Gas-phase Carbon Research Articles

PDRs4All. X. ALMA and JWST detection of neutral carbon in the externally irradiated disk d203-506: Undepleted gas-phase carbon

PDRs4All. X. ALMA and JWST detection of neutral carbon in the externally irradiated disk d203-506: Undepleted gas-phase carbon

Development of a quantum cascade laser absorption spectrometer for simultaneous measurement of 13C-18O and 18O-18O clumping in CO2.

Dual clumped isotope paleothermometry determines carbonate formation temperatures by measuring the frequency of 13C-18O (∆638) and 18O-18O (∆828) pairs in carbonates. It resolves isotopic kinetic biases and thus enables more accurate paleotemperature reconstructions. However, high-precision measurements of 18O-18O clumping using current techniques requires large sample sizes and long acquisition times. We developed a mid-infrared isotope ratio laser spectrometer (IRLS) for simultaneous measurement of the isotopologue ratios ∆638 and ∆828 in gas-phase carbon dioxide (CO2) at room temperature. Our IRLS uses a single laser scanning from 2290.7 to 2291.1cm-1 and a 31 m pathlength optical cell, and it simultaneously measures the five isotopologues required for calculating ∆638 and ∆828: 16O12C16O, 16O13C16O, 16O12C18O, 16O13C18O, and 18O12C18O. In addition, our IRLS can measure 16O12C17O, enabling ∆17O analysis. At ~20°C and a CO2 pressure of ~2Torr, our IRLS system achieved precisions of 0.128‰ and 0.140‰ within 20 s for abundances of the clumped isotopologues 16O13C18O and 18O12C18O, respectively, and precisions of 0.267‰, 0.245‰, and 0.128‰ for 16O12C16O, 16O13C16O, and 16O12C18O. This yielded precisions of 0.348‰ (∆638) and 0.302‰ (∆828) within 25 s. Simulated sample-reference switching highlights the potential of our system and the need for further development. We demonstrated simultaneous measurements of ∆638 and ∆828 in CO2 to precisions of <0.35‰ within 25 s using a room-temperature, single-laser IRLS. Future developments on better resolving 16O12C16O and 16O13C16O peaks and system temperature control could further improve the measurement precision.

Molecular Mechanism for Converting Carbon Dioxide Surrounding Water Microdroplets Containing 1,2,3-Triazole to Formic Acid.

Spraying water microdroplets containing 1,2,3-triazole (Tz) has been found to effectively convert gas-phase carbon dioxide (CO2), but not predissolved CO2, into formic acid (FA). Herein, we elucidate the reaction mechanism at the molecular level through quantum chemistry calculations and ab initio molecular dynamics (AIMD) simulations. Computations suggest a multistep reaction mechanism that initiates from the adsorption of CO2 by Tz to form a CO2-Tz complex (named reactant complex (RC)). Then, the RC either is reduced by electrons that were generated at the air-liquid interface of the water microdroplet and then undergoes intramolecular proton transfer (PT) or switches the reduction and PT steps to form a [HCO2-(Tz-H)]- complex (named PC-). Subsequently, PC- undergoes reduction and the C-N bond dissociates to generate COOH- and [Tz-H]- (m/z = 69). COOH- easily converts to HCOOH and is captured at m/z = 45 in mass spectroscopy. Notably, the intramolecular PT step can be significantly lowered by the oriented electric field at the interface and a water-bridge mechanism. The mechanism is further confirmed by testing multiple azoles. The AIMD simulations reveal a novel proton transfer mechanism where water serves as a transporter and is shown to play an important role dynamically. Moreover, the transient •COOH captured by the experiment is proposed to be partly formed by the reaction with H•, pointing again to the importance of the air-water interface. This work provides valuable insight into the important mechanistic, kinetic, and dynamic features of converting gas-phase CO2 to valuable products by azoles or amines dissolved in water microdroplets.

Infrared bands of neutral gas-phase carbon clusters in a broad spectral range.

