Liberation Of Oxygen Research Articles

Improved activity of SnO for the photocatalytic oxygen evolution

SnO prepared by soft chemistry exhibits a black color and semiconducting properties. The X-ray diffraction indicates a tetragonal symmetry (SG: P4/nmm) with nano crystallites of an average size of 85nm. The forbidden band, determined from the diffuse reflectance is found to be 1.46eV. The electrical conductivity occurs by polaron hopping and follows an Arrhenius type law with activation energy of 0.21eV, the change in the slope at 526K is attributed to the oxidation to SnO2. The photo-electrochemical study shows n type conduction with a flat band potential of −0.45V, close to the photocurrent onset potential (−0.40V). The electrochemical impedance spectroscopy shows the bulk contribution of SnO (Rb=1.7kΩcm2) and decreases down to 1.89kΩcm2 under illumination. The photocatalytic properties have been evaluated for the first time for to the oxygen evolution. The valence band, deriving from Sn2+: 5p orbital with a potential (−0.80VSCE/5.55eV), is suitably positioned with respect to O2/H2O level (∼0.6VSCE), leading to water oxidation under visible light. The best performance occurs at pH∼7 with an oxygen liberation rate of 23µmolmLh−1 (mg catalyst)−1 and a quantum efficiency of 1.2%. An improvement of ∼13% is observed on the system SnO/clay.

Life History Responses and Feeding Behavior of Microcrustacea in Altered Gravity – Applicability in Bioregenerative Life Support Systems (BLSS)

Manned space missions, as for example to the planet Mars, are a current objective in space exploration. During such long-lasting missions, aquatic bioregenerative life support systems (BLSS) could facilitate independence of resupply from Earth by regenerating the atmosphere, purifying water, producing food and processing waste. In such BLSS, microcrustaceans could, according to their natural role in aquatic ecosystems, link oxygen liberating, autotrophic algae and higher trophic levels, such as fish. However, organisms employed in BLSS will be exposed to high acceleration (hyper- g) during launch of spacecrafts as well as to microgravity (μg) during space travel. It is thus essential that these organisms survive, perform and reproduce under altered gravity conditions. In this study we present the first data in this regard for the microcrustaceas Daphniamagna and Heterocypris incongruens. We found that after hyper-g exposure (centrifugation) approximately one third of the D. magna population died within one week (generally indicating that possible belated effects have to be considered when conducting and interpreting experiments during which hyper-g occurs). However, suchlike and even higher losses could be countervailed by the surviving daphnids’ unaltered high reproductive capacity. Furthermore, we can show that foraging and feeding behavior of D. magna (drop tower) and H. incongruens (parabolic flights) are rarely altered in μg. Our results thus indicate that both species are suitable candidates for BLSS utilized in space.

Enhanced Visible-Light-Sensitive Two-Step Overall Water-Splitting Based on Band Structure Controls of Titanium Dioxide and Strontium Titanate

Visible light-induced two-step overall water-splitting was achieved by combining two types of photocatalysts, which were prepared by introducing foreign elements into rutile titanium dioxide (TiO2) and strontium titanate (SrTiO3) with a controlled electronic band structure. Rutile TiO2 and SrTiO3 were doped with chromium and tantalum (Cr,Ta-TiO2) and with rhodium (Rh-SrTiO3), respectively, to introduce visible-light sensitivity. Under irradiation with only visible light from a 420-nm LED lamp, the simultaneous liberation of hydrogen and oxygen with a molar ratio of ~2:1 was achieved with these two types of photocatalysts in the presence of iodate ion/iodide ion as a redox mediator.

Potassium Poly(heptazine imides) from Aminotetrazoles: Shifting Band Gaps of Carbon Nitride‐like Materials for More Efficient Solar Hydrogen and Oxygen Evolution

AbstractPotassium poly(heptazine imide) (PHI) is a photocatalytically active carbon nitride material that was recently prepared from substituted 1,2,4‐triazoles. Here, we show that the more acidic precursors, such as commercially available 5‐aminotetrazole, upon pyrolysis in LiCl/KCl salt melt yield PHI with the greatly improved structural order and thermodynamic stability. Tetrazole‐derived PHIs feature long‐range crystallinities and unconventionally small layer stacking distances, leading to the altered electronic band structures as shown by Mott–Schottky analyses. Under the optimized synthesis conditions, visible‐light driven hydrogen evolution rates reach twice the rate provided by the previous gold standard, mesoporous graphitic carbon nitride, which has a much higher surface area. More interestingly, the up to 0.7 V higher valence band potential of crystalline PHI compared with ordinary carbon nitrides makes it an efficient water oxidation photocatalyst, which works even in the absence of any metal‐based co‐catalysts under visible light. To our knowledge, this is the first case of metal‐free oxygen liberation from water.

