Oxidation Process Of Graphite Research Articles

Sustainable and cost-effective edge oxidized graphite/PEDOT:PSS nanocomposites with improved electrical conductivity

Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is a soft and conjugated polymer whose conductive properties can be properly tuned through doping with various additives or solvents, preserving its excellent processability. In this work PEDOT:PSS was combined with a cost-effective graphite derivative named Edge Oxidized Graphite (EOG) for developing a nanocomposite with improved electrical conductivity, with respect to the pristine PEDOT:PSS, through an easy and environmentally friendly doping process. Firstly, the EOG powders, produced by a green oxidation process of graphite, were deeply characterized through Fourier transform infrared (FT-IR), Thermogravimetric (TGA), and Wide-angle X-ray scattering (WAXD) analysis, showing that this nanofiller has oxygenated functional groups on the sheet edges. The quality and the stability of the EOG dispersions within PEDOT:PSS were investigated at different carbon-filler concentrations, up to high loading of 25 %wt/V of EOG through rheological analyses, demonstrating pseudo-plastic behavior and excellent long-term stability of the inks due to the absence of inhomogeneities and aggregates over time; in fact, the same inks were tested under the same rheological conditions after 21 days, showing the same viscosity trend for all EOG concentrations (%wt/V). Transmission electron microscopy (TEM) and (Scanning Electron microscopy) SEM investigation of spin-coated samples onto glass substrates were performed to morphologically evaluate the nanocomposites and estimate the average size of the sheets, particularly the mean length of 1.2 μm and an approximated thickness of 26 nm of the EOG sheets dispersed into the polymer matrix (PEDOT:PSS) was determined, while WAXD analysis allowed to identify the average layer number of the EOG sheets, obtaining thus, a direct measurement of the EOG sheets aspect ratio equal to 45. Finally, sheet resistance tests showed that the increasing concentration of EOG leads to a significant improvement in the electrical conductivity of the nanocomposites, from 1.1 S/cm for pristine PEDOT:PSS to 21.9 S/cm for nanocomposites with the highest EOG content (25 %wt/V). This work demonstrates the successful development of nanocomposite based on PEDOT:PSS doped with carbon-based filler synthesized through a green and cost-effective process, promoting their use in the production of bio/electrochemical sensors or optoelectronic devices.

Numerical simulation of the transient graphite oxidation process based on a dynamic mesh method

The high-temperature gas-cooled reactor uses graphite-matrix spherical fuel elements to coat the tri-structural isotropic fuel particles (TRISO). In accident conditions, graphite oxidation may cause fuel particle exposure, which further leads to severe radioactive contamination. Therefore, it is very important to study the oxidation behavior of graphite during air-ingress accidents. This work aimed to develop a reaction kinetic model of graphite oxidation based on the Institute of Nuclear and New Energy Technology (INET) experiment correlations and to study the transient process of graphite oxidation using computational fluid dynamics and a dynamic mesh method. The results show that convective diffusion and mass diffusion dominate the distribution of reaction products at different flow rates. The reaction rate in the early stage of oxidation was high and then decreased rapidly until the oxygen consumption rate and supplementation rate reached equilibrium. After that, the oxidation rate decreased slowly due to the reduction of graphite surface area. The fluctuating flow around the graphite leads to anisotropic oxygen concentrations at different inflow angles on the graphite surface. The fluctuations caused a non-uniform ellipsoidal graphite structure, in which graphite has a smaller radius of curvature and pits on the windward side and a larger radius of curvature on the leeward side. The oxidation mass of graphite is in good agreement with the INET experimental data, which shows that this study can provide a method for the estimation of the mass and shape of graphite oxidation.