The identification of species in the interstellar medium requires precise and molecule-specific spectroscopic information in the laboratory framework, in broad spectral ranges and under conditions relevant to interstellar environments. In this work, we measure the gas-phase infrared spectra of neutral carbon clusters, CN (N = 6-11), in a molecular beam. The CN distribution is formed by photofragmentation of C60 molecules, concurrently showing a top-down formation mechanism. A broad spectral range in the infrared between 500-3200 cm-1 (20-3.125 μm) is investigated. We observe strong bands between 5 and 6 μm, in conjunction with novel features in the 3 μm region. Density functional theory calculations reveal that these short wavelength modes correspond to combination bands with significant infrared intensity. Moreover, we identify the N ≤ 10 clusters as linear, while C11 adopts a ring configuration, placing the linear-to-ring transition at N = 11 under our molecular beam conditions. The linearity of C10 is discussed based on the formation pathway from larger clusters in energetic conditions. Given the vast and very precise infrared information already been released from the James Webb Space Telescope mission, this infrared spectroscopic data set in conjunction with information on formation mechanisms is of major relevance for identifying neutral carbon clusters in astronomical environments.

Deep Search for Molecular Oxygen in TW Hya

The dominant form of oxygen in cold molecular clouds is gas-phase carbon monoxide (CO) and ice-phase water (H2O). Yet, in planet-forming disks around young stars, gas-phase CO and H2O are less abundant relative to their interstellar medium values, and no other major oxygen-carrying molecules have been detected. Some astrochemical models predict that gas-phase molecular oxygen (O2) should be a major carrier of volatile oxygen in disks. We report a deep search for emission from the isotopologue 16O18O (N J = 21 − 01 line at 233.946 GHz) in the nearby protoplanetary disk around TW Hya. We used imaging techniques and matched filtering to search for weak emission but do not detect 16O18O. Based on our results, we calculate upper limits on the gas-phase O2 abundance in TW Hya of (6.4–70) × 10−7 relative to H, which is 2–3 orders of magnitude below solar oxygen abundance. We conclude that gas-phase O2 is not a major oxygen carrier in TW Hya. Two other potential oxygen-carrying molecules, SO and SO2, were covered in our observations, which we also do not detect. Additionally, we report a serendipitous detection of the C15N N J = 25/2 − 13/2 hyperfine transitions, F = 3 − 2 and F = 2 − 1, at 219.9 GHz, which we found via matched filtering and confirm through imaging.

Large Myr-old Disks Are Not Severely Depleted of Gas-phase CO or Carbon

We present an ACA search for [C i] 1–0 emission at 492 GHz toward large T Tauri disks (gas radii ≳ 200 au) in the ∼1–3 Myr-old Lupus star-forming region. Combined with Atacama Large Millimeter/submillimeter Array 12 m archival data for IM Lup, we report [C i] 1–0 detections in six out of 10 sources, thus doubling the known detections toward T Tauri disks. We also identify four Keplerian double-peaked profiles and demonstrate that the [C i] 1–0 fluxes correlate with 13CO, C18O, and 12CO(2–1) fluxes, as well as with the gas disk outer radius measured from the latter transition. These findings are in line with the expectation that atomic carbon traces the disk surface. In addition, we compare the carbon and carbon monoxide (CO) line luminosities of a Lupus and literature sample with [C i] 1–0 detections with predictions from the self-consistent disk thermo-chemical models of Ruaud et al. These models adopt interstellar medium carbon and oxygen elemental abundances as input parameters. With the exception of the disk around Sz 98, we find that these models reproduce all the available line luminosities and upper limits, with gas masses comparable to or higher than the minimum-mass solar nebula and gas-to-dust mass ratios ≥10. Thus, we conclude that the majority of large Myr-old disks conform to the simple expectation that they are not significantly depleted in gas, CO, or carbon.

Solution-processable polymers of intrinsic microporosity for gas-phase carbon dioxide photoreduction

Four solution-processable, linear conjugated polymers of intrinsic porosity are synthesised and tested for gas phase carbon dioxide photoreduction. The polymers’ photoreduction efficiency is investigated as a function of their porosity, optical properties, energy levels and photoluminescence. All polymers successfully form carbon monoxide as the main product, without the addition of metal co-catalysts. The best performing single component polymer yields a rate of 66 μmol h−1 m−2, which we attribute to the polymer exhibiting macroporosity and the longest exciton lifetimes. The addition of copper iodide, as a source of a copper co-catalyst in the polymers shows an increase in rate, with the best performing polymer achieving a rate of 175 μmol h−1 m−2. The polymers are active for over 100 h under operating conditions. This work shows the potential of processable polymers of intrinsic porosity for use in the gas phase photoreduction of carbon dioxide towards solar fuels.

