Graphite Oxide Samples Research Articles

Binder free supercapacitor electrodes by hydrothermal deposition of thermally reduced graphite oxide on Nickel foam: Characterization and electrochemical performance

Thermally reduced graphite oxide (TRGO) samples were hydrothermally deposited (120 °C, 12 h) on nickel foam current collector without any binder. TRGO of different reduction levels were synthesized through the thermal reduction of graphite oxide at 100 and 200 °C. The binding affinity of the oxygen functional groups enabled the binder free deposition. We could achieve specific capacitance Csp of 524F/g (at 1 A/g) for Ni/TRGO200 and 136F/g (at 1 A/g) for Ni/TRGO100 electrodes. These values are significantly larger than those till reported for binder free reduced graphite oxide electrodes. The capacitive retention of Ni/TRGO100 is 82.5 % and for Ni/TRGO200 it is 81.5 % over 1000 charge discharge cycles. Coulombic efficiency reaches 99 % and 100 % respectively for Ni/TRGO100 and Ni/TRGO200. Detailed analysis of the electrochemical storage mechanism is also reported.

Striking analogies and dissimilarities between graphene oxides and humic acids: pH-dependent charging and colloidal stability

This study provides a comparative framework on the elucidation of analogies and differences in the interfacial protolytic processes and the associated colloidal behaviour of a typical humic acid (HA) and a set of single-layer graphene oxide (SLGO) and (multi-layered) graphite oxide samples in aqueous electrolyte media. The pH dependence of the surface charge densities of HA and SLGO was explored at three different salt concentrations by potentiometric acid-base titration, along with simultaneous determination of zeta potential and hydrodynamic sizes. Charging curves obtained in the pH range of 3 to 10 by cyclic titrations reveal the presence of a small hysteresis, proving the chemical stability of SLGO and graphite oxides in weakly acidic and alkaline solutions. HA and SLGO display a parallel shift of the pH-dependencies of their negative charge densities with increasing ionic strength, demonstrating a unique combination of particle and polyelectrolyte-like behaviour, which is absent for multi-layered graphite oxide exhibiting charging curves that resemble to “classical” colloidal particles. An accurate purification of SLGO results in inherent change in its surface properties; however, the salt tolerance of aqueous HA solutions is still superior to that of SLGO dispersions.

Stable dark pulses produced by a graphite oxide saturable absorber in a fiber laser cavity.

In this paper, we report for the first time, to the best of our knowledge, the experimental generation of dark pulses in the 1.5 µm band from a passively $Q$Q-switched fiber laser employing graphite oxide as the saturable absorber, generating tunable microsecond pulses with kHz repetition rates. The graphite oxide samples were obtained by recycling the graphite present in Li-ion batteries used in cell phones through a chemical separation and oxidation process. Sample characterization employing x-ray diffraction, solid-state $ ^{{13}}{\rm C} $13C nuclear magnetic resonance, and Raman spectroscopy showed that the produced graphite oxide exhibited a homogeneously oxidized structure. Dark pulse emission could be observed at a relatively low pump threshold of 35 mW in a short 20 m laser cavity, indicating that the graphite oxide acted as a saturable absorber, significantly enhancing the nonlinearity of the laser cavity. Additionally, dark pulse operation was demonstrated at a high stability with a signal-to-noise ratio of 56 dB and a pulse-to-pulse timing jitter of 159.84 fs.

All-Fiber Erbium-Doped Q-Switched Laser With Recycled Graphite Oxide

This work demonstrates a passively Q-Switched fiber laser employing graphite oxide as a saturable absorber, generating tunable microsecond pulses with kHz repetition rates, pulse energies of up to 15.54 nJ and the pulse-to-pulse timing jitter of 46.14 fs. The graphite oxide samples were obtained by recycling the graphite present in Li-ion batteries utilized in cell phone devices through a chemical separation and subsequent oxidation process. Sample characterization employing X-ray diffraction, solid-state nuclear magnetic resonance and Raman spectroscopy showed that the produced graphite oxide exhibited a homogeneously oxidized structure. These results indicate that applications in the physics of pulsed lasers can benefit from the recycling of lithium batteries, directing the process of discarding spent batteries.

