Different Degrees Of Graphitization Research Articles

N-doped carbon derived from thermoplastic and thermosetting polyimides toward electromagnetic waves absorption

Due to stronger tunability, higher stability, and low production costs, polymeric material-based carbon materials are considered to have the potential to become high-performance electromagnetic wave absorbing (EWA) materials. In this work, polymer-derived carbon is made by pyrolyzing thermoplastic polyimide (TPPI) and thermosetting polyimide (TSPI) at different temperatures. Using Raman and XPS analysis, the graphitization degree and defect content of carbonized TPPI and TSPI are obtained. The reflection loss is calculated by through their electromagnetic parameters. The prepared carbonaceous materials exhibit excellent EWA performance. Specifically, the maximum effective absorption band (EABmax) of carbonized TSPI at 1500 C can reach 4.1 GHz with thickness of 1.8 mm, and that of carbonized TPPI at 900 C can reach 4 GHz at lower thickness of 1.6 mm. The different structures of TPPI and TSPI result in different degrees of graphitization and defect content at the same temperature, which further leads to differences in their EWA performance. This work provides inspiration for studying the influence of precursor structure on the EWA preformation of carbon materials obtained through pyrolysis.

Synergistic effect of pore structure and crystalline domains enabling high capacity toward non-aqueous rechargeable aluminum batteries

Rechargeable aluminum batteries (RABs) with low cost and high safety have been regarded as a potential alternative to lithium-ion batteries. Despite the widely used graphite materials, the research on hard carbon with abundant sources and low carbonization temperature is rarely reported. Herein, a series of hard carbon materials with different degrees of graphitization is controllably fabricated through a ball-milling method. It is found that surface-specific area and pore structure are significantly affected by ball-milling time. As a result, the as-optimized product with suitable graphitization degree and pore distribution shows a high capacity (125 mAh·g−1 at 200 mA g−1 after 200 cycles) and excellent cycle stability (82.2 mAh·g−1 at 150 mA g−1 after 500 cycles). Such electrochemical performances can be ascribed to the fact that a proper graphitization degree ensures fast electrons transfer between layers, and multi-pores architectures contribute to accelerating ions migration. This work is expected to guide synthesizing a biomass-derived hard carbon via a facile and low-energy method, which may accelerate the practical application of RABs and facilitates the mass production of cathode carbon materials.

Constructing a conductive and buffer network on microscale silicon-based anodes for high-performance lithium-ion batteries

The structure and characteristics of the electrodes are essential for the performance of microscale silicon-based anodes for lithium-ion batteries. In this study, various carbon sources with different degrees of graphitization, morphologies, and dispersities were utilized as conductive agents for a microstructured silicon electrode. The findings indicate that micron-sized silicon electrodes can benefit from the addition of flake-conductive graphite, particularly SFG-6, which possesses a high degree of graphitization and dispersion, as well as a particle size similar to that of silicon. This combination results in a well-distributed, uniform conductive and buffering network, leading to improved electrochemical performance overall. After 450 cycles, the Si-SFG-6 composite anode exhibited exceptional long-term stability, delivering a specific capacity of 1102 mA·h g−1 at a current density of 200 mA g−1. Furthermore, even at a higher current density of 2000 mA g−1, the reversible capacity remained impressive at 964 mA·h g−1. The results of this study offer valuable insights for optimizing the structure and properties of microstructured silicon-based anodes, with the aim of achieving superior performance in Li-ion batteries.

Visualizing sub-layer structural transformation in carbonized wood tracheid by Raman mapping

Characterizing the pore structure evolution of biomass-derived carbon during processing and exploring the relationship between the porous carbon structure and the intrinsic micro-structure of biomass precursor are of great importance to advance the knowledge of pore creation/evolution mechanism and manufacture demanded pore structures by controlled processing. So far, the manipulation of pore structure still heavily relies on trial-and-error approach due to the lack understanding of the relationship between precursor structure/composition and the pore evolution during processing. In this work, the micro-structural evolution across the multi-layered wood tracheid in carbonization and oxidation processes was revealed by Raman mapping which can provide a unique insight into the pore structure evolution of carbon materials. The different degrees of graphitization enable the differentiation of carbonized forms of lignin and cellulose by Raman mapping and thus quantify the changes of both species during carbonization and oxidation. It is revealed that micropore formation is more related to the degradation of lignin and mesopore formation is closely associated with cellulose. The diffusion of reactive gas through the multi-layered wood tracheid and the corresponding reactions occurred along the diffusion path create the comprehensive porous channels. This work provides a new and convenient method to get a comprehensive understanding of biomass structure/composition in related to the pore structure evolution and allows a more specific regulation of pore structure in biomass-derived porous carbon materials.

