Methane Precursor Research Articles

Microbiology and Ecology of Methylated Amine Metabolism in Marine Ecosystems.

Methylated amines (MAs) are ubiquitous in marine ecosystems, found from surface seawaters to sediment pore waters. These volatile ammonium analogs play important roles in biogeochemical cycles of carbon and nitrogen in the marine water column. They also contribute to the release of climate-active gases, being precursors of the potent greenhouse gas methane through methanogenesis in coastal sediments. Very recently, it also became acknowledged that MAs are important precursors for new particle growth, hence forming cloud-condensation nuclei in the marine atmosphere. Microbial metabolism of MAs has been demonstrated in the marine ecosystems for both Archaea and Bacteria. In this chapter, we summarize the latest developments in analytical methods for quantifying MA concentrations in marine surface water and sediments. We discuss the metabolic pathways leading to the formation and degradation of MAs by marine microbes and the novel biochemistry and structural biology of the enzymes for MA transformation. Lastly, we highlight the need for future research toward a better understanding of the microbiology and ecology of oceanic MA cycles.

Unravelling the effects of blue light on aerobic methane emissions from canola

It is now well documented that plants produce methane (CH4) under aerobic conditions. However, the nature of methane production in plants and all the potential precursors and environmental factors that can be involved in the process are not fully understood. Earlier studies have suggested several chemical compounds, including the amino acid methionine, as precursors of aerobic methane in plants, but none have explored other amino acids as potential precursors or blue light as a driving force of methane emission. We examined the effects of blue light, and the promoter or inhibitor of endogenous ethylene on methane and ethylene emissions, amino acids, and some plant physiological parameters in canola (Brassica napus). Plants were grown under four light conditions: no supplemental blue light, and low, medium, or high blue light, and exposed to three chemical treatments: no chemical application, ethylene promoter (kinetin), or ethylene inhibitor (silver nitrate). Regardless of chemical treatment, blue light significantly increased methane emission, which was accompanied by decreased plant biomass, gas exchange, and flavonoids, but by increased wax, and most amino acids. This study revealed that blue light drives aerobic methane emission from plants by releasing of methyl group from a number of amino acids, and that the methane production in plants may have several pathways.

Decomposition of carbon-bearing compounds and their influence on methane formation in a lignite incubation experiment

Carbon-bearing compounds (glucose, sodium acetate, methanol, yeast extract, and nutrient broth) were added in different proportions to cultures to stimulate methanogenesis in a lignite incubation experiment. Their addition significantly influenced the isotopic composition of methane generated during the fermentation of lignite. Glucose was degraded mainly in the first 2 weeks of incubation, when the atmospheric air was present in the headspace and used for biomass growth. Sodium acetate, methanol, and, presumably, lignite were decomposed in the next phase, in which anaerobic conditions occurred. The simultaneous decomposition of sodium acetate and methanol (as single substrates or as a mixture) with lignite resulted in the formation of methane with δ13C(CH4) values typical for methyl-type fermentation. The identification of decomposed compounds in the mixture of sodium acetate and methanol was accomplished via isotopic analysis of carbon and hydrogen in the methane. The δ2H(CH4) values in the case of methanol biodegradation were characterized by a negative trend over time, in contrast to a positive trend observed when sodium acetate decomposed. This observation may help to identify a very good tracer for the determination of methane precursors during methyl-type fermentation.

Self‐Assembly of Water‐Soluble Platinum(II)‐Based Metallacalixarenes and Tuning Their Conformational Interconversion via Synergistic Effects between Solvents and Anions

The aqueous self-assembly of the flexible ligand L bis(1H-benz[d]imidazole-1-yl)methane and cis-coordinated PtII precursors [(en)Pt2+ , (tmeda)Pt2+ , en=ethylenediamine, tmeda=N,N,N',N'-tetramethylethylenediamine)] led to the formation of the metallacalixarenes with full alternative conformations (e.g., two novel water-soluble metallacalixarenes [M2 L2 ]4+ and [M3 L3 ]6+ with D2 and D3 symmetry, respectively). Their molecular structures were determined by single crystal X-ray analyses in solid state. The two metallacalixarenes present different cavity sizes and the [M3 L3 ]6+ cavity encapsulates one NO3 - . NOESY NMR revealed that the conformational interconversion between 1,3-alternate conformer in methanol and cone conformer in DMSO was tuned via the synergistic effect between solvent and anion. Guest encapsulation is also discussed.

