Showing papers on "Oxygen published in 2015"
TL;DR: In this paper, the Ni2P nanoparticles were used as both cathode and anode catalysts for an alkaline electrolyzer, which generated 10 mA cm−2 at 1.63 V.
Abstract: Electrochemical water splitting into hydrogen and oxygen is a promising method for solar energy storage. The development of efficient electrocatalysts for water splitting has drawn much attention. However, catalysts that are active for both the hydrogen evolution and oxygen evolution reactions are rare. Herein, we show for the first time that nickel phosphide (Ni2P), an excellent hydrogen evolving catalyst, is also highly active for oxygen evolution. A current density of 10 mA cm−2 is generated at an overpotential of only 290 mV in 1 M KOH. The high activity is attributed to the core–shell (Ni2P/NiOx) structure that the material adopts under catalytic conditions. The Ni2P nanoparticles can serve as both cathode and anode catalysts for an alkaline electrolyzer, which generates 10 mA cm−2 at 1.63 V.
1,374 citations
TL;DR: Flexible non-metal oxygen electrodes fabricated from phosphorus-doped graphitic carbon nitride nano-flowers directly grown on carbon-fiber paper exhibit high activity and stability in reversibly catalyzing oxygen reduction and evolution reactions, comparable to that of the state-of-the-art transition- metal, noble-metal, and non-Metal catalysts.
Abstract: Flexible non-metal oxygen electrodes fabricated from phosphorus-doped graphitic carbon nitride nano-flowers directly grown on carbon-fiber paper exhibit high activity and stability in reversibly catalyzing oxygen reduction and evolution reactions, which is a result of N, P dual action, enhanced mass/charge transfer, and high active surface area The performance is comparable to that of the state-of-the-art transition-metal, noble-metal, and non-metal catalysts Remarkably, the flexible nature of these oxygen electrodes allows their use in folded and rolled-up forms, and directly as cathodes in Zn–air batteries, featuring low charge/discharge overpotential and long lifetime
714 citations
13 Feb 2015
TL;DR: The rapid increase of carbon dioxide concentration in Earth's modern atmosphere is a matter of major concern as discussed by the authors. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production.
Abstract: The rapid increase of carbon dioxide concentration in Earth’s modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth’s history.
356 citations
TL;DR: In this paper, a series of nanostructured rods and cubes with different physico-chemical properties have been synthesized, characterized and tested in the total toluene oxidation.
Abstract: This paper reveals the key importance of surface oxygen defects in the oxidation catalytic activity of nanostructured ceria. A series of nanostructured rods and cubes with different physico–chemical properties have been synthesized, characterized and tested in the total toluene oxidation. The variation of the temperature and base concentration during the hydrothermal syntheses of nanostructured ceria leads not only to different ceria morphologies with high shape purity, but also to structures with tuneable surface areas and defect concentrations. Ceria nanorods present a higher surface area and a higher concentration of bulk and surface defects than nanocubes associated with their exposed crystal planes, leading to high oxidation activities. However, for a given morphology, the catalytic activity for toluene oxidation is directly related to the concentration of surface oxygen defects and not the overall concentration of oxygen vacancies as previously believed.
318 citations
TL;DR: It is proposed that a narrow electronic state of significant oxygen 2p character near the Fermi level exchanges electrons with the oxygen adsorbates, highlighting the importance of surface anion-redox chemistry in oxygen-deficient transition-metal oxides.
Abstract: Surface redox centres in metal oxides play a key role in catalytic performance, and the conventional view is that the transition-metal cations dominate this behaviour. Here, the authors perform an in operando spectroscopic study, and find that oxygen anions are a significant redox partner to molecular oxygen.
283 citations
TL;DR: It is demonstrated that nano-structured titanium dioxide, self-doped by oxygen vacancies and selectively exposed with the high-energy {001} facets, exhibits a surprisingly competitive oxygen reduction activity, excellent durability and superior tolerance to methanol.
Abstract: The cathodic material plays an essential role in oxygen reduction reaction for energy conversion and storage systems. Titanium dioxide, as a semiconductor material, is usually not recognized as an efficient oxygen reduction electrocatalyst owning to its low conductivity and poor reactivity. Here we demonstrate that nano-structured titanium dioxide, self-doped by oxygen vacancies and selectively exposed with the high-energy {001} facets, exhibits a surprisingly competitive oxygen reduction activity, excellent durability and superior tolerance to methanol. Combining the electrochemical tests with density-functional calculations, we elucidate the defect-centred oxygen reduction reaction mechanism for the superiority of the reductive {001}-TiO2-x nanocrystals. Our findings may provide an opportunity to develop a simple, efficient, cost-effective and promising catalyst for oxygen reduction reaction in energy conversion and storage technologies.
