Structure Of Graphite Oxide Research Articles

Graphite Oxide – Stages of Formation and a New View on Its Structure

It was shown that the structure of graphite oxide is formed in two stages. The first is hydroxylation of the graphene layers to a level of 4–6 hydroxyls to one coronene fragment (C24). The second is the accumulation of hydroxyl, peroxide, and hydroperoxide groups, accompanied by strong dearomatization of the graphene structure. Epoxide groups, previously considered some of the main oxygen-containing functional groups in graphite oxide, were not detected.

Influence of Electrolytes (TEABF4 and TEMABF4) on Electrochemical Performance of Graphite Oxide Derived from Needle Coke

The structure of needle coke was changed to graphite oxide structure after oxidation treatment with 70 wt.% of nitric acid and sodium chlorate (NaClO3), and the inter-layer distance of the oxidized needle coke was expanded to 6.9 angstroms. The first charge profile of the oxidized needle coke-cell with 1.2 M TEMABF4/acetonitrile solution displayed that the intercalation of electrolyte ions into the inter-layer occurred at 1.0 V, which value is lower than 1.3 V of the oxidized needle coke-cell with 1.2 M TEABF4/acetonitrile solution. After first charge/discharge, the cell using TEMABF4 electrolyte exhibited smaller electrode resistance of 0.05 omega, and larger specific volume capacitance of 25.5 F/ml at the two-electrode system in the potential range 0-2.5 V than those of the cell using TEABF4 electrolyte. Compared to the TEABF4 electrolyte, better electrochemical performance of the TEMABF4 electrolyte in the oxidized needle coke may be caused by the smaller cation (TEMA+) size and better ion mobility in the nanopores between inter-layers.

Tuning the Electronic Structure of Graphite Oxide through Ammonia Treatment for Photocatalytic Generation of H2 and O2 from Water Splitting

Graphite oxide (GO) synthesized from the oxidation of graphite powders exhibits p-type conductivity and is active in photocatalytic H2 evolution from water decomposition. The p-type conductivity hi...

Evidence of band bending and surface Fermi level pinning in graphite oxide

We present the electronic structure of graphite oxide in the vicinity of the Fermi level measured using ultraviolet photoemission and inverse photoemission spectroscopies and compare it with X-ray absorption spectra. The expected p-type behavior of graphite oxide is not observed at the surface and the presence of band bending is invoked. The observed electronic structure of graphite oxide exhibited an n-type semiconducting band structure with a band gap of 2.3±0.4eV. An oxygen related state, at 0.8eV above Fermi level, and the suppression of the unoccupied carbon weighted states at the conduction band minimum suggests that the oxygen vacancies at the surface of graphite oxide contribute to the n-type semiconducting electronic structure of the surface.

Back Cover: Selective Removal of Hydroxyl Groups from Graphene Oxide (Chem. Eur. J. 6/2013)

Selective removal of hydroxyl groups on graphene oxide has been achieved with ethanethiol–aluminium chloride complexes. The reduced graphene material exhibits improved electrochemical properties over its precursor graphite oxide (layered structure of graphite oxide depicted by the red layered wall of Antelope Canyon in Arizona). The selective defunctionalization of oxygen groups on graphene oxide opens up new opportunities for specific tailoring of graphene materials. For more information see the Full Paper by M. Pumera and C. K. Chua on page 2005 ff.

Preparation of graphite oxide (GO) and the thermal stability of silicone rubber/GO nanocomposites

Graphite oxide was synthesized by the oxidation of expanded graphite via a modified Hummers approach. The structure of graphite oxide was evaluated by TEM, XRD, Raman and FTIR. It was found that the structure of expanded graphite can be easily and remarkably disordered by oxidation. Silicone rubber/GO nanocomposites were prepared via a solution intercalation method. The structure of the nanocomposites was studied by XRD. The thermal behavior of the nanocomposites was characterized by TGA and the results showed that the addition of graphite oxide is beneficial to improve the thermal stability of the nanocomposites at high temperature.

Controlling graphite oxide bandgap width by reduction in hydrogen

Transformation of the chemical composition and electron structure of graphite oxide (GO) nanolayers as a result of their annealing in hydrogen has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. It is established that both the chemical composition and bandgap width of GO can be controlled by varying the temperature and duration of heat treatment. By this means, the properties of GO nanolayers can be smoothly changed from dielectric to semiconductor.

Surface acoustic wave response to ambient humidity in graphite oxide structures

The effect of ambient air humidity on surface acoustic waves (SAW) in graphite oxide-lithium niobate structures was investigated. The acoustic wave amplitude and phase strongly depended on the humidity level in structures with graphite oxide films deposited on the free substrate surface. These dependencies were significantly reduced in structures with graphite oxide films deposited on a metalized substrate surface. Fast (sub-second range) response in the acoustic amplitude and phase to step-like humidity changes was observed. Humidity-induced variations in the SAW amplitude and velocity are attributed to acoustoelectric interaction and mass loading due to moisture adsorption by graphite oxide layers.