Highly conductive quasi-defect-free reduced graphene oxide for qualitative scalable production

Herein, we present a potential approach for the qualitative production of quasi-defect-free reduced graphene oxide (QrGO) with semimetallic transport behavior. In rGO, the formation of defects is highly dependent on the oxidation process of graphite. Subsequent exfoliation of graphite oxide, the quasi-defect-free graphene oxide (QGO) shows abundant epoxy and hydroxyl groups which confirmed the suppressed structural deformation. Typical rGO and QrGO are compared to characterize the remarkable electrical, optical, and thermal properties of QrGO. In particular, under low temperature, the unusual carrier transport phenomena of QrGO exhibits a metal-like behavior, unlike typical rGO, which shows an insulator-to-semimetal transition with variable-range hopping conduction behavior. This conduction mechanism, resembling that of mechanically exfoliated graphene, facilitates the fabrication of a QrGO-based conducting film with a high electrical conductivity of ∼1000 S/cm. Moreover, during a 200-h test with temperature and moisture conditions of 85 °C and 85%, respectively, QrGO shows environmental stability with minimal fluctuations in resistance. Furthermore, a conducting paste was fabricated from QrGO in an aqueous solution, showing a highly concentrated solid content and excellent electrical conductivity. It shows great potential for the large-scale production of high-quality chemically exfoliated graphene for practical applications.

Development of rGO/Fe3O4 Composites as Glucose Biosensors

The rGO/Fe3O4 composite is one type of composites that can be used as a biosensor material, especially glucose sensors. The main ingredients of the composite synthesis are graphite and iron sand. The synthesis process of Fe3O4 was done using the coprecipitation method, while the graphite oxidation process was accomplished using the modified Hummer's method. The composites were formed using the ex-situ wet mixing method. The formed iron sand and graphite were characterized using FTIR and XRD, and it was found that Fe3O4 was formed from the appearance of the Fe-O bond, the oxidation process of graphite was seen from the appearance of the C=O bond, and the detection of Fe peaks corresponded to the cubic crystal plane. Likewise, the composites formed were also characterized using FTIR and XRD for identification of the rGO/Fe3O4 composite formation. It was proven from the presence of Fe-O and C-O bonds and the appearance of an amorphous peak of rGO in the XRD results. The performance of the rGO/Fe3O4 composites as the glucose biosensor was examined by varying the mass of Fe3O4 on the composite, using UV-Vis spectroscopy. The performance of the rGO/Fe3O4 composite biosensor in absorbing glucose reached optimum at a mass variation of 0.3 grams of Fe3O4, as demonstrated by by the lowest absorbance peak with an intensity of 0.0048 at a wavelength of 440 nm, corresponding to glucose entrappment of 7.1 mg/gram.

Modification of hydrothermal synthesis using microwave irradiation for ZnO/graphene nanocomposite

Graphene has good physical properties such as electronic, optical and mechanical properties. The unique properties of graphene are interesting to study, especially in the field of electronic devices. Graphene was synthesised with chemical reduction using the Tour method. The oxidation process of graphite into graphene oxide (GO) occurs in a solution with the acidic atmosphere of H2SO4/H3PO4. ZnO/graphene nanocomposite was prepared by modification of hydrothermal synthesis using microwave irradiation. Characterisation of material structures includes SEM-EDX and FTIR. SEM micrograph shows that the morphology of the ZnO/graphene synthesis of oxidising acids H2SO4/H3PO4 9:1 ratio has better performance.

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.

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.

Investigation on the oxidation behavior and multi-step reaction mechanism of nuclear graphite SNG742

ABSTRACT Gas chromatography and numerical methods were used to investigate the oxidation behavior of SNG742 nuclear grade graphite at 500–1100°C with different oxidizing gas flow rates. A four-step overall reaction mechanism was used to describe the graphite oxidation reaction process, which reasonably explains the peak of CO mole fraction at around 700°C with lower flow rates. The kinetic parameters of apparent oxidation reaction and four-step reaction mechanism of SNG742 graphite were obtained through curve fitting of the measured data. The apparent activation energy of SNG742 nuclear graphite is 200.7 ± 14.2 kJ/mol. The effects of temperature and gas velocity on the oxidation rate were analyzed. The graphite oxidation process was effectively simulated using CFD method with porous media model and the four-step reaction mechanism. The simulation results show that increasing the gas flow rate can reduce the thickness of the diffusion boundary layer and influence the diffusion control regime of graphite oxidation. The four-step overall reaction mechanism can better describe the graphite oxidation process than the one-step overall reaction. The porous medium model can effectively simulate the mass diffusion process and surface chemical reaction in the interior porous region of the graphite.

