Carbonaceous Precursor Research Articles

Insight into the Pyrolysis Behaviors of Petroleum-Driven Mesophase Pitch via ReaxFF Molecular Dynamics and In Situ TG-FTIR/MS.

Mesophase pitch is regarded as a profoundly promising candidate for the production of advanced carbon-based multifunctional materials such as carbon fibers, carbon microspheres, and carbon foams owing to its excellent intrinsic properties. Consequently, a deeper understanding of pyrolytic chemistry is indispensable for the efficient and environmentally friendly utilization of mesophase pitch. In this study, details about the structure compositions and microscopic morphologies of petroleum-driven mesophase pitch (pMP) were investigated through ultimate, FTIR, XPS, and 13C-NMR analyses. Furthermore, a large-scale molecular model of typical pMP with 11,835 atoms was constructed to unveil the comprehensive pyrolysis behaviors and the underlying reactions. Significantly, the evolution of specific chemical bonds and the decomposition of crucial molecular fragments were elucidated within an amalgamation of experimental TG-FTIR/MS and ReaxFF MD simulation. Accordingly, three fundamental reaction stages were artificially divided, including the low-temperature reaction, rapid thermal decomposition, and the molecular condensation reaction. During the rapid thermal decomposition stage, the cleavages of C-C and C-O bonds cooperatively contributed to the formation of C2H4 and H2O gaseous products. As the temperature escalated to the molecular condensation stage, the pyrolysis process was governed by the dehydrogenation condensation, accompanied by an augmentation of C-C and H-H bonds and a diminution of C-O and C-H bonds. Additionally, the rare graphitization phenomenon was observed, suggesting a remarkable degree of structural organization in pMP. Overall, the results of ReaxFF MD simulations complement experimental observations, successfully reproducing the microstructure of pMP and atomic-scale pyrolysis behavior, thereby providing invaluable insights for the rational guidance of efficient utilization of pMP and other related carbonaceous precursors.

Hemicellulose-Based Sensors: When Sustainability Meets Complexity.

Hemicelluloses (HCs) are promising sustainable biopolymers with a great natural abundance, excellent biocompatibility, and biodegradability. Yet, their potential sensing applications remain limited due to intrinsic challenges in their heterogeneous chemical composition, structure, and physicochemical properties. Herein, recent advances in the development of HC-based sensors for different chemical analytes and physical stimuli using different transduction mechanisms are reviewed and discussed. HCs can be utilized as carbonaceous precursors, reducing, capping, and stabilizing agents, binders, and active components for sensing applications. In addition, different strategies to develop and improve the sensing capacity of HC-based sensors are also highlighted.

Demystifying In Situ Pyrolysis Chemistry for High-Performance Polyanionic Cathodes in Sodium-Ion Batteries.

The carbon coating strategy has emerged as an indispensable approach to improve the conductivity of polyanionic cathodes. However, owing to the complex reaction process between precursors of carbon and cathode, establishing a unified screening principle for carbonaceous precursors remains a technical challenge. Herein, we reveal that carbonaceous precursor pyrolysis chemistry undeniably influences the formation process and performance of Na3V2(PO4)3 (NVP) cathodes from in situ insights. By investigating three types of carbonaceous precursors, it is found that O/H-containing functional groups can provide more bonding sites for cathode precursors and generate a reducing atmosphere by pyrolysis, which is beneficial to the formation of polyanionic materials and a uniform carbon coating layer. Conversely, excessive pyrolysis of functional groups leads to a significant amount of gas, which is detrimental to the compactness of the carbon layer. Furthermore, the substantial presence of residual heteroatoms diminishes graphitization. In this case, it is demonstrated that carbon dots (CDs) precursors with suitable functional groups can comprehensively enhance the Na+ migration rate, reversibility, and interface stability of the cathode material. As a result, the NVP/CDs cathode displays outstanding capacity retention, maintaining 92% after 10,000 cycles at a high rate of 50 C. Altogether, these findings provide a valuable benchmark for carbon source selection for polyanionic cathodes.