Evolution of tribologically induced chemical and structural degradation in hydrogenated a-C coatings

Abstract The coatings with gradually varying chemical composition and structure were obtained by PECVD method from methane precursor and various admixtures of Ar. The composition of emitted gases and triboemission behaviour were studied for these coatings and correlated with the coating properties and deposition conditions. A new analytical approach was developed that allowed identification of the emitted gas species with much higher accuracy than conventional techniques. For the first time, triboemission of alkanes higher than propane was observed. By the application of kinetic model to the analysis of triboemission time series, chemical and structural degradation in carbon coatings could be traced in course of tribological tests.

Electrochemical Study of Graphene Coated Nickel Foam as an Anode for Lithium-Ion Battery

This study reports the synthesis of a few-layered graphene (GF) thin film on Ni foam by chemical vapor deposition (CVD) technique and investigation of its electrochemical performance as a negative electrode for lithium-ion batteries (LIBs). A standard deposition procedure with a methane precursor was employed to prepare the GF films. The SEM studies revealed the formation of a dark uniform film on the surface of Ni foam’s wires upon the CVD deposition. The film consisted of numerous GF sheets replicating the shape of the Ni grain boundaries over the Ni wire surface. The Raman spectroscopy of the prepared films on the Ni foam confirmed that the samples are a few-layered GF with high quality and purity. In order to evaluate the potential of the use of the prepared materials as an anode in LIBs, their electrochemical performance was studied in coin-type lithium half-cells using cyclic voltammetry (CV) and galvanostatic cycling. The results of CV showed that both graphene and native oxide layer (NiO) on nickel foam exhibit electrochemical activity with respect to lithium ions. Galvanostatic cycling revealed that both GF and NiO contribute to the overall capacity, which increases upon cycling with a stable Coulombic efficiency of around 99%. The designed 3D GF coated NiO/Ni anode demonstrated a gradual increase of its areal charge capacity from 65 μAh cm-2 at the initial cycle to 250 μAh cm-2 at the final 250th cycle.

Enhancing the adhesion of diamond-like carbon films to steel substrates using silicon-containing interlayers

Diamond-like carbon (DLC) films were deposited on AISI 316L stainless steel by using a unipolar pulsed-DC plasma assisted chemical vapor deposition (PACVD) system. In order to improve the adhesion of the DLC films to the substrate, three different silicon-containing interlayers (a-Si:H, a-SiCx:H, and a-SiNx:H) were deposited at two temperatures of 150 and 350 °C using silicon tetrachloride, methane, nitrogen, and hydrogen precursors. The DLC films with silicon-containing interlayers, deposited at 150 °C, did not show appropriate adhesion to the substrate due to the presence of a high amount of chlorine and hydrogen in the structure of the interlayers. By increasing the temperature of the interlayer deposition, the adhesion of DLC films improved significantly. The results of Raman spectroscopy, Nano indentation and adhesion tests showed that the DLC film with a-SiNx:H interlayer exhibited the lowest ID/IG ratio, highest hardness, and highest adhesion to the substrate.

Enhanced Phosphate Release from Anaerobically Digested Sludge Through Sulfate Reduction

This study was conducted to demonstrate enhanced phosphate release in mesophilic anaerobic digestion of sewage sludge in relation to sulfate reduction. Sulfate was added as sulfuric acid to influent sewage sludge at the three levels, 0, 461 and 922 mg-S/L (0, 14.4 and 28.8 mmol/L, respectively). The sewage sludge used was one without artificial modification for 70 days, and then chemically pre-precipitated one artificially prepared by adding 4 g/L (17.9 mmol/L) of FePO4·4H2O for 77 days (influent total phosphorus of 302 and 855 mg/L, respectively). The anaerobic digesters were operated at 35 °C and 20 days hydraulic retention time. The phosphate concentration in digested sludge at the final stage reached 7.3, 89 and 112 mg/L for the sewage sludge without artificial modification, and 114, 258 and 461 mg/L for the chemically pre-precipitated sewage sludge, at the three levels of sulfate addition respectively. The phosphate concentration was almost proportional to the sulfate concentration added, indicating that the introduction of sulfate to anaerobic digestion can enhance phosphate release. The enhanced phosphate release was attributable to sulfate reduction to sulfide and subsequent release of phosphate from ferric or ferrous phosphate. In addition to the above mechanism involving sulfate reduction, phosphate release was estimated to occur from ferric phosphate along with iron reduction. A possible disadvantage of involving sulfate reduction is that part of the methane is lost due to the consumption of methane precursors.

