Graphitization Process Research Articles

Controllable fabrication of graphitic nanocarbon encapsulating FexNiy hybrids for efficient splitting of water

The hybridized electrocatalysts constituted by binary 3d transition nanoparticles with a varied ratio of Fe to Ni were successfully synthesized through a two-step fabrication procedure, a homogeneous precipitation process, and a successive graphitization process. A superior oxygen evolution reaction (OER) efficiency with a yielded remarkable low overpotential of ∼0.26 V and a Tafel slope of ∼56 mV/decade is achieved for the heterostructured Fe1Ni2 nanoparticles coated by graphitic nanocarbon in a 1 mol/L KOH solution. The influencing factors for synthesizing the electrocatalysts, such as the graphitization temperature, the content of iron and the thickness of the carbon shells are also carefully investigated, and improved electrocatalytic efficiency is achieved with appropriate fabrication parameters for the hybridized catalysts. It is considered that the synergistic effect of the defects and electrochemical conductivity of the graphitic carbon shells shows great influences on the electrocatalytic activity. In addition, the detailed electrochemically active surface area and the electrochemical impedance suggest that the FexNiy hybrids coated by graphitic nanocarbon have improved the mass transport and electron transfer rate, resulting in an enhanced electrocatalytic water splitting efficiency. This work opens up a new way to fabricate promising oxygen-evolving catalysts with high-efficiency and low-cost.

Graphene Nanoplatelet (GNPs) Doped Carbon Nanofiber (CNF) System: Effect of GNPs on the Graphitic Structure of Creep Stress and Non-Creep Stress Stabilized Polyacrylonitrile (PAN).

Improving the graphitic structure in carbon nanofibers (CNFs) is important for exploiting their potential in mechanical, electrical and electrochemical applications. Typically, the synthesis of carbon fibers with a highly graphitized structure demands a high temperature of almost 2500 °C. Furthermore, to achieve an improved graphitic structure, the stabilization of a precursor fiber has to be assisted by the presence of tension in order to enhance the molecular orientation. Keeping this in view, herein we report on the fabrication of graphene nanoplatelets (GNPs) doped carbon nanofibers using electrospinning followed by oxidative stabilization and carbonization. The effect of doping GNPs on the graphitic structure was investigated by carbonizing them at various temperatures (1000 °C, 1200 °C, 1500 °C and 1700 °C). Additionally, a stabilization was achieved with and without constant creep stress (only shrinkage stress) for both pristine and doped precursor nanofibers, which were eventually carbonized at 1700 °C. Our findings reveal that the GNPs doping results in improving the graphitic structure of polyacrylonitrile (PAN). Further, in addition to the templating effect during the nucleation and growth of graphitic crystals, the GNPs encapsulated in the PAN nanofiber matrix act in-situ as micro clamp units performing the anchoring function by preventing the loss of molecular orientation during the stabilization stage, when no external tension is applied to nanofiber mats. The templating effect of the entire graphitization process is reflected by an increased electrical conductivity along the fibers. Simultaneously, the electrical anisotropy is reduced, i.e., the GNPs provide effective pathways with improved conductivity acting like bridges between the nanofibers resulting in an improved conductivity across the fiber direction compared to the pristine PAN system.

Revisiting the Oxidation of Graphite: Reaction Mechanism, Chemical Stability, and Structure Self-Regulation.

To fully understand the chemical structure of graphene oxide and the oxidation chemistry of sp2 carbon sites, we conducted a practical experiment and density functional theory combined study on the oxidation process of graphite. The nuclear magnetic resonance, thermogravimetric analysis, and X-ray photoelectron spectroscopy results of unhydrolyzed oxidized graphite indicate that the oxidation process involves the intercalating oxidation, where electrically neutral species is the oxidizing agent, and the diffusive-oxidation, where MnO3+ is the oxidizing agent. An intrinsic formation and conversion path of oxygen-containing functional groups is proposed based on the experimental results and further interpreted with the aid of frontier molecular orbital theory and density functional theory. Meanwhile, the two unique features of the oxidation process of graphite, the chemistry stability of oxygen-containing functional groups in the strong oxidizing medium, and the self-regulation of the oxidation process are theoretically reasoned.