252 citations
238 citations
TL;DR: It is reported that the higher catalytic activity at the relatively low temperature results from the integration of nickel cations, cobalt cations and surface lattice oxygen atoms/oxygen vacancies at the atomic scale.
Abstract: It is crucial to develop a catalyst made of earth-abundant elements highly active for a complete oxidation of methane at a relatively low temperature NiCo2O4 consisting of earth-abundant elements which can completely oxidize methane in the temperature range of 350-550 °C Being a cost-effective catalyst, NiCo2O4 exhibits activity higher than precious-metal-based catalysts Here we report that the higher catalytic activity at the relatively low temperature results from the integration of nickel cations, cobalt cations and surface lattice oxygen atoms/oxygen vacancies at the atomic scale In situ studies of complete oxidation of methane on NiCo2O4 and theoretical simulations show that methane dissociates to methyl on nickel cations and then couple with surface lattice oxygen atoms to form -CH3O with a following dehydrogenation to -CH2O; a following oxidative dehydrogenation forms CHO; CHO is transformed to product molecules through two different sub-pathways including dehydrogenation of OCHO and CO oxidation
224 citations
TL;DR: A reaction mechanism at an oxygen cathode, ruthenium and manganese dioxide nanoparticles supported on carbon black Super P is reported by applying a trace amount of water in electrolytes to catalyse the cathode reactions of lithium–oxygen cells during discharge and charge to significantly reduce the charge overpotential.
Abstract: The main challenges in lithium-oxygen batteries are the low round-trip efficiency and decaying cycle life. Here, the authors present that a trace amount of water in electrolytes facilitates oxygen cathode reactions, enabling the batteries to be operated with small overpotential and good cycling stability.
211 citations
TL;DR: Experimental results suggest that O reacts with chloride, yielding Cl2(-) or ClO(-).
Abstract: The mechanism of interaction of cold nonequilibrium plasma jets with mammalian cells in physiologic liquid is reported. The major biological active species produced by an argon RF plasma jet responsible for cell viability reduction are analyzed by experimental results obtained through physical, biological, and chemical diagnostics. This is complemented with chemical kinetics modeling of the plasma source to assess the dominant reactive gas phase species. Different plasma chemistries are obtained by changing the feed gas composition of the cold argon based RF plasma jet from argon, humidified argon (0.27%), to argon/oxygen (1%) and argon/air (1%) at constant power. A minimal consensus physiologic liquid was used, providing isotonic and isohydric conditions and nutrients but is devoid of scavengers or serum constituents. While argon and humidified argon plasma led to the creation of hydrogen peroxide dominated action on the mammalian cells, argon-oxygen and argon-air plasma created a very different biological action and was characterized by trace amounts of hydrogen peroxide only. In particular, for the argon-oxygen (1%), the authors observed a strong negative effect on mammalian cell proliferation and metabolism. This effect was distance dependent and showed a half life time of 30 min in a scavenger free physiologic buffer. Neither catalase and mannitol nor superoxide dismutase could rescue the cell proliferation rate. The strong distance dependency of the effect as well as the low water solubility rules out a major role for ozone and singlet oxygen but suggests a dominant role of atomic oxygen. Experimental results suggest that O reacts with chloride, yielding Cl2(-) or ClO(-). These chlorine species have a limited lifetime under physiologic conditions and therefore show a strong time dependent biological activity. The outcomes are compared with an argon MHz plasma jet (kinpen) to assess the differences between these (at least seemingly) similar plasma sources.
209 citations
TL;DR: In this article, it was shown that the hypoxia sensor of astrocytes resides in the mitochondria in which oxygen is consumed, leading to mitochondrial depolarization, production of free radicals, lipid peroxidation, activation of phospholipase C, IP3 receptors, and release of Ca(2+) from the intracellular stores.
