Carbon Clusters Research Articles

Oxidized Activated Charcoal Nanozymes: Synthesis, and Optimization for In Vitro and In Vivo Bioactivity for Traumatic Brain Injury.

Carbon-based superoxide dismutase (SOD) mimetic nanozymes have recently been employed as promising antioxidant nanotherapeutics due to their distinct properties. The structural features responsible for the efficacy of these nanomaterials as antioxidants are, however, poorly understood. Here, the process-structure-property-performance properties of coconut-derived oxidized activated charcoal (cOAC) nano-SOD mimetics are studied by analyzing how modifications to the nanomaterial's synthesis impact the size, as well as the elemental and electrochemical properties of the particles. These properties are then correlated to the in vitro antioxidant bioactivity of poly(ethylene glycol)-functionalized cOACs (PEG-cOAC). Chemical oxidative treatment methods that afford smaller, more homogeneous cOAC nanoparticles with higher levels of quinone functionalization show enhanced protection against oxidative damage in bEnd.3 murine endothelioma cells. In an in vivo rat model of mild traumatic brain injury (mTBI) and oxidative vascular injury, PEG-cOACs restore cerebral perfusion rapidly to the same extent as the former nanotube-derived PEG-hydrophilic carbon clusters (PEG-HCCs) with a single intravenous injection. These findings provide a deeper understanding of how carbon nanozyme syntheses can be tailored for improved antioxidant bioactivity, and set the stage for translation of medical applications.

Density Function Theory Predicted Carbon Allotropes: Recent Developments

AbstractThe most recent data on experimentally undiscovered carbon allotropes, predicted by the Density Function Theory (DFT), are reviewed. Classic carbon allotropes, graphenes, carbon nanotubes, fullerenes and their hybrids are being studied using DFT and related methods, resulting a host of potentially existing forms based on 5‐, 6‐, 7‐member cycles and their distinct combinations. Also known are cyclocarbons and large carbon clusters, nanobelts and nanoribbons, liquid, metallic, semiconductive and superhard carbons, which could exist under high or low pressures. These carbon allotropes can contain C atoms in the same hybridization state or be as their mixture, for example sp2+sp3. For several carbon allotropes, possible synthesis methods, properties and applications are proposed.

A parametric optimization approach for radial shaft seal production processes for rubber waste reduction

While engineered rubber products (ERP) offer excellent mechanical and thermal properties suited for demanding industrial applications, the diversity of materials, equipment and processes involved in their processing poses challenges to their cleaner production. Existing literature canvasses recycling and reusing of products at the end-of-life (EOL) stage of the ERP life cycle to control their environmental impact. This research is focused on modes of reducing waste generated in the ERP production processes to minimize the environmental impact at the production stage of the life cycle. A novel experimental procedure grounded on the Shainin System (SS) principles is developed for parametric optimization in complex batch process settings. Unlike the established design of experiment (DoE) approaches based on statistical models, the proposed experimental procedure is based on sequential observational plans to reduce the search space while identifying the dominant family(ies) of causes (called Red X) of niggling defects. The application of the proposed experimental procedure is illustrated at an auto-ancillary cluster in India for reducing the rejection of radial shaft seals (RSS) due to rubber moulding defects. The case study's findings showed a reduction in the cluster's carbon footprint (i.e. 11,715 kg CO2-eq across the cluster), and overall production cost (saving of USD 1.20 million/annum) due to process improvements in the RSS moulding and assembly process.

Reduction of amorphous carbon clusters from the highly disordered and reduced graphene oxide NPs by acoustical shock waves — Towards the formation of highly ordered graphene

