Decrease In O2 Concentration Research Articles

Local reaction microenvironment impacts on H2O2 electrosynthesis in a dual membrane electrode assembly solid electrolyte electrolyzer

Hydrogen peroxide (H2O2) synthesis via the electrocatalytic reduction of oxygen is a sustainable alternative to the energy-intensive anthraquinone oxidation process. The use of gas diffusion electrodes in dual membrane electrode assembly (MEA) solid electrolyte (SE) electrolyzers has substantially improved H2O2 production, but the influence of mass transport and local reaction environment on H2O2 performance in these cell architectures is still unclear and unoptimized. Herein, we investigate the impacts of electrode components and reactor operating conditions on the H2O2 performance and cell potential required to reach current densities up to 400 mA cm−2. Results show an intermediate catalyst loading of 2 mg cm−2 improves H2O2 production through balancing O2 diffusion and active site exposure. Hydrophobic treatment via fluoropolymer improves electrode stability, but addition of >15 wt% fluoropolymer worsens performance, likely by limiting active site accessibility at the catalyst-membrane interface. Moreover, decreasing O2 concentration from typical pure streams to match the composition of air has a negligible effect at moderate current densities (∼50 mA cm−2), but significantly impacts overall performance at higher current densities (∼200 mA cm−2). This work also highlights benefits of operating the reactor with a recycled product stream rather than tuning the flow rate of water over the SE to extremely low values to obtain high H2O2 concentrations, as the latter likely contributes to exacerbated H2O2 degradation in the electrolyzer. This work provides insights into how macroscale system properties in flow cell electrolyzers impact the local reaction environment and mass transport, which in turn dictate overall catalytic performance.

Colour/luminescence changes of transition metal complexes induced by gaseous small molecules for monitoring reaction progress and environmental changes.

Transition metal complexes act as monitoring devices for reaction progress and environmental changes through their color/luminescence changes. In this paper, we focus on colour/luminescence changes induced by gaseous small molecules in the environment. The gradual decrease in O2 content in solution can be monitored by the luminescence enhancement of an Ir(III) complex in dimethyl sulfoxide during photoirradiation. CO2 in air can be captured by a Pt(II) complex in basic aqueous solution, resulting in a colour change from yellow to red to blue-green due to higher degree aggregate formation. Moisture in air induces colour/luminescence changes in Ru(II) and Ir(III) complex salts due to the sorption of H2O into hydrophilic channels in the crystal. Volatile organic compound vapours such as CHCl3 and CH2Cl2 change the purple colour of Pt(II) complex crystals to red and blue, respectively. The purple crystal can adsorb two CHCl3 molecules under ambient conditions but only one CH2Cl2 molecule.

Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems.

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Nevertheless, how long-term deoxygenation affects macrobenthic communities, sediment biogeochemistry and their mutual feedback remains poorly understood. Here, we evaluate the response of the benthic assemblages and biogeochemical functioning to decreasing O2 concentrations along the persistent bottom-water dissolved O2 gradient of the Estuary and Gulf of St. Lawrence (QC, Canada). We report several of non-linear biodiversity and functional responses to decreasing O2 concentrations, and identify an O2 threshold that occurs at approximately at 63 μM. Below this threshold, macrobenthic community assemblages change, and bioturbation rates drastically decrease to near zero. Consequently, the sequence of electron acceptors used to metabolize the sedimentary organic matter is squeezed towards the sediment surface while reduced compounds accumulate closer (as much as 0.5-2.5 cm depending on the compound) to the sediment-water interface. Our results illustrate the capacity of bioturbating species to compensate for the biogeochemical consequences of hypoxia and can help to predict future changes in benthic ecosystems.

