Exfoliation Of Graphite Oxide Research Articles

Elemental Analysis with Sorption Preconcentration by Graphene Oxide for Mineral Water by Inductively Coupled Plasma – Optical Emission and Mass Spectrometries (ICP-OES and ICP-MS)

The paper discusses using sorption preconcentration of elements from mineral waters by graphene oxide. The procedure aims to extract heavy metals such as Cd, Cr, Cu, Pb, Zn and other analytes from solution. Inductively coupled plasma – mass spectrometry (ICP-MS) and inductively coupled plasma – optical emission spectrometry (ICP-OES) were used to determine the analyte content. Graphene oxide was obtained by microwave exfoliation of graphite oxide. The sorption of analytes on the graphene oxide at different pH values and coexisting ion effect were studied in detail. Preliminary preconcentration of analytes provides good extraction recoveries using the optimal conditions. The limits of detection (LODs) of 27 analytes for the developed procedure ranged 0.1 to 200 ng L−1 for ICP-MS and from 5 to 1000 ng L−1 for ICP-OES. Sorption concentration provides recoveries of analytes from 80 to 110%. Graphene oxide was successfully employed for the sorption preconcentration of analytes from mineral and tap water.

Electrodeposition and corrosion behavior of Sn and Sn-reduced graphene oxide coatings on mild steel from the non-cyanide acid chloride bath solution

Reduced graphene oxide (rGO) derived from graphite has received attention among researchers because of its special unique characteristic properties. Based on the studies, rGO-based coatings on stainless steel (SS) act as an anti-corrosive protective coating on stainless steel. Herein, we prepared a few layered rGO via graphite oxide by a simple thermal exfoliation of graphite oxide. Tin and Sn-rGO coatings have been electrodeposited on SS using an optimized acid chloride bath composition in the absence and presence of rGO respectively. The prepared specimens were subjected to an aggressive corrosive environment (aqueous 5% NaCl). The corrosion behavior of Sn and Sn-rGO composite coating has been examined by potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. The potential shifted towards the negative region after polarization for Sn-rGO composite coating compared to pure Sn coating. Also, Sn-rGO composite coating exhibits more resistance when subjected to EIS measurements in 5% NaCl. The change in the surface morphology of coatings before and after exposure to corrosive environments has been observed by Scanning electron microscopy. After exposure to aqueous 5% NaCl, Sn coated specimen exhibited pores on the SS surface whereas fewer pore structures were observed on the SS surface for Sn-rGO coating. The results reveal a significant increase in anti-corrosion properties of Sn-rGO on SS compared to that of pure Sn coating.

Defective graphene decorated with TiO2 nanoparticles as negative electrode in Li-ion batteries

In this work, the performance of novel negative electrodes for Li-ion batteries based on defective graphene synthesized via a scalable thermal exfoliation of graphite oxide and decorated with TiO2 nanoparticles is investigated. Titania polymorphs are interesting as battery electrode materials, owing to their high cycle stability, safety, abundance and negligible solid electrolyte interphase formation and volume changes upon cycling. Defective graphene, on the other hand, can embed TiO2 nanoparticles, forming a conductive hybrid nanocomposite anode material for Li-ion batteries, with improved Li-ion and electron transport, optimising power density. Here we propose two different synthetic approaches for the decoration of graphene with TiO2 nanoparticles: I) a novel chemical route where TiO2 nanoparticles, mainly anatase, were grown on graphene in hydrothermal mild conditions and II) a physical solid-state approach where hydrothermal TiO2 nanoparticles and graphene were mixed together via high energy ball-milling. The synthesized materials were analysed via powder X-ray diffraction, micro-Raman spectroscopy and HR-TEM, while the electrodes were electrochemically tested. Operando synchrotron diffraction was conducted on half-cell to investigate phase transitions in the electrode materials. Even in presence of small amount of graphene, significant improvement in capacity, reversibility, and high-rate capability were observed. In particular, the sample obtained through the addition of 1 wt% of graphene displayed a reversible capacity of more than 180 mA h/g after prolonged and wearing cycling. This result outperforms by 327 % the reversible capacity of pure TiO2 electrode.

