Liberation Of Oxygen Research Articles

Band structure controls of SrTiO3 towards two-step overall water splitting

We prepared two types of SrTiO3-based photocatalyst powders, Bi,Ga-doped SrTiO3 and In,V-doped SrTiO3. UV–visible reflectance spectra of these powders indicated that their band-gaps remained constant in comparison with that of SrTiO3. In conjunction with the reported band structure control of oxides, our results indicated that Bi,Ga-doped SrTiO3 and In,V-doped SrTiO3 formed isolated mini-bands composed of Bi 6s orbitals in the forbidden band above the valence band, composed of O 2p, and V 3d orbitals below the conduction band, composed of Ti 3d, resulting in the observed visible-light absorption. Utilizing the prepared SrTiO3-based photocatalysts, we established a two-step overall water-splitting system, in which simultaneous liberation of hydrogen and oxygen with a molar ratio of ∼2:1 was observed in the presence of I− (NaI) under irradiation with UV-containing light. Moreover, visible light contributed the cycling of I−/IO3− redox mediators, resulting in enhanced hydrogen and oxygen liberation when compared to irradiation with UV light alone.

Sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in Early to Middle Ordovician greenhouse oceans

Despite marine geochemical records indicating widespread oxygenation of the biosphere in the terminal Neoproterozoic Era, Late Cambrian records point to the persistence of deep-water anoxia and potential for development of euxinic conditions. The Late Cambrian SPICE (Steptoean Positive Carbon-Isotope Excursion) event, however, is a globally recognized chemostratigraphic marker that likely represents significant organic carbon burial and subsequent liberation of oxygen to the biosphere. Here, we present high-resolution carbon and sulfur isotope profiles from Early to Middle Ordovician carbonate rocks from the Argentine Precordillera and Western Newfoundland to constrain oceanic redox conditions in the post-SPICE world. Marine C-isotope profiles record relatively stable behavior (excursions < 3‰) that is characteristic of greenhouse climates. Marine S-isotope profiles record short-term (< 10 6 yr), rhythmic variation superimposed over a longer term (~ 10 7 yr) signal. Substantial isotopic heterogeneity between average S-isotope values of different sections (15–25‰) suggests the Ordovician marine sulfate reservoir was not well mixed, indicating a low marine sulfate concentration (likely < 2 mM or less than 10% modern). Short-term variation (7‰ excursions over 1 Myr) is consistent with a small sulfate reservoir size and is best explained by the rhythmic oxidation of a deep-water reactive HS − reservoir. Greenhouse intervals, such as that represented by the Ordovician ocean, are often associated with deep-water anoxia, and the presence of a persistent, deep water HS − reservoir that is fed through bacterial sulfate reduction (BSR) is not unexpected. A broadly sympathetic relationship between carbon and sulfur isotope systems over long time scales (~ 10 7 yr) suggests that the extent of deep-ocean euxinia was moderated by changes in organic productivity, which fueled BSR and production of reduced sulfide species. By contrast, short-term (< 10 6 yr) sulfur isotope variation appears to be decoupled from the marine carbon-isotope signal. We suggest that this apparent decoupling reflects a combination of elevated pCO 2 during greenhouse times—which acts to dampen C-isotope response—and relatively small-scale fluctuations in organic productivity that affected the position of the marine oxycline and the balance of HS − production and reoxidation.

Sodium Bromate: An Eco-Friendly Brominating and Oxidizing Reagent

Sodium bromate is commercially available as an inexpensive stable white crystal, and has been extensively used in organic synthesis as an eco-friendly brominating and oxidizing reagent. It decomposes at 381 ˚C with liberation of oxygen. It can oxidize primary alcohols to aldehydes, secondary alcohols to ketones, sulfides to sulfoxides, hydroquinones and polyaromatics to quinones, thiols to disulfides, iodobenzenes to iodoxybenzenes, and ω,ω-diols to dicarboxylic acids or lactones. Under different sets of conditions, the oxidation can result in the formation of esters and carboxylic acids. [¹] It has been used for oxidative cleavages of alkyl, trimethylsilyl, t-butyldimethylsilyl, tetrahydropyranyl ethers, and ethylene acetals to the corresponding carbonyl compounds. [²] [³] The transformations of benzylidene acetals to hydroxy esters with NaBrO3˙Na2S2O4 in EtOAc-H2O biphasic medium are readily accomplished. [4] [5] Even more interesting is the finding that the reaction of cyclic ethers with sodium bromate in the presence of catalytic amounts of hydrobromic acid gave lactones. [6] Sodium bromate can also serve as an effective bromohydroxylation reagent for alkenes, alkynes, and allylic alcohols. [7] It has also been reported to be a powerful brominating agent for aromatic compounds including phenols, anilines, aromatic ethers, and benzenes. [8] [9]

