O2 Production Rate Research Articles

Atomic-level insights into the activation of nitrogen via hydrogen-bond interaction toward nitrogen photofixation

Summary As the activation of N2 molecules is generally regarded as the bottleneck in N2 reduction, it is of significant importance to develop promising strategies to efficiently activate N2 molecules. Herein, we discovered an innovative approach to activate N2 molecules via hydrogen-bond interaction in N2 photofixation. Porous Cu with surface modification of S atoms (3%-S/Cu) exhibited remarkable catalytic activity and stability in N2 photofixation. Further mechanistic studies revealed that surface S atoms directly participated in the catalytic process by accepting and donating H atoms. In addition, the forming S–H bond significantly promoted the activation of N2 molecules via hydrogen-bond interaction, contributing to the enhanced catalytic activity.

One-pot synthesis of Bi2TiO4F2/BiOBr ferroelectric heterostructure for photocatalytic oxygen evolution

The internal electric field of ferroelectric materials originated from its spontaneous polarization can effectively improve the efficiency of carrier separation. Heterostructure formed by combining ferroelectric materials with semiconductor can further strengthen the photocatalytic property. In this work, ferroelectric material Bi2TiO4F2 has been successfully grown on the BiOBr {001} facet by a facial one-pot hydrothermal synthesis. Benefiting from both the internal electric field derived from the ferroelectric spontaneous polarization of Bi2TiO4F2, and the high-quality heterojunction interface, the O2 production rate of BiOBr/ Bi2TiO4F2 heterojunction reaches 875 μmol g−1 h−1. The possible formation process and reaction mechanism has also been discussed. This research may provide us with some new hints to design new heterostructure photocatalytic materials with both ferroelectricity and active exposure surfaces.

The Contribution of Electrons to the Sputter-produced O2 Exosphere on Europa

Abstract Electrons contribute a strong radiation component to the surface bombardment of Europa. However, they are not typically considered to contribute to erosion of the surface H2O-ice or produce exospheres of radiolytic O2, as laboratory studies on sputtering induced by electrons are sparse. Here we have measured the sputtering yield of H2O-ice induced by 0.5 keV electrons between 14 and 125 K, estimating the composition of the stable products ejected during irradiation. Combining these measurements with updated electron flux measurements, we estimate for the first time that the global surface production rate of O2 from electron-induced sputtering is larger than the production rate previously estimated for all of the ionic components combined. Our results emphasize the importance of electrons in producing exospheres on icy satellites and suggest that these exospheres need not be tied to environments where the surface is being bombarded with heavy ions.

Evaluation of Antioxidant Activities, Oxidation Enzymes, and Quality of Nano-Coated Button Mushrooms (Agaricus Bisporus) during Storage

Agaricus Bisporus is an edible button mushroom that is highly perishable with an extremely short shelf-life at ambient temperature. This work aims to evaluate some antioxidant activities, oxidation enzymes, and determine postharvest qualities of nano-coated mushrooms with the combination of chitosan (CHN) component during storage at 4 °C for (0, 3, 6, 9, and 12 days). Silica/CHN Film strongly delayed the mushroom respiratory spike onset and blocked carbon dioxide passage from inside to the outside, while Titanium/CHN Film (0.035 mmol s−1 kg−1) established the lowest O2 production rate and thiobarbituric acid reactive substances production (6.21 nmol g−1). Silica/CHN Film was mainly effectual for the polyphenol contents (0.39 g kg−1) and antioxidant activities (78.14% and 71.09%) for DPPH and ABTS+ radical scavenging activities, respectively. The results reported that Silica/CHN Film induced the highest (catalase and ascorbate peroxidase) activities, while Titanium/CHN Film recorded the highest (peroxidase and superoxide dismutase) activities of antioxidant enzymes. Besides, Titanium/CHN Film preserved relatively lower contents of hydrogen peroxide (22.40 µmol g−1) and hydroxyl radical (0.16 µmol g−1). In a word, nano-materials used in coating films such as titanium or even silica with the combination of CHN can directly reduce the cell degradation, oxidation processes and enhance the harvested horticultural crops.

