O2 Production Rate Research Articles

2 D Hybrid of Ni-LDH Chips on Carbon Nanosheets as Cathode of Zinc-Air Battery for Electrocatalytic Conversion of O2 into H2 O2.

It remains great challenge to develop precious-metal-free electrocatalysts to implement high-activity electrochemical conversion of O2 into value-added hydroperoxide species (HO2 - ), which are vulnerable when exposed to various transition-metal-based catalysts. A strategy based on steric hindrance and layered nickel-based layered double hydroxide (Ni-LDH) induction has been developed for one-pot inlaying high-density ultrathin 2 D Ni-LDH chips on in situ-grown carbon nanosheets (Ni-LDH C/CNSs). The resulting material exhibits high electrocatalytic selectivity with a faradaic efficiency up to 95 % for oxygen reduction into peroxide and attains a fairly high mass activity of approximately 22.2 A g-1 , outperforming most metal-based catalysts reported previously. Systematic studies demonstrate that the greatly increased defect concentration at Ni edge sites of Ni-LDH chips results in more active sites, which contributes a favorable thermodynamically neutral adsorption of OOH* and adsorbed H2 O2 molecules relatively weakly. Additionally, the modified CNSs effectively suppress H2 O2 decomposition and avoid O-O bond cleavage to produce H2 O by steric effects. The synergistic effect of CNSs and Ni-LDH chips therefore leads to high activity and high selectivity in a two-electron pathway. A proof-of-concept zinc-air fuel cell is proposed and set up to demonstrate the feasibility of green synthesis of peroxide, generating an impressive H2 O2 production rate of 5239.67 mmol h-1 gcat. -1 .

Two layered Bi-based borate photocatalysts MBi2B2O7 (M = Ca, Sr) for photocatalytic degradation and oxygen activation

Layered bismuth-based photocatalytic materials have great potential for environmental purification. In this work, we developed two novel layered bismuth-based borate photocatalysts CaBi2B2O7 (CBBO) and SrBi2B2O7 (SBBO) via solid-phase reaction. The crystal structure, microstructure and optical properties were investigated. The photocatalytic activities were studied by decomposition of tetracycline hydrochloride (TH) and evolution of reactive oxygen species (ROS) under UV light irradiation. The results revealed that CBBO and SBBO exhibit benign TH degradation activity with certain mineralization abilities. Within 4 min illumination, almost 70% and 58% of tetracycline hydrochloride was degraded by CBBO and SBBO, respectively. The quantitative capture experiment of radicals showed that the production rate of OH and O2− was determined to be 1.27 × 10-7 and 10.98 × 10-7 mol·L-1 min-1 for CBBO and 1.01 × 10-7 and 11.75 × 10-7 mol·L-1 min-1 for SBBO, respectively. Density functional theory (DFT) calculation results demonstrated that CBBO has smaller effective masses of electrons and holes than SBBO, which results in higher charge separation efficiency and photocatalytic activity. This work provides two new layered bismuth-based borate photocatalysts for photocatalytic environmental applications.

Physiological responses of peanut seedlings to exposure to low or high cadmium concentration and the alleviating effect of exogenous nitric oxide to high cadmium concentration stress

The physiological responses of peanut seedlings exposed to low (5 µM) or high (200 µM) cadmium (Cd) concentration and the ability of sodium nitroprusside (SNP, a donor of NO) to reverse the harmful effects of Cd on peanut (Arachis hypogaea L.) were studied. Changes in plant growth parameters, chlorophyll content, antioxidant system, nutrient contents and Cd accumulation were investigated. The results showed that SNP and 5 µM Cd improved plant growth and chlorophyll content. Furthermore, antioxidative system was up-regulated, and as a result, the production rate of superoxide radical (O2•−) was reduced. Moreover, the absorption of nutrient elements was not impacted, and Cd toxicity was not observed. However, 200 µM Cd had negative effects on the above measured parameters and dramatically increased the accumulation of Cd in all the plant organs. In the 200 µM Cd treatment, addition of 250 µM SNP stimulated plant growth and increased chlorophyll content. It also enhanced the regulation of antioxidative system and reduced the production rate of O2•− and malondialdehyde (MDA) content. Besides, SNP supply enhanced the absorption of nutrient elements and restrained the absorption and transport of Cd.