The influence of graphite particle size on the synthesis of graphene-based materials and their adsorption capacity

Graphite oxide (GrO) can be considered as one of the most relevant graphene derivatives. Despite the fact that several structural models have been proposed, it has seen that the ultimate structure is a function of the raw graphite affecting directly the graphite oxide characteristics and applications. One of this applications affected by the particle size of the raw graphite is the adsorption. In this work, the structural changes and the adsorptive capacity properties of graphite oxide samples prepared from graphite with different particle size were established. Raman spectroscopy, particle size distribution analysis, XRD, FTIR, elemental analysis and SEM analysis were used for characterizing the products obtained. Methylene blue adsorption experiments of the synthesized materials were performed and data derived from this study were fitted to empirical equations. Graphite oxide obtained from graphite with the lowest particle size produced the highest oxidized structure, which was related to the maximum of adsorption capacity, thus inferring that this material could be used to remove dyes from water and soil as those generated by several industries every year.

Separation and recovery of carbon powder in anodes from spent lithium-ion batteries to synthesize graphene

Based on the structural characteristics of the anodes of lithium-ion batteries, an improved Hummers’ method is proposed to recycle the anode materials of spent lithium-ion batteries into graphene. In order to effectively separate the active material from the copper foil, water was selected as an ultrasonic solvent in this experiment. In order to further verify whether lithium ions exist in the active material, carbon powder, it was digested by microwave digestion. ICP-AES was then used to analyse the solution. It was found that lithium ions were almost non-existent in the carbon powder. In order to further increase the added value of the active material, graphene oxide was obtained by an improved Hummers’ method using the carbon powder. The graphene material was also reduced by adding vitamin C as a reducing agent through a chemical reduction method using graphene oxide. Meanwhile, the negative graphite, graphite oxide and graphene samples were characterized by XRD, SEM, FTIR and TEM. The conductivity of the negative graphite, graphite oxide and graphene was tested. The results show that graphene prepared by a redox method has a better layered structure, less impurities and oxygen groups in its molecular structure, wider interlayer spacing and smaller resistivity.

Hydrogen adsorption by g-C3N4 and graphene oxide nanosheets

The adsorption behavior of hydrogen for synthesized graphitic carbon nitride (g-C3N4) and graphene oxide nanosheets was compared. The structure of the prepared g-C3N4 and graphene oxide samples were studied using TEM, FT-IR spectroscopy and surface area analysis. Textural results of the prepared nanosheets show that the surface area, total pore volume, and average internal diameter of g-C3N4 and graphene oxide samples are similar. The hydrogen adsorption isotherms at 298 K, up to 22 bar pressures were as Type III and the maximum hydrogen storage capacities at 22 bar and 296 K were 1.06 and 1.27 mmol/g for graphite oxide and g-C3N4 samples, respectively. The adsorption results were fitted by Freundlich model, which was related to reversible multilayer adsorption on non-uniform surface active sites with different affinities of both g-C3N4 and graphene oxide adsorbents. Isosteric heat of adsorption of hydrogen on the graphene oxide varies from 8.6 kJ.mol-1 (at low hydrogen uptake) to 4.3 kJ.mol-1. These results are the range of 10.1 to 4.8 kJ.mol-1 for the prepared g-C3N4 sample at same hydrogen uptake. The results show that the interaction between hydrogen molecules and tri-s-triazine units in g-C3N4 structure are stronger than carbon atoms in graphene oxide structure.

Multifunctional low temperature reduced graphite oxides for high performance supercapacitors and SERS applications

Graphene has been extensively investigated in the field of energy storage and optoelectronic applications due to its unique properties like high surface area, good electrical conductivity etc. Here, in the present work, we have synthesized few layer graphene via reduction of graphite oxide at low temperature (100 °C) using hydrazine hydrate and urea for energy storage. We studied the morphological changes occurred in prepared reduced graphite oxide (rGO) samples and activated to achieve better wettability for high capacitive performance and sustainability. The maximum specific capacitance of 300 Fg−1 was observed for activated electrode of rGO reduced with hydrazine hydrate (rGO-HH), while activated electrode of rGO reduced with urea (rGO-Urea) showed specific capacitance of 220 F g−1 at 1 Ag−1 discharge current in aqueous electrolyte. To the best of our knowledge, our rGO-HH shows higher capacitive performance and sustainability than other reports for the reduction process below 150 °C. Additionally, we have successfully demonstrated the suitability of prepared rGO samples as a substrate for surface enhanced Raman spectroscopy (SERS) to detect organic pollutant (Rhodamine 6G) at micro molar concentration for environmental remediation.