High-valence-state nickel-iron phosphonates with urchin-like hierarchical architecture for highly efficient oxygen evolution reaction

The exploitation of highly efficient, low-cost, and durable catalysts for photocatalytic water oxidation is highly desirable in the field of sustainable energy conversion and storage. Here, we demonstrate the preparation of urchin-like 3D nickel-iron phenyl phosphonates (NiFeP) hierarchical architecture fabricated by ultrathin nanosheets for photocatalytic water oxidation with high efficiency. The urchin-like NiFeP hierarchical architecture is prepared by a facile solvothermal synthesis without any organic additives. The urchin-like 3D hierarchical architecture exhibits a large specific surface area and abundant mesopores distribution, which affording more active catalytic sites and multi-electron transport channel. In the presence of high-valence Ni3+ sites could act as the main redox site to decrease the overpotential of water oxidation reaction. In consequence, using [Ru(bpy)3]Cl2 photosensitizer under visible light irradiation, the urchin-like NiFeP photocatalyst demonstrates a high oxygen evolution activity, giving a superior O2 yield of 76% and O2 production rate of 23.66 umol s−1 g−1. Moreover, the urchin-like NiFeP photocatalyst is highly stable for reuse. This work extends the development of transition metal phosphonates and provides a platform for designing high performance, economic and stable catalysts.

High-valence-state Ni–Fe bimetallic phosphonate nanoribbons catalyst for enhanced photocatalytic and electrocatalytic oxygen production

The design and synthesis of economy and efficiency materials for oxygen evolution reaction (OER) have been a continuous hot spot in the field of scientific study. Herein, a high-valence-state two-dimension (2D) NiFe phosphonate-based (NiFeP) nanoribbons catalyst has been constructed through a one-step solvothermal process. The NiFeP nanoribbons exhibit highly active in both photocatalytic and electrocatalytic water oxidation due to the 2D nanoribbons and high-valence Ni3+ sites. The 2D nanoribbons not only provide more reactive sites for OER but also shorten bulk diffusion distance with better photoexcited carrier transport from the interior to the surface. Meanwhile, the existence of high-valence Ni3+ could be acted as an efficient redox site to reduce the overpotential and facilitate the catalytic reaction. In consequence, the NiFeP nanoribbons catalyst demonstrates a superior O2 yield of 65.7% and O2 production rate of 25.97 umol s−1 g−1, which are comparable or even much higher than those other reported transition metal oxide photocatalysts. At last, the possible proton-coupled electron transfer mechanism is also proposed. This study not only demonstrates the potential of a low-cost metal phosphonate OER catalyst but also provides a referential system for the fabrication of high activity and stability catalysts toward replacing noble metals for energy storage and conversion. High-valence-state 2D NiFe phosphonate-based nanoribbons catalyst has been constructed for the first time through a one-step solvothermal process without any organic additives or template agent. The as-prepared catalyst of NiFeP nanoribbons exhibits highly active in both photocatalytic and electrocatalytic water oxidation.

Fuel and oxygen harvesting from Martian regolithic brine

NASA's current mandate is to land humans on Mars by 2033. Here, we demonstrate an approach to produce ultrapure H2 and O2 from liquid-phase Martian regolithic brine at ∼-36 °C. Utilizing a Pb2Ru2O7-δ pyrochlore O2-evolution electrocatalyst and a Pt/C H2-evolution electrocatalyst, we demonstrate a brine electrolyzer with >25× the O2 production rate of the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) from NASA's Mars 2020 mission for the same input power under Martian terrestrial conditions. Given the Phoenix lander's observation of an active water cycle on Mars and the extensive presence of perchlorate salts that depress water's freezing point to ∼-60 °C, our approach provides a unique pathway to life-support and fuel production for future human missions to Mars.

Study on the growth mechanism of dispersed monoclinic BiVO4 in hydrothermal process and its photocatalytic activity

In this paper, the monoclinic BiVO4 was successfully prepared, and the preferentially exposed (010) crystal plane was found. The growth mechanism of monoclinic BiVO4 in the hydrothermal process was also deeply analyzed. We explored the phase and structure changes of samples under different preparation conditions via XRD, FT-IR SEM and TEM in order to analyze the growth mechanism of monoclinic BiVO4 from the perspective of thermodynamics and kinetics. Simultaneously, we calculated the forbidden band width of samples prepared at 90 and 180 °C through UV-Vis spectra and analyzed electron hole recombination of different samples through PL spectra. Besides, in order to reveal the photocatalytic activity, photolysis experiment was performed on the samples. The results show that pure monoclinic BiVO4 with flaky structure was successfully prepared at 120 °C. The monoclinic BiVO4 preferentially grew into the flaky structure along the (010) plane, and eventually the block structure was found. Photolysis water experiment was performed on the samples. The samples prepared at 100 °C was found to have the best photocatalytic performance and an O2 production rate of 788.31 µmol/h/g.

