CO Abundance Research Articles

CO2 to fuel: Role of polymer electrolytes on efficiency and selectivity

Global primary energy consumption, which heavily depends on fossil fuels, is on track for depletion, with projections suggesting exhaustion by 2100. This trajectory is further compounded by the persistent rise in atmospheric CO2 levels, currently at 420 ppm, which significantly contributes to climate change and its detrimental environmental consequences. To address this urgent challenge, various strategies have been proposed, including CO2 capture and storage, as well as its conversion into usable fuels. Leveraging the abundance of CO2 as a carbon source, coupled with sustainable energy resources such as solar, wind, and thermal energy, holds promise for generating value-added goods while mitigating environmental harm. This review focuses on the electrochemical reduction of CO2, presenting a dual-pronged approach aimed at decreasing atmospheric CO2 levels. The imperative to simultaneously combat declining atmospheric CO2 concentrations and advance cleaner, sustainable energy sources underscores the urgency of this endeavor. Specifically, we highlight the pivotal role of diverse polymer electrolytes, encompassing cation, anion, and bipolar membranes, in facilitating electrochemical CO2 reduction. Exploring the impact of functional groups within these membranes on CO2 reduction reaction provides insights into potential advancements in synthesis of eco-friendly fuel from conversion of CO2.

Molecular Weaving Towards Flexible Covalent Organic Framework Membranes for Efficient Gas Separations.

Covalent organic frameworks (COFs) exhibit considerable potential in gas separations owing to their remarkable stability and tunable pore structures. Nevertheless, their application as gas separation membranes is hindered by limited size-sieving capabilities and poor processability. In this study, we propose a novel molecular weaving strategy that combines hydroxyl polymers and 2D TpPa-SO3H COF nanosheets, achieving high gas separation efficiency. Driven by the strong electrostatic interactions, the hydroxyl chains thread through the COF pores, effectively weaving and assembling the composites to achieve exceptional flexibility and high mechanical strength. The penetrated chains also reduce the effective pore size of COFs, and combined with the "secondary confinement effect" stemming from abundant CO2 sorption sites in the channels, the PVA@TpPa-SO3H membrane demonstrates a remarkable H2 permeance of 1267.3 GPU and an H2/CO2 selectivity of 43, surpassing the 2008 Robson upper bound limit. This facile strategy holds promise for the manufacture of large-area COF-based membranes for small-sized gas separations.

Molecular Weaving Towards Flexible Covalent Organic Framework Membranes for Efficient Gas Separations

AbstractCovalent organic frameworks (COFs) exhibit considerable potential in gas separations owing to their remarkable stability and tunable pore structures. Nevertheless, their application as gas separation membranes is hindered by limited size‐sieving capabilities and poor processability. In this study, we propose a novel molecular weaving strategy that combines hydroxyl polymers and 2D TpPa−SO3H COF nanosheets, achieving high gas separation efficiency. Driven by the strong electrostatic interactions, the hydroxyl chains thread through the COF pores, effectively weaving and assembling the composites to achieve exceptional flexibility and high mechanical strength. The penetrated chains also reduce the effective pore size of COFs, and combined with the “secondary confinement effect” stemming from abundant CO2 sorption sites in the channels, the PVA@TpPa−SO3H membrane demonstrates a remarkable H2 permeance of 1267.3 GPU and an H2/CO2 selectivity of 43, surpassing the 2008 Robson upper bound limit. This facile strategy holds promise for the manufacture of large‐area COF‐based membranes for small‐sized gas separations.