Soil pore structure mediates the effects of soil oxygen on the dynamics of greenhouse gases during wetting–drying phases

The timing and magnitude of greenhouse gas (GHG) production depend strongly on soil oxygen (O2) availability, and the soil pore geometry characteristics largely regulate O2 and moisture conditions relating to GHG biochemical processes. However, the interactions between O2 dynamics and the concentration and flux of GHGs during the soil moisture transitions under various soil pore conditions have not yet been clarified. In this study, a soil-column experiment was conducted under wetting–drying phases using three pore-structure treatments, FINE, MEDIUM, and COARSE, with 0 %, 30 %, and 50 % coarse quartz sand applied to soil, respectively. The concentrations of soil gases (O2, nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4)) were monitored at a depth of 15 cm hourly, and their surface fluxes were measured daily. Soil porosity, pore size distribution, and pore connectivity were quantified using X-ray computed microtomography. The soil O2 concentrations were found to decline sharply as soil moisture increased to the water holding capacities of 0.46, 0.41, and 0.32 cm cm−3 in the FINE, MEDIUM, and COARSE, respectively. The dynamic patterns of the O2 concentrations varied across the soil pore structures, decreasing to anaerobic in FINE (<0.01 %) and MEDIUM (0.02 %), and to hypoxic (4.42 %) in COARSE. Correspondingly, the soil N2O concentration was the highest in FINE (101 μL L−1) and the lowest in COARSE (10 μL L−1), whereas the highest surface N2O flux was observed in MEDIUM (131 μg N m−2 h−1). As soil CO2 concentrations declined, CO2 fluxes increased from FINE to MEDIUM to COARSE. Most pores of FINE, MEDIUM, and COARSE were 15–80 μm, 85–100 μm, and 105–125 μm, respectively, in terms of diameter. The X-ray CT visible (>15 μm) porosity in FINE, MEDIUM and COARSE were 0.09, 0.17, and 0.28 mm3 mm−3, respectively. The corresponding Euler-Poincaré numbers were 180,280, 76,705, and −10,604, respectively, indicating higher connectivity in COARSE than in MEDIUM or FINE. In soil dominated by small air-filled porosity which limits gas diffusion and result in low soil O2 concentration, N2O concentration was increased and CO2 flux was inhibited as the moisture content increased. The turning point in the sharp decrease in O2 concentration was found to correspond with a moisture content, and a pore diameter of 95–110 μm was associated with the critical turning point between holding water and O2 depletion in soil. These findings suggest that O2-regulated biochemical processes are key to the production and flux of GHGs, which in turn are dependent on the soil pore structure and a coupling relationship between N2O and CO2. Improved understanding of the intense effect of soil physical properties provided an empirical foundation for the future development of mechanistic prediction models for how pore-space scale processes with high temporal (hourly) resolution up to GHGs fluxes at larger spatial and temporal scales.

Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions

MILD oxy-coal combustion technology is a prospective technology with the potential for CO2 capture and storage, and it is characterized by the intense flue gas recirculation to preheat the fuel and to dilute the oxidizer due to the oxidizer or fuel jet with high velocity. The effect of the primary oxidizer stream jet velocities ranging from 1.7 m/s to 11.2 m/s on the coal ignition and combustion characteristics were experimentally investigated on a flat flame pulverized coal burner at various oxygen concentrations of 5%-21% and gas temperatures of 1473–1873 K under O2/CO2 and O2/N2 atmospheres. The coal flame images were recorded by the digital camera, and the flame structure evolution and ignition delay times of coal particles were analyzed at different primary oxidizer stream jet velocities and hot coflow conditions. The coal combustion radiation spectrum was monitored by an optical fiber spectrometer and the coal particle temperatures were derived with the two-color pyrometry. The results showed that the bright yellow soot flame gradually disappeared with the decrease of O2 concentration when CO2 replaced N2. The difference of ignition delay times between O2/CO2 atmosphere and O2/N2 atmosphere decreased from 2.8 ms to 0.2 ms when the primary air jet velocity increased from 1.7 m/s to 11.2 m/s at 1473 K and 5% O2. This meant the elevated jet velocity was beneficial to offset the delayed effect of the physicochemical properties of CO2 on coal ignition. The peak coal particle temperature increased by 68 K at 1873 K and 5% O2 under O2/CO2 atmosphere with the highest jet velocity owing to the accelerated diffusion of O2 into coal particle stream. Moreover, a dimensionless coal particle temperature parameter η was proposed to characterize the variation of the peak coal particle temperature caused by the improved heat transfer and mass transport between the coflow and coal particles under high jet velocity. The maximum value of η was 1.053 at 1873 K and 21% O2 under O2/CO2 atmosphere with the jet velocity of 11.2 m/s, indicating the increased jet velocity had the predominant effect on the increase of peak particle temperature at high gas temperature and O2 concentration.