An All-Organic D-A System for Visible-Light-Driven Overall Water Splitting.

Direct water splitting over photocatalysts is a prospective strategy to convert solar energy into hydrogen energy. Nevertheless, because of the undesirable electron accumulation at the surface, the overall water-splitting efficiency is seriously restricted by the poor charge separation/transfer ability. Here, an all-organic donor-acceptor (D-A) system through crafting carbon rings units-conjugated tubular graphitic carbon nitride (C-TCN) is proposed. Through a range of characterizations and theoretical calculations, the incorporation of carbon rings units via continuous π-conjugated bond builds a D-A system, which can drive intramolecular charge transfer to realize highly efficient charge separation. More importantly, the tubular structure and the incorporated carbon rings units cause a significant downshift of the valence band, of which the potential is beneficial to the activation for O2 evolution. When serving as photocatalyst for overall water splitting, C-TCN displays considerable performance with H2 and O2 production rates of 204.6 and 100.8µmol g-1 h-1 , respectively. The corresponding external quantum efficiency reaches 2.6% at 405nm, and still remains 1.7% at 420nm. This work demonstrates that the all-organic D-A system conceptualized from organic solar cell can offer promotional effect for overall water splitting by addressing the charge accumulation problem rooted in the hydrogen evolution reaction.

Fast and easy quantitative characterization of methanotroph-photoautotroph cocultures.

Recent research has demonstrated that synthetic methanotroph-photoautotroph cocultures offer a highly promising route to convert biogas into value-added products. However, there is a lack of techniques for fast and accurate characterization of cocultures, such as determining the individual biomass concentration of each organism in real-time. To address this unsolved challenge, we propose an experimental-computational protocol for fast, easy, and accurate quantitative characterization of the methanotroph-photoautotroph cocultures. Besides determining the individual biomass concentration of each organism in the coculture, the protocol can also obtain the individual consumption and production rates of O2 and CO2 for the methanotroph and photoautotroph, respectively. The accuracy and effectiveness of the proposed protocol was demonstrated using two model coculture pairs, Methylomicrobium alcaliphilum 20ZR-Synechococcussp. PCC7002 that prefers high pH high salt condition, and Methylococcus capsulatus-Chlorella sorokiniana that prefers low salt and neutral pH medium. The performance of the proposed protocol was compared with a flow cytometry-based cell counting approach. The experimental results show that the proposed protocol is much easier to carry out and delivers faster and more accurate results in measuring individual biomass concentration than the cell counting approach without requiring any special equipment.

Effects of 5-aminolevulinic acid on osmotic adjustment and antioxidant system in mung bean under chilling stress

Effects of 5-aminolevulinic acid on osmotic adjustment and antioxidant system in mung bean under chilling stress

Kinetic characterization of microalgal-bacterial systems: Contributions of microalgae and heterotrophic bacteria to the oxygen balance in wastewater treatment

Abstract Metabolic activities of microalgae and heterotrophic bacteria were characterized in terms of dissolved O2 uptake and production rates under dark and light conditions, assessing the contribution of both microbial groups to the O2 balance during wastewater treatment. Up to 13 kinetic and stoichiometric parameters were determined, allowing a quantitative description of the O2 production and uptake dynamics. Under dark conditions, the maximum specific O2 uptake rates for microalgae and bacteria were 14.73 ± 2.02 mgO2 gVSS−1 h−1 and 2.37 ± 1.52 mgO2 gVSS−1 h−1, respectively. Microalgae were therefore the largest O2 consumers under dark conditions, being responsible for up to 86 % of the total heterotrophic respiration. Under light conditions (photosynthetic metabolism for microalgae and heterotrophic metabolism for bacteria), microalgae supported a maximum specific O2 production rate of 13.76 ± 1.48 mgO2 gVSS-1 h-1, while bacteria supported a maximum specific O2 uptake of 2.37 ± 1.52 mgO2 gVSS-1 h-1. The oxygenation performance of the microalgal community was therefore superior to the O2 respiration of heterotrophic bacteria under light conditions. The kinetic characterization performed provides critical information about the photosynthetic oxygenation potential, microbial growth and heterotrophic O2 uptake, which is essential for design, optimization, and modeling of wastewater treatment processes.