Bi-reforming of model biogas to syngas over ultrasmall Ru/MgO nano-catalysts prepared via soft template-assisted mechanochemical method

The upgrading of renewable biogas into value-added fuel and chemicals via syngas is of great significance. Ru/MgO nano-catalysts were prepared via novel soft template-assisted mechanochemical method. Comprehensive characterizations (XRD, N2 physisorption, ICP-OES, CO-chemisorption, CO2-TPD, XPS, HAADF-STEM, HRTEM, CH4-TPSR/CO2-TPO, TGA and Raman spectroscopy, etc.) were conducted to deeply analyze the fresh/spent catalysts. The 0.2Ru/MgO-0.2CTAB catalyst showed high initial activity in terms of CH4/CO2 conversion (∼94 %/61 %) and maintained catalytic stability over 120 h in bi-reforming of model biogas, at 800 °C under CH4/CO2/N2/H2O molar ratio of 3:2:1:2.6 and weight hourly space velocity of 30960 mL g-1h−1. CTAB and other soft templates were effective in enhancing the dispersion of Ru nanoparticles (NPs), which contribute to the inhibition of the deep cracking of CH4 and coke accumulation. Alkaline MgO oxide was crucial in the activation of CO2 and the production of active O* species, thus promoting the removal of carbonaceous precursor and inhibiting the coke accumulation. Additionally, the strong interaction between ultrafine Ru NPs and the MgO support significantly contributed to its anti-sintering performance. The combined advantages of narrow size distribution of ultra-small Ru NPs, suitable basicity of MgO as well as the interaction between ultrafine Ru NPs and MgO over 0.2Ru/MgO-0.2CTAB catalyst led to satisfying catalytic performance in bi-reforming of model biogas.

Synthesis of nitrogen-doped amorphous carbon nanotubes from novel cobalt-based MOF precursors for improving potassium-ion storage capability

Amorphous carbon materials with sophisticated morphologies, variable carbon layer structures, abundant defects, and tunable porosities are favorable as anodes for potassium-ion batteries (PIBs). Synthesizing amorphous carbon materials typically involves the pyrolysis of carbonaceous precursors. Nonetheless, there is still a lack of studies focused on achieving multifaceted structural optimizations of amorphous carbon through precursor formulation. Herein, nitrogen-doped amorphous carbon nanotubes (NACNTs) are derived from a novel composite precursor of cobalt-based metal–organic framework (CMOF) and graphitic carbon nitride (g-CN). The addition of g-CN in the precursor optimizes the structure of amorphous carbon such as morphology, interlayer spacing, nitrogen doping, and porosity. As a result, NACNTs demonstrate significantly improved electrochemical performance. The specific capacities of NACNTs after cycling at current densities of 100 mA/g and 1000 mA/g increased by 194 % and 230 %, reaching 346.6 mAh/g and 211.8 mAh/g, respectively. Furthermore, the NACNTs anode is matched with an organic cathode for full-cell evaluation. The full-cell attains a high specific capacity of 106 mAh/gcathode at a current density of 100 mA/g, retaining 90.5 % of the specific capacity of the cathode half-cell. This study provides a valuable reference for multifaceted structural optimization of amorphous carbon to improve potassium-ion storage capability.

Nanoscale Sequential Reactor Design Achieves Effective Removal of Disinfection Byproduct Precursors in Catalytic Ozonation.

Transforming dissolved organic matter (DOM) is a crucial approach to alleviating the formation of disinfection byproducts (DBPs) in water treatment. Although catalytic ozonation effectively transforms DOM, increases in DBP formation potential are often observed due to the accumulation of aldehydes, ketones, and nitro compound intermediates during DOM transformation. In this study, we propose a novel strategy for the sequential oxidation of DOM, effectively reducing the levels of accumulation of these intermediates. This is achieved through the development of a catalyst with a tailored surface and nanoconfined active sites for catalytic ozonation. The catalyst features a unique confinement structure, wherein Mn-N4 moieties are uniformly anchored on the catalyst surface and within nanopores (5-20 Å). This design enables the degradation of the large molecular weight fraction of DOM on the catalyst surface, while the transformed smaller molecular weight fraction enters the nanopores and undergoes rapid degradation due to the confinement effect. The generation of *Oad as the dominant reactive species is essential for effectively reducing these ozone refractory intermediates. This resulted in over 70% removal of carbonaceous and nitrogenous DBP precursors as well as brominated DBP precursors. This study highlights the importance of the nanoscale sequential reactor design and provides new insights into eliminating DBP precursors by the catalytic ozonation process.