Oxygen production at intermediate temperatures using Ca2AlMnO5+δ double perovskite-type oxides

Double-perovskite Ca2AlMnO5+δ exhibits promising oxygen uptake and release capacity at intermediate temperatures (400–700 °C), which makes it an interesting candidate for in situ oxygen production in an integrated gasification combined cycle (IGCC) process. Experiments were conducted at 10 bars by alternating gas feeds of air and various sweep gases to a packed bed filled with 300 g of granular oxygen carrier materials. These realistic operating conditions demonstrated that 15–20% oxygen can be introduced to the sweep gas, which is sufficient for autothermal gasification of solid fuels in IGCC. Argon performed slightly better than CO2 as a sweep gas, presumably because of some CO2 absorption or the higher O2 partial pressure of CO2 that inhibited O2 release. Further O2 concentration increases can be expected from increasing the temperature under reduction by feeding a fuel gas to combust with the released O2, but experiments with H2 did not produce the desired effect because the combustion reaction was too slow at the optimal reactor temperature (~ 600 °C). In general, the reduction stage was more prone to kinetic limitations, as illustrated by a significant decrease in O2 concentration when the sweep flowrate was increased. A longer oxidation stage to fully charge the oxygen carrier also increased O2 concentrations in the sweep, but this requires a process integration such as IGCC where the large quantity of warm depleted air can be effectively utilized. Furthermore, the enthalpy of oxidation of Ca2AlMnO5+δ was obtained from density functional theory modeling, equilibrium conditions in thermogravimetric analysis, packed bed experiments and directly from differential scanning calorimetry. The enthalpy of oxidation obtained by these techniques range from − 166 to − 196 kJ mol−1 O2.

Statistical Study of the Characteristics of Coal Spontaneous Combustion Gases and Temperature

ABSTRACT The occurrence of coal spontaneous combustion has a significant impact on both the safety of personnel and mine recovery. In order to establish an early warning system for combustion, it is crucial to develop a mathematical model that characterizes indicator gases and coal temperature. In this study, we investigated the O2, CO, and CO2 characteristics of data collected from a goaf beam pipe in the Mengcun mine. Our findings demonstrate a linear decrease in O2 concentration with goaf depth and a strong negative correlation between CO and O2. We observed that CO/∆O2 and CO/CO2 increased to a maximum and then decreased as the goaf depth increased. Furthermore, we found that the peaks of these parameters at the same sampling point corresponded to the same goaf depth, and both occurred at the junction between the air-leakage and oxidation zones. By using a logistic model to fit the CO and C2H4 data, we developed a model that characterizes the relationships among CO, C2H4, and coal temperature based on statistical laws. The model provides direct information about the inflection point temperatures of C2H4 and CO, with the former being slightly lower within the same coal sample. The overall difference between the inflection point temperatures is relatively small, about 10°C. The initial temperature ratio of C2H4 and CO remains essentially constant at 3.8. C2H2 concentrations are low and irregular, and the presence of this gas can be used to assess when coal enters the accelerated oxidation stage. This research result provides a new research view for elucidating the distribution characteristics of coal spontaneous combustion index gas.