Effects of NaCl stress on growth of Portulaca oleracea and underlying mechanisms

The purslane Portulaca oleracea L. is a promising crop species for agriculture in saline–alkali soils. Up to date, biochemical and molecular changes in purslane in response to salinity were seldom reported. To investigate biochemical effects of salinity on purslane, seedlings were treated with different concentrations of NaCl for up to 14 days. The results showed that treatments with 150 mM and 200 mM NaCl significantly decreased dry and fresh weight of seedlings, shoot and root length as well as leaflet number on main stem, demonstrating inhibition on purslane growth. Treatments with 100–200 mM NaCl significantly decreased net photosynthetic rate, increased intercellular CO2 concentration, MDA content and production rate of O2−, induced activities of SOD, POD and CAT, suggesting inhibition on photosynthesis and induction of oxidant stress. With longer exposure time, activities of antioxidant enzymes showed decreasing tendency, probably due to denaturation of proteins and damages of cell membrane. In treatments with 150 mM and 200 mM NaCl, Na+ content increased in purslane leaf, stem and root, which then decreased K+ content, probably due to membrane depolarization and regulation of ion channels. Moreover, transcriptome profiles in leaves were compared among treatments with 200 mM for 0, 2, 6, 12 and 24 h. The results suggested that saline treatments down-regulated transcription levels of genes involved in photosynthesis, energy metabolism, lignin biosynthesis and signaling transduction. Overall, the present study uncovered biochemical and molecular responses of purslane to salinity, which should be useful for agriculture of purslane on saline–alkali soils.

Comprehensive analysis of dynamics and hazards associated with cascading failure in 18650 lithium ion cell arrays

Lithium ion batteries (LIBs) are among the most promising technologies for electrical energy storage. However, any exposure of LIBs to abnormal operating conditions may lead to rapid self-heating accompanied by ejection of flammable materials, termed thermal runaway. In a multi-cell array or pack, thermal runaway may propagate to neighboring cells and grow into a large-scale fire. In this work, a new experimental setup was developed to investigate this propagation or cascading failure phenomenon using 12–18 cell arrays constructed from lithium cobalt oxide (LCO) cells of 18650 form factor and 2600 mA h nominal electrical capacity. The arrays, consisting of fully charged cells, were mounted in a specially designed wind tunnel, which provided well controlled environmental conditions. Thermal runaway was initiated in one cell using a small electric heater and observed to propagate through the array using temperature sensors attached to individual cells. The propagation process was studied in both nitrogen and air environments to elucidate the impact of flaming combustion. In addition to the cell temperatures, production rates of O2, total hydrocarbons (THC), CO, CO2 and H2 were measured, and heats generated in chemical reactions between the battery materials and in flaming combustion were computed. In the nitrogen tests, row-to-row propagation speed (SP) showed no significant dependence on the size of the array and was estimated to be 0.08 s−1. When cell arrays were tested in air, SP increased to 0.7 s−1 (about 9 times the nitrogen value) in late stages of cascading failure due to the impact of flaming combustion of ejected materials. Measurements demonstrated that failing LCO cells produced minor mass yields of O2 and H2 in addition to relatively large amounts of CO, THC and CO2. The lower flammability limit of the ignitable portion of ejected gaseous products was determined to be 5.79 ± 0.12 vol.% in air. The chemical heat generation resulting from reactions between battery materials inside and outside the bodies of cells was computed to be 56.6 ± 2.5 kJ per cell. The total amount of heat released from flaming combustion of ejected battery materials during air tests was found to be 60.1 ± 17.5 kJ per cell. The efficiency with which these battery materials were combusted was estimated to be about 56%. The results of this study provide previously unavailable, comprehensive assessment of the failure dynamics and energetics in LIB cell arrays or assemblies. These results are expected to serve as a foundation for effective methodologies for detection, mitigation and prevention of electrical energy storage and electric vehicle fires.