Contact potential and scanning Kelvin force microscopy measurements on sulphate-anion intercalated graphite

In the current interpretative model of graphite anion intercalation, the characteristic blisters, formed after the incipient surface oxidation, have the same structural behaviour of pristine graphite. However, this result is deduced from scanning tunneling microscopy data, which cannot give a chemical fingerprint of the electrode surface. Conversely, the contact potential difference between a reference tip and a sample depends on the chemical as well as on the structural conditions of the surface. As a consequence, in this paper, we combine a contact potential measurement with a scanning Kelvin force microscopy analysis, in order to extract information on electronic changes occurring to the electrode with a sub-micrometre investigation of the surface morphology after the incipient graphite oxidation process in diluted sulphuric acid. The results suggest that, as well as the structural properties, no significant electronic differences occur between blisters and the graphite basal plane after the intercalation process.

Facile and effective oxidation of graphite using sodium metaperiodate

A novel effective and facile oxidation process of graphite using sodium metaperiodate is reported. The formed graphene oxide is confirmed by XRD, XPS and 13C NMR MAS spectra. AFM images show the size of the layer to be around 0.9–1.1nm and the carbon-oxygen ratio is calculated as 2.09. The new method of synthesis can be referred as non-metallic oxidation of graphite, which is easy to remove the impurities with no evolution of toxic gases.

Monothiolation and Reduction of Graphene Oxide via One-Pot Synthesis: Hybrid Catalyst for Oxygen Reduction

The functionalization of graphene provides diverse possibilities to improve the handling of graphene and enable further chemical transformation on graphene. Graphene functionalized with mainly heteroatom-based functional groups to enhance its chemical and physical properties is intensively pursued but often resulted in grafting of the heteroatoms as various functional groups. Here, we show that graphene oxide can be functionalized with predominantly a single type of sulfur moiety and reduced simultaneously to form monothiol-functionalized graphene. The thiol-functionalized graphene shows a high electrical conductivity and heterogeneous electron transfer rate. Graphene is also embedded with a trace amount of manganese impurities originating from a prior graphite oxidation process, which facilitates the thiol-functionalized graphene to function as a hybrid electrocatalyst for oxygen reduction reactions in alkaline medium with an onset potential lower than for Pt/C. Further characterizations of the graphene are performed with X-ray photoelectron spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, and electrochemical impedance spectroscopy. This material contributes to the class of hybrids that are highly active electrocatalysts.

Structural Evolution during the Oxidation Process of Graphite

The structural evolution during the oxidation process of graphite by a modified Hummers method is investigated. The graphite oxide (GO) composition, disorder parameter, and structures are confirmed by means of x-ray diffraction, Fourier transform infrared spectroscopy, Raman, and scanning electron microscope techniques. Results show that: Hydroxyl, carboxyl and ether groups are present in the low-temperature oxide (at 0°C); and the degree of oxidation is increased with a longer oxidation time. The middle-temperature oxidation (35°C) is a transitory stage with a slight change to the GO structures. While for the high-temperature oxidation (95°C), the hydroxyl, carboxyl and epoxide functional groups are largely originated on the GO flakes. Hydroxyl groups are transformed into more epoxide groups with longer oxidation time, and at the same time, ether groups are eliminated, leading to defects (such as holes) on the GO flakes.

Influence of synthesis conditions on properties of green-reduced graphene oxide

Green reduction of graphene oxide (GO) was performed using ascorbic acid (AA) in the presence of poly(sodium 4-styrenesulfonate), which resulted in reduced graphene oxide (PSS–rGO) with excellent solubility and stability in water. Large rGO sheets of 4 μm2 area and 1.1-nm thickness were obtained. The measurements showed that noncovalent functionalization with PSS molecules prevented rGO from aggregation. The parameters of graphite oxidation process and AA:GO w/w ratio were evaluated, and the obtained results showed that the properties of the reduced material (PSS–rGO) can be tailored by proper selection and adjustment of these parameters.