Abstract: In terrestrial mammals, the oxygen storage capacity of the CNS is limited, and neuronal function is rapidly impaired if oxygen supply is interrupted even for a short period of time. However, oxygen tension monitored by the peripheral (arterial) chemoreceptors is not sensitive to regional CNS differences in partial pressure of oxygen (PO2 ) that reflect variable levels of neuronal activity or local tissue hypoxia, pointing to the necessity of a functional brain oxygen sensor. This experimental animal (rats and mice) study shows that astrocytes, the most numerous brain glial cells, are sensitive to physiological changes in PO2 . Astrocytes respond to decreases in PO2 a few millimeters of mercury below normal brain oxygenation with elevations in intracellular calcium ([Ca(2+)]i). The hypoxia sensor of astrocytes resides in the mitochondria in which oxygen is consumed. Physiological decrease in PO2 inhibits astroglial mitochondrial respiration, leading to mitochondrial depolarization, production of free radicals, lipid peroxidation, activation of phospholipase C, IP3 receptors, and release of Ca(2+) from the intracellular stores. Hypoxia-induced [Ca(2+)]i increases in astrocytes trigger fusion of vesicular compartments containing ATP. Blockade of astrocytic signaling by overexpression of ATP-degrading enzymes or targeted astrocyte-specific expression of tetanus toxin light chain (to interfere with vesicular release mechanisms) within the brainstem respiratory rhythm-generating circuits reveals the fundamental physiological role of astroglial oxygen sensitivity; in low-oxygen conditions (environmental hypoxia), this mechanism increases breathing activity even in the absence of peripheral chemoreceptor oxygen sensing. These results demonstrate that astrocytes are functionally specialized CNS oxygen sensors tuned for rapid detection of physiological changes in brain oxygenation. Significance statement: Most, if not all, animal cells possess mechanisms that allow them to detect decreases in oxygen availability leading to slow-timescale, adaptive changes in gene expression and cell physiology. To date, only two types of mammalian cells have been demonstrated to be specialized for rapid functional oxygen sensing: glomus cells of the carotid body (peripheral respiratory chemoreceptors) that stimulate breathing when oxygenation of the arterial blood decreases; and pulmonary arterial smooth muscle cells responsible for hypoxic pulmonary vasoconstriction to limit perfusion of poorly ventilated regions of the lungs. Results of the present study suggest that there is another specialized oxygen-sensitive cell type in the body, the astrocyte, that is tuned for rapid detection of physiological changes in brain oxygenation.
TL;DR: A new strategy was developed to synthesize nonsupported ultrasmall cobalt oxide nanocubanes through an in situ phase transformation mechanism using a layered Co(OH)(OCH3) precursor, which suggested a unique nanocUBane structure, where 13 cobalt atoms fully coordinated with oxygen in an octahedral arrangement to form 8 Co4O4 cubanes, which may be responsible for the exceptionally high OER activity.
Abstract: Oxygen evolution from water poses a significant challenge in solar fuel production because it requires an efficient catalyst to bridge the one-electron photon capture process with the four-electron oxygen evolution reaction (OER). Here, a new strategy was developed to synthesize nonsupported ultrasmall cobalt oxide nanocubanes through an in situ phase transformation mechanism using a layered Co(OH)(OCH3) precursor. Under sonication, the precursor was exfoliated and transformed into cobalt oxide nanocubanes in the presence of NaHCO3–Na2SiF6 buffer solution. The resulting cobalt catalyst with an average particle size less than 2 nm exhibited a turnover frequency of 0.023 per second per cobalt in photocatalytic water oxidation. X-ray absorption results suggested a unique nanocubane structure, where 13 cobalt atoms fully coordinated with oxygen in an octahedral arrangement to form 8 Co4O4 cubanes, which may be responsible for the exceptionally high OER activity.
TL;DR: The molecular components of the oxygen-sensing pathway are described, which include transcription factors that control the expression of hypoxia-induced genes and additional signaling pathways activated by the impact of oxygen deficiency on mitochondrial and chloroplast functioning.
Abstract: Oxygen is an indispensable substrate for many biochemical reactions in plants, including energy metabolism (respiration). Despite its importance, plants lack an active transport mechanism to distribute oxygen to all cells. Therefore, steep oxygen gradients occur within most plant tissues, which can be exacerbated by environmental perturbations that further reduce oxygen availability. Plants possess various responses to cope with spatial and temporal variations in oxygen availability, many of which involve metabolic adaptations to deal with energy crises induced by low oxygen. Responses are induced gradually when oxygen concentrations decrease and are rapidly reversed upon reoxygenation. A direct effect of the oxygen level can be observed in the stability, and thus activity, of various transcription factors that control the expression of hypoxia-induced genes. Additional signaling pathways are activated by the impact of oxygen deficiency on mitochondrial and chloroplast functioning. Here, we describe the molecular components of the oxygen-sensing pathway.