Developing an off-site bicarbonation absorber system to promote microalgal fixation of CO2 in exhaust gas from biogas upgrading

In order to address the risk of explosion due to CH4 from exhaust gas produced during biogas upgrading in closed carbon fixation systems employing photosynthetic microalgae, an off-site bicarbonation absorber system was developed to promote microalgal CO2 fixation under atmospheric pressure. The abundant CO2 in the biogas upgrading exhaust gas (≥90 vol.% CO2, ≤10 vol.% CH4) reacted with a Na2CO3 solution in the off-site bicarbonation absorber to produce NaHCO3, which was used as carbon source for microalgal growth in enclosed column photobioreactors. After the reaction, CH4 was discharged outside the bicarbonation absorber because it did not react with the Na2CO3 solution and was extremely difficult to dissolve in water, thereby avoiding the explosion risk due to accumulated CH4 in the enclosed column photobioreactors. The experimental results showed that the Spirulina growth rate first increased 1.7 times, peaking at 0.6g/L/d, and then decreased when the bicarbonation reaction time (optimal 50min), absorber diameter (optimal 10cm), initial Na2CO3 concentration (optimal 173mM), and exhaust gas aeration rate (optimal 100 sccm) increased. The optimal molar ratio of NaHCO3 to total inorganic carbon in the bicarbonation absorber solution reached 79%. The sufficient HCO3- supply and suitable pH of the microalgal solution improved the synthesis of photosynthetic pigments in the microalgal cells and enhanced their photochemical efficiency and carbon sequestration rates.

Toward a Self-consistent Evaluation of Gas Dwarf Scenarios for Temperate Sub-Neptunes

Abstract The recent JWST detections of carbon-bearing molecules in a habitable-zone sub-Neptune have opened a new era in the study of low-mass exoplanets. The sub-Neptune regime spans a wide diversity of planetary interiors and atmospheres not witnessed in the solar system, including mini-Neptunes, super-Earths, and water worlds. Recent works have investigated the possibility of gas dwarfs, with rocky interiors and thick H2-rich atmospheres, to explain aspects of the sub-Neptune population, including the radius valley. Interactions between the H2-rich envelope and a potential magma ocean may lead to observable atmospheric signatures. We report a coupled interior-atmosphere modeling framework for gas dwarfs to investigate the plausibility of magma oceans on such planets and their observable diagnostics. We find that the surface–atmosphere interactions and atmospheric composition are sensitive to a wide range of parameters, including the atmospheric and internal structure, mineral composition, volatile solubility and atmospheric chemistry. While magma oceans are typically associated with high-temperature rocky planets, we assess if such conditions may be admissible and observable for temperate sub-Neptunes. We find that a holistic modeling approach is required for this purpose and to avoid unphysical model solutions. Using our model framework, we consider the habitable-zone sub-Neptune K2-18 b as a case study and find that its observed atmospheric composition is incompatible with a magma ocean scenario. We identify key atmospheric molecular and elemental diagnostics, including the abundances of CO2, CO, NH3, and, potentially, S-bearing species. Our study also underscores the need for fundamental material properties for accurate modeling of such planets.

Boosted 1,2-Dichloroethane Deep Destruction over CoRu/Al2O3 Bifunctional Catalysts via Surface Oxygen and Water Molecule Synergistic Activation.

Developing efficacious catalysts with superior Cl resistance and polychlorinated byproduct inhibition capability is crucial for realizing the environmentally friendly purification of chlorinated volatile organic compounds (CVOCs). Activating CVOC molecules and desorbing Cl species by modulating the metal-oxygen property is a promising strategy to fulfill these. Herein, a bifunctional CoRu/Al2O3 catalyst with synergistic Co and Ru interactions (Ru-O-Co species) was rationally fabricated, which possesses abundant surface Co2+ and Ruδ+ sites and collaboratively facilitates the activation of lattice oxygen (O2-) and molecular oxygen (O2 → O2- → O-), accelerating 1,2-dichloroethane (1,2-DCE) decomposition via the reaction route of enolic species → aldehydes → carboxylate/carbonate. Furthermore, CoRu/Al2O3 stimulates 1,2-DCE oxidation under humid conditions as H2O molecules can be easily activated to active *OH (potential oxidizing agent) over Ru species, accelerating C-Cl dissociation and Cl desorption and promoting the transformation of catecholate-type (C═O) species to easily oxidizable carboxylic acid (COOH) species, remarkably suppressing the formation of hazardous CCl4 and CHCl2CH2Cl. This study provides critical insights into the development of bifunctional catalysts to synergistically activate surface oxygen species and H2O molecules for industrial CVOC stable and efficient elimination.