Studies on Formation and Decomposition of the Layered Cobaltite LixNayCoO2

Lithium-sodium cobaltite LixNayCoO2(x≈y≈0.5) with ordered layered structure is promising thermoelectric material. Here we report the peculiarities of this phase formation and decomposition processes studied by TG/DTA, XRD, SEM, and TEM methods. Significant weight loss resulting from oxygen liberation and endothermic effect atT≈1000°C are the main features of the LixNayCoO2formation. Decomposition of the ordered phase is accompanied by exothermic effect at≈940°C and the weight increase. Electron microscopic study shows that the lithium-sodium cobaltite decomposes into LiCoO2and γ-Na0.7CoO2. Lattices of the initial phase and formed ones demonstrate mutual orientation.

On the origin of decomposition of triphenyl phosphite ozonide accelerated by ammonia or pyridine water solution

The decomposition of triphenyl phosphite ozonide (TPPO) has been well recognized as a potential source of singlet oxygen (O 2, 1Δ g) for the chemical oxygen–iodine laser. Experimental observations suggested that ammonia or pyridine water solution can accelerate the decomposition of TPPO, and hydroxyl ion is responsible for accelerating singlet oxygen liberation during this decomposition. In this paper, we studied the mechanism of OH −-accelerated reaction using density functional theory (DFT) at B3LYP/6-31+G* levels of theory. The calculations reveal a favorable free energy pathway for hydroxide-accelerated decomposition of TPPO, i.e. nucleophilic addition at phosphorus, followed by elimination of phenoxy group and subsequent liberation of singlet oxygen. The solvent effects were studied using a polarizable continuum model. The frontier molecular orbitals of the ozonides, atom–atom Wiberg bond index and corresponding atomic charges were also investigated to shed further light on the reaction pathway.

In Situ FTIR Spectroscopy Study of Li/LiNi[sub 0.8]Co[sub 0.15]Al[sub 0.05]O[sub 2] Cells with Ionic Liquid-Based Electrolytes in Overcharge Condition

We developed a methodology of in situ Fourier transform infrared (FTIR) measurements of gaseous products formed in an electrochemical cell upon polarization. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathodes were explored at potentials of up to 5.5 V vs Li in the ionic liquid (IL)-based electrolyte solution, LiTFSI/N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. The polarization of the NCA electrodes formed CO 2 and CO due to the liberation of oxygen and the parallel dissolution of nickel ions, which oxidizes the carbon black in the composite electrode. The oxygen was mostly liberated from the NCA and also due to minor contribution from the surface groups on the carbon black additive.

Placental Expression of 2,3 Bisphosphoglycerate Mutase in IGF-II Knock out Mouse: Correlation of Circulating Maternal 2,3 Bisphosphoglycerate and Fetal Growth

Bisphosphoglycerate mutase (BPGM) catalyses the formation of 2,3 bisphosphoglycerate (BPG) a ligand of haemoglobin. BPG facilitates liberation of oxygen from haemoglobin at low oxygen tension enabling efficient delivery of oxygen to tissues. We describe expression of BPGM in mouse labyrinthine trophoblasts, located at the maternal–placental interface. Expression is lower in placentae of igf2 +/− knockout mice, a widely used model of growth restriction, compared to wild type placentae. Circulating maternal BPG increased throughout gestation but this increase was less in wt mothers carrying igf2 +/− pups than in those carrying exclusively wt pups. This reduction was observed well before term and may contribute to the low birth weight of igf2 +/− pups. Strikingly, we also measured reductions of fetal and placental weight in wt littermates of igf2 +/− pups compared to pups developing in an exclusively wt environment. These data suggest that placental expression of BPGM can influence maternal BPG concentrations and supports a hypothesis under which BPG synthesized in the placenta may act on maternal haemoglobin to enhance delivery of oxygen to the developing fetus.