Insight into the change in carbon structure and thermodynamics during anthracite transformation into graphite

The thermodynamic and kinetic mechanisms of Taixi anthracite during its graphitization process were explored. To understand the variation trends of carbon arrangement order, microcrystal size, and graphitization degree against temperature during the graphitization process, a series of experiments were performed using Raman spectroscopy and X-ray diffraction (XRD). Subsequently, the influencing factors of the dominant reaction at different temperatures were analyzed using thermodynamics and kinetics. The results showed that the graphitization process of Taixi anthracite can be divided into three stages from the perspective of reaction thermodynamics and kinetics. Temperature played a crucial role in the formation and growth of a graphitic structure. Meanwhile, multivariate mechanisms coexisted in the graphitization process. At ultrahigh temperatures, the defects of synthetic graphite could not be completely eliminated and perfect graphite crystals could not be produced. At low temperatures, the reaction is mainly controlled by dynamics, while at high temperatures, thermodynamics dominates the direction of the reaction.

Tailoring porous structure and graphitic degree of seaweed-derived carbons for high-rate performance lithium-ion batteries

Hierarchical porous carbons embedded with graphitic domains were synthesized by carbonization of seaweeds with a catalytic graphitization strategy. The Ni2+ ions are pre-chelated with seaweeds precursor (porphyra) to enable a catalyst confined graphitization process and to provide mesopores template. Carbonization temperature is significant in tailoring graphitic degree and porosity structure of porphyra-derived carbons (PDCs). The PDCs carbonized at 900 °C (PDC-900) show favorable features for electrochemical energy storage, which balance the specific surface area (515.7 mm2g-1), degree of graphitization (ID/IG = 0.78), expand graphite interlayer spacing (∼0.342 nm), and N-doping (2.13 wt%). These unique features of PDC-900 not only can supply abundant sites for the storage and insertion of Li ions, but also can facilitate rapid mass transport of electrons and Li ions. Thus, PDC-900 shows remarkable reversible capacity (950 mAhg−1 at 0.1 C), excellent rate capability (352 mAhg−1 at 10 Ag-1), and superior cycling performance (348 mAhg−1 at 5 Ag-1 after 3000 cycles), when used as an anode material for lithium ion batteries.

An intermittent microwave-exfoliated non-expansive graphite oxide process for highly-efficient production of high-quality graphene

Redox methods represented by Hummers’ method are the most frequently-used pathways to prepare graphene, but to date still very low-efficient, because of its time-consuming washing and hard reduction process. Here we report an intermittent microwave-exfoliated non-expansive graphite oxide (GtO) process to prepare a wrinkled graphene with a high reduction degree (C/O: 19.0), a high defect degree, and a high specific surface area (1333.7 m2 g−1). Findings show that the non-expansive GtO without water washing indicates an almost 100% exfoliated success rate during this intermittent microwave process. The obtained graphene shows easy dispersity in organic solvents, and excellent supercapacitor performance in specific capacitance, rate capacity, and especially in cycling lifetime with no decay after 80,000 cycles at 30 A g−1. Consequently, this special microwave process successfully solves the problems of tedious washing and hard reduction in redox methods, thus exponentially boosting the efficiency of preparing graphene.

The degradation of humidity sensitivity of friction for tetrahedral amorphous carbon film by spin-coating hexagonal boron nitride

At present, the strong friction-dependence on the working environments of amorphous carbon films (a-C) is a troublesome problem that limit theirs wide application, especially the environment humidity. In previous studies, it was shown that the incorporation of other elemental atoms into a-C films could control theirs tribological humidity-sensitivity to some extent. Here, a simple and effective method is employed by spin-coating a hexagonal boron nitride (h-BN) layer on surface of tetrahedral amorphous carbon (ta-C) film. It plays an efficient role on the degradation of humidity-sensitivity of friction for ta-C films, as well as reducing the friction. The underling mechanism is attributed to the enhanced graphitization process catalyzed by h-BN, leading to generation of more ordered carbon, thus enabling the low and stable friction.

Content of Long-Lived Radionuclides of Carbon-14 and Chlorine-36 in Reactor Graphite and in the Biosphere (Is there a Problem with Carbon-14 and Chlorine-36 when It Comes to the Processing of Reactor Graphite?)