Thermal relaxation of defects in nanosized mechanically activated МоО3

The regularities of the thermal relaxation of structural defects (paramagnetic centers and microdistortions), as well as the sizes of coherent-scattering regions and the external surface, of mechanically activated МоО3 have been studied with the use of X-ray diffraction, electron paramagnetic resonance, and adsorption/desorption methods. It has been revealed that heating of activated samples at temperatures below 450°C is accompanied by the death of paramagnetic centers, annealing of microdistortions, and liberation of molecular oxygen. It has been assumed that oxygen results from the rupture of deformed Mo–O–Mo bridge bonds formed by its atoms. Above 450°C, recrystallization processes occur, which are accompanied by an increase in the sizes of the coherent-scattering regions and the MoO3 (monoclinic) → MoO3 (orthorhombic) phase transition. The thermal stability of the external particle surface depends on mechanical activation conditions. For samples activated at early stages of activation (fracture regime), the specific surface area decreases by more than an order of magnitude, when a temperature of 450°C is reached. At higher activation doses (friction regime), the sample is not sintered in the same temperature range.

Responses of Microcrustaceans to Simulated Microgravity (2D-Clinorotation) - Preliminary Assessments for the Development of Bioregenerative Life Support Systems (BLSS)

Bioregenerative Life Support Systems (BLSS) are an endeavor to create environments able to maintain human life e.g. on future long-duration space missions like flights to Mars. Based on cyclic biological processes, these systems will be independent from material resupply (such as food, water and oxygen). Due to their central role in limnic ecosystems, herbivorous microcrustaceans could act as key player in aquatic BLSS as they link oxygen liberating, autotrophic producers like algae to higher trophic levels, such as fish. However, before such BLSS can be utilized in space, organisms inhabiting these systems have to be studied thoroughly to disclose the gravitational impact on the biological processes. This is possible in real microgravity, but requires high financial resources, is opportunity-limited or periods of microgravity are very short. Yet, cost-effective and almost permanently accessible tools for gravitational research are ground-based facilities (GBFs), providing simulated microgravity. Among those GBFs is the so called 2D-clinostat. In the present study we demonstrate, that rotation of clinostat tubes does not generate acceleration in form of (predator resembling) small scale turbulence, which can be perceived by Daphnia cucullata. Additionally, embryonal development is not disturbed in subitaneous eggs of Daphnia magna and resting eggs of the ostracod Heterocypris incongruens (besides through restrictions in space within the narrow clinostat tubes), just as subsequent hatching from the respective eggs. Hence, our results indicate that clinorotation is a suitable method to simulate microgravity for microcrustaceans.

Visible-light-sensitive two-step overall water-splitting based on band structure control of titanium dioxide

Visible light-induced two-step overall water splitting was achieved by combining two types of photocatalysts, which were prepared by introducing foreign elements into titanium dioxide (TiO2) with a controlled electronic band structure. Rutile and anatase TiO2 were doped with chromium and tantalum to introduce visible-light sensitivity. Under irradiation with only visible light from a 420-nm LED lamp, the simultaneous liberation of hydrogen and oxygen with a molar ratio of ∼2:1 was achieved with these two types of TiO2-based photocatalysts in the presence of iodate ion/iodide ion as a redox mediator.

Jobs with mostly mental workload may lead to difficulties in oxygen and magnesium liberation into tissues – a staff health survey

Jobs with mostly mental workload may lead to difficulties in oxygen and magnesium liberation into tissues – a staff health survey

Uranium isotopes distinguish two geochemically distinct stages during the later Cambrian SPICE event