TL;DR: In this paper, surface oxidation of monolayer MoS2 (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method.
Abstract: In this work, surface oxidation of monolayer MoS2 (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method. Oxygen interaction with MoS2 shows that, thermodynamically, the surface tends to be oxidized. However, the dissociative absorption of molecular oxygen on the MoS2 surface is kinetically limited due to the large energy barrier at low temperature. This finding elucidates the air stability of MoS2 surface in the atmosphere. Furthermore, the presence of defects significantly alters the surface stability and adsorption mechanisms. The electronic properties of the oxidized surface have been examined as a function of oxygen adsorption and coverage as well as substitutional impurities. Our results on energetics and kinetics of oxygen interaction with the MoS2 monolayer are useful for the understanding of surface oxidation, air stability, and electronic properties of transition-metal dichalcogenides at the atomic scale.
TL;DR: It seems that the electron depletion layer by p-n junction of PdO-SnO2 may impede OH(-) adsorption, and the sensor response in wet atmosphere was greatly enhanced by loading Pd.
Abstract: The effect of water vapor on Pd-loaded SnO2 sensor was investigated through the oxygen adsorption behavior and sensing properties toward hydrogen and CO under different humidity conditions. On the basis of the theoretical model reported previously, it was found that the mainly adsorbed oxygen species on the SnO2 surface in humid atmosphere was changed by loading Pd, more specifically, for neat SnO2 was O–, while for 0.7% Pd-SnO2 was O2–. The water vapor poisoning effect on electric resistance and sensor response was reduced by loading Pd. Moreover the sensor response in wet atmosphere was greatly enhanced by loading Pd. It seems that the electron depletion layer by p–n junction of PdO-SnO2 may impede OH– adsorption.
TL;DR: In this paper, an all-vanadium redox flow battery (VRFB) was constructed with modified carbon paper electrodes in the high-performance no-gap design, and the roundtrip energy efficiency was improved from 63% to 76% at a current density of 200mV.
TL;DR: In this article, the authors examined LiI as an electrolyte and additive in Li oxygen cells with ethereal electrolyte solutions and found that at high concentrations of LiI, the presence of the salt promotes a side reaction that forms LiOH as a major product.
Abstract: Mankind has been in an unending search for efficient sources of energy. The coupling of lithium and oxygen in aprotic solvents would seem to be a most promising direction for electrochemistry. Indeed, if successful, this system could compete with technologies such as the internal combustion engine and provide an energy density that would accommodate the demands of electric vehicles. All this promise has not yet reached fruition because of a plethora of practical barriers and challenges. These include solvent and electrode stability, pronounced overvoltage for oxygen evolution reactions, limited cycle life and rate capability. One of the approaches suggested to facilitate the oxygen evolution reactions and improve rate capability is the use of redox mediators such as iodine for the fast oxidation of lithium peroxide. In this paper we have examined LiI as an electrolyte and additive in Li oxygen cells with ethereal electrolyte solutions. At high concentrations of LiI, the presence of the salt promotes a side reaction that forms LiOH as a major product. In turn, the presence of oxygen facilitates the reduction of I3− to 3I− in these systems. At very low concentrations of LiI, oxygen is reduced to Li2O2. The iodine formed in the anodic reaction serves as a redox mediator for Li2O2 oxidation.
TL;DR: This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces, which play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interface, thus leading to an excellent preferential CO oxidation performance.
Abstract: Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2–x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen...
TL;DR: Thermal treatment under a hydrogen or vacuum atmosphere improved the photoelectrochemical water oxidation activity up to 20 times and oxygen vacancies were created by the treatments in the near surface region, which increased the donor density and passivated the surface states.
Abstract: A one-dimensional zinc ferrite (ZnFe2O4) nanorod photoanode was prepared by a simple solution method on the F-doped tin oxide glass substrate. Thermal treatment under a hydrogen or vacuum atmosphere improved the photoelectrochemical water oxidation activity up to 20 times. The various physical characterization techniques used revealed that oxygen vacancies were created by the treatments in the near surface region, which increased the donor density and passivated the surface states. Hydrogen treatment was more effective and it was important to find optimum treatment conditions to take advantage of the positive role of oxygen vacancy as a source of electron donors and avoid its negative effect as electron trap sites.