Pursuing Truth: Improving Retrievals on Mid-infrared Exo-Earth Spectra with Physically Motivated Water Abundance Profiles and Cloud Models

Atmospheric retrievals are widely used to constrain exoplanet properties from observed spectra. We investigate how the common nonphysical retrieval assumptions of vertically constant molecule abundances and cloud-free atmospheres affect our characterization of an exo-Earth (an Earth-twin orbiting a Sun-like star). Specifically, we use a state-of-the-art retrieval framework to explore how assumptions for the H2O profile and clouds affect retrievals. In the first step, we validate different retrieval models on a low-noise simulated 1D mid-infrared (MIR) spectrum of Earth. Thereafter, we study how these assumptions affect the characterization of Earth with the Large Interferometer For Exoplanets (LIFE). We run retrievals on LIFE mock observations based on real disk-integrated MIR Earth spectra. The performance of different retrieval models is benchmarked against ground truths derived from remote sensing data. We show that assumptions for the H2O abundance and clouds directly affect our characterization. Overall, retrievals that use physically motivated models for the H2O profile and clouds perform better on the empirical Earth data. For observations of Earth with LIFE, they yield accurate estimates for the radius, pressure–temperature structure, and the abundances of CO2, H2O, and O3. Further, at R = 100, a reliable and bias-free detection of the biosignature CH4 becomes feasible. We conclude that the community must use a diverse range of models for temperate exoplanet atmospheres to build an understanding of how different retrieval assumptions can affect the interpretation of exoplanet spectra. This will enable the characterization of distant habitable worlds and the search for life with future space-based instruments.

IGRINS Observations of WASP-127 b: H2O, CO, and Super-solar Atmospheric Metallicity in the Inflated Sub-Saturn

High-resolution spectroscopy of exoplanet atmospheres provides insights into their composition and dynamics from the resolved line shape and depth of thousands of spectral lines. WASP-127 b is an extremely inflated sub-Saturn (R p = 1.311 R Jup, M p = 0.16 M Jup) with previously reported detections of H2O and CO2. However, the seeming absence of the primary carbon reservoir expected at WASP-127 b temperatures (T eq ∼1400 K) from chemical equilibrium, CO, posed a mystery. In this manuscript, we present the analysis of high-resolution observations of WASP-127 b with the Immersion Grating Infrared Spectrometer on Gemini South. We confirm the presence of H2O (8.67σ) and report the detection of CO (4.34σ). Additionally, we conduct a suite of Bayesian retrieval analyses covering a hierarchy of model complexity and self-consistency. When freely fitting for the molecular gas volume mixing ratios, we obtain super-solar metal enrichment for H2O abundance of log10 X H2O = −1.23 −0.49+0.29 and a lower limit on the CO abundance of log10 X CO ≥–2.20 at 2σ confidence. We also report tentative evidence of photochemistry in WASP-127 b based upon the indicative depletion of H2S. This is also supported by the data preferring models with photochemistry over free-chemistry and thermochemistry. The overall analysis implies a super-solar (∼39× Solar; [M/H] = 1.59−0.30+0.30 ) metallicity for the atmosphere of WASP-127 b and an upper limit on its atmospheric C/O ratio as < 0.68.