Experimental investigation on co-combustion characteristics of semi-coke and coal: Insight into synergy and blending method

Co-combustion of semi-coke and coal is a prospective technique for large-scale disposal or utilization of the solid waste. In this paper, the co-combustion behaviors and kinetics of semi-coke and coal were studied by thermogravimetric analysis with a focus on the influence of blending method and synergy. The results indicated that the semi-coke combustion was improved by blending with coal, and the interaction between fuels tended to promote the co-combustion. The ignition and burnout temperatures were positively correlated with the carbon content of the mixture, while the comprehensive combustion index and stability index were negatively correlated with it. The layer blending and partition blending method seemed to show stronger promotion than uniform blending method, and the layer blending method with coal in the upper layer was recommended due to the better combustion behavior. The promotion of coal on semi-coke combustion was less affected in devolatilization stage but weakened by the decrease of O2 concentration in char burnout stage. The apparent activation energy (Ea) of the mixture decreased with the increasing faction of coal. The layer blending method with coal in the upper layer had the lowest Ea in devolatilization stage and relatively high Ea in char burnout stage. The work can give some new insights into waste co-disposal strategy and carbon emission reduction in China.

A Comparison between Statistical Behaviours of Scalar Dissipation Rate between Homogeneous MILD Combustion and Premixed Turbulent Flames

Three-dimensional Direct Numerical Simulations (DNS) data has been utilised to analyse statistical behaviours of the scalar dissipation rate (SDR) and its transport for homogeneous methane-air mixture turbulent Moderate or Intense Low oxygen Dilution (MILD) combustion for different O2 dilution levels and turbulence intensities for different reaction progress variable definitions. Additional DNS has been conducted for turbulent premixed flames and passive scalar mixing for the purpose of comparison with the SDR statistics of the homogeneous mixture MILD combustion with that in conventional premixed combustion and passive scalar mixing. It has been found that the peak mean value of the scalar dissipation rate decreases with decreasing O2 concentration for MILD combustion cases. Moreover, SDR magnitudes increase with increasing turbulence intensity for both MILD and conventional premixed combustion cases. The profiles and mean values of the scalar dissipation rate conditioned upon the reaction progress variable are found to be sensitive to the choice of the reaction progress variable definition. This behaviour arises due to the differences in the distributions of the species mass fractions within the flame. The strain rate contribution and the molecular dissipation term are found to be the leading order contributors in the scalar dissipation rate transport for MILD combustion; whereas, in conventional premixed flames, the terms rising from density variation and reaction rate gradient also play leading roles in addition to the strain rate and molecular dissipation contributions. By contrast, the terms due to density gradient and reaction rate gradient remain negligible in comparison to the leading order contributors in MILD combustion cases due to small density variation because of moderate temperature rise and small reaction rate gradient magnitudes. Furthermore, the qualitative behaviour of the strain rate contribution to the SDR transport in premixed flames is significantly different to that in the case of MILD combustion and passive scalar mixing. The findings of the current analysis indicate that the scalar dissipation rate statistics in MILD combustion show several qualitative similarities to the passive scalar mixing despite major differences with the SDR transport in conventional turbulent premixed flames. This further suggests that the scalar dissipation rate models, which were originally proposed in the context of passive scalar mixing, have the potential to be applicable for MILD combustion but the models for the premixed turbulent combustion may not be applicable for MILD combustion of homogeneous mixtures.

Cr-Fe-Ni-Cu Quaternary Nanostructure as a Substitute for Precious Metals in Automotive Three-Way Catalysts.

The replacement of precious metals (Rh, Pd, and Pt) in three-way catalysts with inexpensive and earth-abundant metal alternatives is an ongoing challenge. In this research, we examined various quaternary metal catalysts by selecting from six 3d transition metals, i.e., Cr, Mn, Fe, Co, Ni, and Cu, equimolar amounts (0.1 mol each), which were prepared on the Al2O3 support (1 mol Al) using H2 reduction treatment at 900 °C. Among 15 combinations, the best catalytic performance was achieved by the CrFeNiCu system. Light-off of NO-CO-C3H6-O2-H2O mixtures proceeded at the lowest temperature of ≤200 °C for CO, ≤300 °C for C3H6, and ≤400 °C for NO when the molar fraction of Cr in Cr x Fe0.1Ni0.1Cu0.1 was around x = 0.1. The activity for CO/C3H6 oxidation was superior to that of reference Pt/Al2O3 catalysts but was less active for NO reduction. The structural analysis using scanning transmission electron microscopy and X-ray absorption spectroscopy showed that the as-prepared catalyst consisted of FeNiCu alloy nanoparticles dispersed on the Cr2O3-Al2O3 support. However, the structural change occurred under a catalytic reaction atmosphere, i.e., producing NiCu alloy nanoparticles dispersed on a NiFe2O4 moiety and Cr2O3-Al2O3 support. The oxidation of CO/C3H6 can be significantly enhanced in the presence of Cr oxide, resulting in a faster decrease in O2 concentration and thus regenerating the NiCu metallic surface, which is active for NO reduction to N2.

