High Oxygen Pressure Research Articles

Performance of Supported Copper Catalysts for Oxidative Degradation of Phenolics in Aqueous Medium: Optimization of Reaction Conditions, Kinetics, Catalyst Stability, Characterization, and Reusability

Catalytic wet oxidation (CWO) of phenolic wastewater containing phenol, o-cresol, and 2,5-dimethylphenol was carried out in a batch reactor (phenolics = 10 g/L, chemical oxygen demand (COD) = 26 000 mg/L, and total organic carbon (TOC) = 7900 mg/L). Using the Box–Behnken experimental design (BBD) approach, the following optimum CWO conditions (catalyst: 5% Cu/AC) for phenolics degradation were found: Ccat = 3.4 g/L, T = 148 °C, PO2 = 0.61 MPa, and pH = 7.4. Under these conditions, TOC and COD removals of 88 and 90%, respectively, were obtained after 4 h of reaction. p-Benzoquinone and hydroquinone were identified as major intermediates, whereas a mixture of carboxylic acids was detected in treated wastewater. At higher oxygen pressures (stoichiometric and above), mineralization of phenolics was improved although the overall degradation was lower probably due to overoxidation. Reaction kinetics, reusability of the catalysts, and detailed characterization of spent catalysts are also discussed in this paper.

Unclear Issues Regarding COVID-19.

Scientists from all over the world have been intensively working to discover different aspects of Coronavirus disease 2019 (COVID-19) since the first cluster of cases was reported in China. Herein, we aimed to investigate unclear issues related to transmission and pathogenesis of disease as well as accuracy of diagnostic tests and treatment modalities. A literature search on PubMed, Ovid, and EMBASE databases was conducted, and articles pertinent to identified search terms were extracted. A snow-ball search strategy was followed in order to retrieve additional relevant articles. It was reported that viral spread may occur during the asymptomatic phase of infection, and viral load was suggested to be a useful marker to assess disease severity. In contrast to immune response against viral infections, cytotoxic T lymphocytes decline in SARS-CoV-2 infection, which can be partially explained by direct invasion of T lymphocytes or apoptosis activated by SARS-CoV-2. Dysregulation of the urokinase pathway, cleavage of the SARS-CoV-2 Spike protein by FXa and FIIa, and consumption coagulopathy were the proposed mechanisms of the coagulation dysfunction in COVID-19. False-negative rates of reverse transcriptase polymerase chain reaction varied between 3% and 41% across studies. The probability of the positive test was proposed to decrease with the number of days past from symptom onset. Safety issues related to infection spread limit the use of high flow nasal oxygen (HFNO) and continuous positive airway pressure (CPAP) in hypoxic patients. Further studies are required to elucidate the challenging issues, thus enhancing the management of COVID-19 patients.

NiCo2O4 films fabricated by reactive molecular beam epitaxy and annealing in various oxygen atmospheres

Nickel cobalt spinel oxide, NiCo2O4, is an important material for spintronics because it exhibits both ferrimagnetic characteristics and electrical conductivity. Because high oxygen pressure during deposition is necessary to obtain useful properties, pulsed laser deposition has been used to fabricate NiCo2O4 films. In this study, we investigated the physical properties of NiCo2O4 films synthesized by reactive molecular beam epitaxy and annealing in a high-pressure oxygen atmosphere. The characteristics of the films strongly depended on the oxygen pressure, and a larger pressure tended to give larger magnetization and higher conductivity. Crystal structure analysis by x-ray diffraction and transmission electron microscopy revealed that the films consisted of a rock salt (Ni,Co)O phase and a spinel NiCo2O4 phase. This phase separation caused the small magnetization and large electric resistance because the rock salt phase was an antiferromagnetic insulator.