Electrical and spectroscopic investigations on the reduction mechanism of graphene oxide

Ultra-large graphene oxide sheets of monolayer thickness were obtained by removing ultrasonication during the conventional oxidation process of graphite. In situ electrical conductivity measurement during the reduction by hydrazine monohydrate vapor and thermal annealing revealed the existence of an onset temperature at which electrical conduction started to occur. Corresponding X-ray photoelectron spectra indicated that an approximately 65% restoration of the sp2 network led to the occurrence of electrical conduction. Reduction by ring-opening of epoxide group by hydrazine treatment seemed to restore the sp2 network, while thermal annealing left a considerable number of defects in the graphene sheet through the formation of volatile gases.

The effect of the parent graphite on the structure of graphene oxide

The effect of the parent graphite on the structure of graphene oxide (GO) is investigated using high purity graphites with a uniform crystallite size. Our results provide direct evidence of how the size of the graphite crystal affects the oxidation process and the functionality and sheet size of the resulting GO. The important role of the crystal boundaries in the graphite with smaller crystallites is confirmed by the smaller size of the GO sheets obtained and also by the presence of carboxylic groups, located at the edges of the sheets. However, functionalization in the graphite with larger crystals mainly occurs in the vicinity of basal plane defects, as evidenced by the larger number of epoxy groups. Thus, this study leads to a better understanding of the oxidation process of graphite and provides a way to produce GOs suitable for different applications.

Oxidation performance of graphite material in reactors

Graphite is used as a structural material and moderator for high temperature gas-cooled reactors (HTGR). When a reactor is in operation, graphite oxidation influences the safety and operation of the reactor because of the impurities in the coolant and/or the accident conditions, such as water ingress and air ingress. In this paper, the graphite oxidation process is introduced, factors influencing graphite oxidation are analyzed and discussed, and some new directions for further study are pointed out

Behavior of manganese dioxide electrodes in a system containing a solid protonic electrolyte

The behavior of manganese dioxide electrodes containing powders of graphite and titanium as electroconducting additives is studied in a system with a solid protonic hydrated electrolyte (SPHE). The MnO2 reduction is accompanied by ion exchange between formed Mn2+ ions and structural protons of SPHE. The open-circuit potentials drift in the anodic direction and stabilize when the MnO2 composition at a boundary with SPHE is close to stoichiometric. The drift is due to conjugated reactions of the MnO2 reduction and the graphite oxidation process that decays with time. With increasing cathodic current density, the solid-phase reduction of MnO2 via an electronic-protonic mechanism becomes predominant. At low polarizing-current densities, the open-circuit and steady-state potentials remain passably stable until the exchange capacity of SPHE by protons is exhausted or MnO2 near the interface with SPHE is spent. The feasibility of using MnO2-SPHE-based amperometric sensors for assaying components whose oxidation in a gas medium yields protons is considered

Magnesium oxide‐iron oxide mass balance constraints and a more detailed model for the relationship between eucrites and diogenites