Numerical study on the effects of reaction conditions on single-particle char combustion in O2/H2O atmospheres

The distributions of temperature, reaction rate, and component concentration in char are significant for the stable char-O2/H2O combustion. Based on the single-particle char combustion numerical model in O2/H2O atmospheres, the present work quantitatively studied the effects of reaction conditions on distributions of temperature, reaction rate, and component concentration in char under O2/H2O conditions. The simulation results show that the char surface temperature is always higher than the center temperature in the heating stage. The H2O and O2 concentrations have little effect on the char heating time and heating rate. The char center temperature gradually exceeds the surface temperature after the heating stage, and this gap narrows with the rise in H2O concentration and the decrease in O2 concentration. The C-O2 and C-H2O reaction rates first increase and then decrease along the char radius, and the ratios of the C-H2O reaction rate gradually reduce along the radius. At 1373 K with 5 % O2/20 % H2O, the ratios are below 20 %. The ratios increase significantly with the rise of temperature to 1673 K, especially in the char center, more than 70 %. The H2O and O2 concentrations in char are higher on the surface than in the center. However, the CO and H2 concentrations show the opposite characteristics, and the distribution of CO2 is highly uniform in char. The char-O2/H2O reaction gradually shifts to the diffusion controlled regime with the rise in temperature and O2 concentration, while it slowly turns to the chemical kinetic controlled regime with the increase in H2O concentration.

P-169 Low 5% VS ultra-low 3% O2 concentration on embryo culture: Is there any difference in quality and ploidy?

Abstract Study question Can embryo culture in 3% O2 concentration improve fertilization and blastocyst formation rates, as well as euploidy rate, compared to 5% O2 embryo culture? Summary answer Ultra-low oxygen concentration (3%) does not seem to improve fertilization and euploidy rate neither embryo quality and blastocyst formation rate. What is known already Low oxygen tension (5%) during embryo culture has found to be beneficial for embryo development, when compared to atmospheric O2 tension (20%). Physiologically, oxygen tension is decreasing from ∼5% in the fallopian tube to ∼2,5% in the uterus and embryos enter the uterus on the post-compaction stage, around Day 4 of their development. Additionally, our previous study demonstrated that euploidy rate was significantly higher in 5% O2 concentration compared to 20%. Thus, the purpose of this study was to evaluate whether culture of embryos to blastocyst stage could benefit from a decrease in O2 concentration, from 5% to 3%. Study design, size, duration This retrospective study, included 176 PGT-A cycles, performed at Embryolab fertility clinic from May 2017 to November 2021. Two study groups were formed, in which oxygen tension was the only different parameter of culture conditions; the 5% O2 Group consisted of 114 PGT-A cycles resulting in 832 embryos and the 3% O2 Group with 62 PGT-A cycles including 479 embryos. Euploidy, fertilization and blastocyst formation rates were compared between the two groups. Participants/materials, setting, methods In all cycles included in the study, injected oocytes were incubated to either 3% O2 or 5% O2. The CO2 concentration was 6% in both groups. Embryos were cultured to blastocyst stage. In good quality available blastocysts (expansion: &amp;gt;3, ICM: A/B, TE: A/B according to Gardner Grading System), trophectoderm biopsy was performed on Days 5/6 and embryos were analyzed for chromosomal abnormalities. All embryos were vitrified after biopsy. Statistical analysis was performed using Mann-Whitney test. Main results and the role of chance Mean female age was similar between 5% and 3% group (37.76±4.7y vs 38.35±4.19y, p = 0.2263). Fertilization rates were similar between two groups (81.04% in 5% VS 81.77 in 3%, p = 0.9718). In 5% O2 Group, cleavage rate (98.86%) was found to be significantly higher, compared to 3% O2 Group (96.86%) (p = 0.003). Blastocyst formation rate (expressed per fertilized oocyte) was found to be significantly higher in the 5% O2 Group (76.56 in 5% VS 67.22 in 3%) (p = 0.029), as well as biopsied blastocyst rate (91.9% in 5% VS 82.29% in 3%) (p = 0.0056). Euploidy rates were found to be similar between the two groups, 26.7 in 5% Group and 26.76 in 3% Group (p = 0.9272). However, more blastocysts were available for biopsy on Days 5/6 in the 5% Group, as shown above. In the 5% Group, 101 embryotransfers have been performed, 54 with positive βHCG and 42 cycles had no euploid embryos after PGT-A. In the 3% Group, 28 embryotransfers have been performed, 18 with positive βHCG, 7 cycles are pending and 24 had no euploid embryos. This is an ongoing study and clinical outcomes remain to be reported and analyzed after the completion of data selection. Limitations, reasons for caution This is a retrospective study in which cycles from the two groups were not performed simultaneously but at different time periods. In addition, all PGT-A cycles were included in the study, regardless the type of infertility (e.g. both male and non-male factor infertility). Wider implications of the findings Based on these results, it is not recommended to decrease oxygen tension below 5% during culture, as this does not improve fertilization and euploidy rates. Nevertheless, embryo quality and blastocyst formation was found to be higher in 5% Group and this findings should be confirmed in a larger sample size. Trial registration number not applicable