Effect of Oxygen Content on Structures of Graphite Oxides

Graphite oxide was synthesized by the oxidation of graphite via a modified Hummers approach. The oxygen content of graphite oxide was tuned by changing the oxidation time. The saturated ratio of oxygen to carbon is 0.47. Furthermore, the effect of oxygen content on the structures of graphite oxide was evaluated by using SEM, TEM, XRD, Raman, FTIR, TG, TPD-MS, and nitrogen adsorption. It was found that the types of functional groups in graphite oxides, which are epoxy, hydroxyl, and carboxyl groups, were independent of oxygen content. However, the interplanar space and BET surface area of graphite oxide linearly increased with increasing O/C ratio. Furthermore, the structure of graphite can be easily and remarkably disordered even by partial oxidation.

Sp2/sp3 Carbon Ratio in Graphite Oxide with Different Preparation Times

Graphite oxide is an amorphous insulator. Although several models have been suggested, its structure remains controversial. To elucidate this issue, five samples were prepared by the Brodie process and the Staudenmaier process. The electronic structure of graphite oxide was examined with X-ray absorption near edge structure and the ratio of sp2 to sp3 bonded carbon atoms was investigated with X-ray photoemission spectroscopy as a function of sample preparation times. It was found that this ratio approaches 0.3 exponentially with a characteristic time of 1.5 weeks. We believe this long characteristic time is the reason the structure has remained unclear.

Temperature dependent structural breathing of hydrated graphite oxide in H 2O

Hydration of graphite oxide by excess of water was studied in the temperature interval 295–230 K. A structural breathing effect is found for fully hydrated graphite oxide near the water solidification/melting point. Expansion of hydrated graphite oxide structure due to insertion of additional water occurs upon cooling down from ambient temperature to the point of water media freezing. Cooling down below the point of water medium solidification results in stepwise contraction of graphite oxide interlayer distance by ∼25% due to partial withdrawal of water from the hydrated structure. Heating back from 230 K to ambient temperature results in graphite oxide structure expansion due absorption of water from medium, thus making a reversible cycle. The effect of structure breathing is important for any chemical treatments performed with graphite oxide in solution, e.g. graphite oxide functionalization and conversion into graphene-related materials.

Electronic structure of graphite oxide and thermally reduced graphite oxide

We present the electronic structure evolution from graphite oxide to thermally reduced graphite oxide. Most functional groups were removed by thermal reduction as indicated by high resolution X-ray photoelectron spectroscopy, and the electrical conductivity increased 6 orders compare with the precursor graphite oxide. X-ray absorption spectroscopy reveals that the thermally reduced graphite oxide shows several absorption peaks similar to those of pristine graphite, which were not observed in graphite oxide or chemically reduced graphite oxide. This indicates the better restoration of graphitic electronic conjugation by thermal reduction. Furthermore, the significant increased intensity of Raman 2D band of thermally reduced graphite oxide compared with graphite oxide also suggests the restoration of graphitic electronic structure (π orbital). These results provide useful information for fundamental understanding of the electronic structure of graphite oxide and thermally reduced graphite oxide.

The Structure of Graphite Oxide: Investigation of Its Surface Chemical Groups

The structure of graphite oxide (GO) has been systematically studied using various tools such as SEM, TEM, XRD, Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), (13)C solid-state NMR, and O K-edge X-ray absorption near edge structure (XANES). The TEM data reveal that GO consists of amorphous and crystalline phases. The XPS data show that some carbon atoms have sp(3) orbitals and others have sp(2) orbitals. The ratio of sp(2) to sp(3) bonded carbon atoms decreases as sample preparation times increase. The (13)C solid-state NMR spectra of GO indicate the existence of -OH and -O- groups for which peaks appear at 60 and 70 ppm, respectively. FT-IR results corroborate these findings. The existence of ketone groups is also implied by FT-IR, which is verified by O K-edge XANES and (13)C solid-state NMR. We propose a new model for GO based on the results; -O-, -OH, and -C=O groups are on the surface.