Exploring the low photosynthetic efficiency of cyanobacteria in blue light using a mutant lacking phycobilisomes

The ubiquitous chlorophyll a (Chl a) pigment absorbs both blue and red light. Yet, in contrast to green algae and higher plants, most cyanobacteria have much lower photosynthetic rates in blue than in red light. A plausible but not yet well-supported hypothesis is that blue light results in limited energy transfer to photosystem II (PSII), because cyanobacteria invest most Chl a in photosystem I (PSI), whereas their phycobilisomes (PBS) are mostly associated with PSII but do not absorb blue photons. In this paper, we compare the photosynthetic performance in blue and orange-red light of wildtype Synechocystis sp. PCC 6803 and a PBS-deficient mutant. Our results show that the wildtype had much lower biomass, Chl a content, PSI:PSII ratio and O2 production rate per PSII in blue light than in orange-red light, whereas the PBS-deficient mutant had a low biomass, Chl a content, PSI:PSII ratio, and O2 production rate per PSII in both light colors. More specifically, the wildtype displayed a similar low photosynthetic efficiency in blue light as the PBS-deficient mutant in both light colors. Our results demonstrate that the absorption of light energy by PBS and subsequent transfer to PSII are crucial for efficient photosynthesis in cyanobacteria, which may explain both the low photosynthetic efficiency of PBS-containing cyanobacteria and the evolutionary success of chlorophyll-based light-harvesting antennae in environments dominated by blue light.

Active Edge-Site-Rich Carbon Nanocatalysts with Enhanced Electron Transfer for Efficient Electrochemical Hydrogen Peroxide Production.

A highly efficient, metal-free carbon nanocatalyst is presented that possesses abundant active, oxygenated graphitic edge sites. The edge site-rich nanocarbon catalyst exhibits about 28 times higher activity for H2 O2 production than a basal plane-rich carbon nanotube with a H2 O2 selectivity over 90 %. The oxidative treatment further promotes the H2 O2 generation activity to reach close to the thermodynamic limit. The optimized nanocarbon catalyst shows a very high H2 O2 production activity, surpassing previously reported catalysts in alkaline media. Moreover, it can stably produce H2 O2 for 16 h with Faradaic efficiency reaching 99 % and accumulated H2 O2 concentration of 24±2 mm. Importantly, we find that the heterogeneous electron transfer kinetics of the carbon-based catalyst is closely related to the electrocatalytic activity, suggesting that first outer-sphere electron transfer to O2 is an important step governing the H2 O2 production rate.

Conjugated trienols and programmed cell death are more closely related to superficial scald than reactive oxygen species in apple fruit stored at low temperature

Superficial scald is a physiological disorder affecting apple fruit during cold storage. Previous studies have reported that multiple factors, such as α-farnesene, ethylene, conjugated trienols (CTols), reactive oxygen species (ROS), and programmed cell death (PCD) are associated with superficial scald. However, the correlation between the factors and scald severity under different storage durations has rarely been reported. In this study, we analyzed how these factors change over time (0 d, 7 d, 30 d, 60 d and 90 d) in association with the incidence of scald in ‘White Winter Pearmain’ apples at low-temperature (5 °C). The results showed that the time for scald to development is short and the incidence of scald increases with storage time. The highest level of α-farnesene was observed after 7 d, whereas, the production rate of CTols, O2−, H2O2, and ethylene gradually increased with time. In addition, specific expression profiling of MdDAD1, MdLSD1 and MdDND1 suggested that PCD was involved with scald development. The correlation analysis showed that content of CTols, the production rate of ethylene, and the expression of MdAFS, MdHMGR2, MdACS1, MdACO1, MdDAD1, and MdLSD1 were strongly associated with superficial scald, whereas, α-farnesene and ROS were weakly associated. These results suggest that CTols and PCD are associated with scald development and that their role is more prominent than ROS. This is a novel perspective on the cause of scald that-can help develop potential solutions to inhibit scald development.