Quantitative analysis of heat release during coal oxygen-lean combustion in a O2/CO2/N2 atmosphere by TG-DTG-DSC

Heat release of coal combustion in an oxygen-lean and multi-gas environment is a common phenomenon, coalfield fires caused by it can lead to serious environmental destruction and loss of coal resources. Simultaneous thermal analysis experiments for Bulianta (BLT, high-volatile bituminous coal) and Yuwu coal (YW, anthracite) in 21vol.%O2/79vol.%N2 and 15vol.%O2/5vol.%CO2/80vol.%N2 were carried out to study the law of heat release. Based on the TG-DTG-DSC curves, the combustion characteristic parameters were analyzed. Decreasing O2 concentration caused a significant reduction of local reactivity and further the decreasing maximum heat release rate for low-rank coal, while increasing CO2 concentration caused a significant thermal lag effect and further the increasing maximum heat release rate for high-rank coal. The relationship between the heat release rate and the reaction rate constant was quantitatively analyzed. At the increasing stage of the heat release rate, the heat release rate of the two coals increased conforming to ExpGro1 exponential model. At the decreasing stage of the heat release rate, the heat release rate of YW coal decreased exponentially with the reaction rate constant, while the heat release rate of BLT coal decreased linearly. Regardless of the atmospheres, the conversion rates corresponding to maximum heat release rate of BLT and YW coal were about 0.80 and 0.50, respectively, indicating that the coal rank played a dominant role. The results are helpful to understand the heat release process of coal oxygen-lean combustion in O2/CO2/N2.

Spatial Mapping of Dissolved Gases in the Danube Delta Reveals Intense Plant-Mediated Gas Transfer