Initiating electropolymerization on graphene sheets in graphite oxide structure

AbstractBecause of its special chemical composition, graphite oxide has peculiar influences on electrochemical processes. The existence of various functional groups significantly affects electropolymerization processes and the formation of conductive polymers. Electrochemical synthesis of polyaniline (as a prototype of conductive polymers) on a paste‐based substrate of graphite oxide was investigated. In this case, the electropolymerization is significantly different from conventional cases, and the polymer is generated just during the first potential cycle. This can be attributed to the fact that graphite oxide can assist the monomer oxidation. Alternatively, electropolymerization was successfully performed inside the graphite oxide layers via electrochemical treatment of aniline‐intercalated graphite oxide in the supporting electrolyte. Although these phenomena are related to the chemical composition of graphite oxide, the graphite prepared by the reduction of graphite oxide also displayed some advantages for the electropolymerization (over natural graphite). There is an emphasis on the morphological investigations throughout this study, because novel morphologies were observed in the system under investigation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2204–2213, 2010

Pressure-Induced Insertion of Liquid Acetone into the Graphite Oxide Structure

An expansion of the graphite oxide structure due to pressure-induced insertion of acetone solvent was observed upon compression at 0.9 GPa. However, conversion into the expanded high-pressure phase is not complete, with the high-pressure and the ambient-pressure phases coexisting even at pressures up to 4.5 GPa. The phase transformation is not correlated with the solidification point of acetone, a behavior similar to that of the graphite oxide/alcohol systems and unlike that of the previously studied graphite oxide/water system. It can be concluded that pressure-induced insertion of solvent into the graphite oxide structure occurs not only for protic solvents (water, methanol, ethanol) but also for aprotic polar solvents (acetone).

Breaking AB stacking order in graphite oxide: ab initio approach

Different bulk structures of graphite oxide were systematically investigated using density functional theory (DFT). Our model consisted of a hexagonal in-plane structure of graphene with hydroxyl and epoxide groups, and different oxidation levels and water content. The graphitic AB stacking order was stable in anhydrous graphite oxide, independent of oxidation levels. The hydrogen bonding interaction of layers became weaker as the oxidation level increased to the saturation limit. When water molecules were present in highly oxidized graphite oxide, the AB stacking order was broken due to entropic disorder. The interlayer distances increased with the oxidation level: the interlayer distance was 5.1 A for low oxidation graphite oxide and 5.8 A for high oxidation graphite oxide. The calculated interlayer distance of hydrated graphite oxide was 7.3 A, which is in excellent agreement with experimental observations.

Pressure-Induced Insertion of Liquid Alcohols into Graphite Oxide Structure

Graphite oxide (GO) immersed in an excess of methanol and ethanol media is found to undergo a phase transformation at about 0.2-0.8 GPa, with an expansion of the unit cell volume by approximately 40%, due to pressure-induced insertion of solvent into interlayer space. The pressure at which the structural expansion occurs does not correlate with the solidification pressure of the alcohol, in contrast to the graphite oxide/water system. The expanded high-pressure phase of GO/ethanol could be quenched back to ambient pressure. Compression of graphite oxide with a 2:1 water/methanol medium revealed a complex anomaly with two steps attributed to insertion of methanol and water at different pressure points.

New insights into the structure and reduction of graphite oxide

Graphite oxide is one of the main precursors of graphene-based materials, which are highly promising for various technological applications because of their unusual electronic properties. Although epoxy and hydroxyl groups are widely accepted as its main functionalities, the complete structure of graphite oxide has remained elusive. By interpreting spectroscopic data in the context of the major functional groups believed to be present in graphite oxide, we now show evidence for the presence of five- and six-membered-ring lactols. On the basis of this chemical composition, we devised a complete reduction process through chemical conversion by sodium borohydride and sulfuric acid treatment, followed by thermal annealing. Only small amounts of impurities are present in the final product (less than 0.5 wt% of sulfur and nitrogen, compared with about 3 wt% with other chemical reductions). This method is particularly effective in the restoration of the π-conjugated structure, and leads to highly soluble and conductive graphene materials.

Inorganic–organic hybrid porous materials based on graphite oxide sheets

Graphite oxide hybrid porous materials were constructed by the cross-linking of graphite oxide sheets using the reaction of organic diisocyanates with the carboxyl and hydroxyl groups on both sides of the sheets. In the inorganic–organic hybrid materials, graphite oxide sheets are building blocks and the diisocyanates are covalent cross-linkers acting as spacers between the sheets. Infrared spectroscopy verified the chemical functionalization of the carboxyl and hydroxyl groups. Raman spectroscopy demonstrated that the skeleton structure of graphite oxide remains after diisocyanate treatment. Nitrogen sorption analysis revealed a much larger surface area of the obtained porous materials compared with that of the powdery graphite oxide, indicating that diisocyanate molecules act as covalently linked nanoscale spacers between the sheets and effectively limit their face-to-face stacking.

A neutron diffraction study of nano-crystalline graphite oxide

The structure of graphite oxide has been studied by neutron diffraction and is found to be nano-crystalline, the diffraction pattern being a mixture of Bragg and diffuse scattering. Three strong Bragg peaks were found in the structure factor from which the layer spacing was calculated and found to be consistent with different structural regions within the graphite oxide, specifically regions of graphitic-like flat hexagons and regions containing oxidized chain-like structures. The neutron scattering pair distribution function is compared to four previously published low energy Monte Carlo structural models of GO.