Structure Of Graphite Oxide Research Articles

Graphite oxide tribo-layer formation under boundary lubrication of diesel fuel

Friction and wear of mechanical components (such as engines) is controlled by some kind of boundary films (also referred to as tribo-layer). In some cases, such boundary film is formed on the contact interface due to a tribo-chemical process in the presence of liquid media. In this paper, we demonstrate the formation of graphite oxide tribo-layer on the contact interface of steel in the presence of diesel fuel liquid media. A Raman spectrometer was used to analyse the tribo-layer structure. Although the intensity is low, it is shown that the tribo-layer has a structure of graphite oxide, demonstrated by the presence of D band peak at approximately 1350 cm−1 and G band peak at approximately 1550 cm−1 in the Raman spectra. Such graphite solid films on the sliding surfaces have ability to control friction and wear. This finding demonstrates the possibility of in-situ formation of solid protective film of a tribo-pair components using the working fluid where the use of lubricants is restricted as they contaminate the working fluid.

Luminescence and energy storage characteristics of coke-based graphite oxide

The substantial escalation in both energy consumption and ecological crisis prompts the utilization of conventional pollution-causing energy resources towards a proficient mode of energy production and storage. The most polluting fossil fuel like coal possesses a highly ordered sp2 carbon clusters, that can be easily tailored into graphene derivatives promising for energy-related applications. However, the impact of crystallinity and quality of the precursor coke on the physicochemical characteristics of extracted carbon nanostructures need to be identified. Herein, we have prepared graphite oxide structures (GrO) from high-quality coal, coke via Improved Hummers' method eliminating the need for toxic NaNO3. The inherent defect states own by coke are also of high significance as it performs the role of various photoluminescence emission centers. The sp2 domains and different surface defects promote excitation independent and dependent luminescence substantiating the distinct multi-emission property of GrO. The extent of functionalization during the oxidation process has also significantly affected the thermal stability of the carbogenic structure. The symmetric galvanostatic charge-discharge curves and lower internal resistance present superior stability and fatser ion transport of as-synthesized GrO. A specific capacitance of 193F/g was obtained at 0.2A/g with excellent capacitance retention over 2500 cycles. The versatile attributes of the coke derived GrO validate its realizable optoelectronics and energy storage applications.

A NEW APPROACH TO THE USE OF TIN OXIDE FILMS FOR RENEWABLE ENERGY SOURCES

In this paper, the technologies of obtaining active elements for lithium-ion batteries based on sputtering of a film of graphite and applying a layer of tin oxide on it are considered. The result obtained, when using a SnO2 film, shows that the parameters of the irreversible capacitance can exceed the values of the return capacitance obtained simply on puregraphite (300-350 mAh / g). This shows the prospect of creating an active anode with a tin graphite oxide structure. Thedirections of optimization of technological processes of obtaining films, the importance of correct selection of thicknessratios, as well as the possibility of transition to the deposition of tin oxide on the carbon structure are highlighted in thework.In contrast to conventional technology, we have been producing anode system of electrode lithium-ion battery using vacuum sputtering on copper foil, which method of high-frequency magnetron deposition applied a layer of graphite and tin, meeting a number of technological requirements.The graphite tin oxide obtained by us has an extremely large variation of values from 380 mAh / g to 690 mAh / g. This is probably due to the raw technology of producing tin graphite by oxidation, as a result of multiphase inclusions of tin oxide. The ambiguity of the graphite structure depending on the film thickness also affects the result.From the presented results, it follows that intensive search for alternative carbon materials for the anode of lithium-ion battery is underway. Although none of the studied materials can compete with carbon at present, it is hoped that composites and nanocomposites of carbon and non-carbon materials will find application in the production of LIA in thenear future.On the basis of the obtained results the possibility of improvement of technical solutions and introduction of new technological processes in the production of lithium-ion batteries is shown, as well as possible directions of improvement of their operational characteristics are analyzed.