Global estimates see river deltas and estuaries contributing about equally to CO2 and CH4 emissions as lakes and reservoirs, despite a factor 6 smaller surface area. Assessing the horizontal gradients in dissolved gas concentrations from large river reaches to connecting canals and wetland lakes remains a challenge in many deltaic systems. To elucidate the processes affecting local CO2 and CH4 concentrations in the Romanian part of the Danube Delta, we mapped dissolved O2, N2, He and Ar using a portable gas-equilibration membrane-inlet mass spectrometer (GE-MIMS), along with CO2, CH4, water temperature and conductivity. We measured the concentrations along the aquatic continuum from a small houseboat during two campaigns, in spring and autumn, to capture different hydrological and plant growth conditions. Delta-scale concentration patterns were comparably stable across seasons. Small connecting channels were highly influenced by the riparian wetland, which was strongest in the eastern part of the biosphere reserve. These sites represented the delta’s CO2 and CH4 hotspots and showed clear signs of excess air, i.e., supersaturation of dissolved noble gases with respect to air-saturated water. As the adjacent wetland was permanently inundated, this signal was likely caused by root aeration of Phragmites australis, as opposed to traditional excess air formation via water table fluctuations in the unsaturated zone. The special vegetation setting with reed growing on floating peat coincided with the highest CO2 and CH4 concentrations (&amp;gt;700 μmol/L CO2 and 13 μmol/L CH4, respectively) observed in an adjacent channel. Shallow lakes, on the other hand, were major sites of photosynthetic production with O2 oversaturation reaching up to 150% in spring. The observed deficit in non-reactive gases (He, Ar and N2) indicated that the lakes were affected by O2 ebullition from macrophytes. According to our estimations, this ebullitive flux decreased O2 concentrations by up to 2 mg/L. This study highlights the effect of plant-mediated gas transfer on dissolved gas concentrations and supports recent studies stressing the need to account for ebullitive gas exchange when assessing metabolism parameters from O2 in shallow, productive settings.

Try or Die: Dynamics of Plant Respiration and How to Survive Low Oxygen Conditions.

Fluctuations in oxygen (O2) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O2 availability. Therefore, decreased O2 concentrations severely affect mitochondrial function. Low O2 concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O2 in combination with light changes—as experienced during re-oxygenation—leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O2 environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O2 tolerance and survival of re-oxygenation), are presented.

Decomposition behaviors of ternary compounds in the Mg-Te-O system at various atmospheric conditions

Thermodynamic studies of the Mg-Te-O system have significant importance in improving Te recovery from pyrometallurgical processes and materials preparation in related fields. Ternary compounds, Mg3TeO6, Mg2Te3O8, MgTe2O5 and MgTe6O13, in the Mg-Te-O system have been synthesized in the present study, and their decomposition behaviors at various atmospheric conditions have been experimentally studied with the TGA-DSC technique. Obtained results showed that: 1) Mg3TeO6 started to decompose to MgO, TeO2, and O2 at 1255.9 °C in the carrying gas of 20% O2 - 80% Ar, and the initial decomposition temperature decreased along with decreasing oxygen concentration in the gas; 2) Mg2Te3O8 decomposed to MgO and TeO2, and when the O2 was rich in the gas, Mg3TeO6 was also found in the product. The initial decomposition temperature of Mg2Te3O8 was 832.1 °C, 839.2 °C, and 839.9 °C, when the O2 concentration in the carrying gas was 20%, 0.1%, and 0.0001%, respectively; 3) The decomposition products of MgTe2O5 were same with that of Mg2Te3O8, and its initial decomposition temperature decreased along with decreasing the O2 concentration in the gas; 4) MgTe6O13 decomposed to MgTe2O5 and TeO2 around 700 °C, and the initial decomposition temperature decreased with decreasing O2 concentration in the gas. Along with increasing temperature, MgTe2O5 converted to Mg3TeO6 through oxidation reactions, and Mg3TeO6 decomposed at elevated temperatures.

Design and comprehensive characterization of novel fiber-optic sensor systems using fast-response luminescence-based O2 probes