Effects of probe and bath ultrasonic treatments on graphene oxide structure

During the synthesis of graphene oxide (GO) sheets, the exfoliation of graphite oxide (GpO) has become a key step to obtain fully exfoliated sheets, and ultrasound is typically applied. We compared the effect of using water bath or probe sonication on the morphological and chemical characteristics of the obtained GO sheets. The properties of these GO sheets were also characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, elemental analysis, ζ-potential analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy. When probe sonication was used directly on the GpO samples, it induced deformities between the layers, causing the GO sheets to acquire a greater rugosity and degree of stacking and degrading their morphological properties. Additionally, probe-sonicated samples showed a noticeable reduction in the number of functional groups available for further chemical transformation. Thus, the use of bath ultrasonication to obtain GO sheets is preferable to probe ultrasonication because it is less invasive, enables easy control of the sample temperature, and causes fewer wrinkles and less damage to the sheet structure and morphology.

Preparation of Graphite Oxide Containing Different Oxygen-Containing Functional Groups and the Study of Ammonia Gas Sensitivity.

A series of graphite oxide samples were prepared using the modified Hummers method. Flake graphite was used as the raw material and the reaction temperature of the aqueous solution was changed (0 °C, 30 °C, 50 °C, 60 °C, 70 °C, 80 °C, and 100 °C). X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectral analysis, X-ray photoelectron spectroscopy, and contact angle tests were performed to characterize the structure, chemical bonding, type, and content of oxygen-containing functional groups of the graphite oxide samples. The results showed that the type and content of each oxygen-containing functional group could be controlled by changing the reaction temperature with the addition of water. As the temperature of the system increased, the degree of oxidation of the graphite oxide samples first increased and then decreased. Too high a temperature (100 °C) of the system led to the formation of epoxy groups by the decomposition of some hydroxyl groups in the samples, causing the reduction of oxygen-containing functional groups between the graphite layers, poor hydrophilic properties, and low moisture content. When the system temperature was 50 °C, the interlayer spacing of the graphite oxide samples was at its highest, the graphite was completely oxidized (C/O = 1.85), and the oxygen-containing functional groups were mainly composed of hydroxyl groups (accounting for approximately 28.88% of the total oxygen-containing functional groups). The high content of hydroxyl and carboxyl groups had good hydrophilic ability and showed the highest moisture content. The sample at 50 °C had better sensitivity to ammonia because of its high hydroxyl group and carboxyl group content, with the sample showing an excellent profile when the ammonia concentration was 20–60 ppm.

Proton conductance and dielectric relaxation in hydrated graphite oxide, studied with impedance spectroscopy

Hydrated graphite oxide samples containing different concentrations of functional groups were investigated with a range of experimental techniques including complex impedance spectroscopy. The activation energies in their conductivities increase with their epoxide concentrations and closely match those in dielectric relaxation. They appear to conduct by a Grotthuss mechanism, involving the exchange of protons between neighboring water molecules and the rotation of water. In the region below room temperature, this conductance is not limited by proton hopping but by water rotation about its hydrogen bond to an epoxide group attached to a graphene plane.

Two Methods for Intercalation of Surfactants into Graphite Oxide.

The intercalation properties of graphite oxide are important; however, the specific processes and mechanisms associated with intercalation have rarely been elucidated. In this paper, two types of surfactants, polyvinylpyrrolidone and tetradecyltrimethylammonium bromide, were used to thoroughly explore the intercalation properties of graphite oxide. The polyvinylpyrrolidone and tetradecyltrimethylammonium bromide-intercalated graphite oxide composites were synthesized under different conditions and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray energy dispersive spectroscopy, and transmission electron microscopy. It was found that polyvinylpyrrolidone could be directly intercalated into the graphite oxide layers and tetradecyltrimethylammonium bromide could not effectively react with the waterdispersed graphite oxide. With a low quantity of polyvinylpyrrolidone, only a part of the graphite oxide was intercalated, and the interlayer spacing of the polyvinylpyrrolidone-intercalated composites increased as the polyvinylpyrrolidone: graphite oxide mass ratio increased. When the graphite oxide was dispersed in a 0.05 N NaOH solution, the tetradecyltrimethylammonium bromide rapidly reacted with the graphite oxide, while the mixture of polyvinylpyrrolidone and graphite oxide could not be effectively separated. The intercalated spacing of the tetradecyltrimethylammonium bromideintercalated graphite oxide increased with the tetradecyltrimethylammonium bromide: graphite oxide mass ratio, but its crystalline structure was not as ordered as the polyvinylpyrrolidone-intercalated graphite oxide prepared in the water solution. The infrared spectra of the two surfactant-intercalated graphite oxide samples revealed that the polyvinylpyrrolidone is bonded to the graphite oxide via hydrogen bonding, while the tetradecyltrimethylammonium bromide is bonded via ionic bonding. The mechanism analysis indicated that the polyvinylpyrrolidone could directly enter the graphite oxide layers in the water solution because of the driving force of hydrogen bonding. However, processes such as graphite oxide exfoliation, reactions between the graphite oxide and tetradecyltrimethylammonium bromide, and reaggregation of the graphite oxide sheets are necessary for the formation of tetradecyltrimethylammonium bromide-intercalated graphite oxide.