Anoxic marine zones were common in early Paleozoic oceans (542–400 Ma), and present a potential link to atmospheric pO2 via feedbacks linking global marine phosphorous recycling, primary production and organic carbon burial. Uranium (U) isotopes in carbonate rocks track the extent of ocean anoxia, whereas carbon (C) and sulfur (S) isotopes track the burial of organic carbon and pyrite sulfur (primary long-term sources of atmospheric oxygen). In combination, these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million-year time scales. Here we report high-precision uranium isotopic data in marine carbonates deposited during the Late Cambrian ‘SPICE’ event, at ca. 499 Ma, documenting a well-defined −0.18‰ negative δ238U excursion that occurs at the onset of the SPICE event's positive δ13C and δ34S excursions, but peaks (and tails off) before them. Dynamic modelling shows that the different response of the U reservoir cannot be attributed solely to differences in residence times or reservoir sizes – suggesting that two chemically distinct ocean states occurred within the SPICE event. The first ocean stage involved a global expansion of euxinic waters, triggering the spike in U burial, and peaking in conjunction with a well-known trilobite extinction event. During the second stage widespread euxinia waned, causing U removal to tail off, but enhanced organic carbon and pyrite burial continued, coinciding with evidence for severe sulfate depletion in the oceans (Gill et al., 2011). We discuss scenarios for how an interval of elevated pyrite and organic carbon burial could have been sustained without widespread euxinia in the water column (both non-sulfidic anoxia and/or a more oxygenated ocean state are possibilities). Either way, the SPICE event encompasses two different stages of elevated organic carbon and pyrite burial maintained by high nutrient fluxes to the ocean, and potentially sustained by internal marine geochemical feedbacks.

Reactions of metal oxides with carbon

The reaction of metal oxides with carbon is investigated. Baikov’s hypothesis regarding the role of atomic oxygen in the reduction of metals and the oxidation of carbon is confirmed theoretically and experimentally. The initial stages in the process include conjugate chemical reactions: dissociation of the oxide with the liberation of atomic and molecular oxygen; and the oxidation of carbon. The reaction of thermodynamically stable metal oxides with carbon is slowed by the accumulation of carbon monoxide in the system and the blocking of the reducing agent’s surface by metal carbides and oxycarbides. The production of silicon ferroalloys from briquetted batch is shown to be promising.

The chemistry of daytime sprite streamers – a model study

Abstract. The chemical processes in daytime sprite streamers in the altitude range of 30–54 km are investigated by means of a detailed ion–neutral chemistry model (without consideration of transport). The focus lies on nitrogen, hydrogen and oxygen species, and in particular on ozone perturbations. Initial effects of the breakdown electric fields at the tip of sprite streamers include a short-term loss of ozone due to ion–chemical reactions, a production of nitrogen radicals, and a liberation of atomic oxygen. The latter leads to a formation of ozone. In terms of relative ozone change, this effect decreases with altitude. The model results indicate that the subsequent ozone perturbations due to daytime sprites streamers differ considerably from the ones of night-time events. For night-time conditions, reactive nitrogen produced at the streamer heads is rapidly converted into significantly less reactive NO2, and there is basically no ozone depletion. The situation is different for daytime conditions where NOx causes catalytic ozone destruction. As a consequence, there is significant ozone loss in sprite streamers in the daytime atmosphere, in particular at higher altitudes. At an altitude of 54 km, ozone in the streamer column has decreased by about 15% fifteen minutes after the sprite event.

Reduction of iron and chromium from oxides by carbon

The reaction of iron and chromium oxides with carbon is considered. The decomposition of carbon monoxide is an important source of carbon at the surface of the iron oxides. In the reaction of Cr2O3 with carbon, the first stage includes dissociation of the oxides, with the liberation of atomic and molecular oxygen, and the formation of carbon oxides. Rapid reduction of chromium is ensured by the reaction of Cr2O3 with C3O2 and elementary carbon, which is produced from oxides.

Hypophosphatemia as a key factor in sudden infant death syndrome (SIDS)?