The journey of exploring the acoustical shock wave-induced solid state phase transitions on polymorphic and allotropy materials have gained enormous momentum in recent years after the invention of the tabletop Reddy tube, but, the knowledge of shock wave-induced phase transitions on allotropy materials is very limited in comparison to the polymorphic materials. Hence, in this framework, we report the shock wave-induced transitions based on the reduction of the amorphous carbon clusters in the highly disordered and reduced graphene oxide nanoparticles (rGO NPs) [rGO — is also called as modified graphene]. The reduction of the disordered carbon in the rGO NPs under shocked conditions is examined by the techniques such as X-ray diffractometry and Raman spectrometer. X-ray crystallographic studies clearly present that as the shock pulses are increased, the intensity of the (002) peak is increased for which the authentication is observed by the Raman spectral analyses wherein it is clearly indicated the decrement and increment of the D and G bands against the exposure of the shock pulses thereby the ID/IG ratios are found to be 1.24, 1.17, 1 and 0.927 for 0, 100, 200 and 400 shocks, respectively. According to the Raman spectral results, the area of the amorphous Raman peak is reduced against the shock pulses such that the values are 98, 82, 81 and 48 for the 0, 100, 200 and 400 shocks, respectively. The removal of amorphous carbon clusters in the rGO NPs can be explained on the basis of the conversion of sp3 to sp2 hybridizations based on the shock wave induced hot-spot nucleation mechanism.

Emission spectra of fullerenes: Computational evidence for blackbody-like radiation due to structural diversity and electronic similarity

The spectral emission of hot ${\mathrm{C}}_{60}$ has been experimentally shown to be broad and continuous, in apparent contradiction with the discrete and narrow absorption spectrum associated with the high symmetry of buckminsterfullerene. In the present work we computationally model the emission spectrum of isolated carbon clusters, assuming a broad distribution of isomers that are likely populated under the experimental conditions. The contributions of individual structures to the global spectrum correspond to the relaxation via recurrent fluorescence and vibrational emission, electronic and vibrational structures being described by a simple but efficient density-functional-based tight-binding scheme. The model predicts a blackbody-like emission spectrum that is naturally broad and correctly accounts for the experimental measurements, except for a maximum that is quantitatively shifted with respect to Wien's displacement law. To quantify such differences, we introduce an emissivity parameter $\ensuremath{\varepsilon}$ as the ratio between the spectral emittance and the corresponding exact blackbody spectrum; $\ensuremath{\varepsilon}$ is numerically found to scale as ${(\ensuremath{\lambda}T)}^{\ensuremath{-}2}$ at leading order with increasing temperature $T$ and for wavelengths $\ensuremath{\lambda}>350$ nm, and we provide a theoretical justification for this behavior. Our results are discussed in the light of the astrophysical detection of interstellar fullerenes, as well as in combustion environments where carbon clusters are relevant in the context of nascent soot particle formation.

Reversible Hydrogen Storage by Planar Hypercoordinate Carbon Clusters

Planar hypercoordinate carbon clusters show a high capacity of hydrogen storage with better stability, as revealed by using density functional theory. The interaction energy of H2 with the cluster lies in between chemisorption and physisorption (0.11–0.19 eV). Topological analysis indicates closed shell-type interaction of H2 with the clusters. The clusters remain stable before and after adsorption. The gravimetric densities are found to be 25.6, 39.7, and 13.5 wt % for planar tetracoordinate, pentacoordinate, and hexacoordinate clusters, respectively. Furthermore, Born–Oppenheimer molecular dynamics simulations indicate the reversibility of adsorption. The clusters can accommodate a large number of H2 molecules and can be released at an elevated temperature (400 K). Our computation reveals that the planar clusters may be used as ideal 2D materials for energy storage.

An approach of repairing concrete vertical cracks using microbially induced carbonate precipitation driven by ion diffusion

