Carbon Condensation Research Articles

Sub-millisecond lithiothermal synthesis of graphitic meso–microporous carbon

Porous carbons with concurrently high specific surface area and electronic conductivity are desirable by virtue of their desirable electron and ion transport ability, but conventional preparing methods suffer from either low yield or inferior quality carbons. Here we developed a lithiothermal approach to bottom–up synthesize highly meso–microporous graphitized carbon (MGC). The preparation can be finished in a few milliseconds by the self-propagating reaction between polytetrafluoroethylene powder and molten lithium (Li) metal, during which instant ultra-high temperature (>3000 K) was produced. This instantaneous carbon vaporization and condensation at ultra-high temperatures and in ultra-short duration enable the MGC to show a highly graphitized and continuously cross-coupled open pore structure. MGC displays superior electrochemical capacitor performance of exceptional power capability and ultralong-term cyclability. The processes used to make this carbon are readily scalable to industrial levels.

Formation of extraterrestrial peptides and their derivatives.

The formation of protein precursors, due to the condensation of atomic carbon under the low-temperature conditions of the molecular phases of the interstellar medium, opens alternative pathways for the origin of life. We perform peptide synthesis under conditions prevailing in space and provide a comprehensive analytic characterization of its products. The application of 13C allowed us to confirm the suggested pathway of peptide formation that proceeds due to the polymerization of aminoketene molecules that are formed in the C + CO + NH3 reaction. Here, we address the question of how the efficiency of peptide production is modified by the presence of water molecules. We demonstrate that although water slightly reduces the efficiency of polymerization of aminoketene, it does not prevent the formation of peptides.

Evolution of fullerenes in circumstellar envelopes by carbon condensation: insights from reactive molecular dynamics simulations

ABSTRACT Fullerenes, including C60 and C70, have been detected in various astronomical environments. Understanding how their structures evolve over time is essential for gaining insights into their life cycle and making further observations. To address this, we conducted reactive molecular dynamics simulations to investigate the evolution of fullerenes in the circumstellar envelopes surrounding carbon-rich asymptotic giant branch stars. Our simulations employed a bottom-up chemistry scheme, wherein fullerenes grow by absorbing and condensing small carbon-based molecules. The results revealed the formation of different structures through heterogeneous reactions based on hydrogen concentration, leading to the emergence of onion-like nanostructures or single-layer fullerenes. To examine the impact of these structural changes on the infrared emission characteristics of fullerenes, we performed quantum chemical calculations. The results indicate that as fullerenes grow larger, additional emission features are introduced in the infrared spectrum. Moreover, two-layered fullerenes show noticeable blueshift or weakening effects on the bands associated with out-of-plane vibration modes.

Understanding Rapid PET Degradation via Reactive Molecular Dynamics Simulation and Kinetic Modeling.

As the demand for PET plastic products continues to grow, developing effective processes to reduce their pollution is of critical importance. Pyrolysis, a promising technology to produce lighter and recyclable components from wasted plastic products, has therefore received considerable attention. In this work, the rapid pyrolysis of PET was studied by using reactive molecular dynamics (MD) simulations. Mechanisms for yielding gas species were unraveled, which involve the generation of ethylene and TPA radicals from ester oxygen-alkyl carbon bond dissociation and condensation reactions to consume TPA radicals with the products of long chains containing a phenyl benzoate structure and CO2. As atomistic simulations are typically conducted at the time scale of a few nanoseconds, a high temperature (i.e., >1000 K) is adopted for accelerated reaction events. To apply the results from MD simulations to practical pyrolysis processes, a kinetic model based on a set of ordinary differential equations was established, which is capable of describing the key products of PET pyrolysis as a function of time and temperature. It was further exploited to determine the optimal reaction conditions for low environmental impact. Overall, this study conducted a detailed mechanism study of PET pyrolysis and established an effective kinetic model for the main species. The approach presented herein to extract kinetic information such as detailed kinetic constants and activation energies from atomistic MD simulations can also be applied to related systems such as the pyrolysis of other polymers.