Effects of Solanum lycopersicum rootstock on biomass, amnio acid content and reactive oxygen species metabolism of grafted seedlings under salt stress

To explore the mechanism of Solanum lycopersicum rootstock function in enhancing salt tolerance of grafted seedlings, we examined the growth, Na+ accumulation, amino acid contents and active oxygen metabolism (ROS) in three grafted seedlings treated with and without 175 mmol·L-1 NaCl conditions. RS grafted seedlings were formed by split grafting using salt-sensitive variety 'Zhongza 9'(S) as scion and salt-tolerant variety 'OZ-006'(R) as rootstock, while the other two experiment materials were the scion self-grafted (SS) and rootstock self-grafted (RR) seedlings. The results showed that NaCl stress significantly increased the salt damage index and Na+ content, concomitantly with substantial decrease in growth rate and chlorophyll content of seedlings. More-over, there were significant differences among the grafting combinations, with an order of SS>RS>RR. NaCl stress significantly increased total amino acid content in the leaves and roots of the grafted seedlings. The amino acid contents were significantly higher than those in the control. There were 9 kinds of amino acid in RR and RS leaves, and 8 kinds in RR and RS roots, with the most significant change in proline. Only 2 and 4 kinds of amino acids in leaves and roots of SS were significantly higher than those in control, respectively. Amino acid contents among three grafted seedlings showed RR>RS>SS under NaCl stress. The contents of amino acid in RR and RS leaves increased by 32.8% and 16.6% compared with SS, and those in RR and RS roots increased by 53.1% and 32.5%, respectively. The changes of ROS were caused by NaCl stress, which enhanced the activities of antioxidant enzymes, the production rate of O2-· and MDA content in both leaves and roots. Among different grafted seedlings, RR had the most prominent increase of antioxidant enzymes activities in leaves and roots, followed by RS, and SS showed the smallest. The active oxygen levels among the three grafted seedlings were show as SS>RS>RR. In summary, rootstock alleviated salt damage of grafted seedlings by inhibiting Na+ transport upward, enhancing amino acid content and antioxidant enzyme activities. The salt tolerance ability showed remarkable difference among three different combinations of rootstock and scion, with a order of RR>RS>SS. Our results suggested that salt tolerance of S. lycopersicum grafted seedlings was mainly affected by the ability of rootstock salt tolerance, followed by scion, and also closely related to the regulation of both amino acid and active oxygen metabolism in seedlings.

Partially Pyrolyzed Binary Metal-Organic Framework Nanosheets for Efficient Electrochemical Hydrogen Peroxide Synthesis.

Herein, we developed a partially controlled pyrolysis strategy to create evenly distributed NiO nanoparticles within NiFe-MOF nanosheets (MOF NSs) for electrochemical synthesis of H2 O2 by a two-electron oxygen reduction reaction (ORR). The elemental Ni can be partially transformed to NiO and uniformly distributed on the surface of the MOF NSs, which is crucial for the formation of the particular structure. The optimized MOF NSs-300 exhibits the highest activity for ORR with near-zero overpotential and excellent H2 O2 selectivity (ca. 99 %) in 0.1 m KOH solution. A high-yield H2 O2 production rate of 6.5 mol gcat -1 h-1 has also been achieved by MOF NSs-300 in 0.1 m KOH and at 0.6 V (vs. RHE). In contrast to completely pyrolyzed products, the enhanced catalytic activities of partially pyrolyzed MOF NSs-300 originates mainly from the retained MOF structure and the newly generated NiO nanoparticles, forming the coordinatively unsaturated Ni atoms and tuning the performance towards electrochemical H2 O2 synthesis.