Oxidized organic molecules in the tropical free troposphere over Amazonia.

New particle formation (NPF) in the tropical free troposphere (FT) is a globally important source of cloud condensation nuclei, affecting cloud properties and climate. Oxidized organic molecules (OOMs) produced from biogenic volatile organic compounds are believed to contribute to aerosol formation in the tropical FT, but without direct chemical observations. We performed in situ molecular-level OOMs measurements at the Bolivian station Chacaltaya at 5240 m above sea level, on the western edge of Amazonia. For the first time, we demonstrate the presence of OOMs, mainly with 4-5 carbon atoms, in both gas-phase and particle-phase (in terms of mass contribution) measurements in tropical FT air from Amazonia. These observations, combined with air mass history analyses, indicate that the observed OOMs are linked to isoprene emitted from the rainforests hundreds of kilometers away. Based on particle-phase measurements, we find that these compounds can contribute to NPF, at least the growth of newly formed nanoparticles, in the tropical FT on a continental scale. Thus, our study is a fundamental and significant step in understanding the aerosol formation process in the tropical FT.

Platinum quantum dots-decorated MXene-derived titanium dioxide nanowire/Ti3C2 heterostructure for use in solar-driven gas-phase carbon dioxide reduction to yield value-added fuels

Solar-driven photocatalytic CO2 reduction to produce valuable chemicals and fuels offers an attractive strategy in alleviating the energy crisis. Pt quantum dots (PtQDs) with TiO2 nanowire (TiO2NW)/Ti3C2 MXene heterostructures (Pt-TiO2NW/Ti3C2) with tight interfacial contacts between the various components were prepared at room temperature via oxidation reactions. The incorporated PtQDs played crucial roles as electron conduction bridges supported by the cocatalyst effect, effectively enhancing the separation efficiencies of photoinduced electron/hole pairs and improving CO2 reduction under simulated solar light irradiation. The Pt-TiO2NW/Ti3C2 heterostructures exhibited remarkable carbon monoxide (CO) and methane (CH4) production at respective rates of 38.14 and 36.15 μmol g−1 after 10 h of simulated solar light irradiation, an apparent quantum yield of 1.68%, and 79.2% selectivity for CH4. The photocatalytic activities of the Pt-TiO2NW/Ti3C2 heterostructures for CO2 reduction were significantly enhanced compared to those of TiO2NW/Ti3C2 and the single-component photocatalysts, and they exhibited remarkable stabilities even after five cycles. In addition, the densities of states and electronic characteristics of Ti3C2 MXene and Pt-TiO2NW/Ti3C2 were studied using density functional theory, and a synergistic mechanism of the improvement in CO2 photoreduction is proposed.

Enhanced oxidation resistance of single crystal tungsten powder by forming tungsten carbide on the surface

The tungsten-type delay composition is composed of tungsten powder, oxidizing agent and binder, but the tungsten powder will be pre-oxidized after long-term storage, which deteriorates the combustion performance of the tungsten-type delay composition. Therefore, it is necessary to improve the oxidation resistance of tungsten powder. Single crystal tungsten powder (SCTP) is successfully prepared through hydrogen reduction at high temperature and short time, and anti-oxidative single crystal tungsten powder (ASCTP) is obtained by adopting carbonization with a carbon source of gas phase (Carbon monoxide), which enables fuller and more uniform reactions. The TEM results show that the surface of the SCTP is coated by the tungsten carbide, which forms synaptic structures on the surface of the SCTP to protect the SCTP from oxidation by surface modification. As a result, it has been confirmed through TG-DSC tests, oxidation experiments and related electrochemical tests that the oxidation resistance performance of the ASCTP is substantially improved compared with that of the SCTP.

Role and dynamics of transition metal carbides in methane coupling.