Inevitable high density of oxygen vacancies at the surface of polar–nonpolar perovskite heterostructures LaAlO3/SrTiO3

The density of polarity-induced oxygen vacancies (VOs) at the LaAlO3 (LAO) surface of LAO/SrTiO3 (STO) (001) heterostructures (HSs) and the density of induced carriers at the interface are quantitatively investigated. Using chemical equilibrium conditions combined with density-functional-theory calculations of total energy, we set up a model for the densities of the VOs and the carriers, which are a function of the thickness of the LAO film, oxygen pressure, and temperature during the LAO/STO HSs growth. For the HSs with over three LAO unit-cell layers, our results show that the presence of a high density (∼1014cm−2) of the VOs is inevitable, even for the HSs grown at high oxygen pressures, and the densities of the VOs and the carriers mainly depend on the LAO thickness and slightly on the oxygen pressure and temperature. Our results also demonstrate that the intrinsic doping cannot occur. The stability of the VOs under high oxygen pressures is attributed to the release of electrostatic energy from the polar electric field in the LAO film.

Effects of Ambient Parameters and Sample Width on Upward Flame Spread over Thermally Thin Solids

Upward flame spread is the most rapid and hazardous of the different modes of flame spread. Moreover, studies on the effects of ambient parameters on flame spread are very important for fire safety on spacecraft systems. Therefore, the effects of pressure (0 kPa to 70 kPa), oxygen mole fraction (0.30 to 0.90) and sample width (0.3 cm to 2 cm) on upward flame spread over thin papers were studied. A flame break-off phenomenon over papers was firstly observed, which occurred more likely at high oxygen and high pressure conditions. Upward flame spread reached a steady state by varying the ambient parameters and using narrow samples. The smaller sample width narrowed the flammability limits. Differences in upward and downward flame spread were discussed. We found that a power law relationship between flame spread rate and pressure remained valid near the extinction limit for upward spread, while the power law broke down in the extinction region for downward spread. The controlling mechanism of upward spread was revealed by a pressure modeling method showing that the upward flame spread rate was proportional to the Grashof number raised to an exponent of 0.257. For upward flame spread over narrow solids, the gas phase kinetics and radiation effects are less important compared to the heat convection in the flame spread process, which is quite different from the downward spread. This study contributes to the fire safety of space vehicles and enhances the understanding of the controlling mechanism of flame spread.

COVID-19 pandemic: structured expansion of ventilation capacities using home respirators

Aufgrund der aktuellen COVID-19-Pandemie besteht ein Bedarf an rascher Aufstockung von Intensiv- und Beatmungskapazitäten. Lieferzeiten für zusätzliche Intensivrespiratoren sind derzeit jedoch nicht absehbar. Eine Möglichkeit, Beatmungskapazitäten nicht nur für COVID-19-, sondern für alle Beatmungspatienten in Akutkrankenhäusern zu steigern, ist der Einsatz von Heimrespiratoren.Heimrespiratoren sind Turbinenrespiratoren, daher üblicherweise nicht auf den Betrieb mit Druckgasanschlüssen angewiesen und können daher auch in Bereichen außerhalb der klassischen intensivmedizinischen Infrastruktur eingesetzt werden. Aufgrund ihrer limitierten technischen Eigenschaften eignen sich Heimrespiratoren nicht zur Behandlung schwer betroffener Patienten, können jedoch nach Stabilisierung zum Weaning eingesetzt werden, wodurch Intensivrespiratoren schneller wieder zur Verfügung stehen.Atmungstherapeuten sind speziell im Gebiet der außerklinischen Beatmung weitergebildete Pflegefachkräfte oder Therapeuten und können beim Einsatz von Heimrespiratoren beispielsweise zum Weaning auf der Intensivstation dieses selbstständig durchführen und so die Intensivpflegefachkräfte entlasten. Aufgrund der COVID-19-Pandemie erfolgt in Oldenburg gegenwärtig zusätzlich eine Basisschulung von Studierenden der Medizin im Umgang mit Heimrespiratoren, um im Krankenhaus im Bedarfsfall unterstützend tätig zu werden.