Microbially induced carbonate precipitation (MICP) is an eco-friendly method of repairing cracks in concrete. However, for vertical cracks appeared in concrete components, the microbial mineralization solution injected into cracks tends to flow out due to gravity, resulting in incomplete crack repair. To address this obstacle, this study presents a novel approach in repairing vertical cracks using MICP with the ingression of calcium and urea driven by ion diffusion. For this purpose, a combined injection and diffusion method (CIDM) is proposed, in which the bacterial solution (ureolytic bacterium Sporosarcina Pasteurii) was first injected into crack and then the crack surface was adhered with a sponge containing the saturated cementation solution (urea and calcium acetate) for continuous ion diffusion. In comparison, the traditional injection method (TIM) is also conducted on the test cylindrical specimens. In addition to the pre-cracked concrete cylinders, four transversely load-induced cracked concrete beams were also utilized in this study and their vertical cracks were treated with CIDM under both loading and unloading conditions. The crack repair effects are evaluated by means of surface observations, microanalysis, water absorption tests and chloride penetration tests. Test results indicate that the proposed CIDM, whereby the calcium and urea are supplied through an ion diffusion approach, is a more effective method to repair vertical cracks than TIM. The generated white precipitations in cracks are confirmed to be calcium carbonate crystals existed in form of vaterite through energy dispersive spectrum (EDS) and X-ray diffraction (XRD) examinations, which also indicate that the CIDM method tends to produce a denser calcium carbonate cluster structure. After crack repairing with CIDM, the improvement coefficients of waterproof performance for the pre-cracked cylinders with widths of 0.1, 0.2 and 0.4 mm are 84.2%, 81.2% and 73.6%, respectively, which is 6%–12% higher than those got from TIM method. Furthermore, the average improvement coefficients of resistance to chloride penetration for vertical cracks with widths from 0.085 mm to 0.162 mm are about 76.9% and 88.5% for the sustain-loaded beams and unloaded beams, respectively.

Evaluation of Molecular Fragmentation in Polycyclic Aromatic Hydrocarbons by Time-of-Flight Secondary Ion Mass Spectrometry

In time-of-flight secondary ion mass spectrometry (TOF-SIMS), ionized molecules and molecular fragments (secondary ions) are generated in collisions of high-energy ions (primary ions) with a solid sample surface. Mass spectra of the emitted secondary ions are typically used to identify molecular species and to determine their spatial distribution on the sample surface. Here, we extend this application in a TOF-SIMS study of a series of polycyclic aromatic hydrocarbons (PAHs) where we focus on the fragmentation of these molecules, with the purpose of better understanding the fragmentation patterns of heavy aromatic molecules in petroleum. For all PAHs, the collision process generated (i) a series of smaller cation fragments and (ii) cations close in size to the original PAH (molecular cations). Stark differences are measured for various PAHs regarding the abundance of smaller fragments versus molecular cations. Observation of hydrogen-deficient (H-deficient) cation fragments indicates the formation of polyynes and allenes. For PAHs producing higher fractions of small cation fragments, these ions are surprisingly hydrogen rich (H-rich). The H/C ratio of fragments does not scale with the fraction of Clar sextet carbon, nor with energies of low-lying electronic transitions. Free radical cation fragments tend to be suppressed. For sufficiently large fragments, aromatic cations appear to be formed and include some free radical aromatics. There is ample production of molecular ions with loss of a single carbon atom or a methine group, which corresponds to the reduction of a 6-membered aromatic ring to a 5-membered ring. There is some enhancement of free radical molecular cations due to the corresponding formation of neutral polyynes. Fragment anions are also produced with a strong preference for very H-deficient carbon clusters, in some cases being the same as carbon cluster anions observed in space. Comparisons of PAH TOF-SIMS spectra with those of asphaltenes are discussed in detail.

Reactive force-field MD simulation on the pyrolysis process of phenolic with various cross-linked and branched structures

Based on the reactive force-field (ReaxFF) molecular dynamics, the thermostability of cross-linked and non-cross-linked phenolic was compared to study the effect of cross-linked and branched structures on the pyrolysis mechanism. The results show that during the pyrolysis process, phenolic tends to break into low-boiling molecules with less than 4 carbon atoms and polymerizes into macromolecules with more than 1500 carbon atoms. The results of residual carbon rate and products distribution confirm that carbon skeleton of phenolic resin with high degree of crosslinking and branching is better preserved and has better thermostability. The reaction kinetics path of phenolic pyrolysis was reasonably summarized, revealing the generation mechanism of low-boiling molecules with less than 4 carbon atoms and large carbon clusters, which is in good agreement with the experimental results of activation energy and chemical bond energy. The reaction kinetics data obtained in this work provide a reliable basis for multi-scale reaction simulation.