Inhibitory effect of propyl gallate on pulp breakdown of longan fruit and its relationship with ROS metabolism

Abstract An excessive ROS accumulation in harvested longan (Dimocarpus longan Lour.) fruit could promote the pulp breakdown and lower the fruit quality. To solve this problem, the influence of propyl gallate, one kind of ROS scavenger, on the ROS metabolism in pulp of postharvest longans and its connection with the breakdown occurrence of longan pulp were investigated. Contrasted to control samples, the propyl gallate-treated group manifested a lower index of pulp breakdown, MDA content, and production rate of O2−., but higher gene expression levels of DlSOD, DlCAT and DlAPX, higher SOD, CAT and APX activities, higher levels of AsA, flavonoid, GSH and total phenolics, and higher ability of scavenging free radicals. These results revealed that propyl gallate inhibited longan pulp breakdown occurrence, which was because propyl gallate enhanced the ROS scavenging ability and reduced ROS generation and accumulation in longan pulp. These activities involved alleviating the oxidative damage of cell membrane and the peroxidation of membrane lipid in longan pulp, which maintained the structural integrity of longan pulp cell membrane and suppressed the pulp breakdown occurrence in postharvest longan fruit.

Ketamine treatment affects hippocampal but not cortical mitochondrial function in prepubertal rats.

Previous reports have shown that ketamine triggered apoptosis in immature developing brain involving mitochondrial-mediated pathways. However, no data for ketamine effects on hippocampal and cortical mitochondrial function are available in prepubertal rats. Twenty-one-day-old Sprague-Dawley rats received ketamine (40mg/kg i.p.) for 3days and were killed 24hr after thelast injection. Hippocampal mitochondria from ketamine-treated rats showed decreased malate-glutamate state 4 and 3 respiratory rates and an inhibition in complex I and IV activities. Hippocampal mitochondrial membrane depolarization and mitochondrial permeability transition induction were observed. This was not reflected in an increment of H2 O2 production probably due to increased Mn-SOD and catalase activities, 24hr after treatment. Interestingly, increased H2 O2 production rates and cardiolipin oxidation were found in hippocampal mitochondria shortly after ketamine treatment (45min). Unlike the hippocampus, ketamine did not affect mitochondrial parameters in the brain cortex, being the area less vulnerable to suffer ketamine-induced oxidative damage. Results provide evidences that exposure of prepubertal rats to ketamine leads to an induction of mitochondrial ROS generation at early stages of treatment that was normalized by the triggering of antioxidant systems. Although hippocampal mitochondria from prepubertal rats were capable of responding to the oxidative stress, they remain partially dysfunctional.

Light absorption and growth response of Dunaliella under different light qualities

Dunaliella sp. (formerly D. salina MACC/C43) was batch-cultured under blue (BL), red (RL), or white light (WL) provided by light-emitting diodes (LED) and white light provided by fluorescent lamps (WF), respectively, to assess growth characteristic. Growth under blue light coupled with red light (BL + RL) was also measured and compared with that under BL, WL, and RL, respectively, in a laboratory-scale photobioreactor. Algae under monochromatic blue light had the highest specific growth rate (μ) with a value of 0.51 day−1, followed by WF (0.49 day−1), WL (0.47 day−1), and RL (0.44 day−1). Red light significantly enhanced Chl a and carotenoid contents, with values of 20.1 and 9.6 pg cell−1, respectively. BL + RL increased the μ (0.20 day−1) compared to those rates under pure BL or RL ranging from 0.17 to 0.18 day−1, in batch culture for 14 days using a photobioreactor with 3.2 L working volume. Cells absorb more photons for photosynthesis in the blue band. Mean extinction coefficient calculated based on the modified Lambert–Bill law at the blue light region (430–480 nm) was 0.885 cm−1, which is 22, 11, and 15% higher than that of the red light region (630–700 nm), green light region (500–560 nm), and photosynthetically active radiation region (400–700 nm), respectively. Blue light also improved the initial slope and the maximum O2 production rate in a photosynthesis–irradiance curve, whereas it lowered the compensation irradiance and dark respiration rate. The photochemistry of photosystem II also displayed its optimal performance under BL. LEDs are a suitable light source for Dunaliella sp. growth, and BL + RL promotes rapid division of algal cells.