Synthesis of thermally stable carbon nanostructures via ethanol pyrolysis in DC plasma jets

Thermostable graphene and carbon nanotubes (CNTs) obtained by the plasma-chemical method were stable when heated to 1300 K. The peculiarity of the obtained materials is associated with the nature of the precursor (ethanol) containing oxygen. It is shown that the composition of the gas phase and the temperature interval for the formation of gaseous precursors depends on the plasma-forming gas used for the pyrolysis of ethanol in a plasma jet: helium, argon, or nitrogen. According to the results of plasma flow simulation, the temperatures of the onset of carbon condensation for helium plasma (2900–2950 K) and argon plasma (2980–3010 K) are quite close, and in the corresponding gas phase the main components are H, H2 and CO, and at lower concentrations there are radicals COOH and OH and HCO+. The nitrogen plasma contains well-represented cyanopolyins responsible for the rearrangement of the gas phase at lower temperatures of 2240–2250 K. It seems that these temperatures are too low for CNT synthesis, so only graphene is formed here. The influence of the combination of H and O in the high-temperature region of plasma flow on the mechanism of formation of precursors of carbon nanostructures has been found.

Formation of Complex Organic Molecules on Interstellar CO Ices? Insights from Computational Chemistry Simulations

The carbon (3P) atom is a reactive species that, according to laboratory experiments and theoretical calculations, condensates with interstellar ice components. This fact is of uttermost importance for the chemistry in the interstellar medium (ISM) because the condensation reaction is barrierless, and the subsequent species formed are still reactive given their open-shell character. Carbon condensation on CO-rich ices forms the C=C=O (3Σ−) species, which can be easily hydrogenated twice to form ketene (H2CCO). Ketene is very reactive in terrestrial conditions, usually found as an intermediate that is difficult to isolate in chemical synthesis laboratories. These characteristics suggest that ketene can be a good candidate to form interstellar complex organic molecules via a two-step process, i.e., its activation followed by a radical–radical coupling. In this work, reactions between ketene and atomic H and the OH and NH2 radicals on a CO-rich ice model have been explored by means of quantum chemical calculations complemented by kinetic calculations to evaluate if they are favorable in the ISM. Results indicate that the addition of H to ketene (helped by tunneling) to form the acetyl radical (CH3CO) is the most preferred path as the reactions with OH and NH2 possess activation energies (≥9 kJ mol−1) hard to surmount in the ISM conditions unless external processes provide energy to the system. Thus, acetaldehyde (CH3CHO) and, probably, ethanol (CH3CH2OH) formation via further hydrogenations, are the possible unique operating synthetic routes. Moreover, from the computed, relatively large binding energies of OH and NH2 on CO ice, slow diffusion is expected, hampering possible radical–radical couplings with CH3CO. The astrophysical implications of these findings are discussed considering the incoming James Webb Space Telescope observations.

Carbon Condensation via [4 + 2] Cycloaddition of Highly Unsaturated Carbon Chains.

We present computational studies of reaction pathways for alkyne/polyyne dimerization that represent plausible early steps in mechanisms for carbon condensation. A previous computational study of the ring coalescence and annealing model of C60 formation revealed that a 1,4-didehydrobenzocyclobutadiene intermediate (p-benzyne derivative) has little to no barrier to undergoing an unproductive retro-Bergman cyclization, which brings into question the relevance of that reaction pathway. The current study investigates an alternative model, which proceeds through an initial [4 + 2] cycloaddition instead of a [2 + 2] cycloaddition. In this pathway, the problematic intermediate is avoided, with the reaction proceeding via a (potentially) more kinetically stable tetradehydronaphthalene derivative. The computational studies of the [2 + 2] and [4 + 2] model systems, with increasing alkyne substitutions, reveal that the para-benzyne diradical of the [4 + 2] pathway has a significantly greater barrier to ring opening than the analogous intermediates of the [2 + 2] pathway and that alkyne substitution has little effect on this important barrier. These studies employ spin-flip, time-dependent density functional theory (SF-TDDFT) to provide suitable treatment of open-shell diradical intermediates.