Absence of superconductivity in Nd0.8Sr0.2NiOx thin films without chemical reduction

The recently reported superconductivity 9-15 K in Nd0.8Sr0.2NiO2/SrTiO3 heterostructures that were fabricated by a soft-chemical topotactic reduction approach based on precursor Nd0.8Sr0.2NiO3 thin films deposited on SrTiO3 substrates, has excited an immediate surge of research interest. To explore an alternative physical path instead of chemical reduction for realizing superconductivity in this compound, using pulsed laser deposition, we systematically fabricated 63 Nd0.8Sr0.2NiOx (NSNO) thin films at a wide range of oxygen partial pressures on various different oxide substrates. Transport measurements did not find any signature of superconductivity in all the 63 thin-film samples. With reducing the oxygen content in the NSNO films by lowering the deposition oxygen pressure, the NSNO films are getting more resistive and finally become insulating. Furthermore, we tried to cap a 20-nm-thick amorphous LaAlO3 layer on a Nd0.8Sr0.2NiO3 thin film deposited at a high oxygen pressure of 150 mTorr to create oxygen vacancies on its surface and did not succeed in higher conductivity either. Our experimental results together with the recent report on the absence of superconductivity in synthesized bulk Nd0.8Sr0.2NiO2 crystals suggest that the chemical reduction approach could be unique for yielding superconductivity in NSNO/SrTiO3 heterostructures. However, SrTiO3 substrates could be reduced to generate oxygen vacancies during the chemical reduction process as well, which may thus partially contribute to conductivity.

Anisotropic character of the metal-to-metal transition in Pr4Ni3O10

As a member of the Ruddlesden-Popper Ln$_{n+1}$Ni$_n$O$_{3n+1}$ series rare-earth-nickelates, the Pr4Ni$_3$O$_{10}$ consists of infinite quasi-two-dimensional perovskite-like Ni-O based layers. Although a metal-to-metal phase transition at Tpt = 157 K has been revealed by previous studies, a comprehensive study of physical properties associated with this transition has not yet been performed. We have grown single crystals of Pr4Ni3O10 at high oxygen pressure, and report on the physical properties around that phase transition, such as heat-capacity, electric-transport and magnetization. We observe a distinctly anisotropic behavior between in-plane and out-of-plane properties: a metal-to-metal transition at Tpt within the a-b plane, and a metal-to-insulator-like transition along the c-axis with decreasing temperature. Moreover, an anisotropic and anomalous negative magneto-resistance is observed at Tpt that we attribute to a slight suppression of the first-order transition with magnetic field. The magnetic-susceptibility can be well described by a Curie-Weiss law, with different Curie-constants and Pauli-spin susceptibilities between the high-temperature and the low-temperature phases. The single crystal X-ray diffraction measurements show a shape variation of the different NiO6 octahedra from the high-temperature phase to the low-temperature phase. This subtle change of the environment of the Ni sites is likely responsible for the different physical properties at high and low temperatures.

Reversible and irreversible structural changes in FeO/Ru(0 0 0 1) model catalyst subjected to atomic oxygen

Islands and thin films of metal oxides grown on metal single-crystal supports constitute well-defined model systems for studying elementary steps of catalytic reactions that take place at the surface of metal-oxide catalysts. Fundamental studies carried out under idealized ultra-high vacuum (UHV) conditions have to be, however, linked to the industrial ones by overcoming the so called “pressure gap”. In the case of oxidation reactions, experiments using high (millibar) oxygen pressures or moderate pressures of highly oxidative gaseous species (such as atomic oxygen) are commonly performed to bridge (at least partially) the two catalytic worlds. We studied the structural changes that occur in ultrathin iron monoxide (FeO) islands and films grown on single-crystal Ru(0 0 0 1) substrate upon exposure to atomic oxygen. The results reveal that room-temperature exposure leads to the formation of oxygen-rich and structurally ill-defined iron oxide and ruthenium oxide species. The transformation can be, however, reverted by vacuum annealing. Exposing FeO/Ru(0 0 0 1) to atomic oxygen at 700 K leads, on the other hand, to an irreversible transformation of the iron oxide to a Fe2O3-like phase. The results contribute to the general understanding of the oxidation reactions over metal-oxide catalysts.