Influence of the oxidizing agent in the synthesis of graphite oxide

The oxidation capacity of several procedures described in the literature which use different oxidizing agents has been exhaustively studied in order to describe the best route for oxidation of this material. The oxidation capacities of different types of materials were evaluated in the synthesis of graphite oxide in an effort to obtain a product with similar characteristics to those provided by commonly employed methods. The results obtained show that graphite oxide structures are greatly influenced by the nature of the oxidizing agent used. It was concluded that it is possible not only to establish the number of oxygenated groups attached to the structure but also, and depending on the oxidizing agent used, to know the stability of graphite oxide. The different characteristics of each graphite oxide obtained could facilitate their use in multiple applications.

New insight of high temperature oxidation on self-exfoliation capability of graphene oxide

The preparation of graphene oxide (GO) via Hummers method is usually divided into two steps: low temperature oxidation at 35 °C (step I oxidation) and high temperature oxidation at 98 °C (step II oxidation). However, the effects of these two steps on the exfoliation capability and chemical structure of graphite oxide remain unclear. In this study, both the functional group content of graphite oxide and the entire evolution of interlayer spacing were investigated during the two steps. Step I oxidation is a slowly inhomogeneous oxidation step to remove unoxidized graphite flakes. The prepared graphite oxide can be easily self-exfoliated but contains a lot of organic sulfur. During the first 20 min of step II oxidation, the majority of organic sulfur can be efficiently removed and graphite oxide still remains a good exfoliation capability due to sharp increasing of carboxyl groups. However, with a longer oxidation time at step II oxidation, the decrease of organic sulfur content is slowed down apparently but without any carboxyl groups forming, then graphite oxide finally loses self-exfoliation capability. It is concluded that a short time of step II oxidation can produce purer and ultralarge GO sheets via self-exfoliation. The pure GO is possessed with better thermal stability and liquid crystal behavior. Besides, reduced GO films prepared from step II oxidation show better mechanical and electric properties after reducing compared with that obtained only via step I oxidation.

Exactly matched pore size for the intercalation of electrolyte ions determined using the tunable swelling of graphite oxide in supercapacitor electrodes.

The intercalation of solvent molecules and ions into sub-nanometer-sized pores is one of the most disputed subjects in the electrochemical energy storage applications of porous materials. Here, we demonstrate that the temperature- and concentration-dependent swelling of graphite oxide (GO) can be used to determine the smallest pore size required for the intercalation of electrolyte ions into hydrophilic pores. The structure of Brodie graphite oxide (BGO) in acetonitrile can be temperature-switched between the ambient one-layer solvate with an interlayer distance of ∼8.9 Å and the two-layer solvate (∼12.5 Å) at low temperature, thus providing slit pores of approximately 2.5 and 6 Å. Using in situ synchrotron radiation X-ray diffraction (XRD) and the temperature dependence of capacitance in supercapacitor devices, we found that solvated tetraethylammonium tetrafluoroborate (TEA-BF4) ions do not penetrate into both the 2.5 and 6 Å slit pores formed by BGO interlayers. However, increasing the electrolyte concentration results in the formation of a new phase at low temperature. This phase shows a distinct interlayer distance of ∼15-16.6 Å, which corresponds to the insertion of partly desolvated TEA-BF4 ions. Therefore, the remarkable ability of the GO structure to adopt variable interlayer distances allows for the determination of pore sizes that are optimal for solvated TEA-BF4 ions (about 9-10 Å). The intercalation of TEA-BF4 ions into the BGO structure is also detected as an anomaly in the temperature dependence of supercapacitor performance. The BGO structure remains to be expanded, even after the removal of acetonitrile, adopting an interlayer distance of ∼10 Å.

Atomic-force-microscopy nanowriting on ultrathin tetrahedral amorphous carbon films

We report the atomic-force-microscopy (AFM)-based nanolithography writing of surface patterns on ultrathin ( 4 V, and (3) the contact pressures in the GPa range results in the formation of a novel carbon phase in a nm-thick surface layer characterized by the lower density, lower mechanical strength, lower electrical conductivity, and increased nanofriction as compared to the original film. The structure of the tip-modified nm-thick layer on the ta-C film is assumed to be a structure of graphite oxide which can be further modified in the presence of water under high contact pressures.