Hydrochars derived from real organic wastes as carbonaceous precursors of activated carbons for the removal of NO from contaminated gas streams

The improvement of air quality in densely-populated urban regions constitutes an environmental challenge of increasing concern. In this respect, the abatement of NO emissions, primarily emanating from combustion processes associated with motor-vehicles, along with industrial/domestic combustion systems, represents one of the main problems. Here, three hydrochars from diverse organic residues were used as activated carbon precursors for their evaluation in the NO removal in two potential application scenarios. Hydrochars were physically activated at 800 °C with pure-CO2 or diluted-O2. These materials were tested in a lab-scale biofilter at different conditions (NO concentration, temperature, relative humidity, NO-containing gas and carbon particle size) and in a larger-scale biofilter to evaluate the long-term NO removal capacity. Hydrochar-derived carbons present a relatively well-developed micro- and mesoporous structure, with BET areas of up to 421 m2/g, and a variety of oxygen surface functionalities (carboxylic, lactone, carbonyl and quinone groups), especially concerning CO2-activated carbons. These exhibited an excellent behaviour at low NO concentration (5 ppmv) between 25 and 75 °C with removal capacities of ≈97 % and > 82 %, respectively; and still good-performance (≈66 %) in a more concentrated gas (120 ppmv). Whilst, carbons obtained by diluted-O2 activation from the same hydrochars, evidenced a higher removal capacity loss at high NO concentration. The O2 presence in the gas stream was confirmed as a crucial factor in the NO elimination, since both co-adsorb on the carbon surface favouring NO oxidation to NO2. Besides, the humidity in the airstream diminished the NO removal capacity from 0.88 to 0.51 mgNO/gcarbon, but still remained at 0.54 mgNO/gcarbon, when the carbon (in pellet) was operated at larger-scale biofilter in 9-fold longer test under humid air. Therefore, this study highlights the potential of renewable carbons to serve as cost-effective component in urban biofilters, to mitigate NO emissions from exhaust gases in biomass boilers and urban semi-close areas.

The oxidation reaction mechanism and its kinetics for a carbonaceous precursor prepared from ethylene tar for use as a cathode material for lithium-ion batteries

The oxidation reaction mechanism and its kinetics for a carbonaceous precursor prepared from ethylene tar for use as a cathode material for lithium-ion batteries

Microscale hydrogen, carbon, and nitrogen isotopic diversity of organic matter in asteroid Ryugu

We report the H, C, and N isotopic compositions of microscale (0.2 to 2 µm) organic matter in samples of asteroid Ryugu and the Orgueil CI carbonaceous chondrite. Three regolith particles of asteroid Ryugu, returned by the Hayabusa2 spacecraft, and several fragments of Orgueil were analyzed by NanoSIMS isotopic imaging. The isotopic distributions of the Ryugu samples from two different collection spots are closely similar to each other and to the Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most individual sub-μm organic grains have isotopic compositions within error of bulk values, but 2–10 % of them are outliers exhibiting large isotopic enrichments or depletions in D, 15N, and/or 13C. The H, C and N isotopic compositions of the outliers are not correlated with each other: while some organic grains are both D- and 15N-enriched, many are enriched or depleted in one or the other system. This most likely points to a diversity in isotopic fractionation pathways and thus diversity in the local formation environments for the individual outlier grains. The observation of a relatively small population of isotopic outlier grains can be explained either by escape from nebular and/or parent body homogenization of carbonaceous precursor material or addition of later isotopic outlier grains. The strong chemical similarity of isotopically typical and isotopically outlying grains, as reflected by synchrotron x-ray absorption spectra, suggests a genetic connection and thus favors the former, homogenization scenario. However, the fact that even the least altered meteorites show the same pattern of a small population of outliers on top of a larger population of homogenized grains indicates that some or most of the homogenization occurred prior to accretion of the macromolecular organic grains into asteroidal parent bodies.