High temperature oxidation behavior of Co-20Re-25Cr-2Si alloy at different oxygen pressures

The oxidation of the quaternary Co-20Re-25Cr-2Si alloy has been studied at 1000−1300 °C for 24 h. On the whole, at high oxygen pressure of 0.1 MPa the alloy shows mass loss while at low oxygen pressure of 3.0×10−5 Pa, however, the alloy shows mass gain. Compared with the irregular kinetics under the oxygen pressure of 0.1 MPa, the kinetics approximately conform to parabolic law under the oxygen pressure of 3.0×10−5 Pa, with the value of oxidation activation energy equal to 262.7 kJ/mol. The scales formed under the oxygen pressure of 0.1 MPa at 1000−1300 °C are very similar. The outermost layer is CoO, followed by a mixed oxide layer probably composed of CoO and CoCr2O4. The innermost layer is probably composed mainly of a thin discontinuous layer of Cr2O3, accounting for the continuous mass loss due to the evaporation of Re element in the form of ReO3. However, the sales formed under the oxygen pressure of 3.0×10−5 Pa are probably composed of an outer thin layer of CoCr2O4 spinel and an inner dense and continuous layer of Cr2O3, which provides the good oxidation resistance for the alloy. The combination of the addition of Si and low oxygen pressure has shown a synergistic effect on the formation of a protective chromia layer.

Local lattice distortions and dynamics in extremely overdoped superconducting YSr2Cu2.75Mo0.25O7.54

A common characteristic of many "overdoped" cuprates prepared with high-pressure oxygen is Tc values ≥ 50 K that often exceed that of optimally doped parent compounds, despite O stoichiometries that place the materials at the edge or outside of the conventional boundary between superconducting and normal Fermi liquid states. X-ray absorption fine-structure (XAFS) measurements at 52 K on samples of high-pressure oxygen (HPO) YSr2Cu2.75Mo0.25O7.54, Tc = 84 K show that the Mo is in the (VI) valence in an unusually undistorted octahedral geometry with predominantly Mo neighbors that is consistent with its assigned substitution for Cu in the chain sites of the structure. Perturbations of the Cu environments are minimal, although the Cu X-ray absorption near-edge structure (XANES) differs from that in other cuprates. The primary deviation from the crystal structure is therefore nanophase separation into Mo- and Cu-enriched domains. There are, however, indications that the dynamical attributes of the structure are altered relative to YBa2Cu3O7, including a shift of the Cu-apical O two-site distribution from the chain to the plane Cu sites. Another effect that would influence Tc is the possibility of multiple bands at the Fermi surface caused by the presence of the second phase and the lowering of the Fermi level.

Combustion Behavior and Mechanism of Ti14 Titanium Alloy.

The combustion behavior and mechanism of Ti14 titanium alloy are studied by promoted ignition combustion tests at different oxygen pressures in this paper. The burning velocity increases at higher oxygen pressures and also increases with longer burning times instead of a constant at the same pressure. The Cu atoms are found enriched in two zones—i.e., the heat affected zone and melting zone during the combustion process—which can prevent the diffusion process of oxygen atoms. The different combustion behavior of Ti14 and Ti-Cr-V alloys is basically controlled by the characteristics of phase structures and chemical reactions.

Phase Stability of Ce-Substituted Magnetoplumbite-Type Sr Ferrite

We studied the phase stability of Ce-substituted magnetoplumbite-type Sr ferrite under various oxygen pressures. We have successfully obtained Ce-substituted samples as revealed from X-ray diffraction and wavelength dispersion X-ray analyses. The solubility limit of Ce in Sr1-xCexFe12O19 was estimated to be $x = 0.24$ at ambient pressure, which is reduced to 0.05-0.10 under higher oxygen pressures. The variation of the $c$ -axis against $x$ and the reduction of the solubility by increasing oxygen pressure suggests that the valence of Ce is not 4+ but 3+. The solubility limit of Ce is dominated not only by the ionic radius but also by the valence instability of Ce.

Efficient Formation of 2,5-Diformylfuran in Ionic Liquids at High Substrate Loadings and Low Oxygen Pressure with Separation through Sublimation

The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using oxygen (1 atm) with a TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) and CuCl catalyst system is investigated using ...