Imidazolium and pyridine bifunctionalized hypercrosslinked polymers as efficient and recyclable catalysts for CO2 cycloaddition

Converting CO2 into precious chemicals is considered to be a fundamental and effective tool for controlling the abundant CO2 emitted. One of the most compelling methods for CO2 conversion is the synthesis of cyclic carbonates by cycloaddition of CO2 with epoxides. However, the development of materials with specific functionalities for CO2 capture and conversion is still considered to be a significant challenge. Herein, a novel imidazolium salts and pyridine skeleton bifunctionalized hypercrosslinked polymers were prepared by FeCl3-catalyted Friedel-Crafts alkylation reaction. Various analytical techniques were used to investigate the properties of the catalysts. The bifunctionalized heterogeneous catalysts exhibited outstanding catalytic performances for CO2 cycloaddition under mild conditions with an excellent yield of up to 99 %. Besides, the catalyst could bear various epoxides and no significant loss of activity after 6 cycles. The properties of metal-free, solvent-free, cocatalyst-free, easy-to-prepare, mild conditions, facility separation and recyclability make the bifunctionalized hypercrosslinked polymers useful for CO2 cycloaddition.

A Tale of Two Molecules: The Underprediction of CO2 and Overprediction of PH3 in Late T and Y Dwarf Atmospheric Models

The sensitivity and spectral coverage of JWST are enabling us to test our assumptions of ultracool dwarf atmospheric chemistry, especially with regards to the abundances of phosphine (PH3) and carbon dioxide (CO2). In this paper, we use Near Infrared Spectrograph PRISM spectra (∼0.8−5.5 μm, R ∼ 100) of four late T and Y dwarfs to show that standard substellar atmosphere models have difficulty replicating the 4.1−4.4 μm wavelength range, as they predict an overabundance of phosphine and an underabundance of carbon dioxide. To help quantify this discrepancy, we generate a grid of models using PICASO, based on the Elf Owl chemical and temperature profiles, where we include the abundances of these two molecules as parameters. The fits to these PICASO models show a consistent preference for orders-of-magnitude higher CO2 abundances and a reduction in PH3 abundance as compared to the nominal models. This tendency means that the claimed phosphine detection in UNCOVER−BD−3 could instead be explained by a CO2 abundance in excess of standard atmospheric model predictions; however, the signal-to-noise ratio of the spectrum is not high enough to discriminate between these cases. We discuss atmospheric mechanisms that could explain the observed underabundance of PH3 and overabundance of CO2, including a vertical eddy diffusion coefficient (K zz) that varies with altitude, incorrect chemical pathways, or elements condensing out in forms such as NH4H2PO4. However, our favored explanation for the required CO2 enhancement is that the quench approximation does not accurately predict the CO2 abundance, as CO2 remains in chemical equilibrium with CO after CO quenches.

Ionic Liquid-Catalyzed CO2 Conversion for Valuable Chemicals.

CO2 is not only the main gas that causes the greenhouse effect but also a resource with abundant reserves, low price, and low toxicity. It is expected to become an important "carbon source" to replace oil and natural gas in the future. The efficient and clean resource utilization of CO2 has shown important scientific and economic value. Making full use of abundant CO2 resources is in line with the development direction of green chemistry and has attracted the attention of scientists. Environmentally friendly ionic liquids show unique advantages in the capture and conversion of CO2 due to their non-volatilization, designable structure, and good solubility, and show broad application prospects. The purpose of this paper is to discuss the research on the use of an ionic liquid as a catalyst to promote the synthesis of various value-added chemicals in CO2, hoping to make full use of CO2 resources while avoiding the defects of the traditional synthesis route, such as the use of highly toxic raw materials, complicated operation, or harsh reaction conditions. The purpose of this paper is to provide reference for the application and development of ionic liquids in CO2 capture and conversion.

