of its substrate in the presence of peroxide species.

Improving Selectivity and Activity of CO2 Reduction Photocatalysts with Oxygen

Summary A highly porous photocatalyst (copper on TiO2 aerogel) was synthesized and applied in aqueous CO2 reduction without using external sacrificial electron donors. For the first time, complete selectivity toward CO and improved catalyst productivity are observed in the presence of oxygen. The optimal activity is achieved in a feed containing 0.5 vol% O2 in CO2. In situ XAS, EPR, and UV-vis measurements suggest, among different Cu oxidation states, Cu(I) to be the most active species in photocatalytic CO2 reduction. Oxygen sensing of the catalyst in the presence of O2/CO2 mixtures indicated an unexpected photoadsorption of oxygen on the titania surface. We propose photooxidation of surface hydroxyl groups to be the electron source for CO2 reduction, which is supported by hydroxyl group consumption, detection of hydroxyl radicals using in situ EPR, and detection of surface peroxide species after the reaction.

Transformation of Uranyl Peroxide Studtite, [(UO2)(O2)(H2O)2](H2O)2, to Soluble Nanoscale Cage Clusters.

The dissolution behavior of uranyl peroxide studtite, [(UO2)(O2)(H2O)2](H2O)2, was examined under a wide range of alkaline aqueous environments with and without the addition of hydrogen peroxide. In the absence of added H2O2, studtite dissolved in aqueous solutions with a tetraethylammonium hydroxide to uranium molar ratio greater than 0.5, and the resulting species in solution characterized by Raman spectroscopy and electrospray ionization mass spectrometry (ESI-MS) is the uranyl peroxide nanocluster U24, [(UO2)(O2)(OH)]2424-. This is the first demonstration of the formation of uranyl peroxide nanoclusters from studtite in a solution lacking additional hydrogen peroxide. In similar systems containing added hydrogen peroxide (0.01 M - 1.0 M), studtite dissolved in solutions with a TEAOH to uranium ratio greater than 0.1, and the resulting uranyl peroxide species in solution was U28, [(UO2)(O2)1.5]2828-.

Effects of H2O2 Concentration on Formation of Uranyl Peroxide Species Probed by Dissolution of Uranium Nitride and Uranium Dioxide.

Dissolution of uranium materials in alkaline aqueous conditions containing H2O2 results in uranyl peroxide species in solution, including anionic uranyl peroxide cage clusters. Uranyl peroxide cage clusters are generally highly soluble in water, where they persist as aqueous macroanions. Previous studies indicate that uranyl cluster speciation and dissolution of uranium materials is impacted by the concentration of alkali metal in solution, but in these studies, high concentrations of H2O2 were used. Herein, the role of hydrogen peroxide concentration is examined relative to the dissolution of powdered UN and UO2. Lower initial H2O2 concentrations reduce dissolution of UO2 and UN and tend to produce simple (small) uranyl peroxide species rather the highly soluble uranyl peroxide clusters. H2O2 availability will have implications for uranyl speciation and solubility where spent nuclear fuel is in contact with water and where alkaline peroxide conditions are used in dissolution of nuclear material.

The Role of Mitochondrial Peroxide Release in the Mechanisms Underlying Age‐Related Sarcopenia

Age related loss of muscle mass and function (sarcopenia) is a major contributor to reduced quality of life in the elderly. Previous studies from our laboratory have shown that denervation induced alterations in muscle mitochondrial reactive oxygen species (ROS) generation is an integral player in this process. To specifically determine the role of mitochondrial function, generation of ROS and lipid peroxides in denervation atrophy, we utilized two transgenic mouse models with increased expression of the hydrogen peroxide scavengers catalase or peroxiredoxin 3, specifically in skeletal muscle. First, we asked whether these mitochondrial antioxidants can reduce denervation induced changes in muscle mitochondrial ROS production and reduce muscle atrophy in a surgical denervation model. Gastrocnemius mass is significantly reduced (~20%) at 7 days post‐sciatic nerve transection in wildtype, skmPrdx3 and skmMCAT mice, i.e., there was no protective effect of hydrogen peroxide scavengers on denervation atrophy. ROS production measured using the fluorescent probe Amplex Red was elevated in permeabilized muscle fibers and isolated mitochondria from denervated hindlimb 7 days post transection and neither Prdx3 or MCAT expression inhibits the signal. This data supports that the Amplex Red signal does not represent hydrogen peroxide alone, but includes the response from other lipid peroxide species and suggests that hydrogen peroxide scavenging is not sufficient to reduce denervation induced atrophy. Next, we asked whether Prdx3 muscle specific expression can modulate the sarcopenia phenotype in an established mouse model of accelerated sarcopenia, mice lacking CuZnSOD (Sod1KO/skmPrdx3Tg mice). ROS generation is significantly elevated in isolated muscle mitochondria from Sod1KO mice, and normalized by Prdx3 overexpression in the Sod1KO/skmPrdx3Tg mice. The oxygen consumption rate is reduced in skeletal muscle mitochondria isolated from Sod1KO muscle and restored by Prdx3 overexpression. We also found that in vitro contractile force generation was decreased by ~20% in Sod1KO mice, and the force reduction wwas rescued in Sod1KO/skmPrdx3Tg mice. Importantly, the muscle atrophy that occurs in the Sod1KO mice is fully restored by Prdx3 overexpression. This finding demonstrates a direct role of skeletal muscle‐specific mitochondrial H2O2 in promoting contractile abnormalities and muscle atrophy. Together these results implicate mitochondrial H2O2 generation as a novel therapeutic target to ameliorate skeletal muscle pathologies and support further studies to elucidate the role of lipid peroxide mediators released by mitochondria in denervation induced atrophy.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Photolysis of Staphyloxanthin in Methicillin-Resistant Staphylococcus aureus Potentiates Killing by Reactive Oxygen Species.