Transition metal carbides have numerous applications and are known to excel in terms of hardness, thermal stability and conductivity. In particular, the Pt-like behavior of Mo and W carbides has led to the popularization of metal carbides in catalysis, ranging from electrochemically-driven reactions to thermal methane coupling. Herein, we show the active participation of carbidic carbon in the formation of C2 products during methane coupling at high temperature that is associated with the dynamics of Mo and W carbides. A detailed mechanistic study reveals that the catalyst performance of these metal carbides can be traced back to its carbon diffusivity and exchange capability upon interaction with methane (gas phase carbon). A stable C2 selectivity over time on stream for Mo carbide (Mo2C) can be rationalized by fast carbon diffusion dynamics, while W carbide (WC) shows loss of selectivity due to slow diffusion leading to surface carbon depletion. This finding showcases that the bulk carbidic carbon of the catalyst plays a crucial role and that the metal carbide is not only responsible for methyl radical formation. Overall, this study evidences the presence of a carbon equivalent to the Mars-Van Krevelen type mechanism for non-oxidative coupling of methane.

NANO CARBON SYNTHESIS FROM MICROALGAE CHLORELLA VULGARIS AS PRECURSOR OF SOLID PHASE CARBON

Nanocarbon is a nanometer-scale substance made entirely of carbon atoms. Generally, the synthesis of nanocarbon is usually conducted using a gas-phase carbon raw material which is toxic. Therefore, the use of solid-phase carbon raw material to synthesize nanocarbon started to develop. In this research, nanocarbon will be synthesized using variations of solid-phase carbon raw material derived from a novel carbon precursor, microalgae Chlorella vulgaris . Nanocarbons produced were analyzed using SEM, XRD, and TEM. SEM analysis did not show the nanocarbon formed. However, this may be due to the nanocarbon being very small. To ensure whether nanocarbon is formed or not, XRD analysis is conducted. XRD analysis shows the possibility of forming carbon nanotubes from the sample with activated carbon as a raw material. There were peaks at diffraction angles of 24–26° and 42–43,5°, which indicated carbon nanotubes. In addition, the dc value of this sample has a value like carbon nanotubes, which is 0.344 nm. In contrast, the other two samples, which used hydrochar and microalgae as raw materials, only indicated activated carbon after the synthesis. The TEM analysis supported by XRD analysis for a sample with activated carbon as a raw material showed the presence of carbon nanotubes. This is indicated by their rope-like morphology, which is not visible in SEM analysis due to their tiny size. At the same time, the other two samples did not show any morphology indicating the presence of nanocarbon. So, it can be concluded that the synthesis of nano carbon has been successfully carried out using activated carbon as raw material and produces nano carbon with the type of carbon nanotubes.

Ultrahigh Metal Content Carbon-Based Catalyst for Efficient Hydrogenation of Furfural: The Regulatory Effect of Glycerol.

The development of high-content non-noble metal nanocatalysts is important for multiphase catalysis applications. However, it is a challenge to solve the agglomeration in the preparation of high-content metal catalysts. In this paper, a carbon-based catalyst (Co@CN-G-600) with 71.28 wt % cobalt metal content was prepared using a new strategy of gas-phase carbon coating assisted by glycerol. The core of this strategy is to maintain the spacing of metallic cobalt by continuous replenishment of dissociated ligands during pyrolysis over gas-phase glycerol. This approach is also applicable to other non-noble metals. When Co@CN-G-600 was further used as a catalyst for the selective hydrogenation of furfural (FF) to prepare furfuryl alcohol (FOL), the yield of FOL was >99.9% under mild conditions of 80 °C, compared to only 8.23% catalytic yield at up to 130 °C for Co@CN-600 without glycerol. The excellent catalytic performance mainly lies in the fact that the introduction of glycerol modulates the size effect, electronic effect, and acidic site intensity of the high-content Co catalyst, which promotes the activation of FF and hydrogen. Meanwhile, the optimized specific surface area and pore structure by glycerol improve the accessibility of high-density active sites and promote more efficient mass transfer. In addition, the introduction of glycerol produced a graphitic carbon layer encapsulation structure relative to Co@CN-600, which substantially improved the cycling stability of the catalyst. This study resolves the paradox of high content and high dispersion of non-noble metal catalysts in the synthesis process and provides a general pathway and example for the preparation of stable high-content metal catalysts.

Spraying Water Microdroplets Containing 1,2,3-Triazole Converts Carbon Dioxide into Formic Acid.