Multiple-color room-temperature phosphorescence regulated by graphitization and carbonyls

Room-temperature phosphorescence with multiple-color activated the widespread interest owing to their promising applications, howbeit, there still exist the insurmountable challenge, especially for elucidating their photoluminescence mechanism and tunable emissions. Here we systematically proposed several carbon dots (CDs) with different degrees of graphitization and amounts of carbonyl while sulfuric acid and ethanol played the critical roles. In brief, sulfuric acid functioned as the carbonization and strong oxidization reagent, while the increasing volumes of ethanol gradually reduced the boiling point of the reactions. Significantly, the energy of these phosphorescent CDs transferred from their excited triplets to oxygen molecules once they were irradiated by UV in aqueous, resulting in the production of the singlet oxygen to oxidize 3,3′,5,5′-tetramethylbenzidine. This finding indirectly provided the evidence for the existence of the phosphorescence rather than delayed fluorescence. Towards the photoluminescence mechanism, their fluorescence of CDs was originated from π-π* transition of CC in the carbon cores and n-π* transition of CO on the surfaces, while RTP was mainly attributed to n-π* transition of the carbonyls. The further evidence suggested that the CDs with different graphitization degrees and amounts of CO regulated their multiple-color phosphorescence. Besides, we employed these CDs for information encryption and preparing LED lamps.

Carbon nanotubes decorated Co/C from ZIF-67/melamine as high efficient microwave absorbing material

The problem of unstable structure and poor impedance matching of single metal-organic framework (MOF) can be avoided by sintering MOFs and melamine composites to fabricate carbon nanotubes-coated cobalt/carbon nanoparticles (Co@C/CNTs). By regulating the mixing ratio of MOF and melamine, different lengths and amount of carbon nanotubes coated porous cobalt/carbon polyhedrons can be obtained, and the catalytic capability of cobalt can be affected to obtain carbon with different degrees of graphitization. The appropriate ratio can change the dielectric magnetic parameters to optimize the impedance matching of the material. As the result, when the mixing ratio of ZIF-67 and melamine was 1:1, the product Co@C/CNTs/PVDF-1:1 shows the lowest reflection loss (−57.6 dB) at the filling amount of 15 wt% with the thickness of 3.01 mm. The effective absorbing bandwidth (EAB) could achieve 5.4 GHz from 12.6 GHz to 18.0 GHz under the filler loading of 10 wt% with the thickness of 2 mm. These results inaugurate a new avenue for obtaining excellent absorbing composites with lightweight, wide EAB and strong absorbing performance.

A Design Strategy of Carbon Coatings on Silicon Nanoparticles as Anodes of High-Performance Lithium-Ion Batteries

Carbon coatings are commonly used to improve the performance of silicon anodes by providing a conductive shell that discourages the formation of excess solid/electrolyte interphase (SEI). Lack of understanding on the links between the properties of carbon components, such as mechanical properties and conductivity, and the electrochemical properties limits the advances in development of high-performance silicon–carbon nanocomposites. Herein, uniform carbon coatings with different degrees of graphitization were formed on the surface of silicon nanoparticles using bitumen as a carbon precursor. Analysis of electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) shows that the carbon coating of higher elasticity and high Li+ diffusion coefficient through the control of carbonizing bitumen coatings on silicon nanoparticles greatly enhanced the electrochemical performance of carbon-coated silicon anodes. The high elasticity provides stable contacts between silicon and carbon coatings and maintains a stable electrode/electrolyte interface (without excessive SEI growth) during long-term cycling. Compared with electronic conductivity, the efficiency of ion diffusion in the carbon coating is found to play an important role in the rate capability of the electrode. This work provides a design strategy to further optimize the performance of the silicon-based anodes.