TL;DR: A noble-metal-free and nanosized transition metal CuFe alloy encapsulated with a graphitic carbon shell as a highly efficient and durable electrocatalyst for the ORR in alkaline solution and affords enhanced charge transfer during the oxygen reduction process and superior durability.
Abstract: Understanding the interaction between a catalyst and oxygen has been a key step in designing better electrocatalysts for the oxygen reduction reaction (ORR) as well as applying them in metal–air batteries and fuel cells. Alloying has been studied to finely tune the catalysts’ electronic structures to afford proper binding affinities for oxygen. Herein, we synthesized a noble-metal-free and nanosized transition metal CuFe alloy encapsulated with a graphitic carbon shell as a highly efficient and durable electrocatalyst for the ORR in alkaline solution. Theoretical models and experimental results demonstrated that the CuFe alloy has a more moderate binding strength for oxygen molecules as well as the final product, OH–, thus facilitating the oxygen reduction process. Furthermore, the nitrogen-doped graphitic carbon-coated layer, formed catalytically under the influence of iron, affords enhanced charge transfer during the oxygen reduction process and superior durability. These benefits were successfully conf...
TL;DR: Limiting oxygen concentration values, which define the minimum partial pressure of oxygen that supports a combustible mixture, have been measured for nine commonly used organic solvents at elevated temperatures and pressures to define safe operating conditions for the use of oxygen with organicsolvents.
TL;DR: A more comprehensive understanding of the relationship between oxygen levels and lipid oxidation is necessary for the development of innovative antioxidant solutions and package designs that prolong the quality of foods containing lipids.
Abstract: The susceptibility of food oil to quality loss is largely determined by the presence of oxygen. This article reviews the current understanding concerning the effect of oxygen types, location, and concentration on the oxidative stability of foods. It also discusses the major factors that influence the interaction between oxygen and lipids such as antioxidants, prooxidants, reactive oxygen species (ROS), environmental conditions, and oxygen scavengers. Research has shown that the amount of oxygen needed to cause oxidation is generally very small and that by reducing oxygen concentration in containers to less than 2%, oxidative stability can be greatly enhanced. However, very few studies have systematically examined the oxygen levels needed to reduce, or inhibit, lipid oxidation processes. Thus, a more comprehensive understanding of the relationship between oxygen levels and lipid oxidation is necessary for the development of innovative antioxidant solutions and package designs that prolong the quality of foods containing lipids.
TL;DR: It is confirmed here that the hydrophilic carbon clusters are unreactive toward nitric oxide radical, which is a potent vasodilator that also has an important role in neurotransmission and cytoprotection and helps to explain the preclinical efficacy of these carbon nanoparticles in mitigating the deleterious effects of superoxide on traumatized tissue.
Abstract: Many diseases are associated with oxidative stress, which occurs when the production of reactive oxygen species (ROS) overwhelms the scavenging ability of an organism. Here, we evaluated the carbon nanoparticle antioxidant properties of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs) by electron paramagnetic resonance (EPR) spectroscopy, oxygen electrode, and spectrophotometric assays. These carbon nanoparticles have 1 equivalent of stable radical and showed superoxide (O2•−) dismutase-like properties yet were inert to nitric oxide (NO•) as well as peroxynitrite (ONOO−). Thus, PEG-HCCs can act as selective antioxidants that do not require regeneration by enzymes. Our steady-state kinetic assay using KO2 and direct freeze-trap EPR to follow its decay removed the rate-limiting substrate provision, thus enabling determination of the remarkable intrinsic turnover numbers of O2•− to O2 by PEG-HCCs at >20,000 s−1. The major products of this catalytic turnover are O2 and H2O2, making the PEG-HCCs a biomimetic superoxide dismutase.
TL;DR: It is shown that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides, and directly demonstrates the limited reversibility of the oxygenated species for the first time.