Study of the wavelength dependence of the absorption function of diesel soot by LII modeling integrating the effect of multiple scattering within aggregates

This work represents a first attempt at proposing a refined LII model suitable for simulating signals collected with excitation wavelengths (EWs) of 266, 355, 532 and 1064 nm. In this context, we implemented a comprehensive version of laser-irradiated soot heat and mass balance equations integrating terms representing the saturation of linear, single- and multi-photon absorption processes, cooling by sublimation, conduction, radiation and thermionic emission, as well as mechanisms depicting soot oxidation and annealing, non-thermal photodesorption of carbon clusters and corrective factors accounting for the shielding effect and multiple scattering (MS) within aggregates. This simulation tool was fully parameterized, by coupling design of experiments with a genetic algorithm-based solver, against data collected at different heights above the burner (HAB) in a diesel spray flame. This allowed to assess values of different model parameters involved in absorption and sublimation terms, which, to date, have never been reported in LII modeling studies for UV EWs (e.g., multi-photon absorption cross sections for C2 photodesorption and saturation coefficients for linear- and multi-photon absorption). The simulation work proposed herein then enabled to infer information regarding the evolution of the absorption function of soot (Eleft(m,lambda right)). Eleft(m,266right), E(m,355) and E(m,532) ranging from 0.25 to 0.51, 0.20 to 0.38 and 0.18 to 0.30, respectively, were notably estimated as a function of the HAB. Alternatively, values ranging from 0.31 to 0.53, 0.26 to 0.44 and 0.22 to 0.38 were assessed while neglecting the effect of MS and provided constant E(m,266)/E(m,1064), E(m,355)/E(m,1064) and E(m,532)/E(m,1064) ratios of 1.4, 1.2 and 1.0, regardless of the HAB. In addition, the obtained results showed that the wavelength dependence of the soot absorption function was quite negligible for EWs higher than 532 nm, irrespective of whether the effect of MS was considered or neglected. On the other hand, aggregate properties were proven to substantially influence the E(m,lambda )/E(m,1064) ratios for decreasing lambda and increasing HAB, thus illustrating the significant effect of aggregation on the optical properties of soot. Finally, the results issued from the different analyses we conducted on the diesel flame investigated in this paper led to the conclusion that values of Eleft(m,lambda right), falling within the 0.38 ± 0.15 and 0.29 ± 0.11 range at 266 and 355 nm, versus 0.25 ± 0.09 at 532 and 1064 nm could be considered as suitable for simulating LII signals of progressively aging aggregated particles.

Part B: Improvement of the Optical Properties of Cellulose Nanocrystals Reinforced Thermoplastic Starch Bio-Composite Films by Ex Situ Incorporation of Green Silver Nanoparticles from Chaetomorpha linum.

The study was used in the context of realigning novel low-cost materials for their better and improved optical properties. Emphasis was placed on the bio-nanocomposite approach for producing cellulose/starch/silver nanoparticle films. These polymeric films were produced using the solution casting technique followed by the thermal evaporation process. The structural model of the bio-composite films (CS:CL-CNC7:3-50%) was developed from our previous study. Subsequently, in order to improve the optical properties of bio-composite films, bio-nanocomposites were prepared by incorporating silver nanoparticles (AgNPs) ex situ at various concentrations (5-50% w/w). Characterization was conducted using UV-Visible (UV-Vis), Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) to understand the structure-property relationships. The FTIR analysis indicated a reduction in the number of waves associated with the OH functional groups by adding AgNPs due to the formation of new hydrogen bonds between the bio-composite matrix and the CL-WE-AgNPs. Based on mathematical equations, the optical bandgap energy, the energy of Urbach, the edge of absorption (Ed), and the carbon clusters (N) were estimated for CS:CL-CNC and CS:CL-CNC-AgNPs (5-50%) nanocomposite films. Furthermore, the optical bandgap values were shifted to the lower photon energy from 3.12 to 2.58 eV by increasing the AgNPs content, which indicates the semi-conductor effect on the composite system. The decrease in Urbach's energy is the result of a decrease in the disorder of the biopolymer matrix and/or attributed to an increase in crystalline size. In addition, the cluster carbon number increased from 121.56 to 177.75, respectively, from bio-composite to bio-nanocomposite with 50% AgNPs. This is due to the presence of a strong H-binding interaction between the bio-composite matrix and the AgNPs molecules. The results revealed that the incorporation of 20% AgNPs into the CS:CL-CNC7:3-50% bio-composite film could be the best candidate composition for all optical properties. It can be used for potential applications in the area of food packaging as well as successfully on opto-electronic devices.