We report the use of 1,2,3-triazole (Tz)-containing water microdroplets for gas-phase carbon dioxide (CO2) reduction at room temperature. Using a coaxial sonic spraying setup, the CO2 can be efficiently captured by Tz and converted to formic acid (HCOOH; FA) at the gas-liquid interface (GLI). A mass spectrometer operated in negative ion mode monitors the capture of CO2 to form the bicarbonate anion (HCO3-) and conversion to form the formate anion (HCOO-). Varied FA species were successfully identified by MS/MS experiments including the formate monomer ([FA - H]-, m/z 45), the dimer ([2FA - H]-, m/z 91; [2FA + Na - 2H]-, m/z 113), the trimer ([3FA - H]-, m/z 137), and some other adducts (such as [FA - H + H2CO3]-, m/z 107; [2FA + Na - 2H + Tz]-, m/z 182). The reaction conditions were systematically optimized to make the maximum conversion yield reach over 80% with an FA concentration of approximately 71 ± 3.1 μM. The mechanism for the reaction is speculated to be that Tz donates the proton and the hydroxide (OH-) at the GLI, resulting in a stepwise yield of electrons to reduce gas-phase CO2 to FA.

An Infrared Laser Sensor for Monitoring Gas-Phase CO2 in the Headspace of Champagne Glasses under Wine Swirling Conditions

In wine tasting, tasters commonly swirl their glasses before inhaling the headspace above the wine. However, the consequences of wine swirling on the chemical gaseous headspace inhaled by tasters are barely known. In champagne or sparkling wine tasting, starting from the pouring step, gas-phase carbon dioxide (CO) is the main gaseous species that progressively invades the glass headspace. We report the development of a homemade orbital shaker to replicate wine swirling and the upgrade of a diode laser sensor (DLS) dedicated to monitoring gas-phase CO in the headspace of champagne glasses under swirling conditions. We conduct a first overview of gas-phase CO monitoring in the headspace of a champagne glass, starting from the pouring step and continuing for the next 5 min, with several 5 s swirling steps to replicate the natural orbital movement of champagne tasters. The first results show a sudden drop in the CO concentration in the glass headspace, probably triggered by the liquid wave traveling along the glass wall following the action of swirling the glass.

Carbon Abundances in Compact Galactic Planetary Nebulae: An Ultraviolet Spectroscopic Study with the Space Telescope Imaging Spectrograph (STIS)

We surveyed a sample of compact Galactic planetary nebulae (PNe) with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST) to determine their gas-phase carbon abundances. Carbon abundances in PNe constrain the nature of their asymptotic giant branch (AGB) progenitors, as well as cosmic recycling. We measured the carbon abundances, or the limits thereof, of 11 compact Galactic PNe, notably increasing the sample of Galactic PNe whose carbon abundance based on HST ultraviolet spectra is available. The dust content of most targets has been studied elsewhere from Spitzer spectroscopy; given the compact nature of the nebulae, both UV and IR spectra can be directly compared to study gas- and dust-phase carbon. We found that carbon-poor (C/O < 1) compact Galactic PNe have an oxygen-rich dust type, while their carbon-enhanced counterparts (C/O > 1) have carbon-rich dust, confirming the correlation between gas- and dust-phase carbon content that was known for Magellanic Cloud PNe. Based on models of expected final yields from AGB evolution, we interpret the majority of the carbon-poor PNe in this study as the progeny of ∼1.1–1.2 M ⊙ stars that experienced some extra mixing on the red giant branch. They went through the AGB but did not go through the carbon star phase. Most PNe in this group have a bipolar morphology, possibly due to the presence of a subsolar companion. The carbon-enhanced PNe in our sample could be the progeny of stars in the ∼1.5–2.5 M ⊙ range, depending on their original metallicity.

A study on the chemical looping combustion of sewage sludge: The emission of NOx and its precursors

Chemical looping combustion (CLC) is a promising low-NOx combustion technology for sewage sludge disposal. Herein, the emissions of NOx and its precursors (NH3 and HCN) during the pyrolysis and CLC processes are investigated on a fixed bed reactor. In particular, the effects of reaction (gas) temperature, sludge ash accumulation, and reaction intermediates (CO2 and H2O) are studied. When temperature increased from 800 to 900 °C, the content of gas-phase carbon is shown to increase from 57.9 to 79.7%. With ash accumulation, the NH3 generation rate increases from 10.8 to 11.7%, and the HCN generation rate decreases from 9.68 to 8.25%. Sludge ash accumulation is shown to promote the release of NH3, but inhibit the release of HCN and NOx. After 8 consecutive CLC cycles, the average removal efficiencies of NH3, HCN, and total N-containing pollutants are ~61%, ≥92%, and ~ 60%, respectively. The presence of CO2 and H2O in the reaction atmosphere is shown to enhance the oxidizability, thereby promoting the formation of NOx. In addition, char gasification and the reforming reaction of N-containing pollutants are promoted, thus leading to the formation of NOx precursors. Furthermore, NO is shown to be the predominant form of NOx in the CLC of sewage sludge.