Abstract: Li-rich oxides continue to be of immense interest as potential next generation Li-ion battery positive electrodes, and yet the role of oxygen during cycling is still poorly understood. Here, the complex electrochemical behavior of Li4FeSbO6 materials is studied thoroughly with a variety of methods. Herein, we show that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides. Moreover, we directly demonstrate the limited reversibility of the oxygenated species (O2(n-); n = 1, 2, 3) for the first time. We also find that during charge to 4.2 V iron is oxidized from +3 to an unusual +4 state with the concomitant formation of oxygenated species. Upon further charge to 5.0 V, an oxygen release process associated with the reduction of iron +4 to +3 is present, indicative of the reductive coupling mechanism between oxygen and metals previously reported. Thus, in full state of charge, lithium removal is fully compensated by oxygen only, as the iron and antimony are both very close to their pristine states. Besides, this charging step results in complex phase transformations that are ultimately destructive to the crystallinity of the material. Such findings again demonstrate the vital importance of fully understanding the behavior of oxygen in such systems. The consequences of these new aspects of the electrochemical behavior of lithium-rich oxides are discussed in detail.
TL;DR: The increased number of oxygen vacancies after plasma treatment resulting in an increased carrier density is interpreted as the main cause for the enhanced oxygen evolution reaction activity and leads to a significant enhancement of the photocurrent response.
Abstract: The incorporation of oxygen vacancies in hematite has been investigated as a promising route to improve oxygen evolution reaction activity of hematite photoanodes used in photoelectrochemical water oxidation. However, introducing oxygen vacancies intentionally in α-Fe2O3 for active solar water splitting through facile and effective methods remains a challenge. Herein, air plasma treatment is shown to produce oxygen vacancies in α-Fe2O3, and ultrathin α-Fe2O3 nanoflakes are used to investigate the effect of oxygen vacancies on the performance of photoelectrochemical oxygen oxidation. Increasing the plasma treatment duration and power is found to increase the density of oxygen vacancies and leads to a significant enhancement of the photocurrent response. The nanoflake photoanode with the optimized plasma treatment yields an incident photo-to-current conversion efficiency of 35.4% at 350 nm under 1.6 V vs RHE without resorting to any other cocatalysts, an efficiency far exceeding that of the pristine α-Fe2O3...
TL;DR: In this paper, a review examines the involvement of cytochrome P450 (CYP) enzymes in the formation of reactive oxygen species in biological systems and discusses the possible involvement of reactive oxidants and enzymes in cancer.
Abstract: This review examines the involvement of cytochrome P450 (CYP) enzymes in the formation of reactive oxygen species in biological systems and discusses the possible involvement of reactive oxygen species and CYP enzymes in cancer. Reactive oxygen species are formed in biological systems as byproducts of the reduction of molecular oxygen and include the superoxide radical anion (∙O2-), hydrogen peroxide (H2O2), hydroxyl radical (∙OH), hydroperoxyl radical (HOO∙), singlet oxygen ((1)O2), and peroxyl radical (ROO∙). Two endogenous sources of reactive oxygen species are the mammalian CYP-dependent microsomal electron transport system and the mitochondrial electron transport chain. CYP enzymes catalyze the oxygenation of an organic substrate and the simultaneous reduction of molecular oxygen. If the transfer of oxygen to a substrate is not tightly controlled, uncoupling occurs and leads to the formation of reactive oxygen species. Reactive oxygen species are capable of causing oxidative damage to cellular membranes and macromolecules that can lead to the development of human diseases such as cancer. In normal cells, intracellular levels of reactive oxygen species are maintained in balance with intracellular biochemical antioxidants to prevent cellular damage. Oxidative stress occurs when this critical balance is disrupted. Topics covered in this review include the role of reactive oxygen species in intracellular cell signaling and the relationship between CYP enzymes and cancer. Outlines of CYP expression in neoplastic tissues, CYP enzyme polymorphism and cancer risk, CYP enzymes in cancer therapy and the metabolic activation of chemical procarcinogens by CYP enzymes are also provided.
TL;DR: Using visible light optical coherence tomography (vis-OCT), accurate and robust measurement of retinal oxygen metabolic rate (rMRO2) noninvasively in rat eyes is demonstrated and has the potential to reveal the fundamental role of oxygen metabolism in various retinal diseases.
Abstract: The lack of capability to quantify oxygen metabolism noninvasively impedes both fundamental investigation and clinical diagnosis of a wide spectrum of diseases including all the major blinding diseases such as age-related macular degeneration, diabetic retinopathy, and glaucoma. Using visible light optical coherence tomography (vis-OCT), we demonstrated accurate and robust measurement of retinal oxygen metabolic rate (rMRO2) noninvasively in rat eyes. We continuously monitored the regulatory response of oxygen consumption to a progressive hypoxic challenge. We found that both oxygen delivery, and rMRO2 increased from the highly regulated retinal circulation (RC) under hypoxia, by 0.28 ± 0.08 μL min-1 (p < 0.001), and 0.20 ± 0.04 μL min-1 (p < 0.001) per 100 mmHg systemic pO2 reduction, respectively. The increased oxygen extraction compensated for the deficient oxygen supply from the poorly regulated choroidal circulation. Results from an oxygen diffusion model based on previous oxygen electrode measurements corroborated our in vivo observations. We believe that vis-OCT has the potential to reveal the fundamental role of oxygen metabolism in various retinal diseases.
