Groups Of Graphite Oxide Research Articles

IR spectral fingerprints of carbonyl groups in graphite oxide: a theoretical study

Non-empirical quantum chemical calculations of various possible fragments in the oxidized carbon layer of graphite oxide were carried out at the DFT level with the hybrid B3LYP functional and the extended double-zeta Gaussian basis set. These fragments contain the carbonyl groups as ketone, carboxyl and lactone functions, either free or hydrogenbonded to hydrating water molecules or closely arranged hydroxyl groups. Using the vibrational energy distribution analysis, the typical spectral ranges of C=O vibrations were identified within the fingerprint region of 1550–1800 cm−1 depending on the kind of the carbonyl group studied and its environment.

Graphite oxide as a polymer-like hydrophilic system with peculiar coordinating properties

Structure-energetic and dynamic characteristics of graphite oxide model segments, as a basic element of which the C54 fragment of a carbon sheet was taken, and their hydration complexes involving a restricted number of water molecules are analyzed. The structure optimization and calculation of normal vibrations were performed at the density functional approximation with the B3LYP hybrid exchange-correlation functional with the basis that involves atomic functions of the 6–31G sets on the skeleton carbon atoms and terminal CH groups of the skeleton and of the 6–31G(d,p) sets on the atoms of all functional groups and water molecules. The ability of the hydroxyl groups of graphite oxide to initiate the reorganization of a three-dimensional H-bonded structure of water into the two-dimensional surface structure and to form very strong hydrogen bonds with water molecules providing their partial ionization was revealed.

Functional Groups of Graphite Oxide: Experimental Data and Ab Initio Modeling

A comparison of the experimental IR absorption spectrum of the synthesized graphite oxide specimen with the calculated (using ab initio approaches) spectra of CnOmHk model systems containing the basic C54 fragment of the graphite layer and various modifying functional groups (hydroxyl, epoxy, carboxyl, and keto groups) in various numbers and combinations in the presence of a small number of solvating water molecules made it possible to clarify the nature of some signals in the medium and characteristic ranges of the IR spectrum of graphite oxide and reveal the role of hydrogen bonding between the functional groups and the water molecules.

Facile reduction of graphene using urea in solid phase and surface modification by N-doped graphene quantum dots for adsorption of organic dyes

Generally, hydrazine reducing method is a common way to prepare the solution-processable graphene from graphite oxide. High toxicity of the hydrazine is the main problem which limits it's using in large-scale implementation. So a green approach for the preparation of graphene from graphite oxide is needed. Here, we introduced a very simple and scalable procedure for efficient reduction of graphite oxide in solid phase, mild temperature reaction and ambient atmosphere. Urea was used as expansion–reduction agent and well mixed with graphite oxide. The mixture was heated at 160°C for 48h. During the reaction, urea decomposes upon heating and releases reducing gases release to remove oxygen containing groups of graphite oxide. After removing residual the unreacted urea by washing with water, the product was dispersed in ethylene glycol and exposed to ultrasound irradiation to obtain well dispersed and de‑oxygenated graphene or reduced graphene oxide (RGO). The obtained results suggest replacing of hydrazine in the reduction of graphite oxide suspensions by a nontoxic and safe reductant agent to produce RGO with high quality and efficiency. In the next step, the obtained RGO was modified by using N-doped graphene quantum dots (N-RGO) to produce an absorbent with high surface area and increased amount of surface functional groups. Experiments indicate that final product has interesting capability to remove organic pollutants from polluted water.

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.

Modifying graphite oxide nanostructures in various media by high-energy irradiation

The alterations of GO nanostructures after γ-ray irradiation in water, air and styrene with an absorbed dose of 200 kGy are systematically investigated. The interlayer structures of the ultimate products are confirmed to be remarkably different from each other due to the distinct changes of functional groups on single-sheets in various media. After irradiation in water, oxygen groups in graphite oxide are shown to be obviously decreased owing to the generation of reductive radicals by the decomposition of water molecules, which is reflected in the decrease of graphite oxide interlayer spacing. The interlayer distance of graphite oxide irradiated in air is found to be significantly increased, which may be attributed to the increase of the hydroxyl groups and the topological defects. However, the graphite oxide seems to be mainly exfoliated and functionalized by the intercalation of the monomers and the grafting of polystyrene chains when irradiated in styrene. It is expected that γ-ray irradiation in different media should be a promising strategy for manipulating nanostructures and properties of graphite oxide for improving its applicability in fields of composites, catalysts and sensors.