Mapping carbon nanotube aspect ratio, concentration and spinning in FCCVD synthesis controlled by sulphur

Floating catalyst chemical vapor deposition (FCCVD) enables ultrafast synthesis of CNTs and other 1D nanoparticles and their direct assembly as macroscopic solids. The chalcogen growth promotor in FCCVD produces high aspect ratio CNTs that can aggregate in the gas phase and form an aerogel which can be continuously spun as macroscopic fibres or sheets. We study the role of sulphur in controlling CNT morphology and aggregation by synthesising CNTs under a wide range of S/C ratios (0.001 to 5 wt.%) and determining their diameter and length distributions, number concentration and form of aggregation. Increasing S/C ratio in this range increases mean number of CNT walls from 1 to 8, decreases mean length from 34 to 6 µm, but CNT number concentration remains approximately constant at 8 × 108#/cm3. Assuming growth within the first 3 cm of the reactor, longitudinal growth rate spans 1.5- 6.5 µm/s for the different CNT morphologies, but with similar mass throughput of 700 attogram/catalyst. This indicates the amount of carbon reaching the catalyst and solidifying as CNT remains constant regardless of the sulphur available in the catalyst, suggesting the rate limiting process is not at the catalyst/promoter interface but instead in the transport of carbonaceous active precursors to the catalyst, either due to their diffusion in the gas phase or decomposition kinetics. The CNTs produced range from polymer-like, which readily bundle and form aerogels, to rod-like that do not. We include aerogelation “phase diagrams” for different CNT concentrations, aspect ratios and CNT bending stiffness.

Electrochemical synthesis of nitrogen-doped graphene quantum dots and their photocatalytic hydrogen evolution application

A very simple electrochemical top-down procedure was employed to obtain pure graphene quantum dots (GQDs) in water and using only graphite as carbonaceous precursor. The graphitic structure of the GQDs has been clearly observed by high-resolution transmission electronic microscopy (HRTEM). Then, the synthesis of N-doped GQDs was allowed by the addition of ammonia in the solution. The nitrogen doping was plainly evidenced by X-ray photoelectron (XPS) and Raman spectroscopies. The role of the electrolytic solution employed during the synthesis has been also discussed. Finally, these N-doped and non-doped GQDs were further used to prepare hybrids by grafting them onto ZnO semi-conductors, and their photocatalytic properties towards water-splitting were investigated. Interestingly, a very important enhancement of the amount of dihydrogen produced was observed with N-doped GQDs, compared to ZnO alone or to hybrids prepared with non-doped GQDs.

Formation of Ediacaran stromatolitic cherts through a combination of biogenic and abiotic processes: New insights from the Bohemian Massif

Stromatolites are remarkable organosedimentary laminated structures that grow gradually through time due to the activity of microorganisms, mostly algae and cyanobacteria. The appearance of stromatolites in formations as old as ∼ 3.7 Ga represents the earliest macroscopic traces of life on Earth. Yet, the biogenic origin of some presumed stromatolites has been questioned as abiotic processes (e.g., fluid precipitation, diagenesis and metamorphism) can also be responsible for the formation of stromatolite-like textures. This is especially true in case of pervasively silicified stromatolites (stromatolitic cherts) that have rarely been reported from Neoproterozoic successions. Here, we present a detailed study of the Ediacaran stromatolitic cherts from the Blovice accretionary complex (Bohemian Massif) that combines petrography, trace element and Si–O isotopic compositions and Raman spectroscopy of organic matter to decipher the complex processes leading to their formation and evaluate the biogenicity of their precursor. Textural evidence (i.e. the presence of pseudomorphs after carbonate/evaporate and micro-ooids, variable thickness and spacing of organic-rich laminae) as well as trace element/isotopic compositions argue for a multi-stage formation of stromatolitic cherts. The primary carbonaceous stromatolitic precursors first formed in shallow-water lagoons with variable salinity at seamount slopes, were then fragmented by surface processes (erosion, mass wasting), and finally silicified by low-temperature hydrothermal fluids. The primary biogenic character of stromatolitic textures is evidenced by the non-equidistant alternation of dark (organic matter-rich) and light laminae with markedly different oxygen isotopic compositions reflecting probably seasonal cycles during stromatolite deposition, enrichment of bio-essential elements (e.g., Cu, Zn, Co and Mn) in dark laminae, and Raman spectra of organic matter indicative for variably matured kerogens. The presence of late-stage diagenetic modifications might be related to subsequent burial and low-grade metamorphism of stromatolitic cherts within the accretionary wedge.