Physicochemical structure, combustion characteristics and SiO2 properties of entrained flow gasification ash

During the gasification process of coal, fine ash (FA) and coarse slag (CS) solid waste are produced, which contain a large amount of residual carbon and ash (mainly SiO2), resulting in energy waste and environmental pollution. Therefore the main goal of this research is to recover the wasted energy from FA and CS. The investigation of the physicochemical structure, combustion characteristics and SiO2 properties of entrained flow gasification ash (EFGA) is an important basis for the valorization of EFGA. The physicochemical, combustion characteristics and SiO2 properties of EFGA in a entrained flow bed of 112,000 Nm3/h gas-forming capacity were investigated, showing that FA and CS undergo different gasification processes, with FA having a more developed pore structure and high specific surface area. FA and CS have different degrees of graphitization, with defects or heteroatoms in FA causing a scattered carbon layer structure with an irregular graphitic carbon crystal structure, and organic molecular functional group fragments forming an indeterminate structure and active sites. The organic molecule functional group fragments constitute an indeterminate structure and active sites. Kinetic analysis shows that the influence of chemical structure on the combustion characteristics of EFGA is higher than that of physical structure. Compared to CS, FA has fewer active sites and a small number of oxygen-containing functional groups, resulting in a weaker combustion reactivity of FA. The combustion activity of EFGA is lower than that of circulating fluidized bed gasification ash and anthracite, making it difficult to be eliminated by direct combustion, although co-combustion is feasible. The specific surface area of SiO2 prepared by EFGA after acid treatment and calcination is small (<39.7086 m2/g), SiO2 exists as crystals and the elemental silicon exists mainly in the form of Si–O, O–Si–O and hydrated silicon dioxide Si–O2-nH2O, which can be used as a raw material for the preparation of silica.

Carbon Composites—Graphene-Oxide-Catalyzed Sugar Graphitization

Utilization of biopolymers to form graphitic carbons is challenged by their high oxygen content and resulting curved and defective carbon lamellae upon high-temperature heat-treatment. Two composites, one with graphene-oxide (GO) and the other with reduced graphene-oxide (rGO) as fillers, respectively, in a matrix of sugar, each for the same added 2.5 wt.%, exhibited different degrees of graphitization compared to pure sugar on its own. Reactive oxygen groups on GO contribute to reactive templating and crystallite formation. Under high-temperature heat-treatment, sugar, a well-known non-graphitizing precursor, is converted to graphitic carbon in the presence of GO. Possessing fewer oxygen groups, rGO forms two phases in the sugar matrix—a non-graphitic phase and a graphitic phase. The latter is attributed to the remaining oxygen on the rGO.

Atomically Dispersed Manganese Lewis Acid Sites Catalyze Electrohydrogenation of Nitrogen to Ammonia

Atomically Dispersed Manganese Lewis Acid Sites Catalyze Electrohydrogenation of Nitrogen to Ammonia

Full color fluorescent carbon quantum dots synthesized from triammonium citrate for cell imaging and white LEDs

Multicolor fluorescent carbon quantum dots (CDs) exhibit prospective applications but the intrinsic reaction and luminescence mechanisms of CDs remain unclear. In this work, full color fluorescent CDs were synthesized through a facile solvothermal treatment with triammonium citrate as the carbon source. By adjusting the reaction temperature, the maximum emission wavelength is tuned from 440 nm for blue CDs (B-CDs) to 625 nm for red CDs (R-CDs), covering the whole visible spectrum range. The emission mechanism is proposed as surface-state-controlled, which results from different degrees of graphitization and increasing of functional groups on the surfaces. Three different surface states are derived from the overlap of the absorption and excitation spectra and the mechanism is established by XRD, Raman, XPS and UV–Vis absorption. The full-color luminescent CDs with high light and pH stability as well as good biocompatibility are successfully employed to image HeLa cells. White LED is fabricated by B-, G-, and R-CDs/polymer films with a near ultraviolet (NUV) semiconductor chip. The results of this research demonstrate that the synthesized CDs can be potentially applied in multi-color displays, white LEDs and biological imaging probes.

Variable Temperature Synthesis of Tunable Flame-Generated Carbon Nanoparticles

In this study, flame-formed carbon nanoparticles of different nanostructures have been produced by changing the flame temperature. Raman spectroscopy has been used for the characterization of the carbon nanoparticles, while the particle size has been obtained by online measurements made by electrical mobility analysis. The results show that, in agreement with recent literature data, a large variety of carbon nanoparticles, with a different degree of graphitization, can be produced by changing the flame temperature. This methodology allows for the synthesis of very small carbon nanoparticles with a size of about 3–4 nm and with different graphitic orders. Under the perspective of the material synthesis process, the variable-temperature flame-synthesis of carbon nanoparticles appears as an attractive procedure for a cost-effective and easily scalable production of highly tunable carbon nanoparticles.