Abstract— According to a currently popular model for petrogenesis on the howardite, eucrite, and diogenite (HED) parent asteroid, the diogenites are not comagmatic with most eucrites but instead formed in separate orthopyroxenite‐dominated plutons. This model can be tested for consistency with mass balance for MgO and FeO, assuming the overall diogenite/(diogenite + eucrite) ratio, d, of the parent asteroid is at least comparable to the average d for the eucrite + diogenite dominated howardite regolith breccias. Average mg# (=MgO/[MgO + FeO]) is much lower for eucrites, especially noncumulate eucrites, than for diogenites. Unless the diogenite parent magmas eventually produced a large proportion of low‐mg# residual basalt and gabbro (RBG), the implied initial magma's mg# is vastly higher than that of any noncumulate eucrite. Starting from a source previously depleted by putative primary eucrite genesis, melt mg# can be estimated as a function of the exchange reaction KD and degree of melting. Using several very conservative assumptions (e.g., assuming that the total [MgO + FeO] concentration is nearly the same in the nascent melt as in the residual solids), the degree of melting required to yield a melt with mg# high enough to satisfy mass balance, without implying an RBG component that accounts for >50% of all eucrites, is an implausibly high 60–80 wt%.The separate orthopyroxenitic plutons (SOP) model also seems inconsistent with the uniform density of melts across the diogenite‐eucrite compositional spectrum (2.77–2.82 g/cm3), which implies that diogenitic magmas should have been as capable as eucrites of extruding to form lavas. This difficulty cannot be reduced by simply assuming that later‐formed magmas were systematically both more plutonic and more MgO‐rich than earlier ones, because the plutonic cumulate eucrites equilibrated with melts systematically lower in mg# than noncumulate eucrites. Conceivably, the bulk mg# of the asteroid's silicate system was increased between primary‐melt eucrite genesis and SOP diogenite genesis by graphite‐fueled reduction of FeO. However, the graphite oxidation process generates a huge proportion of gas, which would have enhanced the buoyancy of the nascent diogenite‐parent magmas, thus exacerbating the difficulty of achieving the implied high degrees of partial melting.To avoid these difficulties but still form most eucrites as rapidly cooled extrusives, I propose the NERD (noncumulate eucrites as extruded residua of diogenites) model. In this model, the diogenites form as early cumulates from a large magma system (probably a global “magma ocean”) that yields a large proportion of eucritic melt as residuum. This residual melt zone undergoes relatively little crystallization during a period when it is episodically tapped to produce extrusions, dikes and sills of rapidly cooled noncumulate eucrites. Slight (∼5–10%) porosity in the nascent eucritic crust keeps it marginally buoyant over the residual melt zone. The common thermal metamorphism of noncumulate eucrites results from baking by superjacent flows during the episodic venting of the melt zone. The NERD model's greatest advantage is that it does not require implausibly high degrees of localized melting in the mature stages of igneous evolution of the HED asteroid.

Study of the oxidation products of ultrapure graphite at 0°C—III. Retention of ethylene-glycol, surface area and kinetics of the oxidation process

Throughout the cold oxidation process of pure graphite, an increase of the basal spacing is produced which allows the penetration of polar liquids between the layers of the graphitic acid formed during the oxidation process. A study has been made of the retention of ethylene-glycol in samples of graphitic acid, oxidized to different degrees, obtained from natural mineralogical graphite and from an artificial graphite. The interlayer surface area has been determined once we know that the sorbate forms a monolayer, and supposing that the area covered by each molecule of the sorbed ethyleneglycol is 22Å 2. The density of the sorbed ethylene-glycol has been determined from the amount of sorbate retained and from the increase of the basal spacings. The values of the interlayer surface area of the most oxidized samples agree with those of the theoretical interlaminar surface area determined by X-rays and composition, and with those determined from the density of ethylene-glycol in benzene and the c parameter. Finally, the retention of ethylene-glycol by different samples tells us how the graphite is transformed into graphitic acid, which gives us an indirect method of determining the specific velocity of the oxidation process of graphite at 0°C.

67. Study of the oxidation products of ultrapure graphite at 0°C. Retention of ethylene glycol, surface area, and kinetics of the oxidation process

Abstract Throughout the cold oxidation process of pure graphite, an increase of the basal spacing is produced which allows the penetration of polar liquids between the layers of the graphitic acid formed during the oxidation process. A study has been made of the retention of ethylene-glycol in samples of graphitic acid, oxidized to different degrees, obtained from natural mineralogical graphite and from an artificial graphite. The interlayer surface area has been determined once we know that the sorbate forms a monolayer, and supposing that the area covered by each molecule of the sorbed ethyleneglycol is 22A 2 . The density of the sorbed ethylene-glycol has been determined from the amount of sorbate retained and from the increase of the basal spacings. The values of the interlayer surface area of the most oxidized samples agree with those of the theoretical interlaminar surface area determined by X-rays and composition, and with those determined from the density of ethylene-glycol in benzene and the c parameter. Finally, the retention of ethylene-glycol by different samples tells us how the graphite is transformed into graphitic acid, which gives us an indirect method of determining the specific velocity of the oxidation process of graphite at 0°C.