The amounts of technogenic carbon and chlorine contained in reactor graphite and in the biosphere are compared. The total amount of 14C on Earth and in the atmosphere, according to a rough estimate, is 2.0 × 108 Ci, while in all reactor graphite in Russia this value is no more than 3 × 107 Ci. The amount of 36Cl in reactor graphite is approximately (0.2–5) × 103 Ci, which is many times less than its content in the ocean, 7.16 × 108 Ci. Therefore, when disposing of reactor graphite waste in a near-surface storage, the yield of 14C and 36Cl will not lead to significant disproportions in their accumulation in the biosphere

Investigation of Changes in the Fine Structure of Graphitizing Carbon Materials during Heat Treatment by X-Ray Diffraction Analysis

The properties of synthetic graphite materials, widely used in advanced fields, are determined by their structure, which is formed in the process of high-temperature (~2500°C) heat treatment. The fine structure of a graphitizing carbon material based on petroleum coke containing 1.3 wt% S at various stages of graphitization was studied by X-ray diffraction analysis. Some of the samples contained the addition of dispersed Fe2O3. It is shown that the heat-treated material in the range 1200°C - 2600°C is heterogeneous, its component composition is determined by the processing temperature and the presence of Fe2O3 additive. The observed dependence of the component composition on the heat treatment temperature suggests that the process of graphitization of the carbon material, apparently, develops through a number of metastable states.

Анализ примесного состава синтетических HPHT-алмазов методом лазерно-искровой эмиссионной спектроскопии в условиях лазерно-индуцированной модификации поверхности

Analysis of impurities in multisectoral plates of boron- and nitrogen-doped synthetic HPHT diamonds was performed by laser-induced breakdown spectroscopy. It was shown that comparative analysis of plasma emission bands during laser-induced graphitization process is effective approach to distinguishing types of diamonds and crystallographic orientations of sectors.

Efficient Removal of Diclofenac from Aqueous Solution by Potassium Ferrate-Activated Porous Graphitic Biochar: Ambient Condition Influences and Adsorption Mechanism.

Porous graphitic biochar was synthesized by one-step treatment biomass using potassium ferrate (K2FeO4) as activator for both carbonization and graphitization processes. The modified biochar (Fe@BC) was applied for the removal of diclofenac sodium (DCF) in an aqueous solution. The as-prepared material possesses a well-developed micro/mesoporous and graphitic structure, which can strengthen its adsorption capacity towards DCF. The experimental results indicated that the maximum adsorption capacity (qmax) of Fe@BC for DCF obtained from Langmuir isotherm simulation was 123.45 mg·L−1 and it was a remarkable value of DCF adsorption in comparison with that of other biomass-based adsorbents previously reported. Thermodynamic quality and effect of ionic strength studies demonstrated that the adsorption was a endothermic process, and higher environmental temperatures may be more favorable for the uptake of DCF onto Fe@BC surface; however, the presence of NaCl in the solution slightly obstructed DCF adsorption. Adsorption capacity was found to be decreased with the increase of solution pH. Additionally, the possible mechanism of the DCF adsorption process on Fe@BC may involve chemical adsorption with the presence of H-bonding and π–π interaction. With high adsorption capacity and reusability, Fe@BC was found to be a promising absorbent for DCF removal from water as well as for water purification applications.

The improved mechanical and tribological properties of amorphous carbon film by doping boron carbide

Recently, we have reported that graphite-like tribolayers formed on the sliding interface is essential to low friction in nitrogen for amorphous carbon-based (a-C) films with low hydrogen content. Therefore, for hydrogen free a-C film, it is necessary to promote the formation of graphite-like tribolayers for friction reduction. Borides has been proved an effective graphitization catalyst that accelerates the graphitization process of different carbon materials, yet has not been tried for a-C film under friction. Here, we fabricated the a-C and B4C doped a-C (B4C/a-C) films on 304 stainless steel substrates by unbalanced magnetron sputtering equipment. Compared to a-C film, B4C/a-C film exhibited better mechanical properties, as well as superior lubrication performance. Therein, the improved mechanical properties of B4C/a-C film are favorable for the excellent wear resistance. Besides, the friction reduction of B4C/a-C film is attributed to catalytic graphitization of tribolayers formed on the sliding interfaces triggered by B4C. This work indicates that B4C/a-C film will become an alternative solid lubricant material for a wide range of applications in the mechanical engineering fields.

Porous Graphene-like Carbon from Fast Catalytic Decomposition of Biomass for Energy Storage Applications.

