Graphene Oxide Samples Research Articles

Graphene Oxide: Study of Pore Size Distribution and Surface Chemistry Using Immersion Calorimetry.

In this work, the textural parameters of graphene oxide (GO) and graphite (Gr) samples were determined. The non-local density functional theory (NLDFT) and quenched solid density functional theory (QSDFT) kernels were used to evaluate the pore size distribution (PSD) by modeling the pores as slit, cylinder and slit-cylinder. The PSD results were compared with the immersion enthalpies obtained using molecules with different kinetic diameter (between 0.272 nm and 1.50 nm). Determination of immersion enthalpy showed to track PSD for GO and graphite (Gr), which was used as a comparison solid. Additionally, the functional groups of Gr and GO were determined by the Boehm method. Donor number (DN) Gutmann was used as criteria to establish the relationship between the immersion enthalpy and the parameter of the probe molecules. It was found that according to the Gutmann DN the immersion enthalpy presented different values that were a function of the chemical groups of the materials. Finally, the experimental and modeling results were critically discussed.

Adsorption and kinetic study of Reactive Red 2 dye onto graphene oxides and graphene quantum dots

The increase of the water pollution has led to the search of new methods and materials for its remediation. In recent years, different carbon nanomaterials have gained importance in the removal of dyes from water. In this research was investigated the adsorption of Reactive Red 2 (RR2) dye onto different graphene oxides and graphene oxide quantum dots at pH values of 2 and 5. The graphene oxide samples were obtained modifying the amount of KMnO4 used and replacing the magnetic stirring by ultrasonic bath in the oxidation reaction. In order to know the surface and structural properties of carbon nanomaterials, these were analyzed by infrared, Raman and energy dispersive X-ray spectroscopies, transmission electron microscopy and field emission scanning electron microscopy, nitrogen-adsorption and through potentiometric titrations was obtained the point of zero charge. The decrease in the amount of KMnO4 used in the Hummers´ reaction induced an increase in the oxygen content of graphene oxide. All carbon nanomaterials presented a high affinity by the RR2 dye at pH = 2, however graphene quantum dots showed the best performance. The removal of RR2 is dependent of the pH, surface area, oxygenated groups and the dimensionality of the carbon nanomaterials. The experimental data are analyzed using pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models to describe the adsorption kinetics from RR2 in aqueous solutions. Based on the highest coefficient of determination values and the lowest standard deviation values, the experimental kinetic data are better adjusted by the Elovich's equation. The adsorption behavior is studied according to the RE values of the dimensionless Elovich's equation.

Exploring Soft Magnetism in Amorphous Carbon Synthesized from Biomass

Some studies of the usage of biomass to produce carbon-based compounds have been reported in the past. Here we report that palmyra sugar can be one of the sources to produce amorphous carbon (a-C) from biomass after the heating treatment at 250°C. In this paper, X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared (FTIR) and Superconducting Quantum Interference Device (SQUID) measurements are reported in order to check the detailed properties of a-C from palmyra sugar. The XRD data at a diffraction peak position (2θ) of ~23o support the formation of a-C. The functional groups detected by FTIR spectra consist of C=C, C-C, C-O, C=O, C-H and O-H. The remnant magnetization (Mr), coercive field (Hc) and saturation magnetization are estimated as ~0.1 10-3 emu/g, ~50 Oe and ~9 10-3 emu/g, respectively. Soft ferromagnetism in a-C from palmyra sugar is confirmed, comparable with the magnetization result in the reduced graphene oxide (rGO) sample from coconut shell and rGO commercial material which have the same mixture hybridization. Some studies of the usage of biomass to produce carbon-based compounds have been reported in the past. Here we report that palmyra sugar can be one of the sources to produce amorphous carbon (a-C) from biomass after the heating treatment at 250°C. In this paper, X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared (FTIR) and Superconducting Quantum Interference Device (SQUID) measurements are reported in order to check the detailed properties of a-C from palmyra sugar. The XRD data at a diffraction peak position (2θ) of ~23o support the formation of a-C. The functional groups detected by FTIR spectra consist of C=C, C-C, C-O, C=O, C-H and O-H. The remnant magnetization (Mr), coercive field (Hc) and saturation magnetization are estimated as ~0.1 10-3 emu/g, ~50 Oe and ~9 10-3 emu/g, respectively. Soft ferromagnetism in a-C from palmyra sugar is confirmed, comparable with the magnetization result in the reduced graphene oxide (rGO) sample from coconut shell and rGO commercial material which have the same mixture hybridization.