Organic‐Inorganic Interaction Recorded by Polycyclic Aromatic Steranes in Continental Epithermal Ore Deposits

AbstractContinental epithermal ore deposits are commonly associated with sedimentary organic matter, oils or solid bitumen. These organics embedded in mineral deposits can convey valuable information of the ore genesis. However, the extent to which the formation of ore minerals was recorded by organic compounds remains largely unknown, as also is how metal‐rich ores interfere with the molecular proxies in the temperature regime envisaged for hydrothermal activity. The molecular compositional changes of various polycyclic aromatic steranes and polycyclic aromatic hydrocarbons and compounds derived from the Jinding Pb/Zn deposit, SW China provide new data. Aliphatic regular steranes are present as traces. The transformation from polycyclic aromatic steranes to unsubstituted polycyclic aromatic hydrocarbons is observed to show an increased trend with increasing hydrothermal alteration levels; this is consistent with the transformation from unsubstituted polycyclic aromatic hydrocarbons to heterocyclic compounds. Dehydrocyclization (aromatization) of polycyclic biological compounds and hydrodecyclization (dearomatization) of polycyclic aromatic compounds are two important reaction pathways in hydrothermal systems with moderate temperature. This detailed investigation of organic‐inorganic interactions of two groups of polycyclic compounds with metal‐rich ores provides insights into the questions on how and to what extent the formation of Pb/Zn deposits can be recorded by organics. This work will improve our understanding of carbon reduction, oxidation or condensation in the deep Earth and the carbon exchange between the Earth's crust and mantle, and may shed light on the processes for ultra‐deep hydrocarbon exploration.

The rocky road to organics needs drying

How simple abiotic organic compounds evolve toward more complex molecules of potentially prebiotic importance remains a missing key to establish where life possibly emerged. The limited variety of abiotic organics, their low concentrations and the possible pathways identified so far in hydrothermal fluids have long hampered a unifying theory of a hydrothermal origin for the emergence of life on Earth. Here we present an alternative road to abiotic organic synthesis and diversification in hydrothermal environments, which involves magmatic degassing and water-consuming mineral reactions occurring in mineral microcavities. This combination gathers key gases (N2, H2, CH4, CH3SH) and various polyaromatic materials associated with nanodiamonds and mineral products of olivine hydration (serpentinization). This endogenous assemblage results from re-speciation and drying of cooling C–O–S–H–N fluids entrapped below 600 °C–2 kbars in rocks forming the present-day oceanic lithosphere. Serpentinization dries out the system toward macromolecular carbon condensation, while olivine pods keep ingredients trapped until they are remobilized for further reactions at shallower levels. Results greatly extend our understanding of the forms of abiotic organic carbon available in hydrothermal environments and open new pathways for organic synthesis encompassing the role of minerals and drying. Such processes are expected in other planetary bodies wherever olivine-rich magmatic systems get cooled down and hydrated.

Constraining the Origin and Age of the Thermal and Cold Water in the Lake Natron Basin, Northern Tanzania

Springs on the eastern and western shores of Lake Natron Basin (LNB), located within the eastern branch of the East Africa Rift System (EARS) in Northern Tanzania had a discharge temperature that ranged between 34.0 °C and 51.2 °C, while the pH varied from 8.0 to 10.7. The electrical conductivity (EC) ranged between 5,007 µS/cm and 49,200 µS/cm. Cold waters had a temperature of 31.9 °C to 32.5 °C, while the pH ranged between 8.0 and 8.3, and the EC ranged between 1,401 µS/cm and 3,806 µS/cm. The stable isotope composition varied between -2.4 ‰ and -5.3 ‰ for δ18O, and -15.5 ‰ to -29.3 ‰ for δ2H. The isotopic composition of thermal and cold water of LNB indicates a significant contribution of meteoric water in the recharge of the hydrothermal system. However, thermal water is affected by evaporation, water-rock interaction, carbon dioxide (CO2) exchange and condensation processes. Tritium analysis indicated that the spring water in the LNB hydrothermal system has a residence time of more than 50 years.
 Keywords: thermal water; Lake Natron Basin; stable isotopes; springs.