Bimetallic MOF-74-based mixed matrix membrane for efficient CO2 separation

The bimetallic Ni(Zn)-MOF-74 nanoparticles were fabricated by the metal substitution method and doped into a polyether-polyamide block copolymer (Pebax 1657) matrix to obtain mixed matrix membrane (MMM) for CO2/CH4 separation. The pore structure and chemical properties of Ni(Zn)-MOF-74 nanoparticles were controlled by changing the molar ratio of Ni/Zn, and the effect of heterometallic on the gas separation performance of MMMs was studied. In particular, when the molar ratio of Ni/Zn was 2:1, the Pebax/Ni(Zn)-MOF-74-21 MMMs has the optimal CO2 separation performance. The main reason was that Ni(Zn)-MOF-74-21 has the smallest pore size (0.68 nm) and abundant CO2 adsorption sites, which could effectively prevent the entry of CH4 molecules after preferentially adsorbing one or two CO2 molecules, and improve the selectivity of CO2/CH4 molecules. Furthermore, the unreplaced pore size of 1.48 nm and the increased polymer chain spacing in Ni(Zn)-MOF-74-21 nanoparticles could provide a fast transport channel for CO2 and improve the permeability of MMMs. The developed Pebax/Ni(Zn)-MOF-74-21 MMMs loaded with 2 wt% filler displayed a CO2/CH4 selectivity of 33.7 and a high CO2 permeability of 719.9 barrer, exceeding the gas separation performance of many previously reported MOF-74-based MMMs. The results showed that the development and design of bimetallic organic framework was an important way to obtain high performance MOF-74-based MMM.

Gas phase Elemental abundances in Molecular cloudS (GEMS)

Context. We explore the chemistry of the most abundant C-, O-, S-, and N-bearing species in molecular clouds, in the context of the IRAM 30 m Large Programme Gas phase Elemental abundances in Molecular Clouds (GEMS). Thus far, we have studied the impact of the variations in the temperature, density, cosmic-ray ionisation rate, and incident UV field in a set of abundant molecular species. In addition, the observed molecular abundances might be affected by turbulence which needs to be accounted for in order to have a more accurate description of the chemistry of interstellar filaments. Aims. In this work, we aim to assess the limitations introduced in the observational works when a uniform density is assumed along the line of sight for fitting the observations, developing a very simple numerical model of a turbulent box. We searched for any observational imprints that might provide useful information on the turbulent state of the cloud based on kinematical or chemical tracers. Methods. We performed a magnetohydrodynamical (MHD) simulation in order to reproduce the turbulent steady state of a turbulent box with properties typical of a molecular filament before collapse. We post-processed the results of the MHD simulation with a chemical code to predict molecular abundances, and then post-processed this cube with a radiative transfer code to create synthetic emission maps for a series of rotational transitions observed during the GEMS project. Results. From the kinematical point of view, we find that the relative alignment between the observer and the mean magnetic field direction affect the observed line profiles, obtaining larger line widths for the case when the line of sight is perpendicular to the magnetic field. These differences might be detectable even after convolution with the IRAM 30 m efficiency for a nearby molecular cloud. From the chemical point of view, we find that turbulence produces variations for the predicted abundances, but they are more or less critical depending on the chosen transition and the chemical age. When compared to real observations, the results from the turbulent simulation provides a better fit than when assuming a uniform gas distribution along the line of sight. Conclusions. In the view of our results, we conclude that taking into account turbulence when fitting observations might significantly improve the agreement with model predictions. This is especially important for sulfur bearing species which are very sensitive to the variations of density produced by turbulence at early times (0.1 Myr). The abundance of CO is also quite sensitive to turbulence when considering the evolution beyond a few 0.1 Myr.