Synthesis of Graphite Oxide with Different Surface Oxygen Contents Assisted Microwave Radiation.

Graphite oxide is synthesized via oxidation reaction using oxidant compounds that have lattice defects by the incorporation of unlike functional groups. Herein, we report the synthesis of the graphite oxide with diverse surface oxygen content through three (B, C, D) different modified versions of the Hummers method assisted microwave radiation compared with the conventional graphite oxide sample obtained by Hummers method (A). These methods allow not only the production of graphite oxide but also reduced graphene oxide, without undergoing chemical, thermal, or mechanical reduction steps. The values obtained of C/O ratio were ~2, 3.4, and ~8.5 for methodologies C, B, and D, respectively, indicating the presence of graphite oxide and reduced graphene oxide, according to X-ray photoelectron spectroscopy. Raman spectroscopy of method D shows the fewest structural defects compared to the other methodologies. The results obtained suggest that the permanganate ion produces reducing species during graphite oxidation. The generation of these species is attributed to a reversible reaction between the permanganate ion with π electrons, ions, and radicals produced after treatment with microwave radiation.

Study of ultraviolet-visible light absorbance of exfoliated graphite forms

Despite the fact that there have been many studies of graphite exfoliation, none really addresses the issue of starting form of graphite. To address this issue various graphite forms (solid, powder and sooth) and graphite oxide (powder) are exfoliated in acetonitrile and studied via ultraviolet-visible (UV-Vis) spectroscopy. In different graphite forms two major absorbance peaks are observed at 223 nm and 273 nm corresponding to graphene oxide and graphene dispersions, respectively. The intensity change of the peaks refers to the layer number change. The intensity ratios of these peaks give information about the concentration of the exfoliation products. We observed that graphite oxide sample has the thinnest graphene dispersions among the compared samples, whereas graphite rod has the thickest. It appears that few layer graphene oxide dispersions exist more in graphite sooth and graphite oxide samples. Graphite oxide UV-Vis spectrum reveals two new absorbance peaks at 312 nm and 361 nm in addition to the graphene oxide and graphene dispersion peaks. To our knowledge these peaks were not observed before. We think that these new peaks are formed due to conjugated polyenes that affect π → π* plasmon peak.

The effect of the thermal reduction on the kinetics of low-temperature 4He sorption and the structural characteristics of graphene oxide

The kinetics of the sorption and the subsequent desorption of 4He by the starting graphite oxide (GtO) and the thermally reduced graphene oxide samples (TRGO, Treduction = 200, 300, 500, 700 and 900 °C) have been investigated in the temperature interval 1.5–20 K. The effect of the annealing temperature on the structural characteristics of the samples was examined by the x-ray diffraction (XRD) technique. On lowering the temperature from 20 to 11–12 K, the time of 4He sorption increased for all the samples, which is typically observed under the condition of thermally activated diffusion. Below 5 K the characteristic times of 4He sorption by the GtO and TRGO-200 samples were only weakly dependent on temperature, suggesting the dominance of the tunnel mechanism. In the same region (T < 5 K) the characteristic times of the TRGOs reduced at higher temperatures (300, 500, 700 and 900 °C) were growing with lowering temperature, presumably due to the defects generated in the carbon planes on removing the oxygen functional groups (oFGs). The estimates of the activation energy (Ea) of 4He diffusion show that in the TRGO-200 sample the Ea value is 2.9 times lower as compared to the parent GtO, which is accounted for by GtO exfoliation due to evaporation of the water intercalated in the interlayer space of carbon. The nonmonotonic dependences Ea(T) for the GtO samples treated above 200 °C are determined by a competition between two processes—the recovery of the graphite carbon structure, which increases the activation energy, and the generation of defects, which decreases the activation energy by opening additional surface areas and ways for sorption. The dependence of the activation energy on Treduction correlates well with the contents of the crystalline phase in GtO varying with a rise of the annealing temperature.