Multichannel photodissociation dynamics in CS2 studied by ultrafast electron diffraction.

The structural dynamics of photoexcited gas-phase carbon disulfide (CS2) molecules are investigated using ultrafast electron diffraction. The dynamics were triggered by excitation of the optically bright 1B2(1Σu+) state by an ultraviolet femtosecond laser pulse centred at 200 nm. In accordance with previous studies, rapid vibrational motion facilitates a combination of internal conversion and intersystem crossing to lower-lying electronic states. Photodissociation via these electronic manifolds results in the production of CS fragments in the electronic ground state and dissociated singlet and triplet sulphur atoms. The structural dynamics are extracted from the experiment using a trajectory-fitting filtering approach, revealing the main characteristics of the singlet and triplet dissociation pathways. Finally, the effect of the time-resolution on the experimental signal is considered and an outlook to future experiments provided.

Effect of thermodynamic parameters on properties of silicon-carbon films prepared by radio-frequency plasma-enhanced chemical vapor deposition for anti-reflective and photo-luminescent coatings

This work reports an experimental study on the synthesis of hydrogenated amorphous silicon-carbon (a-SiC:H) films with improved antireflective and photo-luminescent characteristics. These films were prepared by plasma-enhanced chemical vapor deposition at a radio frequency of 13.56 MHz, varying the thermodynamic parameters of pressure, gas flows, and temperature. Silane (SiH4), methane (CH4), and hydrogen (H2) were the precursor gases. In a first experiment, composition in gas phase was varied and correlated to the composition in solid phase. Absorption spectra, conductivity, refractive index, optical gap, and photoluminescence (PL) were analyzed. Optical gap and fraction of carbon in gas phase showed a linear dependence with the atomic fraction of carbon in solid phase. Results indicated that the Si0.4C0.6 alloy exhibited a high PL as well as an optimal combination of optical gap and refractive index to be applied as antireflective coating. The subsequent optimization of PL was carried out by a fractional experiment, by varying pressure, H2 flow, and temperature. Results revealed that PL can be improved at high pressure, without H2 flow, and low temperature during glow discharge. Enhancement of PL was correlated to the proper concentration of silicon and carbon in the films, low dark conductivity, negative AM 1.5 conductivity, fluctuating current at low voltage, the increment of Si−H2, C−H2, and C=C bonds, along with vibrational energies in the range of 3190–3585 cm−1.

Open-atmosphere flame synthesis of monolayer graphene

An open-atmosphere, unconfined setup comprising a novel multiple inverse-diffusion flame (m-IDF) burner modified with extended precursor tubes is employed to synthesize graphene on substrates. Growth conditions of mono-, bi-, and few-layer graphene (MLG, BLG, and FLG, respectively) are investigated, with systematic variation of parameters such as substrate temperature, methane-to-hydrogen volume flow rate ratio (JCH4:JH2), growth duration, post-flame flow profiles, substrate material, precursor species (e.g., CH4, C2H2, C2H4), and in-situ post-growth hydrogen annealing. Graphene growth on copper is observed for a wide range of temperatures from 850 °C to 1000 °C, with high-quality BLG created at a substrate temperature of 1000 °C with JCH4:JH2 of 1:100 for 5 min growth duration. A sequential in-situ post-growth hydrogen annealing treatment, where the hydrocarbon precursor flow is terminated but the hydrogen m-IDFs are maintained, is found to be effective for etching adlayers of graphene. As such, BLG is reduced to MLG by increasing the post-growth hydrogen annealing duration at 1000 °C to 10 min. In-situ gas-phase Raman measurements characterize the evolution of the gas-phase precursor species in the synthesis flow field. CH2 is determined to be the main gas-phase carbon species needed near the substrate to form graphene in our flame synthesis system.