Preparation and structure of graphite oxide functionalized with 1-aminopyrene

Preparation and structure of graphite oxide functionalized with 1-aminopyrene

Sintesis dan Karakterisasi Grafena dengan Metode Reduksi Grafit Oksida Menggunakan Pereduksi Zn

Graphene is a thin material, has a hexagonal two-dimentional lattice and is considered as an interesting material for adsorption process. Nowadays, graphene has been known as a potential material for diverse application, such as adsorbent. In this study graphene was synthesized from graphite. Furthermore, graphene was applied for adsorption of dichloro diphenyl trichloroethane (DDT). Graphene was synthesized by Hummer’s method using hydrothermal and reduced by Zn. The samples were characterized by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) methods. The results of the XRD showed graphene structure in the 2θ, appeared at 23.9369 with interlayer spacing was about 3.71763 Å, compared with graphite oxide structure in the 2θ appeared at 11.2055 with interlayer spacing was about 7.89649 Å. The results of SEM analysis showed graphene has one layer with planar hexagonal structure and seems transparent whose single layer and multi layers. The graphene adsorption was analyzed by using the UV-Visible spectrophotometer. The results indicated the surface area of graphene was shown as 46.8563 m2/g. The amount of DDT adsorbed by graphene during 15 minutes was 7.5859 mg/g. This adsorption mechanism of DDT and graphene might be due to π-π and hydrogen interactions. Keywords: Adsorption, dichloro diphenyl trichloroethane (DDT), graphena. DOI: http://dx.doi.org/10.15408/jkv.v2i1.2233

Refining the Structure of Graphite Oxide through Selective Labeling of Functional Groups

The various inherent functional groups within graphite oxide (GO) are of significant interest for numerous research applications exploiting their reactivity. While there has been much advance in the research of graphenes and GO over the years, our current understanding of GO structure is primarily derived using spectroscopic techniques such as XPS, NMR, FTIR and Raman spectroscopies. In contrast, we report an alternative electrochemical approach to investigate the composition of GO, previously developed to study surface functionalities within other carbon-based materials. In separate reactions, four electroactive labels were first employed to selectively label the various functional groups in GO, followed by their subsequent quantification using cyclic voltammetry. Distinct functional group compositions were consequently found depending on the choice of GO oxidation method, either via chlorate or permanganate oxidations. An additional advantage of the method is the ability to distinguishing the types of carbonyl groups such as quinonyl species over isolated ketones. Thus, we noted that permanganate oxidation produced GO with its carbonyls mainly existing as 1,2-quinones, while chlorate oxidation resulted primarily in aliphatic ketones. Furthermore, carboxylic groups that were erstwhile thought to be responsible for the acidic nature of GO were observed to be low in permanganate-GO and non-existent in chlorate-GO. We also deduced that epoxides likely exist as the main functionality within permanganate-GO, and discuss that the relatively low labelled-hydroxyl content may be due to previously proposed disproportionation reactions which result in formation of other groups. Overall, this selective labelling and electrochemical detection method has provided an improved and refined understanding of GO structures.

Preparation and structure of graphite oxide functionalized with 1-aminopyrene

Preparation and structure of graphite oxide functionalized with 1-aminopyrene

Modified structure of graphene oxide by investigation of structure evolution

The structure of graphite oxide and graphene oxide (GO) has been studied previously using various analyses and computer simulations. Although some oxygen functional groups (OFGs) are accepted as the main functionalities in GO, the structure of GO has remained elusive. In this regard, GO was produced using the modified Hummers method and was investigated using X-ray diffraction pattern, Fourier transform infrared analysis and Boehm titration method. Based on the obtained results, a modified model was proposed for GO based on the model of Lerf-Klinowski. OFGs include highly carboxyl groups and phenols with few epoxides, lactones and ketones agglomerated in some regions due to hydrogen bonding between functional groups. Trapped water molecules were shown between the GO sheets which strongly affected the distribution of OFGs and their aggregation by hydrogen bonding.