Methanation of CO2 over alkali-promoted Ru/TiO2 catalysts: II. Effect of alkali additives on the reaction pathway

The effect of alkali (Li, Na, K, Cs) promotion of TiO2 on the CO2 hydrogenation pathway has been investigated over 0.5%Ru/TiO2 and 5%Ru/TiO2 catalysts, employing in situ FTIR spectroscopy (DRIFTS) and transient-mass spectrometry techniques. In the case of 0.5%Ru/TiO2 catalysts, characterized by well-dispersed Ru particles, specific activity and selectivity toward methane increases significantly with the addition of suitable amount of alkalis. The nature and population of Ru-bonded carbonyl species, formed on the surface of 0.5%Ru/TiO2 catalyst under CO2 hydrogenation conditions, varies significantly upon alkali promotion. The population of reactive Rux-CO species, which has been previously found to be direct methane precursors, increases in the presence of alkalis following a trend similar to that of specific activity. Results of DRIFT and mass spectrometry experiments provide evidences that alkali promotion enhances the dissociative adsorption of CO and hydrogenation of the so formed surface carbon to methane, which seems not to be operable over the unpromoted 0.5%Ru/TiO2 catalyst. In the case of 5%Ru/TiO2 catalysts, characterized by large Ru particles, both CO2 methanation activity and the nature/population of intermediate surface species seems not to be significantly affected by the presence of sodium. It is suggested that the structure sensitivity of the reaction predominates to the effect of alkali promotion and therefore, CO2 methanation activity cannot be further improved.

Variation in photon flux during extended photochemical aerosol experiments: Implications for atmospheric laboratory simulations

In order to simulate the interaction of sunlight with planetary atmospheres, including Pluto, Titan and the early Earth, many laboratory studies have used high-power broadband lamps with spectral features that extend into the vacuum-ultraviolet (VUV, <200 nm) to initiate photochemistry relevant to the atmosphere of interest. In many cases, experiments are run on the order of hundreds of hours with no accounting for how the photon flux within the system may be evolving with lamp age or a possible buildup of films over optical surfaces when working with high-yield photochemical systems. Given that the nature of photochemistry depends on the ratio of photons to reactants, variations in flux must be taken into account if the system is to be fully understood. In this study, standard N2O actinometry was used to measure the VUV flux of high-intensity deuterium lamps before, during, and after the photochemical synthesis of Titan analog aerosols made from methane or benzene precursors. It was found that VUV photon flux can be decreased by over 50% in under 10 h at higher number densities, with recorded flux losses of over 75% during extended (>60 h) photochemical experiments. While this is only one model system, it is apparent that changes in photon flux during simulations must be taken into account if adequate comparisons of the photochemical kinetics to their respective planetary environments are to be made.

Modification of hydrophobicity properties of diamond like carbon films using glancing angle deposition method

We report the effect of glancing angle deposition (GLAD) method on hydrophobicity properties of diamond like carbon (DLC) films. DLC films were manufactured using direct ion beam method by methane (CH4) precursor gas at different incident flux angles (α = 0°, 45°, 75°, and 85°). We indicated increment in water contact angle from 83.6° to 119.4° with increasing the deposition angle and porosity of films. The top and cross sectional field emission scanning electron microscope (FESEM) images of films indicated noticeable changes in structure and morphology of the prepared specimens as functions of incident angles.