Confronted with the severe situation that the pace of resistance acquisition is faster than the clinical introduction of new antibiotics, health organizations are calling for effective approaches to combat methicillin‐resistant Staphylococcus aureus (MRSA) infections. Here, an approach to treat MRSA through photolysis of staphyloxanthin, an antioxidant residing in the microdomain of S. aureus membrane, is reported. This photochemistry process is uncovered through transient absorption imaging and quantitated by absorption spectroscopy, Raman spectroscopy, and mass spectrometry. Photolysis of staphyloxanthin transiently elevates the membrane permeability and renders MRSA highly susceptible to hydrogen peroxide attack. Consequently, staphyloxanthin photolysis by low‐level 460 nm light eradicates MRSA synergistically with hydrogen peroxide and other reactive oxygen species. The effectiveness of this synergistic therapy is well validated in MRSA planktonic culture, MRSA‐infected macrophage cells, stationary‐phase MRSA, persisters, S. aureus biofilms, and two mice wound infection models. Collectively, the work demonstrates that staphyloxanthin photolysis is a new therapeutic platform to treat MRSA infections.

A MnII MnIII -Peroxide Complex Capable of Aldehyde Deformylation.

Ribonucleotide reductases (RNRs) are essential enzymes required for DNA synthesis. In class Ib Mn2 RNRs superoxide (O2.- ) was postulated to react with the MnII2 core to yield a MnII MnIII -peroxide moiety. The reactivity of complex 1 ([MnII2 (O2 CCH3 )2 (BPMP)](ClO4 ), where HBPMP=2,6-bis{[(bis(2-pyridylmethyl)amino]methyl}-4-methylphenol) towards O2.- was investigated at -90 °C, generating a metastable species, 2. The electronic absorption spectrum of 2 displayed features (λmax =440, 590 nm) characteristic of a MnII MnIII -peroxide species, representing just the second example of such. Electron paramagnetic resonance and X-ray absorption spectroscopies, and mass spectrometry supported the formulation of 2 as a MnII MnIII -peroxide complex. Unlike all other previously reported Mn2 -peroxides, which were unreactive, 2 proved to be a capable oxidant in aldehyde deformylation. Our studies provide insight into the mechanism of O2 -activation in Class Ib Mn2 RNRs, and the highly reactive intermediates in their catalytic cycle.

Effect of chronic administration of arachidonic acid on the performance of learning and memory in aged rats.

BackgroundArachidonic acid (AA, C20:4, ω-6) is a ω-6 polyunsaturated fatty acid (PUFA) and plays diverse roles in cell signaling. Numerous reports on the effects of ω-3 PUFAs, such as docosahexaenoic acid (DHA, C22:6, ω-3) and eicosapentaenoic acid (EPA, C20:5, ω-3) on learning and memory impairments of rats are available, however, the role of AA on brain cognition is largely unknown.ObjectiveIn this study, our aim was to investigate the effect of oral administration of AA on spatial memory-related learning ability in aged (100 weeks) male rats.DesignOne group was per orally administered 240 mg/kg per day AA oil and the other group was administered the similar volume of control oil. Five weeks after the start of the administration, rats were tested with the partially baited eight-arm radial maze to evaluate two types of spatial memory-related learning ability displayed by reference memory errors (RMEs) and working memory errors (WMEs). Also, the time required to complete the task was recorded. The levels of lipid peroxide (LPO) and reactive oxygen species (ROS) were measured, as an indicator oxidative stress in the plasma and brain corticohippocampal brain tissues.ResultsThe scores of RMEs and WMEs, which are analogous to long-term and short-term memory, respectively, were not affected, however, the trial time was shorter in the AA-administered rats than that of the controls. AA also significantly increased the degree of oxidative stress both in the plasma and corticohippocampal brain tissues.ConclusionsOur results suggest that though AA deposition in the corticohippocampal tissues of senescent rats caused a faster performance activity, which is reminiscent to hyperactive behavior of animals, the spatial learning ability-related memory of the rats, however, was not improved.