DFT Study on the Oxidation Mechanism of Common Cyclic Carbonates in the Presence of BF4– Anions

Oxidative decomposition reactions of common cyclic carbonates in the presence of BF4- anions were investigated using density functional theory. A polarized continuum model was utilized to model solvent effects in the oxidation of ethylene carbonate (EC) and propylene carbonate (PC) clusters. We have found that the presence of BF4- significantly reduces EC and PC oxidation stability, from 7.11 to 6.17 and from 7.10 to 6.06 V (vs Li+/Li), respectively. The sequence of EC and PC oxidative decomposition paths and the oxidative products were affected by the BF4- anion. The decomposition products of the oxidized EC-BF4- contained CO2, vinyl alcohol, and acetaldehyde, while the decomposition products of the oxidized PC-BF4- contained CO2, acetone, and propanal, in agreement with the previous experimental studies. The oxidative decomposition reactions for PC-BF4- are compared with those for the isolated PC, PC2, PC-ClO4-, and PC-PF6-.

The stability and reactivity of neutral and charged aluminium doped carbon clusters (Al1,2C2-70,±)

The stability and reactivity of Al-doped linear and quasi-linear carbon chains (Al1,2C2-70,±) were computationally investigated using various reaction and binding energy parameters. The dissociation of the clusters was studied via the elimination of Al, C from the neutral species, Al0,+, C0,+ the cationic species, and Al0,-, C0,- from the anionic species. The stability was further examined based on electron elimination reactions, such as electron detachment from Al1,2C2-7- and ionization of Al1,2C2-7. The study proceeded by formulating a novel relative energy parameter, which was generated from the binding energy values. The lowest energy dissociation channels of Al1,2C1-70,± were the Al and Al+ elimination from the neutral/anionic and cationic clusters, respectively. Under the dissociation conditions, the even-carbon species (m = 2,4,6) AlCm (doublet), AlCm+ (triplet), AlCm- (singlet), Al2Cm (singlet), Al2Cm+ (doublet) were found to be more stable than that of the odd-carbon clusters (m = 3,5,7), irrespective of the spin states. In the case of Al2Cm-, the odd carbon clusters were found to be more stable. The stability orders based on the widely used highly endothermic C-elimination reaction were found to be significantly different. We have systematically addressed the above disparities and have commented on how to accurately predict the abundance of the species under extreme experimental conditions. The reactivity of Al1,2-doped clusters was found to be higher than the bare carbon chains. Based on the bond-strength parameters calculated using AIM analysis, the Al1,2-doping led to an activated Al-C bond rather than the carbon chains, eventually resulting in reactive meal-carbon clusters. The Al-C bonding was discussed using electron density at the Al-C bond critical points (ρAl-C), the vibrational frequency of the Al-C bond (νAl-C), bond length (rAl-C), the NBO charge on the Al atoms (qAl) and with the molecular orbital diagrams. The results of the current investigations can be highly relevant to astrochemistry, spectroscopy, material, and organometallic chemistry communities.

Decoupling effects of C3H3/C4H5/i-C4H5/CN radicals on the formation and growth of aromatics: A ReaxFF molecular dynamics study

This paper demonstrates the effects of C3H3/C4H5/i-C4H5/CN radicals on the formation and growth of aromatic hydrocarbons, particular types of polycyclic aromatic hydrocarbons (PAHs) such as heavier-PAHs, cyclopentafused PAHs (CP-PAHs), through reactive force field molecular dynamics simulations under 2250K and 2500K. Adding non-acetylene radicals enhanced the early-stage mass growth of aromatics to varying degrees. However, the later-stage mass growth and aromaticity degree were weakened by adding radicals except for the C3H3 radical. The reactivity of acetylene and additional radicals showed that the additional C3H3 radicals accelerated the consumption of radical pools, and the interaction reaction between C3H3 was responsible for the consumption of radical pools for the C3H3 additive case. The consumption of i-C4H5 was significantly faster than that of C4H5, whereas the consumption of acetylene in the two simulation cases was essentially the same. Thus, the i-C4H5 simulation case formed more intermediate species C6H7 than C4H5 radical. As for the formation of less-studied PAHs, i-C4H5 radicals generated more heavier PAHs and CP-PAHs than straight butyl C4H5 isomers. Finally, the effect of nitrogen-containing radical CN, which normally resides in ammonia fuel, was analyzed. Several factors explained the stronger enhancement in aromatic mass growth, but the relatively lowest aromatization degree resulted from the additional CN radicals. The reactions between CN and acetylene formed carbon–nitrogen species that participated less in the formation and growth of aromatics. The potential reactions between CN radical and aromatics led to ring-opening reactions and the formation of nitrogen-membered rings, which accelerated the mass growth of carbon clusters but inhibited the development of aromaticity degree. The least amount of CP-PAHs was found in CN cases compared with hydrocarbon radical cases.