Impact of growth kinetics on the interface morphology and magnetization in La1/3Sr2/3FeO3/La2/3Sr1/3MnO3 heterostructures

The ability to create atomically perfect, epitaxial heterostructures of correlated complex perovskite oxides using state-of-art thin film deposition techniques has generated new physical phenomena at engineered interfaces. Here we report on the impact of growth kinetics on the magnetic structure and exchange coupling at the interface in heterostructures combining layers of antiferromagnetic La1/3Sr2/3FeO3 (LSFO) and ferromagnetic La2/3Sr1/3MnO3 (LSMO) on (0 0 1)-oriented SrTiO3 (STO) substrates. Two growth orders are investigated, (a) LSMO/LSFO/STO(0 0 1) and (b) LSFO/LSMO/STO(0 0 1), where the LSFO layer is grown by molecular beam epitaxy and the LSMO layer by high oxygen pressure sputtering. The interface has been investigated using electron microscopy and polarized neutron reflectometry. Interdiffusion over seven monolayers is observed in LSMO/LSFO (a) with an almost 50% reduction in magnetization at the interface and showing no exchange coupling. However, the exchange bias effect ( mT at 10 K) could be realized when the interface is atomically sharp, as in LSFO/LSMO (b). Our study therefore reveals that, even for well ordered and lattice-matched structures, the kinetics involved in the growth processes drastically influences the interface quality with a strong correlation to the magnetic properties.

Unveiling the pinning behavior of charged domain walls in BiFeO3 thin films via vacancy defects

Manipulation of electronic states in functional ferroelectrics is promising for next generation electronics devices. The charged domain walls in ferroelectric materials especially facilitate the electronic state modulation and are promising for developing interface-based devices. However, the major challenges impeding the application are their intentional manipulation and the elusive pinning behavior. Here, results that charged domain walls in BiFeO3 films can be pinned and regulated by oxygen vacancy planar distributions controlled by oxygen pressure during film growth are reported. Using aberration-corrected scanning transmission electron microscopy complemented by theoretical simulations, rich pinning behavior of tail-to-tail charged domain walls by oxygen vacancy plates is revealed. At high annealing oxygen pressure, 71° charged domain walls are stabilized by narrow vacancy plates. Decreasing the oxygen pressure, the transformation from 71° to 109° charged domain walls happens by expanding the vacancy plates, as collaborated by phase field simulations. Besides, the 71°-109° charged domain wall pairs are stabilized due to further interaction between two neighboring vacancy plates. These results provide the active modulation of the electronic states and illuminate the rich pinning behavior of domain walls by vacancy defects in ferroelectrics, which in turn could provide implications for designing potential electronics devices.

Depolymerization of lignin by wet air oxidation

In the present study, effect of temperature (150–250 °C) and pressure (500–1500 psi) was investigated for depolymerization of lignin by wet air oxidation (WAO). Commercial alkali lignin was used as representative lignin material. The degradation/oxidation products of WAO treatments were identified to understand the potential value of the depolymerization products. Depolymerization efficiency of alkali lignin was also compared to lignin extracted from corn stover and eastern redcedar (cedar) under the same WAO condition. Isovanillic acid was found to be the main product of WAO at 150 °C and 1000 psi oxygen conditions. The higher temperature (200 and 250 °C) and higher oxygen pressure (1000 and 1500 psi) conditions led to formation of more oxidized products, mostly carboxylic acid-derived compounds. The results showed that alkali lignin was more vulnerable to depolymerization compared to the lignins extracted from corn stover and cedar.

Observation of drastic changes in the magnetic response of epitaxial TbMnO3 thin films upon Al-doping