Dear Sir, Sudden Infant Death Syndrome or SIDS remains an important cause of mortality in infants. The 2011 publication of Siren and Siren (1) and the subsequent letter to the editor (2) focus on critical diaphragm failure as a possible cause and provide plausible evidence. However, these articles do not explore the metabolic basis for this critical diaphragm failure. Several authors, including Aubier et al. (3) and Fiaccadori et al. (4) have described that the diaphragm is extremely susceptible to hypophosphatemia, and this may be the origin of the symptoms reported by Siren and Siren. Hence, it may well be the yet unexplored underlying mechanism responsible for SIDS. A reason for suspecting hypophosphatemia as the cause for SIDS is because neonates are extremely prone to developing hypophosphatemia as shown in numerous publications (e.g. (5-8)). A very brief period of stress, like separation from the mother or a brief period of illness, can result in phosphaturia severe enough to result in the loss of 50% of the free phosphate pool within 24 hours. This results in an immediate drop in blood phosphate levels. Worse, this hypophosphatemia can subsequently become aggravated over the course of 1–2 weeks without obvious visible symptoms and despite resumption of normal eating behavior, something not reported in older subjects. In infants with risk factors for SIDS like intrauterine growth retardation, exposure to cigarette smoke, male sex, and heat stress, this phosphaturetic stress response is enhanced possibly through augmented or longer-lasting sympathetic activity (9,10), and, hence, they are more prone to develop severe hypophosphatemia and ATP deficiency. Hypophosphatemia not only affects contraction of the diaphragm, but it is also involved in the formation of 2,3-diphosphoglycerate (2,3-DPG; more correctly referred to as 2,3-bisphosphoglycerate) in erythrocytes. This 2,3-DPG regulates the release of oxygen from hemoglobin. Tissues with a high metabolic activity result in high levels of 2,3-DPG in the blood causing the liberation of oxygen (11-13). Hypophosphatemia impedes the formation of 2,3-DPG, which subsequently prevents the release of oxygen from hemoglobin and, in effect, suffocates the tissue. Thus, severe hypophosphatemia results in signs of asphyxiation despite adequate access to free air (14), either through inducing an ATP deficiency affecting the diaphragm or through inhibiting oxygen release from hemoglobin. For example, in briefly stressed subjects, in parallel with the drop in plasma phosphate, a doubling of the ratio of pCO2/pO2, an increase in SpO2, and lactic acidosis were observed but without obvious visible signs of distress. If severe enough, this could lead to death from inner suffocation (SIDS). The presence of fetal hemoglobin may also play a role in SIDS. Fetal hemoglobin purportedly has a higher binding affinity for oxygen (15) and thus could predispose an infant to SIDS when 2,3-DPG is compromised. Other symptoms of SIDS can also be explained by hypophosphatemia. Hypophosphatemia can lead to petechiae: minor hemorrhages caused by platelet dysfunction (16,17) and often seen postmortem in SIDS victims. Similarly, pulmonary edema (18) has been linked to hypophosphatemia, as have cardiac arrhythmias (19,20). Hypophosphatemia is also implicated in the morbidity and mortality associated with refeeding syndrome (21) and in hypophosphatemic rickets, which is more prevalent in boys (22) in line with a higher incidence of SIDS in boys. Siren and Siren's (1) comment that REM sleep inhibits intercostal muscles compounded by diurnal rhythms in blood phosphate could explain why SIDS strikes during night-time REM sleep. Also, phosphate has a seasonal rhythm with lows in the winter which could explain a higher prevalence of SIDS in this season, and 2,3-DPG is lower in infants exposed to cigarette smoke which could explain a higher incidence of SIDS in houses of smokers (23,24). In summary, both the etiology as well as the symptoms of SIDS can be explained by hypophosphatemia. A brief stressor can induce hypophosphatemia in infants, particularly in those with SIDS risk factors, and aggravate it despite resumption of normal food intake. This since the urinary loss of phosphate induced by stress or a large drop in metabolic rate and the subsequent enhanced phosphate demand for re-started anabolic processes cannot be quickly compensated by normal dietary intake. This hypophosphatemia can aggravate to the point of affecting O2 release from red blood cells through a depletion of 2,3-DPG or affect diaphragm contractility through ATP deficiency, either one which leads to death from apparent suffocation: SIDS.

PF.07 Expression of 2, 3-Bisphosphoglycerate Mutase (BPGM) in Human Placenta

IntroductionBPGM is an enzyme in erythrocytes and trophoblasts, which synthesises 2, 3-bisphosphoglycerate (2, 3-BPG), a facilitator of oxygen liberation from haemoglobin. In an insulin-like growth factor II knockout mouse model...

Structural phase transitions in YBaCo4O7 + x cobaltate upon variations in oxygen content, according to X-ray diffraction data obtained using synchrotron radiation

According to thermogravimetric data, the equilibrium oxygen content in layered YBaCo4O7 + x cobaltate varies stepwise from x ≈ 1.4 to x ≈ 0 when temperature is varied in the range of 300–400°C. Detailed ex situ and in situ structural investigations using synchrotron radiation show that variation in the oxygen content in YBaCo4O7 + x is accompanied by substantial reordering of the crystal structure and has the character of a first-order phase transition between two rigorously determined phases that differ by the parameters and symmetry of the crystal lattice as well as by the oxygen content. In addition to uniquely high oxygen liberation upon heating, dx/dT, great mechanical stresses that lead to the material cracking and complicate its practical use are a consequence of the character of stepwise transitions in YBaCo4O7 + x.