Transition from carbon clusters to ε, θ-carbides in a quenched and aged low-carbon ferritic steel

Carbon redistribution is one of the fundamental issues in quenched and aged carbon steels, which results in carbon clustering and carbide precipitation. Carbon clusters and carbides act as obstacles for dislocations, which have been known closely correlated with strengths of steels. In this study, conventional TEM, atomically-resolved TEM and In-situ heating TEM observations were carried out to understand carbon redistribution in a low-carbon ferritic steel aged at 473 K. Some ε-carbides were uniformly precipitated in the matrix, and the others were heterogeneously precipitated along dislocations. These ε-carbides were coexisted with carbon clusters with c/a ratio of 1.1, assumed to be the formation of Zener-ordered Fe8C. Moreover, θ-carbides were found precipitated from ε-carbides via dissolution of ε-carbides, confirmed by In-situ heating TEM experiments. These results suggested that Zener ordering should be the fundamental step for the following carbide precipitation sequences in the steel aged at 473 K.

Novel bake hardening mechanism for bainite-strengthened complex phase steel

• Yield strength of materials can be greatly improved after pre-strain and baking. • Dislocation as fast channels for carbon diffusion promotes cementite formation. • Carbon clusters gathered at the dislocations act as precursors of cementite. • Cementite precipitation is main reason for increase in strength of bainite steel. In the automobile industry, stamping and paint baking processes are used to strengthen components, and this not only saves costs, but also further reduces the bodyweight of automobiles. In this work, the bake hardening mechanism of the complex phase (CP) steel CP980 was explored by comparing it with that of DP1180, which has a clear bake hardening mechanism and a carbon content similar to that of CP980. By analyzing the bake hardening response and the microstructural changes of the two steels, we found that the bake hardening process of CP980 was divided into three stages. In the first two stages, the carbon atoms diffused into dislocations to form Cottrell atmosphere pinning dislocations, and excess carbon atoms formed carbon clusters or low-temperature carbide pinning dislocations that were similar to DP1180. In the third stage, the dislocation acted as rapid channels for carbon diffusion, and fine cementite gradually formed when the carbon clusters gathered at the dislocations as precursors, resulting in precipitation hardening. This novel bake-hardening (BH) mechanism is crucial for obtaining a comprehensive understanding of the strain-baking behavior of advanced high-strength steals (AHSS).

Carbon Migration Behavior during Rolling Contact in Tempered Martensite and Retained Austenite of Carburized SAE4320 Steel

The changes in the state of carbon in tempered martensite and retained austenite in carburized SAE4320 steel under the rolling contact fatigue (RCF) were investigated using atom probe tomography (APT). In the tempered martensite, the carbons in solid solution and in carbon cluster were readily transferred to the preexisting metastable (ε) carbide due to rolling contact, resulting in a localized change from tempered martensite to ferrite accompanied by the growth of carbides. This supports the recently proposed dislocation assisted carbon migration theory. On the other hand, retained austenite with uniformly distributed enriched solute carbon was partially transformed into the very fine deformation-induced martensite due to rolling contact. Furthermore, carbon seemed to be partitioned into retained austenite from the deformation-induced martensite during further rolling contact cycles. This is a new insight into the characteristics of deformation-induced martensite and retained austenite generated by rolling contact. The present study provides a plausible explanation to the phenomenon that the deformation-induced martensitic transformation improves the RCF life.