Effect of oxide defect on photocatalytic properties of MSnO3 (M = Ca, Sr, and Ba) photocatalysts

Since energy transfer to oxygen species is generally considered to be the critical step during the O2−-driven photocatalytic reaction, it is important to develop approaches to design the oxygen defects induced photocatalysts to improve the performance of oxygen chemisorption. Here we report that a new strategy of oxide defect controlled MSnO3 catalyst is served to turn light into chemical energy by improving species chemisorption on the surface. CaSnO3 with the Ca/Sn ratio of 2.7 (2.7-CaSnO3) rich in oxygen vacancies exhibited a high photocurrent performance and an efficient photocatalytic activity. A superior photo efficiency is achieved for 2.7-CaSnO3, which reduces 93.9% MB dyes within 30 min under 100 mW/cm2 white LED light irradiation, approximately 3.2 times larger than its stoichiometric one. Under the same LED light irradiation, 577.4 μmol h−1 g−1 of H2 and 62.0 μmol h−1 g−1 of O2 are realized over 2.7-CaSnO3. The chemisorption improved by oxygen defects in 2.7-CaSnO3 enables the transfer of photogenerated electrons to oxygen species in space. Therefore, oxygen molecules are activated into superoxide radicals on the oxygen defect-rich MSnO3 successfully. After more oxygen defects doping, the hydrogen evolution rate increases from 553.3 to 1152.7 μmol h−1 g−1, while O2 production rates increases from 62.0 to 129.1 μmol h−1 g−1. The hydrogen reduction treatment further revealed that the enhancement of both hydrogen and oxygen evolution was realized by introducing more oxygen vacancies into 2.7-CaSnO3.

Superior stability and photocatalytic activity of Ta3N5 sensitized/protected by conducting polymers for water splitting

In the study, we used two conducting polymers, polyaniline (PANI) and polypyrrole (PPy), to sensitize Ta3N5, thereby enhancing its photocatalytic activity, and then applied this novel photocatalyst to overall water splitting to produce hydrogen and oxygen even under visible light irradiation. The two polymers increased the charge transfer efficiency, prevented the recombination of the generated electrons and holes of the Ta3N5 photocatalyst, and thereby enhanced its electron-hole separation efficiency and improved its photocatalytic activity for efficient visible light water splitting. The two polymers completely covering the Ta3N5 particles facilitated charge transfer for quick migration of the generated electrons and holes to the polymer surface and thus prevented contact between the holes and nitride of Ta3N5. Therefore, these conducting polymers also protected the Ta3N5 particles from self-photocorrosion during long-term water splitting. Because of the existence of the protonated nitrogen (-N+) state in PPy, the electric conductivity of PPy was lower than that of PANI, which lowered the sensitizing ability of PPy compared to that of PANI. Thus, the water splitting efficiency of Ta3N5/PANI was higher than that of Ta3N5/PPy. The production rates of H2 and O2 generated from water splitting of Ta3N5/PANI were 60.5 and 30.2 (μmol. g−1cat. h−1), respectively.

Novel overall photocatalytic water splitting of tantalum nitride sensitized/protected by conducting polymers

Polyaniline (PANI) and polythiophene (PTh) conducting polymers have been used to sensitize Tantalum Nitride (Ta3N5) to enhance its photocatalytic activity. The synthesized materials exhibited novel photocatalytic activity for overall water splitting to produce hydrogen and oxygen even excited by visible light irradiation. The used PANI and PTh sensitizers enhanced the charge transfer efficiency and minimized the high recombination rate of the photo-excited electrons (e-) and holes (h+) of the Ta3N5 photocatalyst (enhanced e-/h+ separation efficiency of the Ta3N5) leading to increase in its photocatalytic activity for efficient visible light water splitting. We also investigated that the used PANI and PTh completely covering the Ta3N5 particles could acted as charge acceptors for quick migration of the produced h+ to their surface and thus minimizing contact between the nitride of the Ta3N5 and the produced h+, which could oxidize the nitride. It means that the used conducting polymers also protected the Ta3N5 particles from self-photocorrosion. Therefore, the synthesized tantalum nitride sensitized/protected by PANI or PTh could be applied for long-term water splitting. The production rates of H2 and O2 generated from water splitting of Ta3N5/PANI were higher than that of the Ta3N5/PTh because the electric conductivity of the PANI was higher than that of the PTh.