Semi-quantitative analysis of molecular composition for petroleum fractions using electrospray ionization high-resolution mass spectrometry

The developments of high-resolution mass spectrometry and soft ionization technologies have enabled the molecular characterization of petroleum fractions. However, quantitative analysis of molecular composition for petroleum is far from being achieved. In this study, semi-quantitative analysis of molecular composition for the whole compounds in heavy petroleum fractions was carried out. Hydrocarbons and various heteroatoms in the heavy petroleum fractions were characterized by only electrospray ionization coupled with high-resolution mass spectrometry. The molecular composition of various types of compounds were calculated and integrated quantitatively based on bulk chemical composition. The semi-quantitative molecular compositions of four heavy petroleum fractions with largely different bulk properties were comprehensively characterized in multiple dimensions such as carbon number distribution, condensation degree, molecular weight, mass fraction, and molecule number. More than 5,000 molecules, which classified into 16 compound classes of seven groups were quantitatively characterized from the four fractions. The accuracy of the analysis seems acceptable according the H/C ratio comparation between that derived from element analysis and the semi-quantitative molecular composition. Representative molecule set containing structural information was also proposed based on the semi-quantitative results.

Two-stage carbon condensation model during detonation of high explosives

During detonating of high explosives with a negative oxygen balance, one of the products of the chemical reaction is condensed carbon. However, the lack of experimental data does not allow us to give a quantitative assessment of the carbon condensation process today. In this paper, a two-stage model of carbon condensation during the detonation of high explosives is proposed. We used small-angle X-ray scattering method to study the dynamics of the formation of carbon nanoparticles during the detonation of charges of a mixture of TNT and RDX.

Theoretical algorithm for fast calculation of interatomic bonds as applied to metallic hydrogen and carbon condensates

A method for calculating the potential energy of interatomic interaction, an alternative to the use of significant computer resources, is proposed. The algorithm was tested on the example of 1S-1S bonds, in particular, in hydrogen, as well as 2S-2S and 2 P-2P bonds, in particular, in carbon. It is shown that bound states can be formed in all three cases, but the interacting atoms must overcome the potential barrier. The presence of a barrier makes it possible to explain a number of known features in the formation of the corresponding condensates.

On melting temperature of carbon produced in detonation combustion of acetylene

A mathematical model of gas detonation of over-riched hydrocarbon-oxygen mixtures has been formulated. The model implies numerical studying the equilibrium flows of detonation products provided that there is condensation of free carbon. To describe thermodynamic properties of carbon condensate, reference data for graphite have been used. The calculations have been compared with the known results of experimental research, in which the detonation of acetylene-oxygen mixture in a tube with one closed end results in nanoscale particles of carbon material with special properties. We assumed that melting temperature of such a material, which is about 3100 K, is lower than that of graphite. Only such a way of correcting melting temperature yields the best agreement (with accuracy of about 3%) between calculation and experimental dependence of detonation front velocity on molar fraction of acetylene in the mixture.

Chemistry-mediated Ostwald ripening in carbon-rich C/O systems at extreme conditions

There is significant interest in establishing a capability for tailored synthesis of next-generation carbon-based nanomaterials due to their broad range of applications and high degree of tunability. High pressure (e.g., shockwave-driven) synthesis holds promise as an effective discovery method, but experimental challenges preclude elucidating the processes governing nanocarbon production from carbon-rich precursors that could otherwise guide efforts through the prohibitively expansive design space. Here we report findings from large scale atomistically-resolved simulations of carbon condensation from C/O mixtures subjected to extreme pressures and temperatures, made possible by machine-learned reactive interatomic potentials. We find that liquid nanocarbon formation follows classical growth kinetics driven by Ostwald ripening (i.e., growth of large clusters at the expense of shrinking small ones) and obeys dynamical scaling in a process mediated by carbon chemistry in the surrounding reactive fluid. The results provide direct insight into carbon condensation in a representative system and pave the way for its exploration in higher complexity organic materials. They also suggest that simulations using machine-learned interatomic potentials could eventually be employed as in-silico design tools for new nanomaterials.