Simultaneous and rapid determination of three organophosphorus pesticides from vegetable and cereal samples with a magnetic dispersive solid-phase microextraction method by gas chromatography-mass spectrometry

ABSTRACT A straightforward and fast magnetic dispersive solid-phase microextraction method (MDSPME) as a sample preparation procedure coupled with gas chromatography/mass spectroscopy (GC/MS) was developed to measure three organophosphorus pesticides (OPPs), including ethion, diazinon, and chlorpyrifos, from fruit and cereal samples. Magnetic Fe3O4@ reduced graphene oxide nanocomposites as an excellent sorbent were synthesised based on several steps such as graphite oxide preparation, graphite oxide exfoliation, graphene oxide reduction, and chemical co-precipitation of magnetic Fe3O4 methods. Nine factors affected in the MDSPME procedure were thoroughly optimised using the design of experiment approach. The Plackett-Burman design and central composite design were utilised for screening the significant factors and for optimising the factors, respectively. The calibration curves of ethion, diazinon, and chlorpyrifos were linear in the ranges of 0.008–4.5, 0.01–4.0, and 0.01–4.5 ng ml−1 with R-squared of 0.9953, 0.9923, and 0.9981, respectively. The proposed method has high preconcentration factors (PF ≥ 220), low sample solution consumption (5.0 ml), and fast extraction time (5.0 min) for the OPPs determination. Analysis of real samples, including rice and cucumber samples, was shown that the proposed procedure is the suitable sample preparation and determination method for the measurement of OPPs with a recovery percentage in the range of 91.3%-102.2% and RSDs lower than 7.2%. The method has great advantages including low desorption solvent consumption, simple operation, and suitable RSDs for the OPPs determination in the fruit and cereal samples with complex matrices.

Highly conductive quasi-defect-free reduced graphene oxide for qualitative scalable production

Herein, we present a potential approach for the qualitative production of quasi-defect-free reduced graphene oxide (QrGO) with semimetallic transport behavior. In rGO, the formation of defects is highly dependent on the oxidation process of graphite. Subsequent exfoliation of graphite oxide, the quasi-defect-free graphene oxide (QGO) shows abundant epoxy and hydroxyl groups which confirmed the suppressed structural deformation. Typical rGO and QrGO are compared to characterize the remarkable electrical, optical, and thermal properties of QrGO. In particular, under low temperature, the unusual carrier transport phenomena of QrGO exhibits a metal-like behavior, unlike typical rGO, which shows an insulator-to-semimetal transition with variable-range hopping conduction behavior. This conduction mechanism, resembling that of mechanically exfoliated graphene, facilitates the fabrication of a QrGO-based conducting film with a high electrical conductivity of ∼1000 S/cm. Moreover, during a 200-h test with temperature and moisture conditions of 85 °C and 85%, respectively, QrGO shows environmental stability with minimal fluctuations in resistance. Furthermore, a conducting paste was fabricated from QrGO in an aqueous solution, showing a highly concentrated solid content and excellent electrical conductivity. It shows great potential for the large-scale production of high-quality chemically exfoliated graphene for practical applications.

Insights into the Electrical Characterization of Graphene-like Materials from Carbon Black

A new class of graphene-related materials (GRMs) obtained as water suspensions through a two-step oxidation/reduction of a nanostructured carbon black, namely graphene-like (GL) materials, has recently emerged. GL materials undergo self-assembly in thin amorphous films after drying upon drop-casting deposition on different surfaces. The GL films, with thicknesses of less than a micron, were composed of clusters of nanoparticles each around 40 nm in size. The exploitation of the GL films for different options (e.g., bioelectronic, sensoristic, functional filler in composite) requires a deep characterization of the material in terms of their electric transport properties and their possible interaction with the surface on which they are deposited. In this work, a careful electrical characterization of GL films was performed at room temperature and the results were compared with those achieved on films of benchmark graphenic materials, namely graphene oxide (GO) materials, obtained by the exfoliation of graphite oxide, which differ both in morphology and in oxidation degree. The results indicate a non-linear current–voltage relationship for all the investigated films. The extrapolated dielectric constant (ε) values of the investigated GRMs (GL and GO materials) agree with the experimental and theoretically predicted values reported in the literature (ε~2–15). Because similar conductance values were obtained for the GL materials deposited on glass and silicon oxide substrates, no significant interactions of GL materials with the two different substrates were highlighted. These results are the starting point for boosting a feasible use of GL materials in a wide spectrum of applications, ranging from electronics to optics, sensors, membranes, functional coatings, and biodevices.