The oxidation reaction mechanism and its kinetics for a carbonaceous precursor prepared from ethylene tar for use as an anode material for lithium-ion batteries

The oxidation reaction mechanism and its kinetics for ethylene tar were investigated in order to obtain a suitable anode material for Li-ion batteries. The oxidation of ethylene tar was divided into 3 stages (350–550, 550–700 and 700–900 K) according to the thermogravimetric curve. To reveal the oxidation reaction mechanism, the components of the gases evolved at different stages were analyzed by mass spectrometry and infrared technology. Based on these results the reaction was divided into 4 stages (323–400, 400–605, 605–750 and 750–860 K) to perform simulation calculations of the kinetics. Using the iso-conversion method (Coats-Redfern) to analyze the linear regression rates (R2) between 17 common reaction kinetics models and experimental data, an optimum reaction kinetics model for expressing the oxidation of ethylene tar was determined and the results were as follows. (1) During oxidation, the side chains of aromatic compounds first react with oxygen to form alcohols and aldehydes, leaving peroxy-radicals on aromatic rings. Subsequently, the aromatic compounds with peroxy-radicals undergo polymerization/condensation reactions to form larger molecules. (2) A fourth-order reaction model was used to describe the first 3 stages in the oxidation process, and the activation energies are 47.33, 18.69 and 9.00 kJ·mol−1 at 323–400, 400–605, 605–750 K, respectively. A three-dimensional diffusion model was applied to the fourth stage of the oxidation process, and the activation energy is 88.37 kJ·mol−1 at 750–860 K. A high softening point pitch was also produced for use as a coating of the graphite anode, and after it had been applied the capacity retention after 300 cycles increased from 51.54% to 79.07%.

Universal high-performance bulk graphites from natural flake graphite by rapid sintering

High performance graphites (HPGs) are a key material in modem industries; however, prevailing HPGs are short of comprehensive properties in many aspects, i.e., a specific property of HPGs is always achieved at the cost of other properties. And the production of HPGs is highly costly and causes severe environmental problems. Current HPGs are derived from various carbonaceous precursors, excluding nature flake graphite (NFG), the best graphite source. Typically, NFG-based bulk graphite has poor mechanical properties because NFG is difficult to sinter. Here we report the preparation and comprehensive properties of a new family of universal HPGs (U-HPGs) that can be mass-produced with moderate conditions by sintering NFG slightly mixed with diamond, where units of onion carbon (OC) with NFG (OC@NFG) act as building blocks. OC@NFG creates a strong interfacial network between the NFGs, giving the U-HPGs outstanding strength and moderate hardness. With U-HPGs being more than 93 % graphitization, the flexural strength exceeds 100 MPa, far superior to mainstream commercial graphites. OC@NFG also bestows U-HPGs with excellent thermal conductivity(＞125 W m−1 K−1 at room temperature). For such structure provides a 3D path for electrons inside U-HPGs, the as-produced material has significant electronical conductivity. This work presents new insights into this old yet important material and allows for innovative design of HPGs for various applications.

Si@C anode with excellent electrochemical performance for lithium-ion batteries: Microcapsules composed of N-doped carbon shell and diffusely distributed nano-silicon inside

As a promising candidate for the next generation of new anode materials, the modification and optimization of silica-based anode materials are significant. Using chitosan (CS) as the carbonaceous precursor, the N-containing Si@C microcapsules were prepared by emulsification cross-linking combined with high-temperature pyrolysis method. The microcapsule structure offers additional space for nano-Si and effectively enhances the electrochemical properties of the anode. Moreover, optimizing the CS:Si ratio is advantageous in achieving a synergistic effect between silicon and carbon. When CS:Si = 4:1, the first specific capacity was 762.78 mAh/g and the retention rate was 69.27 % after 100 cycles. To further enhance the material properties, urea was added to a ratio of CS:Si = 4:1 as an N supplement for elemental doping modification. The specific capacity of the anode had a positive correlation with N content within a certain range. As the N content increases, the pyridine-N content and density of C vacancies also increase, which improves the storage form and diffusion path of Li+. When 0.75 g urea was added, the first reversible specific capacity reached 1108.88 mAh/g and the retention rate was 92.41 % after 100 cycles. This work offers environmentally friendly and safe methods, as well as a new modification concept for N-doped microsphere-encapsulated silicon-carbon composites.