The ESO SupJup Survey

Context. It has been proposed that the distinct formation and evolutionary pathways of exoplanets and brown dwarfs may affect the chemical and isotopic content of their atmospheres. Recent work has indeed shown differences in the 12C/13C isotope ratio, which have provisionally been attributed to the top-down formation of brown dwarfs and the core accretion pathway of super-Jupiters. Aims. The ESO SupJup Survey is aimed at disentangling the formation pathways of isolated brown dwarfs and planetary-mass companions using chemical and isotopic tracers. The survey utilises high-resolution spectroscopy with the recently upgraded CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES+) at the Very Large Telescope, covering a total of 49 targets. Here, we present the first results of this survey: an atmospheric characterisation of DENIS J0255-4700, an isolated brown dwarf near the L-T transition. Methods. We analysed its observed CRIRES+ K-band spectrum using an atmospheric retrieval framework in which the radiative transfer code petitRADTRANS was coupled with the PyMultiNest sampling algorithm. Gaussian processes were employed to model inter-pixel correlations. In addition, we adopted an updated parameterisation of the pressure-temperature profile. Results. Abundances of CO, H2O, CH4, and NH3 were retrieved for this fast-rotating L-dwarf. The ExoMol H2O line list provides a significantly better fit than that of HITEMP. A free-chemistry retrieval is strongly favoured over equilibrium chemistry, caused by an under-abundance of CH4. The free-chemistry retrieval constrains a super-solar C/O-ratio of ~0.68 and a solar metallicity. We find tentative evidence (~3σ) for the presence of 13CO, with a constraint on the isotopologue ratio of 12CO/13CO = 184−40+61 and a lower limit of ≳97, which suggests a depletion of 13C compared to the local interstellar medium (12C/13C ~ 68). Conclusions. High-resolution, high signal-to-noise K-band spectra provide an excellent means of constraining the chemistry and isotopic content of sub-stellar objects, which is the main objective of the ESO SupJup Survey.

Olivine nanoparticles for Fast Atmospheric CO2 capture at Ambient Conditions

AbstractTo mitigate climate change, CO2 sequestration from the atmosphere is being considered as a method to reduce its greenhouse effect and subsequently lower the Earth's surface temperature. A promising approach is the storage of CO2 in minerals, of which Olivine is a promising candidate due to its Earth abundance and high CO2 absorption capacity, which is of the order of 50 wt.%. A bottleneck for Olivine carbonation is the slow reaction rate at ambient conditions, which previously resulted in supplying CO2 at extreme pressures and temperatures to force carbonation. In this study, nanoscale Olivine particles are fabricated, which due to their high surface‐to‐volume ratio, reach a very high carbonation conversion at a time scale of minutes at ambient conditions. The carbonation is measured by X‐ray photoelectron spectroscopy (XPS), which yielded both the presence of carbonates as well as information on the Olivine oxidation state, in agreement with electron diffraction analysis. This work forms the basis for employing Olivine nanoparticles, as fabricated by the relatively simple method of magnetron sputtering, to capture CO2 from the atmosphere at economic conditions.

Catalytic Regio- and Enantioselective Remote Hydrocarboxylation of Unactivated Alkenes with CO2.

The catalytic regio- and enantioselective hydrocarboxylation of alkenes with carbon dioxide is a straightforward strategy to construct enantioenriched α-chiral carboxylic acids but remains a big challenge. Herein we report the first example of catalytic highly enantio- and site-selective remote hydrocarboxylation of a wide range of readily available unactivated alkenes with abundant and renewable CO2 under mild conditions enabled by the SaBOX/Ni catalyst. The key to this success is utilizing the chiral SaBOX ligand, which combines with nickel to simultaneously control both chain-walking and the enantioselectivity of carboxylation. This process directly furnishes a range of different alkyl-chain-substituted or benzo-fused α-chiral carboxylic acids bearing various functional groups in high yields and regio- and enantioselectivities. Furthermore, the synthetic utility of this methodology was demonstrated by the concise synthesis of the antiplatelet aggregation drug (R)-indobufen from commercial starting materials.

Multifunctional diamond‐based catalysts: Promising candidates for energy conversions in extreme environments—A mini‐review