Oxygen Liberation from Stabilized Zirconia upon Changing DC Polarization Condition

AbstractThe compositional change of stabilized zirconia upon the change of oxygen chemical potential was studied by applying DC-polarization method to a galvanic cell using stabilized zirconia as the electrolyte. The flow of excess charge observed upon the change of the DC-polarization condition was found due to the oxygen liberation from the bulk of the electrolyte. The total amount of liberated oxygen determined by the excess charge was analyzed in terms of the compositional change of the electrolyte due to the change of oxygen chemical potential profile in the electrolyte. The calculated values based on the increase or decrease of the electronic defects could not account for the experimental values. However, the ones based on the reduction of impurity oxides were in good agreement with the experimental values. Considerable amount of oxygen can be released from or absorbed into the zirconia electrolyte by the redox reaction of impurity oxide. It is noteworthy that this phenomenon may cause serious errors to the transport properties of electronic defect determined with the use of the relaxation processes.

Hydrogen and Oxygen Evolution Photocatalysts Synthesized from Strontium Titanate by Controlled Doping and Their Performance in Two-Step Overall Water Splitting under Visible Light

A visible-light-induced two-step overall water splitting was achieved by combining two types of photocatalysts prepared by introducing foreign elements into the identical mother structure with a controlled electronic band structure. Strontium titanate (SrTiO3) was selected as the mother structure and was doped with either vanadium (and sodium) or rhodium to introduce visible light sensitivity. By utilizing these two types of SrTiO3-based photocatalysts, simultaneous liberation of hydrogen (H2) and oxygen (O2) with a molar ratio of ∼2:1 was achieved in the presence of iodate ion (IO3–)/iodide ion (I–) as a redox mediator under irradiation with only visible light (>420 nm).

Corrosion behavior of ceramic structural materials in an electrolytic reduction process

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 alloying structural materials. Therefore, the choice of the optimum material for the processing equipment that handles molten salt is critical. We investigated the corrosion behaviors of CaO-stabilized ZrO2 (CSZ) and mullite (Al6Si2O13) at 650°C for 168 h in molten (1, 3) wt% Li2O–LiCl. The as-received and tested specimens were examined by scanning electron microscopy/X-ray energy dispersive spectrometry and X-ray diffraction. CSZ showed a much better hot-corrosion resistance in the presence of Li2O–LiCl molten salt than mullite. The surface corrosion layers of mullite consisted of LiAlSiO4 in 1 wt% Li2O–LiCl, and a LiAlO2 phase appeared as the Li2O concentration increased to 3 wt%. Furthermore, Li2SiO3 was the only corrosion product observed at 3 wt% Li2O–LiCl. The surface corrosion layers of CSZ were composed mainly of tetragonal-ZrO2 with partial monoclinic-ZrO2 in 1 wt% Li2O–LiCl, and a Li2ZrO3 phase appeared at 3 wt% Li2O–LiCl. There was no corrosion product detached from the surface for those specimens. CSZ was beneficial for increasing the hot-corrosion resistance of the structural materials that handle high-temperature molten salts containing Li2O.

O2-Filled Swimbladder Employs Monocarboxylate Transporters for the Generation of O2 by Lactate-Induced Root Effect Hemoglobin

The swimbladder volume is regulated by O2 transfer between the luminal space and the blood In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the “Root effect.” While O2 generation is critical for fish flotation, the molecular mechanism of the secretion and recycling of lactic acid in this critical process is not clear. To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 17 members of the H+/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Electrophysiological analyses demonstrated that MCT1b is a high-affinity lactate transporter whereas MCT4b is a low-affinity/high-conductance lactate transporter. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute-specific transcellular transport. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b.

The mechanism of local blood acidification in the swimbladder by spatially organized monocarboxylate transporters

The gas in the swimbladder of teleost fish is composed primarily of O2, and the swimbladder volume is regulated by O2 transfer between the luminal space of the swimbladder and the blood. In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the “Root effect.” To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 16 members of the H+/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute‐specific transcellular transport. Electrophysiological analyses demonstrated that MCT1b is a high‐affinity lactate transporter whereas MCT4b is a low‐affinity/high‐conductance lactate transporter. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b.