Effect of oxygen and hydrogen on microstructure of pyrolytic carbon deposited from thermal decomposition of methane and ethanol

Chemical vapor infiltration (CVI) is the most extensive industrial preparation of carbon/carbon (C/C) composites. Precursor affects the CVI process considerably. In the present study, using carbon fiber bundles as preforms, methane and ethanol as precursors, the C/C composites were densified by decomposition of various gases in CVI. The thickness and texture of deposited pyrolytic carbon (PyC) were characterized by polarized light microscopy (PLM). The microstructure of PyC was analyzed by Raman spectroscopy. The morphologies of PyC were characterized by scanning electron microscopy (SEM). The composition of PyC was detected by X-ray photoelectron spectroscopy (XPS). Adding hydrogen in methane precursor resulted in a sharp decrease in the deposition rate and texture of PyC. Mixture of methane and ethanol as the precursor improved the deposition rate and texture remarkably. Besides, O element in ethanol was not remained as a constitution of PyC, and it was removed before the formation of PyC.

The evolution of chemical groups and isotopic fractionation at different maturation stages during lignite pyrolysis

In this study, the evolution of different chemical groups and isotopic fractionation at different maturation stages of coals were investigated by gold-tube pyrolysis, detailed geochemical analysis and theoretical calculations based on Density Function Theory (DFT). The results from non-isothermal pyrolysis of lignite revealed that the conversion and hydrocarbon generation of lignite can be divided into four maturation stages in the range of Ro from 0.35 to 4.66%. Fourier-transform infrared spectra (FTIR) results of residual coals showed that the evolution of different functional groups dominates the generation of oil and gas products at different maturation stages. Correspondingly, the activation energy for methane generation was fitted into four Gaussian distributions, which elucidated different formation mechanisms or precursors of methane. Theoretical calculations indicated that the difference of isotopic fractionation kinetics for the cleavage of different chemical groups dominates carbon and hydrogen isotopic compositions of methane during lignite pyrolysis. By calculation of the isotopic fractionation factor (α=k∗/k) for the cleavage of ethyl and methyl radical, a simplified model was established to predict the carbon isotopic ratios of ethane (δ13C2) with and without cracking. Moreover, thermodynamic calculations confirmed that the occurrence of recombination between ethane and polycyclic aromatics is available at temperatures between 25 and 650°C. It is also demonstrated that the isotopic exchange between ethane and methyl aromatics can occur and will result in the depletion of D for residual coals and 13C for ethane during this process. Hence, the recombination reactions should be responsible for the rollover of δ13C2 at extremely high maturity both in experimental and geological conditions.

The optical and chemical properties of discharge generated organic haze using in-situ real-time techniques

Organic hazes formed from methane are present in many planetary and satellite atmospheres and influence surface and atmospheric processes. Here we examine the compositional and optical properties of laboratory generated hazes, or tholins, formed with varying amounts of methane using spark discharge excitation. By studying the optical and chemical properties together as a function of methane precursor concentration, the radiative impact of haze can be better understood. To determine the complex refractive index of tholin, we combine two spectroscopic techniques: photoacoustic spectroscopy and cavity ring-down spectroscopy (PASCaRD). The refractive indices are retrieved at λ = 405 and 532 nm. Quadrupole aerosol mass spectrometry is used along with a technique that utilizes isotopically labeled and unlabeled methane gas to quantify elemental composition. Tholin optical and compositional measurements are performed within a flow system, eliminating the need for tholin collection on a substrate and possible post-collection changes. We observe n values within the range of n values from most previous studies. However, the observed k values, like most others from recent studies, are significantly lower than the values from Khare et al. (1984) (Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Callcott, T.A., Williams, M.W. [1984]. Icarus 60, 127–137) that are commonly used in data retrieval programs and models. In addition, comparing the tholin k values to their approximate nitrogen and aromatic content suggests both chemical constituents are important factors for increased aerosol absorption.