Localized eddy current heating-driven synthesis and regeneration of porous carbons at mitigated energy cost

Porous carbons (PCs), widely deployed sorbents in diverse areas, are usually synthesized by thermochemically carbonizing carbonaceous precursors and thermally regenerated at great energy-cost. To seek alternative solutions to such energy penalty and based on the exceptional localized Eddy current heating (LECH) capacity of metal objects upon their exposure to an alternating magnetic field, LECH-driven synthesis of PCs is explored and exemplified by using nickel foam (NF)-delivered LECH to drive carbonization of phenolic resin (PR) infilled within the voids of NF, producing varied PC-incorporated NFs (NF@PCs). Compared with the PCs prepared by using conventional tubular furnace heating, LECH-driven carbonization of PR is able to produce PCs at lower temperature and with greatly enhanced porosity, surface area and graphitization degree, which are mainly resulting from the localized heating nature of LECH. Driven by the same NF-delivered LECH, the moisture adsorbed in the LiCl-loaded NF@PC can be rapidly and completely released at moderate temperature, demonstrating the highly efficient LECH-driven regeneration of PCs. Given that the LECH is delivered by cost-effective and widely available NFs, occurs within the matrix of PR and PC bulk solid, and remotely triggered by an external magnetic field with greatly mitigated energy loss, LECH-driven carbonization of PR and water desorption from PCs thus demonstrated a new, energy-efficient and low-cost strategy to effectively synthesize and regenerate PCs.

Laser induced graphene for EMI shielding and ballistic impact damage detection in basalt fiber reinforced composites

Basalt fiber has been widely used in a variety of industries due to its unique properties and relatively low cost. However, the nature of electrical insulation of basalt fiber limits its application in the field of functional composite materials such as electromagnetic interference (EMI) shielding materials. Laser-induced graphene (LIG) is a form of three-dimensional carbon nanomaterial, which could be generated by scribing a laser on many carbonaceous precursors. In this work LIG film obtained by double-sided etching Polyimide (PI) paper was embedded in the basalt fiber laminates to fabricate multi-functional basalt fiber composites. The effects of LIG film insertion on Mode I and Mode II fracture toughness and out-of-plane ballistic impact resistance of basalt fiber laminates were investigated. The basalt fiber laminates with LIG inserted retain their original mechanical properties in terms of fracture toughness and impact resistance. While the conductivity and electromagnetic shielding performance of basalt fiber laminate after LIG insertion have been greatly improved. The EMI shielding effectiveness of the basalt fiber laminates is increased to ∼20 dB after one layer of LIG was inserted, and to ∼50 dB after three layers of LIG were inserted, for the X-band frequency range. The damage localization of the basalt fiber laminates was demonstrated by arraying the rectangular LIG strips in the shape of hash key and in-situ monitoring the electric resistance changes.

Tailored Properties of Carbon for Supercapacitors by Blending Lignin and Cellulose to Mimic Biomass as Carbonaceous Precursor.

KOH-activated carbon materials prepared from biomass-derived carbon source, cellulose and lignin, were compared. Mixtures of different ratios of cellulose and lignin were used to partially mimic biomass as carbon source. This allows tailoring and optimizing of the KOH activated carbon materials by getting rid of the restriction of the intrinsic proportion of cellulose and lignin in specific biomass. The results indicate that cellulose use results in a more porous structure, whereas lignin use leads to more partially activated graphite structure. The activated carbon material (CL1) prepared from blend of cellulose with lignin in mass ratio of 1 : 1 exhibits a high specific surface area of 2000.39 m2 g-1 , and in TEABF4 /ACN (tetraethylammonium tetrafluoroborate dissolved in acetonitrile) electrolyte it showed a maximum specific capacitance of 136.10 F g-1 , a maximum energy density of 18.11 Wh kg-1 , and a capacitance retention of 85.04 % under current density as high as 15 A g-1 .