A novel carbon material made of porous graphene-like nanosheets was synthesized from biomass resources by a simple catalytic graphitization process using nickel as a catalyst for applications in electrodes for energy storage devices. A recycled fiberboard precursor was impregnated with saturated nickel nitrate followed by high-temperature pyrolysis. The highly exothermic combustion of in situ formed nitrocellulose produces the expansion of the cellulose fibers and the reorganization of the carbon structure into a three-dimensional (3D) porous assembly of thin carbon nanosheets. After acid washing, nickel particles are fully removed, leaving nanosized holes in the wrinkled graphene-like sheets. These nanoholes confer the resulting carbon material with ≈75% capacitance retention, when applied as a supercapacitor electrode in aqueous media at a specific current of 100 A·g–1 compared to the capacitance reached at 20 mA·g–1, and ≈35% capacity retention, when applied as a negative electrode for lithium-ion battery cells at a specific current of 3720 mA·g–1 compared to the specific capacity at 37.2 mA·g–1. These findings suggest a novel way for synthesizing 3D nanocarbon networks from a cellulosic precursor requiring low temperatures and being amenable to large-scale production while using a sustainable starting precursor such as recycled fiberwood.

Simple construction of ruthenium single atoms on electrospun nanofibers for superior alkaline hydrogen evolution: A dynamic transformation from clusters to single atoms

Abstract The challenges for preparing metal single atoms (MSAs) catalysts are facile synthesis approaches and the suitable supports with strong coordination to stabilize MSAs. Herein, we reported a facile strategy to synthesize the Ru single atoms (Ru SAs) through the dynamic transformation from clusters to single atoms by combining the electrospun technology and NH3-assisted graphitization process. The small Ru nanoclusters (NCs) supported on carbon nanofibers (CNFs) were in situ converted into Ru SAs in N-doped CNFs under the NH3 treatment. Through controlling the NH3 treatment time and graphitization temperatures, the Ru nanocrystals exhibit a dynamic transformation from nanoclusters to single atoms. The results indicate that the Ru NCs with larger amounts of Ru SAs exhibit superior HER activity in alkaline media with low overpotential of 34 mV at 20 mA cm−2, which is even significantly better than commercial Pt/C catalysts. The mass activity of Ru SAs/NCNFs is about 390 A g−1Ru at an overpotential of 100 mV, which is ~3.5 times higher than that of commercial Pt/C (110 A g−1Pt). This strategy will provide a new way for the large-scale production of MSAs transformed from different metal nanoparticles or nanoclusters.

Enhancement of flaky graphite cleaning by ultrasonic treatment.

In this study, the aim is to simplify the graphite cleaning process. In order to achieve flotation for graphite effectively, ultrasonic treatment was used as a pre-treatment technique. Flotation tests were conducted using different ultrasound power and ultrasonic treatment time. The influences of ultrasonic treatment on particle sizes, morphologies, wettability, the content of surface elements and on the flotation effect of flaky graphite were investigated. The results of ultrasonic treatment for graphite flotation were compared with the results of conventional flotation. The results showed that ultrasonic treatment not only changed the size of flaky graphite, but also eliminated impurities on the graphite surface. Additionally, the ultrasonic treatment improved the hydrophobicity of graphite. It was observed that ultrasound can remove not only silicate impurities but also most other metal impurities. The yield, carbon content and recovery of flotation concentrate were 91.46%, 95.17% and 96.12% after ultrasonic treatment for 4 min with ultrasound power 1600 W, which were 5.83%, 2.86% and 8.84% higher than that of conventional flotation, respectively. The graphite after ultrasonic treatment was conducted only one times flotation, the carbon content in concentrate products had reached 95%. This study indicates that intensifying graphite flotation by ultrasonic treatment can shorten the graphite cleaning process.

The behavior of radioactive metals (Am, Eu, Sr) during the processing of radioactive graphite in salt melts

The behavior of Am, Eu, Sr radionuclides was investigated by thermodynamic modeling method at heating of radioactive graphite in NaCl – KCl – Na2CO3 – K2CO3 molten salt with additives of nickel oxide NiO. The integrated thermodynamic analysis was carried out by means of TERRA software in temperature range 373-3273 K to determine possible composition of condensed and gaseous phases. It was established that americium is in gaseous state in temperature range 2773-3273 K. Europium is in the forms of gaseous EuO and Eu in temperature range 2373-3273 K. Strontium is in the forms of gaseous SrCl2, SrCl, Sr, SrO in temperature range 2373-3273 K.