Specific features of the reaction of vanadyl acetylacetonate with tert-butyl hydroperoxide

Reaction of vanadyl acetylacetonate with tert-butyl hydroperoxide (benzene, 20°C) at any molar ratio leads to the elimination of ligand and its oxidation mainly to CO2 and acetic acid. At the (acac)2VO: t-BuOOH ratio above 1:10 liberation of oxygen partially in the singlet state takes place.

Annealing Effects on Zn(Co)O: From Para- to Ferromagnetic Behavior

Zn1−xCoxO nanocrystals were produced by forced hydrolysis in diethyleneglycol. The as-produced crystals are paramagnetic. However, heating at 400 °C under a nitrogen atmosphere for 1 h induces ferromagnetism at room temperature, characterized by coercive field (0.38 kOe) and magnetization at 10 kOe (0.10 μB/Co) similar to the values reported recently for nanocrystalline Co:ZnO aggregates. To understand this evolution, we have characterized the samples by chemical and physical analyses including X-ray diffraction (XRD), transmission electron microscopy (TEM), UV−visible−IR absorption spectroscopy, magnetic measurements, and EPR experiments. These analyses show that the Co ions are incorporated into the wurtzite structure, forming a Zn1−xCoxO solid solution. X-ray diffraction and electron microscopy failed to detect secondary phases, neither before nor after the thermal treatment. However, the shape of the nanoparticles is modified and becomes more spherical upon annealing, which gives evidence of an important diffusion of atomic species. X-band electron paramagnetic resonance (EPR) reveals the presence of magnetic clusters in the annealed samples. Both the magnetic and optical properties show that these are Co clusters that have grown at the expense of the cobalt diluted in the host matrix. The thermal treatment survey performed by thermogravimetric analysis coupled with mass spectrometry and IR spectroscopy gives evidence of desorption of organic species and liberation of oxygen from the surface of the particles. This study then suggests that the origin of the magnetism believed to be intrinsic to the material in many prior works is extrinsic in nature and is due to the diffusion of cobalt and oxygen species at the surface of the particles, where Co forms nanoclusters while most of the oxygen is liberated in the annealing process.

Nanowire-structured titanate with anatase titania: Characterization and photocatalytic activity

Nanowire-structured titanate with titanium(IV) oxide (titania) was obtained by calcination of potassium ion-containing titanate nanowires prepared through alkali treatment of titania nanoparticles. The presence of potassium ions in the as-synthesized titanate nanowires was required for maintenance of the nanowire structure under the conditions of post-heat treatment. The crystallite structure, composition, morphology, specific surface area, pore volume distribution, and optical properties were found to be dependent on the temperature at which titanate nanowires were calcined. Photocatalytic activity was examined using three probe reactions: oxidative decomposition of acetic acid in an aqueous solution, oxygen liberation from an aqueous silver sulfate solution, and hydrogen liberation from an aqueous methanol solution in the presence of hexachloroplatinic acid as a precursor of photodeposition of platinum particles. Detailed characterization and results of photocatalytic activity tests revealed that titanate crystallites greatly contributed to the photocatalytic activities of the calcined nanowires except for photocatalytic hydrogen liberation. It was found that platinum was preferentially photodeposited on anatase crystallites rather than on titanate crystallites for hydrogen liberation.

New Method for Determination of Molybdenum(VI) through Flow Injection Analysis Via the Consumption of Liberated Oxygen from Reaction System Ammonia-Hydrogen peroxide-Molybdenum(VI) in the Presence of Pyrogallol

This piece of research work aims to study one of the most difficult reaction and determination due to continuous and rapid variation of reaction products and the reactants. As molybdenum (VI) aid in the decomposition of hydrogen peroxide in alkaline medium of ammomia, thus means a continuous liberation of oxygen which cuases and in a continuous manner a distraction in the measurement process. On this basis pyrogallol was used to absorbe all liberated oxygen and the result is an a clean undisturbed signals. Molybdenum (VI) was determined in the range of 4-100 ?g.ml-1 with percentage linearity of 99.8% or (4-300 ?g.ml-1 with 94.4%) while L.O.D. was 3.5 ?g.ml-1. Interferring ions (cations and anions) were studied and their main effect was reduced using mini column cataining resin, or the separation of molybdenum via its precipitation prior to injection. The reaction system and manifold were used to determine pyrogallol (4-40 ?g.ml-1, L.O.D. 80 ?M) and hydrogen peroxide (0.1-5M, L.O.D. 50 mM). Relative standard diviation was better the 1%.