Graphene‐Based Magnetocaloric Composites for Energy Conversion

Herein, a simple, versatile, and cost‐effective method to fabricate innovative thermal conductive magnetocaloric (MC) composites, which offers a smart solution to manufacture active elements with desired geometries, overcoming the current thermal and mechanical limits of the most studied MC materials, is presented. The composite is prepared by embedding powder of a MC material in an epoxy matrix enriched with a graphene‐based material, obtained by thermal exfoliation of graphite oxide. The graphene‐enriched composite shows a significant improvement of the MC time response to the magnetic field, due to the formation of a 3D network that bridges the MC particles and reduces the metal–matrix contact resistance, thus creating a percolation path for an efficient heat transfer. Because of the simplicity and scalability of the preparation method and the great enhancement in response time, these new functional composites represent an important step for the effective application of MC materials in thermomagnetic devices for the energy conversion.

Asymmetric supercapacitors based on nickel decorated graphene and porous graphene electrodes

Thermal exfoliation of graphite oxide is a scalable way to produce macroscopic amount of defective graphene-based compounds with high specific surface area, ideal as electrode materials in high-performance electrochemical supercapacitors. In order to increase the stored energy, defective graphene has been decorated with Ni nanoparticles without exposing the system to air. During the first charge cycle in an aqueous electrolyte (KOH 3.5 M), Ni anchored to graphene proved to easily convert to Ni(OH) 2 at the nanoscale and hence to reversibly assume Ni 2+ and Ni 3+ valence during cyclic voltammetry, through its conversion to NiOOH. Such reversible faradaic mechanism led to a one order of magnitude increase of the specific capacitance of electrodes, reaching up to 1900 F/g at 2 mV/s in KOH 3.5 M. An asymmetric supercapacitor was obtained by coupling a pure graphene negative electrode with a Ni decorated graphene positive one. The supercapacitor, operating with aqueous electrolyte, was successfully cycled in the 0–1.5 V voltage range, reaching a maximum specific energy of 37 Wh/kg and a maximum specific power of 5 kW/kg. The devices displayed good reversibility and retained 72% of the specific energy over 10 thousand of cycles. Such promising results disclose to possible industrial implementation of graphene-based supercapacitors, for a wide range of energetic application.

Temperature-controlled exfoliation of graphite oxide: studies of defects and transport properties of graphene oxide

The quality, structural defects, and transport properties of GO can be tailored by maintaining ultrasonic bath temperature. Herein, the effect of temperature-controlled exfoliation on the structural defects and transport properties of the resulting graphene oxide (GO) sheets are examined. The large crystallite size (12.23 nm) and low defect density (2.16 × 1011 cm−2) are found at 20 °C exfoliations. Highly oriented GO sheets were exfoliated at 20 °C which was confirmed through Bernal-stacking proportions (∼30%). Furthermore, electrical transport properties are high at 10 °C exfoliation temperature while optimum at other temperatures, calculated through impedance spectroscopy. Comparatively, smooth, wrinkle-free, and lesser bulges are found at 20 °C and 30 °C exfoliation temperatures.