A sluggish mid-Proterozoic biosphere and its effect on Earth's redox balance.

The possibility of low but nontrivial atmospheric oxygen (O2) levels during the mid‐Proterozoic (between 1.8 and 0.8 billion years ago, Ga) has important ramifications for understanding Earth's O2 cycle, the evolution of complex life and evolving climate stability. However, the regulatory mechanisms and redox fluxes required to stabilize these O2 levels in the face of continued biological oxygen production remain uncertain. Here, we develop a biogeochemical model of the C‐N‐P‐O2‐S cycles and use it to constrain global redox balance in the mid‐Proterozoic ocean–atmosphere system. By employing a Monte Carlo approach bounded by observations from the geologic record, we infer that the rate of net biospheric O2 production was 3.5−1.1+1.4 Tmol year−1 (1σ), or ~25% of today's value, owing largely to phosphorus scarcity in the ocean interior. Pyrite burial in marine sediments would have represented a comparable or more significant O2 source than organic carbon burial, implying a potentially important role for Earth's sulphur cycle in balancing the oxygen cycle and regulating atmospheric O2 levels. Our statistical approach provides a uniquely comprehensive view of Earth system biogeochemistry and global O2 cycling during mid‐Proterozoic time and implicates severe P biolimitation as the backdrop for Precambrian geochemical and biological evolution.

All-solid-state Z-scheme system of NiO/CDs/BiVO4 for visible light-driven efficient overall water splitting

Solar light driven photocatalytic water splitting to produce hydrogen (H2) and oxygen (O2) on large scale is a promising solution to acquire the clean and sustainable energy sources. Enlightened by mimicking natural Z-scheme photosynthesis, the artificial visible light-driven water splitting photocatalyst of NiO/carbon dots/BiVO4 (NiO/CDs/BiVO4) composite was constructed. The designed NiO/CDs/BiVO4 as all-solid-state Z-scheme photocatalyst exhibits efficient photocatalyatic activity for overall water splitting without any cocatalysts or scavengers. In the Z-scheme system, the NiO and BiVO4 can respectively act as H2 evolution and O2 evolution photocatalysts, while the CDs can serve as solid electron mediator. The optimal NiO/CDs/BiVO4 photocatalyst shows the H2 and O2 production rates of 1.21 and 0.60 μmol·h−1, respectively, with the CDs concentration in the composite of 5 wt% and the mass ratio of NiO to BiVO4 of 3. The incorporation of CDs employed as the solid-state electron mediator boosts the effective electron transfer and charges separation, resulting in the improved photocatalytic activity of the designed Z-scheme system.

CaO2 based Fenton-like reaction at neutral pH: Accelerated reduction of ferric species and production of superoxide radicals

One challenge in H2O2 based Fenton-like reaction is to break through the limitation of slow reduction of ferric species (FeIII). Present work describes a dramatic acceleration of Fenton-like reaction at neutral pH by using calcium peroxide (CaO2) as a source of hydrogen peroxide (H2O2) and EDTA as a chelating agent of ferric ions. In an optimized condition, phenol degradation in the H2O2 system displayed an initial latent time of 60 min, while phenol can be degraded immediately and removed completely in 30 min in the CaO2 system. Visual MINTEQ analyses indicated Fe-EDTA− was the active species in the reaction. The contribution of 1O2 in CaO2 system was excluded by the poor selectivity in phenol conversion and the comparable 1O2-TEMP EPR signals in both CaO2 and H2O2 systems. Kinetic analyses using chloroform as the probe of O2·− suggested the high production rate of O2·−, which is four orders of magnitude higher than that in H2O2 system. The mechanism of the accelerated CaO2 based Fenton-like reactions was featured by that two electrons coming from CaO2 can be utilized to promote reduction of FeIII: an inner sphere electron transfer takes place to reduce FeIII-EDTA and produce O2·−, and subsequently O2·− provides an electron to reduce another FeIII-EDTA. The revealed intrinsic reducibility in CaO2 based Fenton-like reaction represents a new strategy to break through the well-known rate limiting step of FeIII reduction in Fenton-like reaction and facilitate the removal of organic pollutants at neutral pHs, and also indicates a promising source of O2·− for diverse applications.