TL;DR: In this paper, the degradation of catalysts induced by H 2 O 2 was investigated by contacting them ex situ with various amounts of H 2 o 2 and showed that the degradation increased with increasing amounts of HO 2 2.
Abstract: 7 8 Fe-N-C and CoN -C materials are promising catalysts for reducing oxygen in fuel cells. The degradation of such catalysts induced by H 2 O 2 was investigated by contacting them ex situ with various amounts of H 2 O 2. The degradation increased with increasing amounts of H 2 O 2. The effect was most severe for Cr-N-C followed by Fe-N-C and last by CoN -C. Treatment with H 2 O 2 leads to diminished oxygen reduction activity at high potential and/or reduced transport properties at high current density in fuel cell. From spectroscopic characterisation, it was found that 66 and 80% of the CoN x C y and FeN x C y moieties present in pristine catalysts survived the extensive H 2 O 2 treatment, respectively. In parallel, the activity for oxygen reduction was divided by ca 6–10 for Fe-N-C and by ca 3 for CoN -C. The results suggest that the main degradation mechanism in fuel cell for such catalysts is due to a chemical reaction with H 2 O 2 that is generated during operation. The super-proportional decrease of the oxygen reduction activity with loss of FeN x C y and CoN x C y moieties suggests either that only a small fraction of such moieties are initially located on the top surface, or that their turnover frequency for oxygen reduction was drastically reduced due to surface oxidation by H 2 O 2 .
TL;DR: ROS trapping experiments demonstrated that although the direct hole oxidation was mainly responsible for phenol photodegradation on both g-C3N4 catalysts, molecular oxygen activation processes on their surface greatly influenced the whole phenol degradation efficiency.
Abstract: The selectivity of molecular oxygen activation on the exfoliated graphitic carbon nitride (g-C3N4) and its influence on the photocatalytic phenol degradation process were demonstrated. Compared with bulk g-C3N4, the exfoliated nanosheet yielded a 3-fold enhancement in photocatalytic phenol degradation. ROS trapping experiments demonstrated that although the direct hole oxidation was mainly responsible for phenol photodegradation on both g-C3N4 catalysts, molecular oxygen activation processes on their surface greatly influenced the whole phenol degradation efficiency. Reactive oxygen species and Raman spectroscopy measurements revealed that oxygen was preferentially reduced to ·O2– by one-electron transfer on bulk g-C3N4, while on g-C3N4 nanosheet the production of H2O2 via a two-electron transfer process was favored due to the rapid formation of surface-stabilized 1,4-endoperoxide. The latter process not only promotes the separation of photogenerated electron–hole pairs but also greatly facilitates reacti...
TL;DR: In this article, the authors performed ReaxFF-molecular dynamics simulations of the oxidation of aluminum nanoparticles (ANPs) at three different temperatures (300, 500, and 900 K) and two different initial oxygen densities (0.13 and 0.26 g/cm3) to elucidate the mechanism of oxidation kinetics of the ANPs and to study the oxidation states in the oxide layer.
Abstract: We performed ReaxFF-molecular dynamics (MD) simulations of the oxidation of aluminum nanoparticles (ANPs) at three different temperatures (300, 500, and 900 K) and two different initial oxygen densities (0.13 and 0.26 g/cm3) to elucidate the mechanism of oxidation kinetics of the ANPs and to study the oxidation states in the oxide layer. Our result shows that the mechanism of the oxidation of the ANPs is as follows: hot-spots and high-temperature areas are created by adsorption and dissociation of oxygen molecules on the surface of the ANPs; void spaces are generated because of hot-spots and high-temperature areas; the void spaces significantly lower a reaction barrier for oxygen diffusion (by up to 92%) and make this process exothermic. Subsequently, an oxide layer is developed by this accelerated oxygen diffusion. Our results also indicate that the oxidation of the ANPs depends on combined effects of the temperature and the oxygen gas pressure because such conditions have effects on not only the oxide l...