The influence of Al3+ doping on the ferromagnetic response of epitaxial TbMn1-xAlxO3 (x = 0, 0.1) thin films (~100 nm) was studied experimentally. TbMnO3 and TbMn0.9Al0.1O3 films (~100 nm thin) were epitaxially grown on (001)-SrTiO3 substrates by means of the high-pressure oxygen DC magnetron sputtering technique. X-ray diffraction patterns clearly showed that both films were epitaxial, with the c-axis oriented in the (00ℓ) direction. X-ray photoelectron spectroscopy analysis confirmed that the nominal valence of the Mn ions in the TbMnO3 film is 3+. Although a small shake-up peak was observed in the Mn 2p edge of the TbMn0.9Al0.1O3 film, depth-profiling experiments showed that the presence of this peak was only a surface effect. Anomalous ferromagnetism was observed in the pristine TbMnO3 films, which seemed to be caused by coupling between the magnetization and the epitaxial strain, due to the lattice mismatch between the film and substrate. Interestingly, drastic changes in the ferromagnetic response of the TbMnO3 films were observed upon Al3+ substitution at the Mn3+ positions (chemical pressure). Although Al3+ and Mn3+ ions are isovalent, the smaller size of the Al3+ ions brings about further microstructural strain, which clearly influenced the ferromagnetism observed in the TbMnO3 films. The introduction of Al3+ ions into the TbMnO3 lattice resulted in a shift of the (00ℓ) reflections to lower angles as compared with those of the TbMnO3 films. The TbMnO3 films showed a well-defined transition at ~42 K, which corresponds to the magnetic ordering temperature from the paramagnetic phase to the sinusoidal antiferromagnetic structure of the Mn spins. The antiferromagnetic transition shifted to lower temperatures for the TbMn0.9Al0.1O3 thin films. The experimental results demonstrated that the magnetic response of the single-phase spin-driven multiferroic TbMnO3 can effectively be tuned by both epitaxial strain and chemical pressure at the Mn site.

Exhaled Volatile Organic Compounds Precedes Pulmonary Injury in a Swine Pulmonary Oxygen Toxicity Model.

PurposeInspiring high partial pressure of oxygen (FiO2 > 0.6) for a prolonged duration can lead to lung damage termed pulmonary oxygen toxicity (PO2T). While current practice is to limit oxygen exposure, there are clinical and military scenarios where higher FiO2 levels and partial pressures of oxygen are required. The purpose of this study is to develop a non-invasive breath-based biomarker to detect PO2T prior to the onset of clinical symptoms.MethodsMale Yorkshire swine (20–30 kg) were placed into custom airtight runs and randomized to air (0.209 FiO2, n = 12) or oxygen (>0.95 FiO2, n = 10) for 72 h. Breath samples, arterial blood gases, and vital signs were assessed every 12 h. After 72 h of exposure, animals were euthanized and the lungs processed for histology and wet-dry ratios.ResultsSwine exposed to hyperoxia developed pulmonary injury consistent with PO2T. Histology of oxygen-exposed swine showed pulmonary lymphatic congestion, epithelial sloughing, and neutrophil transmigration. Pulmonary injury was also evidenced by increased interstitial edema and a decreased PaO2/FiO2 ratio in the oxygen group when compared to the air control group. Breath volatile organic compound (VOC) sample analysis identified six VOCs that were combined into an algorithm which generated a breath score predicting PO2T with a ROC/AUC curve of 0.72 defined as a of PaO2/FiO2 ratio less than 350 mmHg.ConclusionExposing swine to 72 h of hyperoxia induced a pulmonary injury consistent with human clinical endpoints of PO2T. VOC analysis identified six VOCs in exhaled breath that preceded PO2T. Results show promise that a simple, non-invasive breath test could potentially predict the risk of pulmonary injury in humans exposed to high partial pressures of oxygen.

Uncovering ferroelectric polarization in tetragonal (Bi1/2K1/2)TiO3\u2013(Bi1/2Na1/2)TiO3 single crystals

We report the robust ferroelectric properties of (1 − x)(Bi1/2Na1/2)TiO3–x(Bi1/2K1/2)TiO3 (x = 33%) single crystals grown by a top-seeded solution growth process under a high oxygen-pressure (0.9 MPa) atmosphere. The sample exhibit a large remanent polarization of 48 μC/cm2 and a sizeable piezoelectric strain constant of 460 pm/V. Neutron powder diffraction structural analysis combined with first-principles calculations reveals that the large ferroelectric polarization comparable to PbTiO3 stems from the hybridization between Bi-6p and O-2p orbitals at a moderately negative chemical pressure.