Structure of graphene oxide membranes in solvents and solutions.

The change of distance between individual graphene oxide sheets due to swelling is the key parameter to explain and predict permeation of multilayered graphene oxide (GO) membranes by various solvents and solutions. In situ synchrotron X-ray diffraction study shows that swelling properties of GO membranes are distinctly different compared to precursor graphite oxide powder samples. Intercalation of liquid dioxolane, acetonitrile, acetone, and chloroform into the GO membrane structure occurs with maximum one monolayer insertion (Type I), in contrast with insertion of 2-3 layers of these solvents into the graphite oxide structure. However, the structure of GO membranes expands in liquid DMSO and DMF solvents similarly to precursor graphite oxide (Type II). It can be expected that Type II solvents will permeate GO membranes significantly faster compared to Type I solvents. The membranes are found to be stable in aqueous solutions of acidic and neutral salts, but dissolve slowly in some basic solutions of certain concentrations, e.g. in NaOH, NaHCO3 and LiF. Some larger organic molecules, alkylamines and alkylammonium cations are found to intercalate and expand the lattice of GO membranes significantly, e.g. up to ∼35 Å in octadecylamine/methanol solution. Intercalation of solutes into the GO structure is one of the limiting factors for nano-filtration of certain molecules but it also allows modification of the inter-layer distance of GO membranes and tuning of their permeation properties. For example, GO membranes functionalized with alkylammonium cations are hydrophobized and they swell in non-polar solvents.

Refinements to the structure of graphite oxide: absolute quantification of functional groups via selective labelling.

Chemical modification and functionalization of inherent functional groups within graphite oxide (GO) are essential aspects of graphene-based nano-materials used in wide-ranging applications. Despite extensive research, there remains some discrepancy in its structure, with current knowledge limited primarily to spectroscopic data from XPS, NMR and vibrational spectroscopies. We report herein an innovative electrochemistry-based approach. Four electroactive labels are chosen to selectively functionalize groups in GO, and quantification of each group is achieved by voltammetric analysis. This allows for the first time quantification of absolute amounts of each group, with a further advantage of distinguishing various carbonyl species: namely ortho- and para-quinones from aliphatic ketones. Intrinsic variations in the compositions of permanganate versus chlorate-oxidized GOs were thus observed. Principal differences include permanganate-GO exhibiting substantial quinonyl content, in comparison to chlorate-GO with the vast majority of its carbonyls as isolated ketones. The results confirm that carboxylic groups are rare in actuality, and are in fact entirely absent from chlorate-GO. These observations refine and advance our understanding of GO structure by addressing certain disparities in past models resulting from employment of different oxidation routes, with the vital implication that GO production methods cannot be used interchangeably in the manufacture of graphene-based devices.

Polypyrrole/Graphene Oxide Composite Electrodes for High Energy Density Supercapacitor

Polypyrrole/Graphene oxide composite material (PPy/GO) was synthesized using an in-situ chemical polymerization method. The formation of composite had been shown by the analysis of Fourier transfer of infrared spectroscopy and X-ray diffraction data. Scanning electron and transmission electron microscopy clearly showed sheet-like layered structure of graphite oxide surrounded by polypyrrole. Electrochemical properties were characterized by electrochemical station. We demonstrated the intercalation of conducting polypyrrole into the graphite sheets, and that as electrodes for supercapacitor, the PPy/GO composites (GO0.54) with PPy to GO mass ratio of 5:3 showed a competitive capacitance of 337 F g-1 at a scan rate of 2 mV s-1 than that of PPy alone. Given the electrical and electrochemical properties, we prospect that the PPy/GO composites should find applications in supercapacitors.