Generation Mechanism of Localized Wear of Cu-impregnated Carbon-based Pantograph Contact Strip

Localized wear of pantograph contact strips is a significant problem affecting the current-collecting systems in electric railways, because it may cause fusion of the pantograph head, resulting in devastating damage to the overhead contact wire. However, the causes of localized wear of carbon-based contact strips have not been clarified, and thus, effective prevention measures cannot been established. The purpose of this study is to clarify the generation mechanism of localized wear in copper-impregnated carbon-based contact strips. In this study, the actual locally worn strips were analyzed with a micro Raman spectrometer. The sliding wear behavior of contact strips with different degrees of graphitization of the carbon substrate was investigated using a block-on-ring-type wear tester.

An overlooked issue for high-voltage Li-ion batteries: Suppressing the intercalation of anions into conductive carbon

Summary High-voltage Li-ion batteries have been extensively studied to increase energy density of batteries. However, their cycling stability has remained poor, despite various strategies being proposed to overcome the issues of high-potential cathodes, such as electrolyte oxidation and transition metal dissolution. Herein, we report anion intercalation into the cathode conductive carbon as an overlooked yet critical issue. We propose a concentrated sulfolane (SL)-based electrolyte that prevents anion intercalation via two mechanisms: (1) by offering a high activation barrier to intercalation via its strong anion-Li+ interaction and (2) by forming a sulfur-containing, anion-blocking SL-derived interphase. This electrolyte, used with graphitized acetylene black, which is oxidatively stable but usually susceptible to anion intercalation, enables the stable operation of a Li2CoPO4F/graphite full cell (cut-off voltage = 5.2 V), with 93% capacity retention after 1,000 cycles and an average Coulombic efficiency of ≥99.9%. This is a pivotal strategy to enhance the reversibility of >5 V Li-ion batteries on a commercial level.

Off/on switchable smart electromagnetic interference shielding aerogel

Summary Smart electromagnetic interference (EMI) shielding materials with tunable EM wave response characteristics are attractive for future EM devices. Here, we report an off/on switchable EMI shielding material that can be tuned from EM wave transmission to shielding and vice versa by mechanical compression and decompression. This smart material is prepared by filling conductive carbon nanoparticles into wood-derived lamellar carbon aerogel, showing reversible compressibility and strain-sensitive conductivity. The original aerogel has good impedance matching and low dielectric loss, allowing the EM wave to pass through. Mechanical compression enables the carbon nanoparticles to establish highly conductive pathways in the aerogel, which significantly increases the conductivity of aerogel and thus activates its EMI shielding performance. This function switch is reversible by repeatedly compressing and decompressing the aerogel. The availability of such a never-before-realized off/on switchable EMI shielding material provides an opportunity for the development of advanced smart EM devices.

High adsorption of methylene blue from water onto graphenic materials: Effect of degree of graphitization and analysis of kinetic models

AbstractThe removal by adsorption of methylene blue dye from water using two‐dimensional (2D) (graphene oxide and reduced graphene oxide) and three‐dimensional (3D) (graphite and graphite oxide) carbon structures was studied. Two graphites with different degrees of graphitization were used to evaluate the significance of the carbon structural order in the adsorption efficiency, and therefore, the economic repercussions, because the degree of graphitization is related with the cost. Graphene oxides showed the best performance in methylene blue adsorption, with a removal of around 90%. The adsorption process was strongly influenced by the surface oxygenated groups, and electrostatic interaction was the main mechanism of adsorption. The degree of graphitization of the precursor does not have a strong influence on the adsorption results of methylene blue. Thus, graphene oxide with a lower degree of graphitization represents an economical and efficient adsorbent for the removal of methylene blue from water. The kinetic study was realized in pseudo‐first order, pseudo‐second order, and Elovich kinetic models in their linear and non‐linear forms. According to the determination coefficient and the standard deviation, the experimental data were best fitted to the Elovich model in its non‐linear form.