Origin of optical bandgap fluctuations in graphene oxide

In this work, we explore the electrical, optical and spectroscopic properties of different Graphene Oxide (GO) samples focusing on new oxidative strategies to tune their physicochemical properties. Three types of GO samples were prepared by changing the oxidative conditions resulting in carbonyl-, epoxy- or hydroxyl-rich GO. These materials were characterized by UV-VIS absorption, Raman spectroscopy and X-ray diffraction. The experimental results indicate that all samples exhibit oxidation and exfoliation degrees typical of graphene oxides obtained by using the modified Hummers’ method. The optical bandgap values were measured using the Tauc’s plot from UV-VIS data and showed that the stoichiometry of GO impacts the width of the bandgap. The carbonyl-rich sample presented the lowest gap around 3.20 ± 0.02 eV, while epoxy- and hydroxyl-rich GOs showed out gaps of about 3.48 ± 0.07 and 3.72 ± 0.05 eV, respectively. These experimental results are consistent with theoretical calculations of bandgaps obtained with coronene and circumcoronene GO models. The calculations were obtained using different theoretical approaches, such as: Huckel, PM3, AM1 and DFT. The present work suggests that a precise tuning of the optical bandgap of GOs can be achieved by only changing their stoichiometry thus allowing their use in a large range of electronic applications.

Preheated self-aligned graphene oxide for enhanced room temperature hydrogen storage

This study explored the hydrogen adsorption capacity of self-assembled aligned graphene oxide at room temperature. The characteristics of as-prepared graphene oxide were determined by scanning electron microscopy, Raman spectroscopy, and X-ray diffractometry techniques. Three different temperatures were taken for preheating, i.e., 25, 250, and 400 °C. The maximum adsorption pressure was given to 20 bar, and we evaluated the hydrogen adsorption competency at room temperature (25 ± 2 °C). The maximum hydrogen storage capacity was achieved ~2.5 wt%, which was found for the graphene oxide sample preheated at 400 °C. This hydrogen storage capacity was 67% and 40% more than the graphene oxide samples preheated at 25 and 250 °C, respectively. Such an enhancement of hydrogen storage capacity in the self-aligned graphene oxide samples at room temperature is attributed to reduced interlayer spacing and increased topological defects in preheated graphene oxide samples at 400 °C.

Preparation of high surface area nitrogen doped graphene for the assessment of morphologic properties and nitrogen content impacts on supercapacitors

Supercapacitors have been caught great attention owing to their high power density and fast charge/discharge ability with superior capacitance retention which originates from the formation of an electrical double layer on high surface area electrodes. In this study, Two-step organic sol-gel procedure is applied to graphene oxide to produce high surface area nitrogen doped graphene samples varying in surface area and nitrogen content. The higher impacts of specific surface area and porosity on capacitative performance of graphene than nitrogen content are observed in different electrolytes. All the samples give superior capacitative performance than those of graphene oxide and blank sample, but higher in acidic electrolyte than the alkaline yielding a volumetric specific capacitance of ~118 F·cm−3 with Coulombic efficiency of >99% and capacitance retention >80% after 10,000 successive cycle. Based on the weight of active material, the maximum gravimetric energy density is as high as 39 Wh·kg−1 in acidic electrolyte at 0.1 A·g−1, which is almost 2.6 times of graphene oxide used in this study.

Studying the effect of low doses of gamma and beta irradiations on graphene oxide samples

Graphene oxide (GO) sheets have many applications such as biomedical, solar cells, batteries, supercapacitors and biosensors. The product of GO sheets was irradiated in the air by gamma-rays (60Co source) and beta particles (90Sr source). Positron Annihilation Doppler-Broadening technique was used to study the effect of radiation on GO samples. The interlayer spacing (d-spacing) of GO layers was measured by X-ray diffraction before and after irradiation processes. The d-spacing of GO was decreased after beta particles and gamma-ray irradiation. Raman spectroscopy measurements were performed on irradiated and non-irradiated GO samples. The measured data showed that the disorder parameter defect ratio for the gamma-ray irradiation was decreased. Fourier transform infrared spectra were applied to obtain information on the functional groups attached to irradiated and non-irradiated GO samples. The results obtained a reduction in oxygen-functional groups of the GO samples as well as the optical absorption spectra of all samples were measured.

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.