Role of low-dimensional carbon nanostructures in hybrid material as anticorrosive coating

In this work, different low-dimensional carbon nanostructures (graphite oxide, graphene oxide and amino-functionalized graphene oxide and graphite oxide) integrated into a hybrid, organic-inorganic matrix, were developed, obtaining different nanocomposite coatings. The hybrid matrix was obtained from an inorganic component, tetraethyl orthosilicate, and an organic composition resin, diglycidyl ether bisphenol-A. Each of the different coatings were separately applied on AISI 1018 carbon steel surfaces. The corrosion test was carried out by Electrochemical Impedance Spectroscopy on the coated metal in two different media, saline and acidic. The resistance to charge transfer was higher for coating containing graphene oxide in both electrolytes. A comparison between the coating's performance containing graphite oxide and graphene oxide showed that the exfoliation of graphite oxide is important to have a greater distribution and intercalation of the low dimensionality sheets inside the hybrid matrix up to form a uniform protective barrier. Wear test were carried out and structural stability of the coatings after 100 cycles was demonstrated, showing the persistent SiOSi groups produce a protection against corrosion to AISI 1018 carbon steel.

Combined capacitive and electrochemical charge storage mechanism in high-performance graphene-based lithium-ion batteries

Improvements in lithium (Li)-ion battery technology can be achieved by developing novel, high-performance electrode materials. Graphene appears to be a good candidate as an anode material for Li-ion batteries thanks to the similarity with graphite, the good electrical conductivity, the ability to achieve fast charge and discharge cycles, and the higher capability to host Li ions. Our previous studies demonstrated the capability of intercalating Li in graphene-based electrodes with a high specific capacity of 500 mA h/g at C/5 current. In this study, graphene, synthesized through scalable thermal exfoliation of graphite oxide, and hydrogenated graphene are used to assemble optimized Li-ion half-cells, which are systematically characterized by means of electrochemical measurements. Hydrogenated graphene boasts an impressive reversible specific capacity with fast charge/discharge capabilities, exceeding 370 mA h/g even at 25 C rate. Diffusion mechanisms of Li are characterized at different states of intercalation by means of electrochemical impedance spectroscopy. In addition, a novel combined electrostatic and electrochemical charge storage mechanism of Li ions in graphene-based electrodes is proposed, based on three-electrode cyclic voltammetry investigation. Furthermore, graphene and hydrogenated graphene anodes are paired with commercial cathode materials to study the feasibility of their application to full cells.

Thermally reduced graphene/nafion modified platinum disk electrode for trace level electrochemical detection of iron

This paper presents a thermally reduced graphene/nafion modified platinum disk electrode (TRG/NF/PDE) for sensitive detection of iron (Fe) using square wave voltammetry (SWV). The graphene was synthesized by thermal exfoliation of graphite oxide in nitrogen atmosphere with an eco-friendly procedure. The morphologies of thermally reduced graphene and thermally reduced graphene/nafion were characterized by field emission scanning electron microscopy (FESEM). Electrochemical behaviors of the electrode before and after modification were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the TRG/ND/PDE exhibited excellent electrocatalysis toward Fe. A linear calibration curve was established in the range from 1 to 200 ppb for Fe. With a pre-concentration time of 180 s, a limit of detection based on three times of the background noise was calculated to be 0.08 ppb for Fe. The method was successfully employed for the detection of Fe in real water samples.

Rapid Production of Thermally Exfoliated Graphene with a Large Specific Surface Area by Introducing a Spray Predrying Process

Thermal exfoliation of graphite oxide (GTO) is a rapid and efficient method to obtain thermally exfoliated graphene (TEG) on a large scale. Generally, the effect of the thermal exfoliation process is studied to obtain a high specific surface area (SSA), whereas the importance of the predrying process is rarely discussed. In the present work, the influence of spray-assisted predrying on the final exfoliation of GTO was investigated. It was found that the introduction of spray drying did not change the basic units of the thermally exfoliated products comprised of six to eight layers of porous structures. However, it contributed to the formation of loose and more disordered structures, highly susceptible to the destruction caused by the gas generated during thermal exfoliation. Consequently, a higher SSA of 870 ± 74 m2·g–1 with more pores among all the structural units could be obtained. This work helps to understand the influence of spray drying on the TEG, and conveniently associates the predrying and thermal exfoliation processes to achieve a continuous operation.