Investigation of Pristine Graphite Oxide as Room-Temperature Chemiresistive Ammonia Gas Sensing Material.

Graphite oxide has been investigated as a possible room-temperature chemiresistive sensor of ammonia in a gas phase. Graphite oxide was synthesized from high purity graphite using the modified Hummers method. The graphite oxide sample was investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetry and differential scanning calorimetry. Sensing properties were tested in a wide range of ammonia concentrations in air (10–1000 ppm) and under different relative humidity levels (3%–65%). It was concluded that the graphite oxide–based sensor possessed a good response to NH3 in dry synthetic air (ΔR/R0 ranged from 2.5% to 7.4% for concentrations of 100–500 ppm and 3% relative humidity) with negligible cross-sensitivity towards H2 and CH4. It was determined that the sensor recovery rate was improved with ammonia concentration growth. Increasing the ambient relative humidity led to an increase of the sensor response. The highest response of 22.2% for 100 ppm of ammonia was achieved at a 65% relative humidity level.

Influence of Different Improved Hummers Method Modifications on the Characteristics of Graphite Oxide in Order to Make a More Easily Scalable Method

Different samples of graphite oxide (GrO) were prepared by modification of the Improved Hummers Method reported in the literature. Graphite was used as the raw material and KMnO4 and H2SO4 were used as chemical reagents. GrO samples were analyzed by Raman spectroscopy, SEM, TEM, elemental analysis, X-ray diffraction, N2 adsorption–desorption, and thermogravimetric analysis. The results indicate that, after optimizing the synthesis method, the oxidation time was reduced from 12 to 3 h, coagulation step was removed, wash step was halved, use of H3PO4 during the oxidation step was no longer necessary, the production of graphite oxide per batch was increased, and the amount of graphite that could be processed was increased five times. Therefore, synthesis costs were significantly lower than those related to the published Improved Hummers Method. An economic assessment for the industrial scale demonstrated that this process could be viable from the third year after its implementation.

Effect of Interlayer Distance and Oxygen Content on Proton Conductivity of Graphite Oxide

The effect of interlayer distance and oxygen content on proton conductivity of graphite oxide is presented. Bulk-state proton conductivities were measured using coin-shaped pellets of three different graphite oxide samples, namely, H-GO, S-GO, and B-GO, generated respectively from the techniques of Hummers, Staudenmaier, and Brodie. The extent of oxidation, nature of functional groups, interlayer distances, and morphologies are studied through Raman spectroscopy, XPS, powder XRD pattern, and SEM images. The proton conductivities follow the trend H-GO > S-GO > B-GO. In the XPS study, the total oxygen contents were found to follow the trend H-GO > B-GO > S-GO, whereas the interlayer distances obtained from the powder XRD patterns show the trend H-GO > S-GO > B-GO. Beside the nature of the functional groups and extent of oxidation, the interlayer distance displays a significant effect on the proton conductivity values. The temperature-dependent Arrhenius plots reveal the activation energy (Ea) of the samples...

Fluorinated microwave exfoliated graphite oxide: structural features and double layer capacitance

ABSTRACTFluorinated microwave exfoliated graphite oxide (MEGO) samples containing 5.7–29.3 at.% of fluorine were prepared by gas phase treatment of MEGO with XeF2. According to X-ray photoelectron spectroscopy and infrared spectroscopy data, fluorination of MEGO occurs at C=C bonds while leaving the oxygenated domains intact, and increases the O/C ratio. Cyclic voltammetry studies of fluorination effect on double layer capacitance of MEGO shows 67% growth of its specific capacitance, making such and related carbon materials prospective for supercapacitor applications.

Synthesis of the Exfoliated Graphite from Graphite Oxide

This article is devoted to investigation of the synthesis process of exfoliated graphite. Exfoliated graphite was obtained from graphite oxide using thermal exfoliation. Graphite oxide samples were synthesized using modified Hummers method. The influence of the synthesis process parameters such as heating rate, temperature, exposure time on the properties of graphite oxide were investigated. The as-received exfoliated graphite were tested as electrode for supercapacitors. The capacitance of the supercapacitors based on exfoliated graphite varied in a range of 17-129 F/g.