Photocatalytic Water Splitting on Rh/K₄Nb6O17 Nanosheets.

The layered potassium niobate, K₄Nb6O17, is known as a photocatalyst for hydrogen production from water splitting under UV light. Here we show that potassium niobate nanosheets can be obtained by exfoliation of K₄Nb6O17 followed by proton exchange. Photocatalytic water splitting has been improved in this work by loading Rh nanoparticles as cocatalyst. The catalysts were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy analysis (XPS), and ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Their photocatalytic activities were in (i) an aqueous MeOH, used as sacrificial hole scavengers for hydrogen production and (ii) pure water for hydrogen and oxygen production under UV light irradiation. The potassium niobate nanosheets with uniform dispersion of Rh nanoparticles exhibited a very high photocatalytic overall water splitting activity, where the H₂ production and O₂ production rate were 142 μmol h-1 g-1 and 68 μmol h-1 g-1, which was about 10 times higher than that exhibited by the origin K₄Nb6O17 photocatalyst.

Effect of temperature and feeding on carbon budgets and O2 dynamics in Pocillopora damicornis

Studying carbon dynamics in the coral holobiont provides essential knowledge of nutritional strategies and is thus central to understanding coral ecophysiology. In this study, we assessed the carbon budget inPocillopora damicornis(using H13CO3) as a function of feeding status and temperature stress. We also compared dissolved oxygen (O2) fluxes measured at the colony scale and at the polyp scale. At both scales, O2production rates were enhanced for fed vs. unfed corals, and unfed corals exhibited higher bleaching and reduced photosynthetic activity at high temperature. Unfed corals exclusively respired autotrophically acquired carbon, while fed corals mostly respired heterotrophically acquired carbon. As a consequence, fed corals excreted on average >5 times more organic carbon than unfed corals. Photosynthate translocation was higher under thermal stress, but most of the carbon was lost via respiration and/or mucus release (42-46% and 57-75% of the fixed carbon for unfed and fed corals, respectively). Such high loss of translocated carbon, coupled to low assimilation rates in the coral tissue and symbionts, suggests thatP. damicorniswas nitrogen and/or phosphorus limited. Heterotrophy might thus cover a larger portion of the nutritional demand forP. damicornisthan previously assumed. Our results suggest that active feeding plays a fundamental role in metabolic dynamics and bleaching susceptibility of corals.

Solution-phase vertical growth of aligned NiCo2O4 nanosheet arrays on Au nanosheets with weakened oxygen-hydrogen bonds for photocatalytic oxygen evolution.

Vertical heterojunctions of two-dimensional (2D) semiconducting materials have attracted more and more research interest recently due to their unique optical, electrical, and catalytic properties and potential applications. Although great progress has been made, vertical integration of the layered materials formed by 2D semiconductor nanosheets and 2D plasmatic metal nanosheets remains a huge challenge. Here, we demonstrate for the first time a solution-phase growth of vertical plasmatic metal-semiconductor heterostructures in which aligned NiCo2O4 nanosheet arrays vertically grow on a single Au nanosheet, forming vertically aligned NiCo2O4-Au-NiCo2O4 sandwich-type heterojunctions with hierarchical open channels. Such vertical NiCo2O4-Au-NiCo2O4 heterojunctions can effectively promote the separation and transfer of a photoinduced charge. Density functional theory (DFT) studies and time-resolved transient absorption spectroscopy show that electrons transfer from NiCo2O4 to Au, and the formation of the heterojunction weakens the H-O bond of H2O. Due to the unique structure and superiority of the component, the vertical NiCo2O4-Au-NiCo2O4 heterojunctions exhibit significant activity with an O2 production rate of up to 33 μmol h-1 and long-term stability for photocatalytic water oxidation. We calculated the apparent quantum efficiency (AQE) to be 21.9% for NiCo2O4-Au-NiCo2O4 heterojunctions at the wavelength λ = 450 ± 10 nm, which is higher than that of NiCo2O4 nanosheets (10.9%), Au nanosheets (0.96%) and other photocatalysts. The present study paves the way for the controlled synthesis of novel vertical heterojunctions based on 2D semiconductor nanosheets and 2D metal nanosheets for efficient photocatalysis.