The detection of O2 using optical techniques has now become very important and significant progress has been made in this area over the past few years. The measurement of O2 concentration is a key parameter for diverse applications such as in life sciences, environmental monitoring, industry and biological research, and luminescence-based sensors are a valuable tool for measurements of this type. Often commercial sensors are unable to respond within a short time frame and drift over time - this demonstrates the importance of developing and validating a new technological approach. Given that need, a new sensor has been developed, with a specially-formed tip design coated with a very thin Platinum(II) 5,10,15,20-Tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP)-containing a polystyrene layer. The performance and reproducibility of the sensor design has been studied by comparing three identically fabricated sensor probes, showing that the new probe design has extreme fast response times – of a maximum value, Δt90max ≈ 390 ms for increasing and Δt90max ≈ 250 ms for decreasing O2 concentrations. The sensors created had an accuracy of better than ± 0.03 % O2 over the detection range investigated (between 0 % and 20 % O2) and showed a very stable performance over many hours of use. Examining this in detail through extended continuous use, over 12 h in a 0 % O2 solution, the probe stability was confirmed, showing a very low drift of luminescence decay time of ≈ 0.025 %/h (0.01 µs/h). Furthermore, the temperature ‘cross-talk’ has been studied in the important region between 25 °C and 40 °C (so that temperature corrections can be applied) and its mechanical stability, as well as allowing for compensation for any effects seen, has been confirmed. Given the success of the design developed, this work offers both an effective probe design and illustrates many important criteria for the selection of highly effective O2-sensitive coating materials and thus their use as a measurement tool for different quality control (QC) applications in industry.

Oxygen-depletion by rapid ammonia oxidation regulates kinetics of N2O, NO and N2 production in an ammonium fertilised agricultural soil

Oxygen (O2) is a key factor driving the expression of N-cycle-related functional genes and regulating nitrogenous gas production in the soil. However, how and to what extent the associated gene transcription and corresponding gas kinetics interact with the transition of soil O2 status caused by N fertilisation, remains poorly understood. In this context, we conducted a robotized incubation experiment using a He/O2 atmosphere with different amounts of ammonium-based fertiliser (0 (control), 60 (AS60) and 200 mg N kg−1 (NH4)2SO4 (AS200)) applied to an agricultural soil with a strong nitrification potential under three different initial O2 levels (oxic 21%, sub-oxic 3%, and anoxic 0%) over 14 days. Through repeated measurements of N2O, NO, and N2 concentrations and kinetics of mineral N following the decline of O2 concentrations, we found that higher ammonium addition (200 vs. 60 mg N kg−1) caused faster O2 consumption in the headspace and induced up to 238 times higher net accumulation of N2O under initially oxic headspace condition. We speculate that this was due to: 1) the rapid transition of O2 status from oxic to anoxic due to vigorous ammonia oxidation; and 2) the increased N2O/(N2O + NO + N2) ratio of denitrification with higher N addition. The amoA and nosZ gene transcript numbers changed significantly in response to ammonium addition and decreasing O2 concentration, whereas high-throughput sequencing revealed a significant structural alteration of the soil microbiota along with the transition of O2 status. Our results highlight that the vigorousness of oxygen depletion in the soil matrix driven by rapid ammonia oxidation is the proximal factor that regulates gas kinetics in high nitrification-potential soil when O2 diffusion is limited. This implies that practices which reduce hotspots of ammonia oxidation have the potential to mitigate N2O emissions from nitrifier denitrification and denitrification in agricultural soil.

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish

Direct and Indirect Bactericidal Effects of Cold Atmospheric-Pressure Microplasma and Plasma Jet.

The direct and indirect bactericidal effects of dielectric barrier discharge (DBD) cold atmospheric-pressure microplasma in an air and plasma jet generated in an argon-oxygen gas mixture was investigated on Staphylococcus aureus and Cutibacterium acnes. An AC power supply was used to generate plasma at relatively low discharge voltages (0.9–2.4 kV) and frequency (27–30 kHz). Cultured bacteria were cultivated at a serial dilution of 10−5, then exposed to direct microplasma treatment and indirect treatment through plasma-activated water (PAW). The obtained results revealed that these methods of bacterial inactivation showed a 2 and 1 log reduction in the number of survived CFU/mL with direct treatment being the most effective means of treatment at just 3 min using air. UV–Vis spectroscopy confirmed that an increase in treatment time at 1.2% O2, 98.8% Ar caused a decrease in O2 concentration in the water as well as a decrease in absorbance of the peaks at 210 nm, which are attributed NO2− and NO3− concentration in the water, termed denitratification and denitritification in the treated water, respectively.