Structure, Activity, and Faradaic Efficiency of Nitrogen-Doped Porous Carbon Catalysts for Direct Electrochemical Hydrogen Peroxide Production.

Carbon materials doped with nitrogen are active catalysts for the electrochemical two-electron oxygen reduction reaction (ORR) to hydrogen peroxide. Insights into the individual role of the various chemical nitrogen functionalities in the H2 O2 production, however, have remained scarce. Here, we explore a catalytically very active family of nitrogen-doped porous carbon materials, prepared by direct pyrolysis of ordered mesoporous carbon (CMK-3) with polyethylenimine (PEI). Voltammetric rotating ring-disk analysis in combination with chronoamperometric bulk electrolysis measurements in electrolysis cells demonstrate a pronounced effect of the applied potentials, current densities, and electrolyte pH on the H2 O2 selectivity and absolute production rates. H2 O2 selectivity up to 95.3 % was achieved in acidic environment, whereas the largest H2 O2 production rate of 570.1 mmol g-1 catalyst h-1 was observed in neutral solution. X-ray photoemission spectroscopy (XPS) analysis suggests a key mechanistic role of pyridinic-N in the catalytic process in acid, whereas graphitic-N groups appear to be catalytically active moieties in neutral and alkaline conditions. Our results contribute to the understanding and aid the rational design of efficient carbon-based H2 O2 production catalysts.

Construction of 2D/2D BiVO4/g-C3N4 nanosheet heterostructures with improved photocatalytic activity

In this work, a two dimensional (2D)/2D BiVO4/g-C3N4 heterostructure with strong interfacial interaction was successfully constructed. The as-prepared BiVO4/g-C3N4 heterostructures exhibit distinctly enhanced visible light photocatalytic performance toward the degradation of Rodanmin B (RhB) and water splitting to oxygen (O2) as compared to pristine g-C3N4 and BiVO4, which can be attributed to the strong interfacial interaction and abundant 2D coupling interfaces, facilitating efficient charge separation. Among the composites with various ratios, the BiVO4-10/g-C3N4 sample achieves the optimum photocatalytic activity for the degradation of RhB, and reached 15.8 and 4.3 times compared to pure g-C3N4 and BiVO4. Moreover, the corresponding composite reached a high O2-production rate of 0.97 μmol h−1 under visible light irradiation, which is 12.1 and 2.8 times higher than that of pure g-C3N4 and BiVO4, respectively. It was demonstrated that the efficiency of electron-hole separation has certain contribution to the photocatalytic performance over the BiVO4/g-C3N4 heterostructure. The present study suggests that the unique 2D/2D BiVO4/g-C3N4 hybrid nanosheets should be conducive to improve the photocatalytic performance of organic pollutant degradation and water splitting.

Cobalt-based cubane molecular co-catalysts for photocatalytic water oxidation by polymeric carbon nitrides

In artificial photocatalysis, sluggish kinetics of hole transfer and the high recombination rate of charge have been the Achilles’ heel of photocatalytic conversion efficiency. The development of co-catalysts for promoting exciton splitting and charge separation has therefore gained continuous attention. Herein, “Co4O4” cubane complex Co4O4(O2CMe)4(py)4 (1a, py = pyridine derivatives), serves as a homogeneous molecular co-catalyst which is engineered into the framework of pristine polymeric carbon nitride (PCN) for water oxidation with light illumination. This modification strategy maximizes the contact areas between co-catalysts and reactants, reduces the over-potential of oxygen producing and accelerates the interface transfer rate of electron-hole pairs, thus leading to enhanced reaction kinetics for photocatalytic water oxidation. Compared with pristine PCN, the photocatalytic O2 production rate up to 19-fold-enhanced in the presence of molecular co-catalyst. This work emphasizes the importance of developing effective, stable and earth-abundant molecular co-catalysts for the promotion of water-splitting photocatalysis.