Theoretical Investigations on Graphite Oxide Immersed in Water or Methanol

Different structures of graphite oxide (GO) with and without water are optimized by density functional theory. Without H2O in interlayer space, the optimized interlayer distances are about 6 Å, smaller than the experimental values of 6.5–7 Å. On the other hand, the interlayer distances of hydrated graphite oxide structures are in good agreement with experimental observations. Based on the optimized GO structures, we then simulate the immersion of GO in water or methanol by molecular dynamics. For the dry GO, water and methanol molecules do not enter the nanopore. While for the hydrated GO, the liquid molecules enter the interlayer space and enlarge the interlayer distance, semi-quantitatively reproducing the experimental phenomena.

Effect of graphite oxide structure on the formation of stable self-assembled conductive reduced graphite oxide hydrogel

As a novel tissue engineering material and transistor, reduced graphite oxide (rGO) hydrogel is attracting more and more attention, and a stable and highly electrical conductive rGO hydrogel is the cornerstone for these applications. We controlled the structures of graphite oxides (GOs) with three different methods and the corresponding assembled rGO hydrogels were obtained using Vitamin C (VC) as the reducing agent and the stability and electrical resistance of the rGO hydrogel were studied. The results showed that the appropriate interlayer distance and grain size of GO prepared by two-step oxidation were beneficial for VC molecules to insert in the interspace between layers for the reduction. After reduction, the loose and tangled network structure was well assembled, which determines the stability and electrical conductivity of the resulted rGO hydrogel.

Effect of the Hydrothermal Reaction Temperature on Three-Dimensional Reduced Graphene Oxide's Appearance, Structure and Super Capacitor Performance

Three-dimensional reduction of graphene oxide with a series of different degrees of reduction was performed by the hydrothermal method in the temperature range from 120 to 220 °C, with graphene oxide sols as the precursor and prepared by graphite oxide gels. The effect of the temperature of the hydrothermal reaction on the materials¹ appearance, structure, and super capacitor performance was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The results show that the prepared three dimensional reduction of graphene oxide was porous and reticulated, and its volume and inner mesh aperture gradually decreased with increasing temperature, while its degree of reduction and order increased at the same time, and its structure gradually transformed to the graphite oxide structure. However, thematerialsspecific capacitance

Graphite oxide/polypyrrole composite electrodes for achieving high energy density supercapacitors

Fabrication and characterization of high energy density supercapacitor based on graphite oxide/polypyrrole (GO/PPy) composites is reported. Improvement in charge storage has been obtained by exfoliation of graphite oxide sheets via intercalation of polypyrrole. The formation of composite has been shown by the analysis of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transfer of infrared spectroscopy data. Scanning electron and transmission electron microscopy clearly show sheet-like layered structure of graphite oxide surrounded by polypyrrole. Supercapacitors fabricated using this composite system result in a reduced equivalent series resistance value ~1.85 Ω. Such low value can be attributed to the intercalation of conducting polypyrrole into the graphite sheets. A specific capacitance of ~181 F g−1 in 1 M Na2SO4 aqueous electrolyte with a corresponding specific energy density of ~56.5 Wh kg−1 could be achieved. These values make GO-based materials suitable for their use as electrodes in high performance supercapacitors.

Graphite and graphene oxide electrodes for lithium ion batteries

Graphite oxide (GRO) was synthesized using Hummer's method by oxidation of pure graphite and subsequently converted into graphene oxide (GR) by a chemical conversion method to be used as electrode material in the lithium-ion batteries. Obtained materials were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Transmission electron microscopy results reveal cloth-type structure of GRO and GR with a thickness of 10nm. The specific discharge capacity of GRO electrode on stainless-steel mesh is 759.4mAh/g at a current density 100mA/g and 796.2mAh/g at 50mAh/g; on copper mesh 940mAh/g at current density 50mA/g and 825mAh/g at 100mA/g With a GR electrode on stainless-steel mesh a capacity of 897.7mAh/g at 50mA/g and 786.9mAh/g at 100mA/g and on copper mesh 824mAh/g and 790mAh/g at current densities 50 and 100mA/g were obtained.