Microwave-assisted thin reduced graphene oxide-cobalt oxide nanoparticles as hybrids for electrode materials in supercapacitor

In recent times, microwave synthetic strategies have been considered as one of the facile methods for the development of efficient supercapacitor electrodes. Reduced graphene oxide containing cobalt oxide (rGO@Co3O4/CoO) hybrids were synthesized via single-step microwave irradiation in which the uniform Co3O4/CoO nanoparticles were attached in thin layers of rGO nanosheets. During short time of single-step microwave irradiation process, three kind of phenomena occurs as (i) reduction and exfoliation of graphite oxide into rGO nanosheets, (ii) decomposition of cobalt(II) acetate into Co3O4/CoO nanoparticles and (iii) rGO nanosheets covers the Co3O4/CoO nanoparticles. The BET surface area and pore diameter range of rGO@Co3O4/CoO hybrids were 133.2 m2g−1 and 5–45 nm, respectively, which shows the mesoporous structure formation of hybrids. Electrochemical evaluations of rGO@Co3O4/CoO hybrids as electrode materials for supercapacitor shows specific capacitance of 276.1 F g−1 (scan rate of 5 mV s−1) and long-term cycling stability as 82.37% capacitance retention after 10,000 cycles (scan rate of 60 mV s−1) in 0.1 M KOH electrolyte solution. The Co3O4/CoO nanoparticles with conducting scaffolds rGO structure will pave an encouraging alternative for electrode materials and suggesting good potential for supercapacitors applications.

Fabrication of graphene-like structured solid acid catalysts and their application in the saccharification of cellulose

Graphene oxide, which exhibits extraordinary acidic properties and a high theoretical surface area, is a good candidate for the catalytic transformation of biomass resources to valuable chemicals and biofuels. In this study, graphene oxide was prepared through various graphite oxide exfoliation methods, including sonication, microwave irradiation, and freeze-thaw cycling, and the activity of the prepared catalysts was evaluated in the saccharification of cellulose. The results indicated that graphene oxide prepared via these methods exhibited superior catalytic performances compared to graphite oxide; however, no significant difference in the catalytic activity of the graphene oxide catalysts was observed based on the exfoliation method used. Therefore, we proposed that thinning of graphite oxide improves its catalytic activity by increasing the contact efficiency between the substrate and the catalyst; however, this is not dependent on the exfoliation method used to prepare the graphene oxide.

Extraordinary thermal behavior of graphene oxide in air for electrode applications.

The thermal stability of solution-exfoliated graphene oxide (GO) in air is one of the most important physical properties influencing its potential applications. To date, the majority of the GO prepared by the KMnO4-based oxidation of graphite is thermally unstable in air due to the presence of highly oxidative functional groups, such as carboxyl and lactol groups that possess defective basal plane structures. Here, we demonstrate that less defective and metal ion-free GO nanosheets including those with a high oxidation level can remain very stable even above 300 °C under ambient conditions. These GO nanosheets were produced by the exfoliation of graphite oxide fabricated by the modified Brodie method in NH4OH solution, effectively excluding metal ions that can promote the thermal decomposition of GO in air at elevated temperatures. The deoxygenation of ammonia-assisted GO (AGO) was initiated at temperatures above 200 °C, while GO exfoliated in the KOH solution (KGO) decomposed, even at 180 °C. Notably, AGO was exceptionally resistant at 400 °C, even at a very slow heating rate of 2 °C min−1. Conversely, KGO was significantly oxidized, even at 250 °C. The superior thermal stability of AGO is favorable for the fabrication of conductive surface graphene films and conductive fibers by low-temperature annealing.

Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide.