Insights into the surface oxidation modification mechanism of nano-diamond: An atomistic understanding from ReaxFF simulations

Nano-diamond is widely utilized in various fields due to its excellent properties. However, in comparison with micron-sized materials, the higher surface energy of nano-diamond can make it easy to agglomerate, which seriously impedes its application. Heat treatment is an effective method to reduce agglomeration and improve dispersion. Therefore, it is important to elucidate the micro-surface modification mechanism of nano-diamond during heat treatment. In this work, ReaxFF molecular dynamics simulations are applied to study the dissociation and adsorption processes of H2O and O2 on the diamond surface as well as the forms of mass loss and surface terminal groups under different crystal plane orientations during heat treatment. The simulation results show that the adsorption of H2O is dominant in (100) surface and forms C-H and C-OH as well as C-OH and H3O+. The adsorption of O2 forms CO and C-O-C on the (100) surface, C-O-O-C on the (110) surface, and CO on the (111) surface, respectively. During heat treatment, carbon atoms can be oxidized to CO or CO2, causing mass loss. Furthermore, the diamond shows different degrees of graphitization under three orientations. This work provides a theoretical basis for understanding the surface oxidation modification mechanism of nano-diamond from an atomistic perspective.

Activated carbon obtained from amazonian biomass tailings (acai seed): Modification, characterization, and use for removal of metal ions from water

Acai seed was used herein as an Amazon biomass waste for the synthesis of activated and modified carbon in order to find a possible use for the large volume of residues generated during the processing of this fruit and to add value to this residue. Activated carbon materials were used to remove Pb2+, Fe2+, and Mg2+ metal ions from water. The efficiency of removal of these ions by the acai seed activated carbon was compared with that by commercial activated carbon. Activated carbon materials were prepared by carbonization and chemical activation using two KOH impregnation ratios, namely 1:1 (ACK1) and 5:1 (ACK5), by mass. These samples were modified by treatment with nitric acid under microwave heating (ACK1-M) and (ACK5-M), respectively. The result of the elemental analysis indicated that this biomass has carbon and sulfur contents of 43.29% and 0.10% wt, respectively. The textural parameters showed that the obtained activated carbon samples presented high surface areas between 1462 and 2774 m2 g−1. Raman analysis revealed the different degrees of graphitization of the activated carbon materials. Boehm titration identified the presence of phenolic, carboxylic, and lactonic groups in samples that were confirmed by Fourier transform infrared spectroscopy. In the metal adsorption tests, ACK5-M showed better removal efficiency, reaching 86% removal for Pb2+, 69% for Fe2+, and 8% for Mg2+in 1 h of contact time; these results were superior to those obtained for commercial carbon. The results indicated that acai seed can be used for the production of activated carbon and can also be used for metal removal.

Highly Dispersed CoO on Graphitic Mesoporous Carbon as an Efficient Catalyst for Fischer–Tropsch Synthesis

Mesoporous carbon (MC) supports with different degrees of graphitization are prepared via the pyrolysis of furfuryl alcohol with SBA-16 as the hard template. The Co/MC-x catalysts (where x = 800, 1...

Carbonaceous photonic crystals prepared by high-temperature/hydrothermal carbonization as high-performance microwave absorbers

Carbonaceous photonic crystals (CPCs) were prepared from peacock feather fibers (PFF) via high-temperature carbonization (HTC) and hydrothermal carbonization (HC), and by comparing the optical reflection microphotographs, the CPCs-HTC and CPCs-HC still owned the structural coloration as the natural PFF. Raman results showed that the ID/IG value of CPCs-HTC was higher than the one of CPCs-HC, demonstrating more defects and higher graphitization degree of CPCs-HTC. Due to the presence of defects and the different degrees of graphitization, complex permittivity of CPCs can be controlled. The microwave absorption performance of 30 wt% CPCs-HTC was better than the CPCs-HC. The minimum reflection loss (RL) of CPCs-HTC was − 57.9 dB when the frequency was 7.3 GHz and the thickness was 2.5 mm. The frequency range, in which the RL values were less than − 10 dB, was 6.4–8.5 GHz. Compared with other biomass-derived materials, the CPCs-HTC shows several advantages, such as the specific photonic structure, simple preparation process and excellent microwave absorption performances. Thus, CPCs-HTC has the potential to be a lightweight microwave absorption material.