Studies on the Adsorption Behavior of 152+154Eu (III) on Synthesized Graphene Oxide

Graphene oxide (GO) Samples are locally synthesized for use in sorption and radionuclides removal studies of 152+154Eu (III). The samples were characterized by FT-IR, X-ray diffraction (XRD) and electron scanning microscopy (SEM). These samples are used to study the adsorption of some inorganic acids HCl, HNO3, H2SO4 and H3PO4 as well as organic acetic, oxalic, citric, tartaric and EDTA acids from dilute solutions at low concentrations. The adsorption behavior of 152+154Eu (III) was studied under static conditions. Effects of: pH solution, contact time, particle size, concentration of metal ion and adsorption kinetics temperature are intensively studied in this study. Thermodynamic parameters such as Gibbs free energy changes (∆G◦), enthalpy (∆H◦) and entropy (∆S◦) are estimated. The adsorption, isotherms and kinetics process was analyzed using various models. In the case of Eu (III), adsorption is found to obey Langmuir isotherm stronger than Freundlich isotherm and the pseudo-second order kinetics mathematics the data for adsorption.

Effect of Different Reduction Methods on the Structure of Graphene Oxide

The samples of graphene oxide were prepared by Hummers method, and then they were reduced and dried by different methods. The effects of different treatment methods on the graphene oxide’s morphology, size and oxygen content were analysed by IR, Roman and TEM. The results show that the reduction method of increasing temperature can effectively reduce the oxygen content of graphene oxide but increase the defect density. However, the ultrasonic cell pulveriser can effectively reduce the oxygen content of graphene oxide in the reduction process and has little effect on the defect density. Therefore, low-defect and low-oxygen reduced graphene oxide can be quickly obtained by an ultrasonic cell pulveriser.

Analysis of Carbon and Carbon-Containing Materials by X-Ray Photoelectron Spectroscopy

The results of the analysis of carbon-containing materials are presented based on an analysis of the peaks of X-ray photoelectron spectroscopy (XPS) formed by the electrons leaving the analyzed sample in a vacuum without energy loss (peak shape analysis, PSA) and based on the interpretation of the widest possible area of energy loss adjacent to the photoelectron spectroscopy (PES) peak. It is shown that the PES analysis of diamond-like materials containing alloying additives, the concentration of which is comparable with the concentration of carbon, is not effective. The PES analysis of graphene oxide samples that were heat-treated to remove oxygen gave detailed information about the laws of the energy loss of photoelectrons emitted from the 1s level, which determines the allotropic variety of carbon.

Development of New Carbon-Based Electrode Material from Oil Palm Waste-Derived Reduced Graphene Oxide and Its Capacitive Performance Evaluation

This paper is an expansion of our previous work on the synthesis of graphene oxides and reduced graphene oxides from different kinds of oil palm waste-based feedstocks, namely, OPL (oil palm leaf), PKS (palm kernel shell), and EFB (empty fruit bunch). Here, the electrochemical measurements of the resulting reduced graphene oxides derived via mild-temperature annealing reduction of the graphene oxides were accomplished using cyclic voltammetry and galvanostatic charge/discharge processes. The findings put forward their promising features for supercapacitor applications. For instance, the reduced graphene oxide derived using EFB precursor (rGOEFB) which has a BET surface area of 117 m2 g-1exhibits a specific capacitance of 688 F g−1at an applied current density of 0.8 A g-1. This is higher than that observed for reduced graphene oxides derived from oil palm leaf (rGOOPL), palm kernel shell (rGOPKS), and the commercially acquired graphite (rGOCG), which possessed specific capacitance values of 632, 424, and 220 F g−1, respectively. It can be deduced that the specific capacitance of the reduced graphene oxide samples increases in the following order: (rGOCG) < (rGOPKS) < (rGOOPL) < (rGOEFB). In summary, these new classes of carbon-based nanomaterials could be applied as efficient electrode materials for supercapacitor application with potential good performance. With this novel green and sustainable approach, various carbon-based nanomaterials can be fabricated for a broad range of multifunctional applications.

Surface area measurements of graphene and graphene oxide samples: Dopamine adsorption as a complement or alternative to methylene blue?