Extremely defect graphene oxide (dGO) is proposed as an advanced sorbent for treatment of radioactive waste and contaminated natural waters. dGO prepared using a modified Hummers oxidation procedure, starting from reduced graphene oxide (rGO) as a precursor, shows significantly higher sorption of U(VI), Am(III), and Eu(III) than standard graphene oxides (GOs). Earlier studies revealed the mechanism of radionuclide sorption related to defects in GO sheets. Therefore, explosive thermal exfoliation of graphite oxide was used to prepare rGO with a large number of defects and holes. Defects and holes are additionally introduced by Hummers oxidation of rGO, thus providing an extremely defect-rich material. Analysis of characterization by XPS, TGA, and FTIR shows that dGO oxygen functionalization is predominantly related to defects, such as flake edges and edge atoms of holes, whereas standard GO exhibits oxygen functional groups mostly on the planar surface. The high abundance of defects in dGO results in a 15-fold increase in sorption capacity of U(VI) compared to that in standard Hummers GO. The improved sorption capacity of dGO is related to abundant carboxylic group attached hole edge atoms of GO flakes as revealed by synchrotron-based extended X-ray absorption fine structure (EXAFS) and high-energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) spectroscopy.

Boosting CO2 Conversion with Terminal Alkynes by Molecular Architecture of Graphene Oxide-Supported Ag Nanoparticles

Summary Carboxylation of terminal alkynes with CO2 via direct C–H bond activation is a highly appealing way to capture and convert CO2 but faces great challenges and difficulty. Here, we report an efficient catalyst that is prepared simply through introduction of p-tert-butylaniline into graphite oxide powders followed by localized growth of Ag nanoparticles (NPs). The bulky nature of p-tert-butylaniline facilitates the powder exfoliation, giving rise to mass production of uniform modified graphene oxide (tert-GO) nanosheets of 4 nm in thickness. Notably, Ag/tert-GO shows excellent catalytic activity for converting alkynes regardless of containing electron-donating or electron-withdrawing groups under mild reaction conditions. The synergy of the amide linkages on tert-GO nanosheets and the supported small-sized Ag NPs is recognized as the vital role in promoting adsorption of CO2 and subsequent conversion.

Anodic Aqueous Electrophoretic Deposition of Graphene Oxide on Copper Using Different Cathode Materials

The effect of four different cathode materials on the anodic deposition of graphene oxide (GO) nanosheets was studied experimentally. First, synthesis of graphite oxide from graphite powder was done by modified Hummers' method. Ultrasonic technique was adopted for the preparation of the stable aqueous suspension of GO by using liquid exfoliation of graphite oxide. Deposition of GO coating on copper sheets (the anode) was done via electrophoretic deposition (EPD) at the same operating condition (5V, 2 min, concentration of 0.5 mg/ml of GO per deionized water) with different cathode materials (copper, stainless steel, aluminum and graphite). The coatings’ morphological and microstructure were investigated using scanning electron microscope (SEM) and the effect of the current density in the EPD process was obtained. The change in the deposition weight was also measured. It was ascertained that the cathode’s material is a major factor can affect the GO’s EPD process and the characteristics of the final coating.

Graphene from waste and bioprecursors synthesis method and its application: A review

Recently, carbonaceous material such as porous carbon, carbon nanotubes (CNTs), graphene, graphene oxide (GO) and activated carbon has received tremendous attention from researchers. To date, the exploration of graphene is still in vast. Graphene has been applied in various applications which include polymer composites, energy storage, fuel cell and biomedical applications. This is due to its unique characteristics such as large surface area and high remarkable electronic, mechanical and thermal properties. Even though chemical vapor deposition (CVD) has been established as an effective method to synthesize graphene, but the yield is low and may not compatible in certain applications. In addition, the chemical process of the production of graphene from exfoliation of graphite oxide involves hazardous and toxic reagents. Currently, bio-waste materials have been a great source for production of carbon. Furthermore, bio-waste materials are abundant and proper disposal method is needed. Hence, preparation of graphene from waste and biomass precursors is a new alternative to overcome the afore mentioned problem. Therefore, this paper will be focused on the method of synthesizing graphene from glucose, rice husk, chitosan, corn stalk core and plastic waste. The application of graphene derived from each bioprecursor for dye removal, adsorption of toxic and heavy metals, gas storage and supercapacitors will also be reviewed.