Geochemical characterization of scoriaceous and unmelted micrometeorites from the Sør Rondane Mountains, East Antarctica: Links to chondritic parent bodies and the effects of alteration

Micrometeorites originate from the interplanetary dust complex and continuously fall to the Earth’s surface in large amounts. About 10 to 20% of micrometeorites are not melted upon reaching the Earth’s surface, preserving the primary features and characteristics of the parent material. Consequently, unmelted micrometeorites, together with scoriaceous micrometeorites, an intermediate form between cosmic spherules and unmelted micrometeorites, are pivotal in documenting the nature and evolution of interplanetary dust as well as the modifications experienced by micrometeorites during atmospheric entry. Based on their petrographic features, here we identified and characterized 64 scoriaceous and unmelted micrometeorites with diameters varying between 90 and 410 μm from fine-grained sediment sampled in the Sør Rondane Mountains of East Antarctica. Based on their size distribution, the micrometeorites from the Sør Rondane Mountains show a clear distinction between unmelted micrometeorites (<300 μm) and cosmic spherules (>400 μm) and imply an accumulation mechanism or exposure history distinct from other collections (e.g., Transantarctic Mountains). Different exposure windows, weathering processes and environmental factors (e.g., snow cover) could affect the size and composition of preserved particles.A selection of the particles (n = 49) was further characterized for geochemical composition and high-precision oxygen isotope ratios to identify potential parent bodies and document their alteration histories. About 63% of the particles, exhibiting both coarse- and fine-grained textures, derive from carbonaceous chondritic precursors. Two particles (∼4%) display anomalously 16O-poor isotopic compositions similar to that previously observed for (giant) cosmic spherules and unmelted micrometeorites, classified as “group 4” particles. These particles are thought to originate from an unidentified chondritic parent body located in a specific region of the protoplanetary disk or may have been characterized by a distinct alteration history, with recent studies linking them to CY carbonaceous chondrites. Only a single fine-grained particle (∼2%) can be assigned to ordinary chondritic parentage with confidence. The partially hydrated fine-grained matrix suggests this particle might be consistent with a Semarkona-like parent body. Approximately 10% of the studied particles exhibit extensive evidence for secondary terrestrial weathering with formation of (hydr)oxides during residence in the Antarctic environment, preventing detailed parent body identification. Ten particles (∼20%) could not be assigned to a specific parent group due to ambiguous oxygen isotope values. Overall, the parent body statistics from this study agree with those reported for different collections of a similar size fraction. Clear associations between textural groups and parent bodies could not be established. Even though unmelted micrometeorites are generally considered pristine and often do not exhibit any obvious petrographic evidence of terrestrial weathering, the chemical and isotopic data obtained here confirm that alteration can occur at the microscale and any data on unmelted particles from Antarctic subaerial collections should be evaluated with caution.

强耦合氧化钼氮碳复合材料的制备及其锂离子存储性能研究

Molybdenum oxide (MoO3) is an attractive anode material for lithium-ion batteries (LIBs); however, its low electrical conductivity, large volume expansion after lithiation, and slow Li-ion diffusion kinetics severely limit its practical applications. Here, ultrafine MoO3 nanoparticles (NPs) (10–15 nm) are synthesized from heavily Mo/N-doped carbonaceous precursors, resulting in MoO3 NPs confined in an N-doped carbon network. This design allows fast electron conduction and short Li-ion diffusion paths; meanwhile, abundant N species and O vacancies on the MoO3 surface lower the Li-ion adsorption barrier and together contribute to the durable Li-ion storage at high current rates. Notably, the obtained nanocomposite NC-MoO3 exhibits a high capacity of 1362 mA h g−1 (0.1 A g−1) and maintains a reversible capacity of 394 mA h g−1 at 10.0 A g−1. A coin-type full LiFePO4//NC-MoO3-400 cell obtains a large specific capacity of 81 mA h g−1 at 5 C. Our work inspires the design and confinement synthesis of other transition metal oxides embedded in conducting carbon networks for practical LIB applications.