The possible use of dopamine, monitored spectroscopically, as a probe molecule for surface area measurements is investigated. Using high surface area carbon materials, including both graphene and graphene oxide (GO), the method is established as a complement or alternative to methylene blue or conventional N2 (BET) adsorption. The molecular reorientation (flat to vertical) of dopamine on the graphene and GO surface provides a direct indication of the monolayer coverage and the rapid adsorption (within 10 min to saturation) offers high convenience. The smaller dopamine molecule size and less self-repulsion compared to methylene blue can be considered to yield a more closely-packed surface coverage on the materials of interest. Especially for materials with complex morphologies and internal structures, the dopamine adsorption will therefore lead to a more ‘correct’ measurement.

Assessment of Antioxidant Activity of Pure Graphene Oxide (GO) and ZnO-Decorated Reduced Graphene Oxide (rGO) Using DPPH Radical and H2O2 Scavenging Assays

In this work, zinc oxide-decorated graphene oxide (ZnO–rGO) was successfully synthesized with a fast reflux chemical procedure at 100 °C. An equal mass ratio of graphene oxide (GO) and zinc acetate was used as starting materials dissolved, respectively, in ultrapure distilled water and dimethylformamide (DMF). Particularly, pure GO was synthesized using Hummers modified protocol by varying the mass ratio of (graphite:potassium permanganate) as follows: 1:2, 1:3, and 1:4, which allow us to obtain six types of pure and decorated samples, named, respectively, GO1:2, GO1:3, GO1:4, ZnO–rGO1:2, ZnO–rGO1:3, and ZnO–rGO1:4 using reflux at 100 °C. X-ray diffraction, FTIR, and Raman spectroscopy spectra confirm the formation of wurzite ZnO in all ZnO-decorated samples with better reduction of GO in ZnO–rGO1:4, confirming that a higher degree of graphene oxidation allows better reduction during the decoration process with ZnO metal oxide. Antioxidant activity of pure and zinc oxide-decorated graphene oxide samples were compared using two different in vitro assays (DPPH radical and H2O2 scavenging activities). Considerable in vitro antioxidant activities in a concentration-dependent manner were recorded. Interestingly, pristine GO showed more elevated scavenging efficiency in DPPH tests while ZnO-decorated GO was relatively more efficient in H2O2 antioxidant assays.

Simple process and uncomplicated reduction of graphene oxide

In this work reduced graphene oxide (rGO) was performed by modified Hummers method and thermal reduction process, modifying the thermal exposure times (2, 4, 6 and 8 h) and maintaining a constant temperature (200 °C). It was possible to observe the morphological and structural variation in all the samples. SEM analysis shows agglomerates with different dimensions (1–10 μm) in all the samples. The XRD analysis displays two characteristic peaks in graphene oxide (GO) samples, associated with (002) and (100) planes, corresponding to 10.57° and 42.20° in the 2-theta scale. The rGO samples show the increase in (002) plane associated with graphite (27° in 2-theta scale), proving the reduction process. FTIR analysis presents all the absorption bands for GO and rGO samples, showing the main functional groups like; hydroxyl, ketone, alkene, epoxy and carboxyl groups. Finally, Raman spectroscopy exhibits the vibrational characteristic modes of graphitic materials corresponding to D, G, and 2D bands, in which it is possible to differentiate between GO and rGO. Currently, the reduction processes use high temperatures, so it is necessary to reduce them with the commitment to obtain rGO of good quality and a considerable energy saving.

One-pot redox synthesis of graphene from waste graphite of spent lithium ion batteries with peracetic acid assistance

In order to meet increasingly urgent application requirements for energy storage and aviation materials, it is necessary to facilitate the rapid, low-cost, large-scale preparation of high-quality graphene. In this study, reduced graphene oxide (rGO) was prepared from the waste graphite of spent lithium batteries by a one-pot redox reaction using a ternary system contains sulfuric acid, potassium permanganate and peracetic acid. Peroxyacetic acid was first used in the system to effect oxidation and reduction preparation of graphene to avoid additional reduction steps. XRD, XPS, SEM, TEM, FT-IR, and Raman spectroscopy analyses showed that reduced graphene oxide samples synthesized from waste graphite (L-rGO) and commercial graphite (C-rGO) have similar microscopic morphologies and structural characteristics. Therefore, lithium ion battery waste graphite is a good potential resource for the preparation of high-quality rGO. The carbon-to-oxygen ratios of L-rGO and C-rGO were 1.79 and 4.25, respectively, indicating that peracetic acid effectively reduced graphene oxide to rGO. The yield of rGO was calculated to be 61.2%, which means that rGO can be produced on a large scale using this method.

Reduced Graphene Oxide Obtained by Hummers and Marcano-Tour Methods: Comparison of Electrical Properties.