New Method for Determination of Molybdenum(VI) through Flow Injection Analysis Via the Consumption of Liberated Oxygen from Reaction System Ammonia-Hydrogen peroxide-Molybdenum(VI) in the Presence of Pyrogallol

This piece of research work aims to study one of the most difficult reaction and determination due to continuous and rapid variation of reaction products and the reactants. As molybdenum (VI) aid in the decomposition of hydrogen peroxide in alkaline medium of ammomia, thus means a continuous liberation of oxygen which cuases and in a continuous manner a distraction in the measurement process. On this basis pyrogallol was used to absorbe all liberated oxygen and the result is an a clean undisturbed signals. Molybdenum (VI) was determined in the range of 4-100 ?g.ml-1 with percentage linearity of 99.8% or (4-300 ?g.ml-1 with 94.4%) while L.O.D. was 3.5 ?g.ml-1. Interferring ions (cations and anions) were studied and their main effect was reduced using mini column cataining resin, or the separation of molybdenum via its precipitation prior to injection. The reaction system and manifold were used to determine pyrogallol (4-40 ?g.ml-1, L.O.D. 80 ?M) and hydrogen peroxide (0.1-5M, L.O.D. 50 mM). Relative standard diviation was better the 1%.

No Water, No Cyanobacteria—No Calc-alkaline Magmas: Progressive Oxidation of the Early Oceans May Have Contributed to Modernize Island-Arc Magmatism

A remarkable change in Earth history took place in Late Archean time. The time-span 3.0-2.5 Ga marks the progressive end of the low-P, high-T subduction regime and komatiitic magmatism. This coincides with a period of rapid crustal growth, when up to 70% of the present continental masses formed. Most authors would agree that such change indeed took place, although the why and how remain a controversial issue. By the end of the Archean, calc-alkaline magmatism was firmly established, and a key point relates to the nature of these arc-related igneous rocks. These magmas are not only characterized by silica enrichment, but are also more oxidized than their primitive counterparts (e.g., komatiites, MORBs). Thus, an increase in the oxygen fugacity of the upper mantle is here regarded as the turning point that allowed formation of calc-alkaline complexes during Archean time. In this respect we suggest that the appearance of cyanobacteria more than 3.7 billion years ago, may have played a decisive role in changing the old Archean tectonomagmatic scenario, by increasing the oxidizing potential of the oceans, and therefore inducing iron oxide precipitation onto the ocean floors in the form of FeO(OH)-like minerals. If subduction processes, whatever the type, were already active by Early—Meso Archean time (as seems to be the case), it follows that a massive amount of iron oxides must have been introduced into the mantle wedge. The melting of these chemical sediments would have resulted in liberation of oxygen, thus contributing to the oxidation of this realm, and therefore, triggering the onset of "modern" calc-alkaline, magmatism.

Preparation and Characterization of Bismuth Tungstate Polycrystalline Flake-Ball Particles for Photocatalytic Reactions

Micrometer-sized spherical polycrystalline particles of bismuth tungstate (Bi2WO6) of a hierarchical “flake-ball” shape were prepared by a facile hydrothermal reaction without using any surfactants and polymers as structure-directing agents. The flake-ball particles were assemblies of polycrystalline flakes composed of rectangular platelets with a lateral size of a few hundred nanometers and thickness of 20−35 nm. An excess amount of a tungstate precursor (10%) and an acidic condition (pH 1.2) during the hydrothermal reaction were required to obtain a high yield of uniform particles with the flake-ball architecture. The mechanism by which the flake-ball particles are formed is discussed. The photocatalytic activities under ultraviolet light irradiation were investigated by using oxygen liberation from water, oxidative decomposition of acetic acid in an aqueous solution, and oxidative decomposition of gaseous acetaldehyde. The photocatalytic activity level of the flake-ball particles was higher than the photocatalytic activity levels of other Bi2WO6 samples prepared by conventional solid-state and hydrothermal reactions using a stoichiometric amount of a tungstate precursor. It was revealed that the 10% excess amount of tungsten plays a key role in the high level of photocatalytic activity of flake-ball particles.