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.

Ultrafast carrier phonon dynamics in NaOH-reacted graphite oxide film

NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast carrier dynamics of the sample were studied by time-resolved transient differential reflection (ΔR/R). The data show two exponential relaxation processes. The slow relaxation process (∼2ps) is ascribed to low energy acoustic phonon mediated scattering. The electron-phonon coupling and first-principles calculation results demonstrate that -OH and -ONa groups in the sample are strongly coupled. Thus, we attribute the fast relaxation process (∼0.17ps) to the coupling of hydroxyl and -ONa groups in the sample.

Synthesis of Graphene with Microwave Irradiation in Liquid Phase

Graphite oxide was synthesized with Hummers method using natural flake graphite as carbon source, and then graphene was prepared through microwave irradiation in N-methyl-2-pyrrolidinone (NMP) solvent. NMP solvent was heated selectively during the microwave irradiation process, meantime, the oxygen containing groups of graphite oxide were decomposed into CO, CO2 and H2O gases, resulting in the exfoliation and reduction of graphite oxide. XRD, SEM, EDS, TEM, HRTEM, SAED, XPS and Raman were performed to characterize the syn- thesized graphene. The results indicate that the synthesized graphene is transparent with several microns in size, which consists of 2-5 graphitic layers with high crystalline structure. The synthesized graphene can disperse ho- mogenously in the NMP solvent.

Forming mechanism of nitrogen doped graphene prepared by thermal solid-state reaction of graphite oxide and urea

Nitrogen doped graphene was synthesized from graphite oxide and urea by thermal solid-state reaction. The samples were characterized by transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, element analysis, and electrical conductivity measurement. The results reveal that there is a gradual thermal transformation of nitrogen bonding configurations from amide form nitrogen to pyrrolic, then to pyridinic, and finally to “graphitic” nitrogen in graphene sheets with increasing annealing temperature from 200 to 700 °C. The products prepared at 600 °C and 700 °C show that the quantity of nitrogen incorporated into graphene lattice is ∼10 at.% with simultaneous reduction of graphite oxide. Oxygen-containing functional groups in graphite oxide are responsible for the doping reaction to produce nitrogen doped graphene.

Functionalization of Graphene Sheets via Chemically Grafting of PMMA Chains Through in-situ Polymerization

In this work, we report the preparation of graphene nanoplatelet which covalently functionalized with PMMA chains by introduction of vinyl groups onto graphene surface through simple esterification reaction between hydroxyl groups of graphite oxide and methacrylic anhydride. The synthesis is followed by in-situ polymerization with MMA monomers. The structural properties were characterized with X-ray diffraction spectroscopy (XRD) and scanning electronic microscopy (SEM) that showed the crystalline graphite is converted to individual layers during the synthesis steps. The grafting of PMMA chains was monitored with IR spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The TGA results revealed 40% wt of PMMA chains chemically grafted onto graphene surface. Significant increase in glass transition temperature (Tg) and existence of polymer chains in two positions (physically absorbed and chemically grafting onto graphite surface) are indicated by differential scanning calorimetric (DSC) analysis.

The synthesis and characterization of copper-based metal–organic framework/graphite oxide composites

New composites of a copper-based metal–organic framework and graphite oxide were synthesized with different ratios of HKUST-1 (also called MOF-199) and graphite oxide. These compounds, as well as the parent materials, were characterized by X-ray diffraction, sorption of nitrogen, FT-IR spectroscopy, thermal analyses, scanning electron microscopy, and sorption of hydrogen. The composites exhibit features similar to HKUST-1 as well as an increased porosity compared to the parent materials. The formation of new small pores is demonstrated by an increase in the hydrogen uptake. The results suggest that the building process of the composites occurs via the reaction/binding of the copper dimers from the HKUST-1 with/to the functional groups in graphite oxide (epoxy, carboxylic, hydroxylic, sulfonic).

Polymeric Modification of Graphene through Esterification of Graphite Oxide and Poly(vinyl alcohol)

Polymeric Modification of Graphene through Esterification of Graphite Oxide and Poly(vinyl alcohol)