A pathway to peptides in space through the condensation of atomic carbon

Organic molecules are widely present in the dense interstellar medium, and many have been synthesized in the laboratory on Earth under the conditions typical for an interstellar environment. Until now, however, only relatively small molecules of biological interest have been demonstrated to form experimentally under typical space conditions. Here we prove experimentally that the condensation of carbon atoms on the surface of cold solid particles (cosmic dust) leads to the formation of isomeric polyglycine monomers (aminoketene molecules). Following encounters between aminoketene molecules, they polymerize to produce peptides of different lengths. The chemistry involves three of the most abundant species (CO, C and NH3) present in star-forming molecular clouds, and proceeds via a novel pathway that skips the stage of amino acid formation in protein synthesis. The process is efficient, even at low temperatures, without irradiation or the presence of water. The delivery of biopolymers formed by this chemistry to rocky planets in the habitable zone might be an important element in the origins of life.

Modeling of soot formation in a tractor diesel engine running on methanol and methyl ether of rapeseed oil

When studying the process of formation of soot nuclei in a flame, it is necessary to pay attention to the sequence of chemical transformations of fuel molecules in order to determine the concentration of dangerous toxic components in the exhaust gases (EG) of a diesel internal combustion engine (DICE). Today, numerous studies are being conducted to establish a detailed kinetic mechanism of the process of carbon condensation and gasification in a DICE. Despite significant progress in understanding the essence and some regularities of the processes occurring in a DICE, it is not yet possible to compile a numerical model that can predict the main indicators of soot content. A semi-empirical mathematical model of soot formation and burnout in a DICE is presented, compiled on the basis of a kinetic model that reliably predicts the dynamics of soot content in the cylinder and the concentration of soot in the EG in a wide range of operating modes of a DICE. The model makes it possible to facilitate the process of studying the factors of soot formation and reduce the cost of conducting experimental studies related to the search for alternative fuels and improving the design of a DICE, optimizing the operation of fuel supply and gas distribution systems.

Melting Point of Carbon Particles behind the Gas Detonation Front

A mathematical model of gas detonation of fuel-enriched mixtures of hydrocarbons with oxygen has been formulated, which makes it possible to numerically study the equilibrium flows of detonation products in the presence of free carbon condensation. Reference data for graphite were used to describe the thermodynamic properties of carbon condensate. The calculations are compared with the known results of experimental studies in which, when detonating an acetylene-oxygen mixture in a pipe closed at one end, it is possible to obtain nanoscale particles from a carbon material with special properties. It is assumed that the melting point of such a material is lower than that of graphite and is about 3100 K. Only with such an adjustment of the melting temperature, the best agreement (with an accuracy of about 3 %) was obtained between the calculated and experimental dependence of the detonation front velocity on the molar fraction of acetylene in the mixture.

Following carbon condensation by in situ TEM: towards a rational understanding of the processes in the synthesis of nitrogen-doped carbonaceous materials

In situ TEM heating experiments combined with extensive chemical, structural and sorption analysis reveal the nanoscale mechanism of porosity formation in carbonaceous materials obtained directly from molecular precursors.

A Comparative Study of Atmospheric Chemistry with VULCAN

Abstract We present an update of the open-source photochemical kinetics code VULCAN to include C–H–N–O–S networks and photochemistry. The additional new features are advection transport, condensation, various boundary conditions, and temperature-dependent UV cross sections. First, we validate our photochemical model for hot Jupiter atmospheres by performing an intercomparison of HD 189733b models between Moses et al., Venot et al., and VULCAN, to diagnose possible sources of discrepancy. Second, we set up a model of Jupiter extending from the deep troposphere to upper stratosphere to verify the kinetics for low temperature. Our model reproduces hydrocarbons consistent with observations, and the condensation scheme successfully predicts the locations of water and ammonia ice clouds. We show that vertical advection can regulate the local ammonia distribution in the deep atmosphere. Third, we validate the model for oxidizing atmospheres by simulating Earth and find agreement with observations. Last, VULCAN is applied to four representative cases of extrasolar giant planets: WASP-33b, HD 189733b, GJ 436b, and 51 Eridani b. We look into the effects of the C/O ratio and chemistry of titanium/vanadium species for WASP-33b, we revisit HD 189733b for the effects of sulfur and carbon condensation, the effects of internal heating and vertical mixing (K zz) are explored for GJ 436b, and we test updated planetary properties for 51 Eridani b with S8 condensates. We find that sulfur can couple to carbon or nitrogen and impact other species, such as hydrogen, methane, and ammonia. The observable features of the synthetic spectra and trends in the photochemical haze precursors are discussed for each case.