Safer modified Hummers’ method for the synthesis of graphene oxide with high quality and high yield

We report on an improved method for the synthesis of graphene oxide based on the modified Hummers’ method proposed by Marcano et al Different steps of the process were optimized. First, the concentration of the reactants and the reaction conditions were optimized to improve the efficiency of the oxidation process of graphite. The Raman spectrum of the GO shows the typical D and G typical of graphite oxide materials. The contribution of the area under the band D to the total area is 98%, confirming that almost the whole graphene was oxidized (high oxidation yield). Furthermore, the quantification of the C 1s XPS spectrum of our GO nanosheets indicates that about 77 wt% of oxygen in the form of oxygenated groups is bonded to the carbon nanosheets. Second, the reaction time was minimized to 12 h, without compromising the quality (as confirmed by micrography). Third, the production of toxic gases has been reduced. Fourth, a thermal treatment was introduced instead of the vacuum drying procedure traditionally used, greatly diminishing the overall graphite oxide processing time that includes: the reactant preparation, graphite oxidation process, rinsing and dispersion procedures, and drying (the drying time went from 12 h to 2 h). Reducing the total time by a half, compared to other methods, is an important finding considering scaling for industrial production.

Improved Thermal Conductivity and Ablation Resistance of Microdiamond‐Modified C/C Composites after Diamond Graphitization

C/C composites with diamond addition are prepared, and a 1600 °C heat treatment is conducted to investigate the effects of diamond graphitization on the ablation resistance and thermal conductivity of the composites. With diamond content increasing, a higher degree of stress graphitization occurs to the surrounding pyrolytic carbon (PyC) due to the enhanced stress accumulation in the diamond stacking region during graphitization process. After heat treatment at 1600 °C, the single diamond/PyC interface is substituted by complex diamond/graphite and graphite/PyC interfaces which results in a more compact structure and enhanced interface strength. Benefiting from the optimized interface microstructure and reduced closed pores after diamond graphitization, higher thermal conductivities are achieved for C/C–diamond composites. The ablation performance of the composites is improved due to the better oxidation resistance of diamond particles, increased compactness of diamond stacking region, and optimized thermal properties of the composites.

Role of inherent pyrite in coal on physicochemical structure of activated carbon and adsorption capacity

Pyrite is the most common inorganic iron-bearing mineral in coal. In order to reveal the influence of inherent pyrite on physicochemical structure and adsorption performance of AC, in this study, different content of pyrite (0.5%, 1%, 2%, 3%) were physically mixed with Yangcheng coal and briquetted, carbonized and steam activated for activated carbon (AC) preparation. As-obtained ACs’ morphology, pore texture, carbon crystallite structure and surface chemistry were characterized by SEM, BET, XRD and FTIR, respectively. The results show that pyrite (FeS2) transformed into hematite (Fe2O3) during AC preparation. Pyrite promotes the interaction between water vapor and carbon and enhances the rate of gasification reactivity by inhibiting the growth of heavy aromatic structures, catalyzing the graphitization process and enhancing the surface chemical properties. The total specific area and specific surface area of micropore of 2%FeS2/AC are up to 836 m2/g and 644 m2/g, which are 58.6% and 46.9% higher than AC, respectively. The 2 h sulfur capacity of 2%FeS2/AC is up to 65.2 mg/g, which is 18.8% greater than that of AC (54.9 mg/g), the mechanism of which was proposed: absorbed gaseous SO2 finally transformed into H2SO4 in macropores and forming an acid macro-environment where most Fe2O3 attacked by the generated H2SO4 on the AC’s pore surface to form Fe2(SO4)3. Fe3+ can promote the oxidation of SO3 to form H2SO4, and a redox cycle of Fe2+ and Fe3+ was established. Moreover, 1%FeS2/AC shows the highest Rhodamine B (RhB) adsorption, and the capacity of RhB is 168 mg/g, which is 41.2% higher than that of AC.

Nanodiamond graphitization at heating and irradiation

In this work the graphitization and thermal stability of detonation nanodiamonds were studied. Received data showed that the temperature of graphitization of nanodiamond particles lies in wide range and the temperature of graphitization beginning depend on the particle size. It is established the influence of heating rate on the size of nanodiamond conglomerates. The analysis of literature shows that the graphitization processes take place at irradiation. Depending on the type and irradiation dose the point defects, amorphous and graphite phases can form in the diamond structure. Annealing of irradiation samples showed the defect structure restore to ideal lattice and the release of stored energy.