Microbial methane from in situ biodegradation of coal and shale: A review and reevaluation of hydrogen and carbon isotope signatures

Stable carbon and hydrogen isotope signatures of methane, water, and inorganic carbon are widely utilized in natural gas systems for distinguishing microbial and thermogenic methane and for delineating methanogenic pathways (acetoclastic, hydrogenotrophic, and/or methylotrophic methanogenesis). Recent studies of coal and shale gas systems have characterized in situ microbial communities and provided stable isotope data (δD-CH4, δD-H2O, δ13C-CH4, and δ13C-CO2) from a wider range of environments than available previously. Here we review the principal biogenic methane-yielding pathways in coal beds and shales and the isotope effects imparted on methane, document the uncertainties and inconsistencies in established isotopic fingerprinting techniques, and identify the knowledge gaps in understanding the subsurface processes that govern H and C isotope signatures of biogenic methane. We also compare established isotopic interpretations with recent microbial community characterization techniques, which reveal additional inconsistencies in the interpretation of microbial metabolic pathways in coal beds and shales. Collectively, the re-assessed data show that widely-utilized isotopic fingerprinting techniques neglect important complications in coal beds and shales.Isotopic fingerprinting techniques that combine δ13C-CH4 with δD-CH4 and/or δ13C-CO2 have significant limitations: (1) The consistent ~160‰ offset between δD-H2O and δD-CH4 could imply that hydrogenotrophic methanogenesis is the dominant metabolic pathway in microbial gas systems. However, hydrogen isotopes can equilibrate between methane precursors and coexisting water, yielding a similar apparent H isotope signal as hydrogenotrophic methanogenesis, regardless of the actual methane formation pathway. (2) Non-methanogenic processes such as sulfate reduction, Fe oxide reduction, inputs of thermogenic methane, anaerobic methane oxidation, and/or formation water interaction can cause the apparent carbon isotope fractionation between δ13C-CH4 and δ13C-CO2 (α13CCO2-CH4) to differ from the true methanogenic fractionation, complicating interpretation of methanogenic pathways. (3) Where little-fractionating non-methanogenic bacterial processes compete with highly-fractionating methanogenesis, the mass balance between CH4 and CO2 is affected. This has implications for δ13C values and provides an alternative interpretation for net C isotope signatures than solely the pathways used by active methanogens. (4) While most of the reviewed values of δD-H2O - δD-CH4 and α13CCO2-CH4 are apparently consistent with hydrogenotrophic methanogenesis as the dominant pathway in coal beds and shales, recent microbial community characterization techniques suggest a possible role for acetoclastic or methylotrophic methanogenesis in some basins.

Regional and seasonal radiative forcing by perturbations to aerosol and ozone precursor emissions

Abstract. Predictions of temperature and precipitation responses to changes in the anthropogenic emissions of climate forcers require the quantification of the radiative forcing exerted by those changes. This task is particularly difficult for near-term climate forcers like aerosols, methane, and ozone precursors because their short atmospheric lifetimes cause regionally and temporally inhomogeneous radiative forcings. This study quantifies specific radiative forcing, defined as the radiative forcing per unit change in mass emitted, for eight near-term climate forcers as a function of their source regions and the season of emission by using dedicated simulations by four general circulation and chemistry-transport models. Although differences in the representation of atmospheric chemistry and radiative processes in different models impede the creation of a uniform dataset, four distinct findings can be highlighted. Firstly, specific radiative forcing for sulfur dioxide and organic carbon are stronger when aerosol–cloud interactions are taken into account. Secondly, there is a lack of agreement on the sign of the specific radiative forcing of volatile organic compound perturbations, suggesting they are better avoided in climate mitigation strategies. Thirdly, the strong seasonalities of the specific radiative forcing of most forcers allow strategies to minimise positive radiative forcing based on the timing of emissions. Finally, European and shipping emissions exert stronger aerosol specific radiative forcings compared to East Asia where the baseline is more polluted. This study can therefore form the basis for further refining climate mitigation options based on regional and seasonal controls on emissions. For example, reducing summertime emissions of black carbon and wintertime emissions of sulfur dioxide in the more polluted regions is a possible way to improve air quality without weakening the negative radiative forcing of aerosols.

Polymeric amorphous carbon films with high hardness

Polymeric amorphous carbon films are grown from acetylene precursor gas using the immersive PECVD method. The optical and mechanical properties of the obtained samples are measured and compared to those grown from methane precursor gas using a similar method. The samples are found to have similar optical properties such as Tauc gap and refractive index, while having significantly different mechanical properties. Samples grown from acetylene have over 200% increases in their micro-hardness and residual stress over those from methane. Even with the significant increase, the residual stress of the samples from acetylene is still very low (<0.9GPa), making this type of amorphous carbon films suitable for many applications. The sp2 ternary phase diagram is used to show the distinctivity of the microstructures of the obtained samples, and in the process demonstrates itself as a useful tool for characterizing and classifying amorphous carbon films.