Pro-inflammatory feedback activation cycle evoked by attack of Vibrio cholerae cytolysin on human neutrophil granulocytes

Vibrio cholerae cytolysin (VCC) is a pore-forming toxin that is secreted in precursor form (pro-VCC) and requires proteolytic cleavage in order to attain membrane-permeabilizing properties. Pro-VCC can be activated both in solution and membrane-bound state. Processing of membrane-bound pro-VCC can in turn be achieved through the action of both cell-associated and soluble proteases. The current investigation describes the interaction of VCC with human neutrophil granulocytes. It is shown that pro-VCC binds to these cells and is cleaved by cell-bound serine proteases. Membrane permeabilization leads to granulocyte activation, as witnessed by the generation of reactive oxygen metabolites and liberation of granule constituents. A mutant toxin with unaltered binding properties but devoid of pore-forming activity did not elicit these effects. The secreted proteases cleave and activate further bound- and non-bound pro-VCC. A positive feedback loop is thus created that results in enhanced cytotoxicity towards both the targeted granulocytes and towards bystander cells that are not primarily killed by the protoxin. Thus, activation of neutrophil granulocytes by VCC fuels a positive feedback cycle that will cripple immune defence, augment inflammation, and enhance the cytotoxic action of the toxin on neighbouring tissue cells.

High temperature corrosion of superalloys in a molten salt under an oxidizing atmosphere

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. So, it is essential to choose the optimum material for the process equipment for handling a molten salt. In this study, corrosion behavior of Inconel 713LC, Nimonic 80A and Nimonic 90 in a molten LiCl–Li 2O salt under an oxidizing atmosphere was investigated at 675 °C for 72–216 h. Inconel 713LC alloy showed the highest corrosion resistance among the examined alloys. Corrosion products of Inconel 713LC were Cr 2O 3, NiCr 2O 4, Ni and NiO, and those of Nimonic 80A were Cr 2O 3, LiFeO 2, (Cr, Ti) 2O 3 and Li 2Ni 8O 10 while Cr 2O 3, (Cr, Ti) 2O 3, LiAlO 2 and CoCr 2O 4 were produced from Nimonic 90. Inconel 713LC showed a local corrosion behavior and Nimonic 80A, Nimonic 90 showed a uniform corrosion behavior.

Grain Boundary Defects Induced Switching in Zn- Bi- Mo Ceramic

Three Zinc Molybdenum ceramic samples doped Bi have been prepared according to the chemical formula (1-x) ZnO – 0.2MoO3 – xBi2O3, where (x = 0.2, 0.5, 1.0) mol %. The samples were studied at room temperature through X-ray Diffraction analysis, SEM, EDAX, I-V characteristics and C-V measurements. The results decleared the presences of two phases; ZnO as a major phase beside Bi2MoO6 as a minor phase. At lower Bi additions; Bi and Mo ions are highly segregated at the grain boundaries, while at higher additions more homogenous distribution for these ions inside the grain is observed. Some pores are observed around the batches of the minor phase and at the grain boundaries. The grain size is enlarged with increasing Bi addition; while the number and size of the pores are decrease. Creation of the pores is attributed to oxygen liberation from the surface of the sample during sintering. Formation of Schottky barrier is indicated via I-V and C-V measurements and attributed to Zn vacancies at the grain boundary. Interface potential barrier, donor density, interface state density and barrier width are decrease with increasing Bi addition. I-V characteristics revealed voltage switching. The switching voltage E0 decreases with increasing Bi addition and it is reproducible even after several on-off cycles.