Changes in Land Use Carbon Emissions and Coordinated Zoning in China

Carbon emissions from land use changes have become one of the main sources of regional carbon emissions. In order to explore its changes, based on the MCD12Q-LUCC data of MODIS from 2001 to 2019 using the carbon emission coefficient method, clustering, and outlier analysis method, the spatial characteristics of land use carbon emissions in various provinces in China in the past 19 years were discussed from the perspectives of carbon emission economy contributive coefficient, carbon ecological support coefficient, and their coupling and coordination relationship. The results showed that:① from 2000 to 2019, the national land use carbon emissions increased significantly; however, after 2011, the growth rate of carbon emissions became flat, whereas the growth of carbon sinks was relatively slow, and the gap between the two was still large. ② Clustering and outlier analysis showed that during the study period, the high-value agglomeration centers of land use carbon emissions in various provinces and cities across the country shifted from Guangdong, Jiangsu, and other provinces to Hebei, Shanxi, Inner Mongolia, and other provinces, and the agglomeration status became increasingly obvious. ③ The economy contributive coefficient of carbon emissions in all provinces and cities across the country had the spatial characteristics of being high in the south and low in the north, and the ecological support coefficient gradually developed from high in the west to low in the east, followed by that in the north, and the coupling coordination between the two showed a downward trend. ④ Based on the economy contributive of carbon emissions and carbon ecological support, this study divided the provinces into four categories:low-carbon maintenance area, economic development area, carbon sink development area, and comprehensive optimization area. We also put forward our own development suggestions, striving to achieve carbon neutrality and low-carbon sustainable development.

Study on surface thermal oxidation of silicon carbide irradiated by pulsed laser using reactive molecular dynamics.

Pulsed lasers are a powerful tool for fabricating silicon carbide (SiC) that has a hard and brittle nature, but oxidation is usually unavoidable. This study presents an exploration of the oxidation mechanism of 4H-SiC in oxygen and water under different temperatures via reactive force field molecular dynamics. Single pulse irradiation experiments were conducted to study the oxygen content of the laser-affected zone through energy dispersive x-ray spectrometry. The results show that laser-induced thermal oxidation is a complex dynamic process with the interactions among H, C, O, and Si atoms. The oxidation zone includes an oxide layer, a graphite layer, and a C-rich layer. With an increase in oxygen concentration, the amorphous oxide layer changes from silicon oxide to silicon dioxide. In addition, the formation of carbon clusters at the interface between SiOx and C-rich layers promotes the desorption of the oxide layer. The mechanism revealed in this study provides theoretical guidance for high-quality processing of 4H-SiC at atomic and close-to-atomic scales.

A plausible molecular mechanism to explain near-infrared continuum emission: Recurrent fluorescence

Context. Very small grains and large hydrocarbon molecules are known to convert a fraction of the ultraviolet (UV) and visible stellar radiation to near- and mid-infrared (IR) photons via stochastic heating and subsequent radiative de-excitation. However, no convincing explanation for the near-IR continuum emission observed in some reflection nebulae and planetary nebulae has been provided so far. Aims. We aim to investigate the extent that recurrent fluorescence originating from stellar photon absorption by Cn (n = 24, 42, 60) carbon clusters can account for the IR emission detected in various interstellar environments. To this aim, we modelled the collective emission signature of a carbon cluster sample induced by irradiation from a 20 000 K blackbody source. From the obtained results, we set out to determine the fraction of interstellar carbon locked up in the emitting objects. Methods. The collective emission signature was computationally determined for different structural families encompassing cages, flakes, pretzels, and branched isomers by means of a kinetic Monte Carlo stochastic approach based on harmonic vibrational densities of states. The collective emission spectra result from the overall radiative cooling of a large population of neutral carbon clusters, during which recurrent fluorescence and vibrational emission compete with each other. Results. Our modelling shows that recurrent fluorescence from C60 cages and flakes (with little or no sp1 carbon atoms) and C42 cages are able to explain the near-IR continuum emission observed in several reflection nebulae and planetary nebulae. Assuming that the continuum emission observed towards NGC 7023 is due to recurrent fluorescence induced by UV or visible photon absorption in neutral cage carbon clusters containing about 30–60 atoms, the carriers contain about 0.1–1.5% of the interstellar carbon abundance.