The aim of this paper is the comparison of structural, morphological and electrical properties of graphene oxide synthesized by Hummers and Marcano-Tour approaches and reduced graphene oxide obtained by hydrothermal hydrazine-assisted route. Obtained materials were characterized by XRD, scanning electron microscopy, low temperature nitrogen absorption and impedance spectroscopy. It was determined that reduced graphene oxide obtained by Hummers route is formed by plate-like agglomerates with respectively short distance between graphene layers that consist of plate-like particles with smaller average diameter and larger average thickness. Reduced graphene oxide that was synthesized by Marcano-Tour method is mesoporous solid material and consists of randomly aggregated linear fragments of carbon packages. It was suggested that dominant charge transport mechanism for both graphene oxide samples was proton conductivity. Both: charge migrating in graphene fragments and the morphologically sensitive charge hopping between them were observed for reduced graphene oxide.

High performance catalytic system with enhanced durability in PEM fuel cell

In this work, gold nanoparticles decorated on reduced graphene oxide (Au/rGOs) samples were synthesized by employing the eco-friendly microwave-assisted process (MW). This rapid process has proven to be a viable and trustworthy new method for Au/rGOs preparation ensuring the simultaneous reduction of GO and obtaining of Au nanoparticles through a simple and facile one-step reaction in aqueous solution. The structure and morphology of prepared Au/rGOs were characterized using scanning electron microscopy (SEM), Raman spectroscopy, BET surface area. These analyses revealed good phase stability and distinct morphology. The as-prepared Au/rGO was involved in developing of a new membrane electrode assembly (MEA) and in-situ tested in long-time operation of PEMFC. The electrochemical stability of the innovative cathode was evaluated using an accelerated stress test (AST) - cycling potential protocol. The performed aggressive AST demonstrated excellent stability, thus we report an ORR electrocatalyst with enhanced durability. Moreover, this study extends the method applicability in respect to the preparation of other noble metal nanoparticles decorated on reduced graphene oxide.

Fabrication of anti-corrosion nitrogen doped graphene oxide coatings by electrophoretic deposition

This work assesses anti-corrosion properties of graphene and N-doped graphene coatings deposited on copper by an electrophoretic method. Graphene oxide (GO) precursor was synthesized by an improved Hummers' method, whereas N-doping was performed hydrothermally in the presence of ammonia. After nitrogenation, doped graphene oxide samples (NGO) contained a reduced amount of oxygen and about 9% w/w nitrogen as pyridinic, pyrrole, and graphitic groups. Nevertheless, it was possible to obtain a stable aqueous dispersion of NGOs, a prerequisite for the EPD process. According to SEM images, the EPD coatings were compact with minor defects. On the contrary, GO coating possessed cracks and large pores that resulted from gas evolution during electrolysis. Electrochemical studies showed that all coatings prevented copper from corrosion in saline solution, however, the nitrogenated coatings did not exhibit better anti-corrosion properties than reduced graphene oxide coating. A reasonable explanation of this finding is that some positive properties of the nitrogenated coatings, in terms of anti-corrosion action, like low hydrophilicity and good adhesion, were counteracted by their catalytic activity towards oxygen reduction reaction.

A nanocomposite prepared from metal-free mesoporous carbon nanospheres and graphene oxide for voltammetric determination of doxorubicin.

A metal-free catalyst is described that consists of a composite that can be prepared from mesoporous carbon spheres (MCS) and graphene oxide (GO) under mild aqueous synthetic conditions. The reduced graphene oxide (rGO) sheets tend to aggregate, but due to the insertion of MCS, the aggregation is prevented. This leads to a larger surface area and more adsorption sites for the cancer drug doxorubicin (DOX). The π-interaction between DOX and rGO is also beneficial for the adsorption of DOX. A glassy carbon electrode (GCE) was modified with the composite and used to detect low levels of DOX, typically at a peak potential near -0.45V (vs. Ag/AgCl). The modified GCE has a wide linear response range (10nM - 10μM), a low limit of detection (1.5nM; at S/N = 3), excellent selectivity, long-term storage stability and reproducibility. It was applied to the determination of DOX in spiked serum where it gave reliable results. Graphical abstract Schematic representation ofthe preparation of mesoporous carbon spheres/reduced graphene oxide (MCS/rGO) sample, and the CV scan of doxorubicin (DOX) on MCS/rGO based nanoprode.