Dose-dependent decomposition rate constants of hydrogen peroxide in small-scale bio filters

This study investigated rates of hydrogen peroxide (H 2O 2) degradation in biofilters, to provide information for more accurate treatment regimes in recirculation systems and more accurate prediction of effluent H 2O 2 concentrations. Sodium percarbonate (2Na 2CO 3·3H 2O 2) was applied to small-scale recirculation systems with active bio filters. Three different treatment dosages corresponding to an initial hydrogen peroxide (H 2O 2) concentration ( C 0) of 13.0, 26.0 or 39.0 ppm were used ( N = 18). Decomposition rate constants ( k e) of H 2O 2 were identified by exponential regression analysis of recurrent water samples from treatment start to complete decomposition. The chemical fate of H 2O 2 obeyed first order kinetics with half-lives inversely correlated with C 0. Decomposition rate constants were significantly related to the amount of organic matter (BOD 5) and initial dosage of H 2O 2, and ranged from k e = 0.451 ( C 0 = 26 ppm; BOD 5 = 2.0 mg O 2/l) to k e = 3.686 h −1( C 0 = 13 ppm; BOD 5 = 16.1 mg O 2/l). Surface specific reduction (SSR) of H 2O 2 in biofilters was positively related to dosage concentration for both levels of BOD 5, where SSR from 55 to 220 mg H 2O 2 m −2 t −1 were found. Oxygen liberation was positive correlated to C 0 and BOD 5, indicating that hyperoxic conditions can arise if large amounts of sodium percarbonate are added to water with high organic matter content. This study assesses the environmental fate of H 2O 2 in a closed recirculation system with biofilters, simulating recirculation aquaculture systems. The information can be applied to hydraulic model to predict actual treatment concentrations in aquaculture facilities and to assess effluent pulse from simulated treatment regimes.

Fick's law of diffusion depth profiles applied to the degradation of oxidized polystyrene during ARXPS analysis

AbstractAngle‐resolved x‐ray photoelectron spectroscopy (ARXPS) measurements were made, using Al Kα and Mg Kα radiation alternately, on a polystyrene sample that had been exposed to a helium plasma. It was observed that oxygen was introduced into the sample surface by the plasma treatment, and that some of it was lost over a period of 5 h under x‐ray irradiation in the vacuum of the spectrometer. Laplace transforms of Fick's law of diffusion profiles were derived and applied to the data. The ARXPS results obtained in this study are consistent with a sample history in which the oxidation of the polymer surface resulting from exposure to plasma is controlled by a diffusion process, whereas the loss of oxygen during exposure to x‐rays is principally controlled by a first‐order reaction such as the liberation of oxygen (presumably as CO2) from carbon–oxygen groups by the action of radicals created by the ionizing radiation. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Investigation of femtosecond laser assisted nano and microscale modifications in lithium niobate

A study of the physicochemical modifications at micro and nano scales as a result of femtosecond laser processing is essential to explore the viability of this process to write surface and subsurface structures in transparent media. To this end, scanning probe and transmission electron microscopy and spectroscopy techniques were used to study these modifications in lithium niobate. A variable power Ti:Sapphire system (800nm,300fs) was used to determine the ablation threshold of (110) lithium niobate, and to write these structures in the substrate for subsequent analysis. Higher processing energies were used to amplify the laser-induced effects for a clear understanding. Evidences of a number of simultaneously occurring mechanisms such as melting, ablation, and shockwave propagation are observed in the scanning electron microscope (SEM) micrographs. X-ray diffraction (XRD), Auger and electron dispersive spectroscopy (EDS) studies indicate loss of lithium and oxygen from the immediate surface of the processed region. Raman spectroscopy analysis indicates an unchanged chemical composition in the bulk, though at a loss of crystallinity. The surface and subsurface damage structures display a different nature of the amorphous and damaged material subregions, as observed in the respective transmission electron microscopy micrographs. A variation in oxygen counts is observed in the amorphous subregions, indicative of oxygen liberation and elemental segregation during the process. The oblate subsurface structure contains a void at the top, indicative of localized explosive melting and rapid quenching of the affected material. Thus, femtosecond laser writing produces different structures on the surface and the subsurface of the material. These results provide physicochemical insight towards writing chemically and spatially precise structures using femtosecond lasers, and will have direct implications in optical memory and waveguide writing and related applications.