Different adsorption-degradation behavior of methylene blue and Congo red in nanoceria/H2O2 system under alkaline conditions

The Fenton-like activity of nanoceria has attracted intensive attention for wastewater treatment in recent years. During the Fenton-like reaction, the adsorption of organic pollutants on catalyst surface plays a key role in their degradation. In this work, the adsorption-degradation of methylene blue (MB) and Congo red (CR) in nanoceria/H2O2 system was investigated under alkaline conditions. The MB exhibited weak adsorption on nanoceria surface via electrostatic attraction, while strong Lewis acid–base interactions between CR and cerium ions was observed. Moreover, the adsorption of MB was enhanced in the presence of H2O2 by the formation of surface peroxide species, but an adsorption competition existed between H2O2 and CR. With more Ce3+, CeO2 nanorods could degrade CR efficiently as Fenton-like catalyst. But the degradation of MB catalyzed by ceria was much lower than that of CR in the presence of H2O2.

Direct and Selective Electrochemical Vapor Trace Detection of Organic Peroxide Explosives via Surface Decoration.

The ability to detect traces of highly energetic explosive materials sensitively, selectively, accurately, and rapidly could be of enormous benefit to civilian national security, military applications, and environmental monitoring. Unfortunately, the detection of explosives still poses a largely unmet arduous analytical problem, making their detection an issue of burning immediacy and a massive current challenge in terms of research and development. Although numerous explosive detection approaches have been developed, these methods are usually time-consuming, require bulky equipment, tedious sample preparation, a trained operator, cannot be miniaturized, and lack the ability to perform automated real-time high-throughput analysis, strongly handicapping their mass deployment. Here, we present the first demonstration of the "direct" electrochemical approach for the sensitive, selective, and rapid vapor trace detection of TATP and HMTD, under ambient conditions, unaffected by the presence of oxygen and hydrogen peroxide species, down to concentrations lower than 10 ppb. The method is based on the use of Ag-nanoparticles-decorated carbon microfibers air-collecting electrodes (μCF), which allow for the selective direct detection of the organic peroxide explosives, through opening multiple redox routes, not existent in the undecorated carbon electrodes. Finally, we demonstrate the direct and rapid detection of TATP and HMTD explosive species from real-world air samples.

Nickel oxide nanoparticles cause substantial physiological, phytochemical, and molecular-level changes in Chinese cabbage seedlings

Nickel oxide nanoparticles (NiO NPs) are utilized in various industries and their release into the environment may lead to the pollution of agricultural areas. However, assessing the toxicity of NiO NPs in major food crops is difficult due to the limited information available on their toxicity. The present investigation was carried out to evaluate how NiO NPs affect plant growth, photosynthetic efficiency, and phytochemical content, as well as changes at the transcriptional level of these phytochemicals in Chinese cabbage seedlings. Chlorophyll, carotenoid, and sugar contents were reduced, while proline and the anthocyanins were significantly upregulated in NiO NPs-treated seedlings. The levels of malondialdehyde, hydrogen peroxide, and reactive oxygen species, as well as peroxidase (POD) enzyme activity, were all enhanced in seedlings exposed to NiO NPs. The levels of glucosinolates and phenolic compounds were also significantly increased in NiO NPs-treated seedlings compared to control seedlings. The expression of genes related to oxidative stress (CAT, POD, and GST), MYB transcription factors (BrMYB28, BrMYB29, BrMYB34, and BrMYB51), and phenolic compounds (ANS, PAP1, and PAL) were significantly upregulated. We suggest that NiO NPs application stimulates toxic effects and enhances the levels of phytochemicals (glucosinolates and phenolic compounds) in Chinese cabbage seedlings.

Tuning the structural properties of CeO2 by Pr and Fe codoping for enhanced visible‐light catalytic activity

AbstractBACKGROUNDIron (Fe)3+ has much a smaller ion radius than cerium (Ce)4+ but praseodymium (Pr) ions have a similar radius to Ce ions with the same valence. Hence, it is interesting to tune the structural properties, including lattice deformation, band gap and oxygen vacancy (Ov), of CeO2 by Pr and Fe codoping for enhanced visible‐light catalytic activity.RESULTSA series of Ce1‐x‐yPrxFeyO2‐σ (x = 0∼0.012, y = 0.003∼0.031) nanoparticles were prepared by a simple one‐step sol‐gel method. The structural properties of CeO2, including crystal deformation (cell lattice from 5.4069 to 5.4195), band gap (from 2.20 to 2.93), oxygen vacancies (Ov from 0.15% to 9.03%), and peroxide species (O22− from 0.37% to 1.09%) can be finely tuned by Pr and Fe codoping. Among ten samples, Ce0.982Pr0.003Fe0.015O2‐σ with proper structural properties showed the highest photocatalytic activity towards the degradation of acid orange 7. The first reaction rate constant reaches 0.0687 min−1, 9.3 and 7.7 times that of Ce0.994Pr0.006O2‐σ and Ce0.985Fe0.015O2‐σ, respectively. The mechanism was found to involve ·OH, ·O2− and photogenerated holes.CONCLUSIONThe structural properties of CeO2 can be finely and easily tuned by Pr and Fe codoping. Thus, the photocatalytic activity of CeO2 under visible light irradiation was boosted. © 2019 Society of Chemical Industry