AbstractIn order to properly utilize the abundant CO2 and water resources, various catalytic materials have been developed to convert them into valuable chemicals as renewable fuels electrochemically or photochemically. Currently, most studies are conducted under mild laboratory conditions, but for some extreme environments, such as Mars and space stations, there is an urgent need to develop new catalysts satisfying such special requirements. Conventional catalytic materials mainly focus on metals and narrow bandgap semiconductor materials, while the research on wide and ultrawide bandgap materials that can inherently withstand extreme conditions has not received enough attention. Given the robust stability and excellent physico‐chemical properties of diamond, it can be expected to perform in harsh environments for electrocatalysis or photocatalysis that has not been investigated thoroughly. Here, this review summarizes the catalytic functionality of diamond‐based electrodes with various but tunable product selectivity to obtain the varied C1 or C2+ products, and discusses some important factors playing a key role in manipulating the catalytic activity. Moreover, the unique solvation electron effect of diamond gives it a significant advantage in photocatalytic conversions which is also summarized in this mini‐review. In the end, prospects are made for the application of diamond‐based catalysts under various extreme conditions. The challenges that may be faced in practical applications are also summarized and future breakthrough directions are proposed at the end.

Reducing carbon emissions through sustainable energy integration at off-grid cellular sites: a case study of Nepal

ABSTRACT Information and communication technology is the key enabler for digitalisation and increased productivity in cross-cutting sectors. Telephone towers are the main infrastructure to enable digital connectivity and renewable energy sources are used to supply power to mobile towers at off-grid areas. In this paper, the economic and environmental aspects of sustainable energy supply in off-grid sites have been evaluated. Three stand-alone sites having solar PV, diesel generators, and hybrid power solutions integrated with battery storage are taken for the study. The result shows the solar PV solution is economically feasible with an energy cost of 0.18$/kWh and environmentally adaptable. The diesel generator power supply has a higher energy cost of 0.59$/kWh and abundant CO2 emission of 421.85tCO2 for a life period. The hybrid power solution has better energy cost(0.38$/kWh) and CO2 emission (213.72tCO2) than the diesel generator. Considering reliability, the hybrid power solution has better performance in terms of energy cost and GHG emission. Solar PV solution has a key role in developing green infrastructure. A solar PV system integrated with a diesel generator and battery storage is a must for an uninterrupted power supply. The outcomes of the study encourage telecom operators to go for green cell towers sustainably.

In situ measurements of dissolved gases in xylem sap as tracers in plant physiology

Abstract Trees transport gases from the ground into the atmosphere through the process of transpiration. Tracing gases transported through this mechanism continuously and under field conditions remains an experimental challenge. Here we measured gases dissolved in the tree sap in situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2 and CO2) from the soil, through the trees, into the atmosphere. We constructed and inserted custom-made semi-permeable membrane probes in the xylem of a fir tree and measured gas abundances at different heights using a portable gas equilibrium membrane-inlet mass spectrometer (‘miniRUEDI’). With this method, we were able to continuously measure the abundances of He, Ar, Kr, N2, O2 and CO2 in sap over several weeks. We observed diurnal variations of CO2 and O2 concentrations that reflected tree physiological activities. As a proof of the concept that trees do uptake dissolved gases in soil water, we irrigated the tree with He-enriched water in a tracer experiment and were able to determine upward sap flow velocity. Measurements of inert gases together with reactive species, such as CO2 and O2, allowed separation of the physical transport and exchange of gases derived from the soil or atmosphere from biological reactions. We discuss the opportunities that our technique provides for continuous in situ measurements of gases in the tree sap.

Substrate Promiscuity of Thermoplasma acidophilum Malic Enzyme for CO2 Fixation Reaction.

CO2 fixation technology has gained attention as a method to effectively utilize the abundant CO2 in the atmosphere by converting it into useful chemicals. However, since CO2 is a highly stable molecule, many of the currently developed methods for chemical CO2 fixation require harsh conditions and reactive reagents. The establishment of efficient and sustainable processes is eagerly awaited. In this study, we investigated a biocatalytic process and achieved a carboxylation reaction under mild conditions (37 °C, 0.1 MPa CO2) using a biocatalyst, Thermoplasma acidophilum NADP+-malic enzyme (TaME), and gaseous CO2 by coupling enzymatic coenzyme regeneration. We also demonstrated for the first time that the carboxylation reaction by ME proceeds not only with pyruvate, a natural substrate, but also with 2-ketoglutarate.