A Direct Z‐Scheme Van Der Waals Heterojunction (WO3·H2O/g‐C3N4) for High Efficient Overall Water Splitting under Visible‐Light

Achieving overall water splitting is crucial for the effective application of recycling solar energy. Here, we design and construct a direct Z‐scheme van der Waals heterojunction composed by ultrathin WO3·H2O and g‐C3N4 nanosheets to achieve efficient overall water splitting without adding any sacrificial agents. This WO3·H2O/g‐C3N4 system can efficiently transport the electrons, which leading to a considerable improvement in the photocatalytic performance. Due to the suitable band edge potentials for H2, O2 evolution, and remarkable charge transfer, the direct WO3·H2O/g‐C3N4 Z‐scheme system exhibits prominent photocatalytic activity for both H2 and O2 production under visible‐light illumination, the H2, O2 production rate up to 482 and 232 µmol g−1 h−1 respectively, which is greatly higher than the H2 evolution of g‐C3N4 nanosheets (109 µmol h−1 g−1) and the O2 evolution of WO3·H2O nanosheets (57 µmol h−1 g−1) under the same condition. The measured quantum efficiency of the WO3·H2O/g‐C3N4 heterojunction reaches 6.2% at 420 nm.

Inorganic carbon and nitrogen assimilation in cellular compartments of a benthic kleptoplastic foraminifer

Haynesina germanica, an ubiquitous benthic foraminifer in intertidal mudflats, has the remarkable ability to isolate, sequester, and use chloroplasts from microalgae. The photosynthetic functionality of these kleptoplasts has been demonstrated by measuring photosystem II quantum efficiency and O2 production rates, but the precise role of the kleptoplasts in foraminiferal metabolism is poorly understood. Thus, the mechanism and dynamics of C and N assimilation and translocation from the kleptoplasts to the foraminiferal host requires study. The objective of this study was to investigate, using correlated TEM and NanoSIMS imaging, the assimilation of inorganic C and N (here ammonium, NH4+) in individuals of a kleptoplastic benthic foraminiferal species. H. germanica specimens were incubated for 20 h in artificial seawater enriched with H13CO3− and 15NH4+ during a light/dark cycle. All specimens (n = 12) incorporated 13C into their endoplasm stored primarily in the form of lipid droplets. A control incubation in darkness resulted in no 13C-uptake, strongly suggesting that photosynthesis is the process dominating inorganic C assimilation. Ammonium assimilation was observed both with and without light, with diffuse 15N-enrichment throughout the cytoplasm and distinct 15N-hotspots in fibrillar vesicles, electron-opaque bodies, tubulin paracrystals, bacterial associates, and, rarely and at moderate levels, in kleptoplasts. The latter observation might indicate that the kleptoplasts are involved in N assimilation. However, the higher N assimilation observed in the foraminiferal endoplasm incubated without light suggests that another cytoplasmic pathway is dominant, at least in darkness. This study clearly shows the advantage provided by the kleptoplasts as an additional source of carbon and provides observations of ammonium uptake by the foraminiferal cell.

A Green Method to Determine VUV (185 nm) Fluence Rate Based on Hydrogen Peroxide Production in Aqueous Solution

A mini-fluidic vacuum ultraviolet/ultraviolet (VUV/UV) photoreaction system (MVPS) was developed in our previous study. Based on the MVPS, a green method to determine VUV fluence rate has been developed using the production rate of H2 O2 when water is exposed to 185nm VUV. The H2 O2 production followed pseudo-zero-order reaction kinetics well over the first 10min of VUV/UV exposure. This new method was well calibrated with a standard cis-cyclooctene cis-trans photoisomerization actinometer as recommended by the International Union of Pure and Applied Chemistry. The apparent quantum yield for H2 O2 production by 185nm VUV irradiation of water was determined to be 0.024±0.002. As the solution pH increased from 5.0 to 8.0, the H2 O2 production rate decreased from 0.83 to 0.40μmmin-1 . Dissolved oxygen had a negligible influence on the H2 O2 production. This study proposes a novel VUV fluence rate determination method with advantages of nontoxicity, low detection limits, low costs and convenience, and it can be used as a good alternative to traditional actinometers.