Formate‐derived H2, a driver of hydrogenotrophic processes in the root‐zone of a methane‐emitting fen

Wetlands are important sources of globally emitted methane. Plants mediate much of that emission by releasing root-derived organic carbon, including formate, a direct precursor of methane. Thus, the objective of this study was to resolve formate-driven processes potentially linked to methanogenesis in the fen root-zone. Although, formate was anticipated to directly trigger methanogenesis, the rapid anaerobic consumption of formate by Carex roots unexpectedly yielded H2 and CO2 via enzymes such as formate-H2 -lyase (FHL), and likewise appeared to enhance the utilization of organic carbon. Collectively, 57 [FeFe]- and [NiFe]-hydrogenase-containing family level phylotypes potentially linked to FHL activity were detected. Under anoxic conditions, root-derived fermentative Citrobacter and Hafnia isolates produced H2 from formate via FHL. Formate-derived H2 fueled methanogenesis and acetogenesis, and methanogenic (Methanoregula, Methanobacterium, Methanocella) and acetogenic (Acetonema, Clostridum, Sporomusa) genera potentially linked to these hydrogenotrophic activities were identified. The findings (i) provide novel insights on highly diverse root-associated FHL-containing taxa that can augment secondary hydrogenotrophic processes via the production of formate-derived H2 , (ii) demonstrate that formate can have a 'priming' effect on the utilization of organic carbon, and (iii) raise questions regarding the fate of formate-derived H2 when it diffuses away from the root-zone.

Optical properties of oxygen doped diamond-like carbon thin films

In this work, oxygen doped diamond-like carbon thin films were deposited on silicon substrates by a RF-PECVD method using mixture of methane (CH4), argon (Ar) and oxygen (O2) precursor gases. The refractive index (n), extinction coefficient (k) and thickness of the thin films were measured by spectroscopic ellipsometry method (SE). The absorption coefficient (α) and optical band gap were also derived. The structure of the films was investigated by Raman spectroscopy. Fourier Transform Infra-Red (FTIR) spectroscopy was used to measure the transmittance in the midwave infrared (mid IR) region and to identify existing bonds in the structure of the films. The results showed that these films were ideal to use them as antireflective coatings for silicon optics in mid IR. Oxygen doping did not significantly change optical properties; and did not have undesirable effect on the antireflection property. Among the films, the oxygen doped diamond-like carbon film that was deposited with 5.6% volume oxygen had highest refractive index, lowest optical gap and minimum film deposition rate.

Structures of microbial communities found in anaerobic batch runs that produce methane from propionic acid—Seeded from full-scale anaerobic digesters above a certain threshold

The volatile fatty acid propionate inhibits anaerobic digestion during organic waste treatments. To examine potential microbial interactions that accelerate propionate oxidation, anaerobic digestion systems seeded with various types of anaerobic sludge were analyzed. Seed samples were collected from 10 different full-scale anaerobic reactors in South Korea. Propionate oxidation was estimated as the methane production rate per gram of propionate used per day. Two domestic sewage sludge showed the highest methane production rate values, 109.1±4.2 and 74.5±8.6mL CH4/(g propionate∙d). A food waste recycling wastewater source exhibited the lowest methane production rate, 33.2±2.6mL CH4/(g propionate∙d). To investigate how the microbial community structure affected propionate oxidation, qualitative molecular analyses were carried out using denaturing gradient gel electrophoresis. Methanosaeta concilii, an aceticlastic methanogen, was detected in most batch runs. Smithella propionica, a unique propionate oxidizer and simultaneous producer of acetate, was found in domestic sewage sludge sources showing the highest methane production rate; in contrast, Desulfobulbus rhabdoformis, a sulfate reducer coupled with the consumption of acetate to be used as a precursor of methane, was observed in food waste recycling wastewater sludge source showing the lowest methane production rate. Thus, we propose that S. propionica, a syntrophic acetate producer using propionate, might cooperate with aceticlastic methanogens for high methane production during anaerobic digestion that included propionate.