Chemical Exfoliation Of Graphite Research Articles

Deep analysis of adsorption isotherm for rapid sorption of Acid Blue 93 and Reactive Red 195 on reactive graphene.

Graphene-based adsorbent was prepared by adopting a green synthetic route via the chemical exfoliation of graphite and low-temperature thermal activation. Prepared reactive graphene (RG) was characterized through various techniques, and its adsorption capabilities for textile dye removal were investigated for Acid Blue-93 (AB) and Reactive Red-195 (RR) under different operational conditions. The dye sorption equilibrium and mechanism were comprehensively studied using isotherm and kinetic models and compared statistically to explain the sorption behavior. Results show AB and RR adsorption by RG attains equilibrium in 60min and 70min, with a high sorption quantity of 397mgg-1 and 262mgg-1 (initial dye concentration of 100mg L-1), respectively. The dye sorption anticipates that the high surface area (104.52 m2 gm-1) and constructed meso-macroporous features of RG facilitated the interaction between the dye molecules and graphitic skeleton. The R-P isotherm fitted the best of equilibrium data, having the least variance in residuals for both dyes (AB = 0.00031 and RR = 0.00047). The pseudo-second order model best fitted the kinetics of sorption on RG, with chemisorption being the predominant process delimiting step. The overall results promise the dye removal capability of RG to be an efficient adsorbent for azo-based dyes from textile effluents.

High-quality ultra-flat reduced graphene oxide nanosheets with super-robust lubrication performances

The development of high-performance graphene has been driven by increasingly growing industrial demands. Due to the compatibility of high-efficient and low-cost, chemical exfoliation of graphite is currently a common synthesis method of graphene. Unfortunately, there is not an effective chemical way to prepare high-quality graphene nanosheets for industry application. Working under a harsh condition is also a challenge for their engineering application. Herein, high-quality ultra-flat reduced graphene oxide (UF#G) nanosheets with near-perfect integrity were synthesized by a chemical exfoliation method. Taking the advantage of metal ion from the oxidant agent, the manganese compounds are in situ uniformly deposited on the surface of reduced graphene oxide (rGO) nanosheets in a weak alkali environment, thus protecting the nanostructure from being damaged by gaseous products during chemical reduction process. UF#G can reduce the coefficient of friction (COF) and wear depth of the lubricated interfaces by 49% and 93% at a heavy load (2.5 GPa), compared with pure grease (P.G). Especially, the UF#G-based lubricant has superior lubricating stability with long-operating life of more than 216,000 cycles, which is beyond previous results for both state-of-the-art nanocoatings and nanolubricants. UF#G together with the lubricant generate a robust chemical-mixing tribofilm consisting of a carbon-adsorbed layer and a CaSO4-deposited layer, which is contributed to the super-robust lubrication performances. The ultra-flat nanostructure of UF#G further improves the lubrication by interlayer-sliding effect. This work provides high-quality ultra-flat reduced graphene oxide nanosheets enabled by a novel chemical-exfoliation route with super-robust lubrication performances.

Facile synthesis of nanostructured ZnO–rGO based graphene and its application in wastewater treatment

In the present work, graphene oxide GO is prepared by chemical exfoliation of graphite using Hummer’s method. A facile and green synthesis of ZnO–rGO nanocomposite is performed using aloe vera plant extract. The characterization tools (XRD, FTIR, FESEM, HrTEM, AFM) proved the formation of single phase of ZnO–rGO nanocomposite. Since the environmental contamination caused by Cd(II) ion is a world issue, it has a harmful effect, especially on the human health and environment. Subsequently, our goal in this work is to find an accurate method for detection and adsorption of toxic Cd(II). ZnO and ZnO–rGO nanocomposites are prepared for removing Cd(II), and on behalf of increasing its removal efficiency, GO is added. The results showed a great improvement in removal efficiency reached up to 90% at pH 6 after 90 min.

Methods to Scale Down Graphene Oxide Size and Size Implication in Anti-cancer Applications.

Despite considerable progress in the comprehension of the mechanisms involved in the origin and development of cancer, with improved diagnosis and treatment, this disease remains a major public health challenge with a considerable impact on the social and economic system, as well as on the individual. One way to improve effectiveness and reduce side effects is to consider responsive stimuli delivery systems that provide tailor-made release profiles with excellent spatial and temporal control. 2D nanomaterials possess special physicochemical properties (e.g., light, ultrasonic and magnetic responses) and biological behaviors such as endocytosis, biodistribution, biodegradation, and excretory pathways, which lead to their use in various biomedical applications. In particular, among 2D nanomaterials, graphene and its derivatives, namely graphene oxide (GO) nanomaterials, have attracted enormous attention in cancer diagnosis and therapy because they combine, in a unique material, extremely small size, NIR absorption, delocalized electrons, extremely high surface area, and versatile surface functionality. Taking into account the fundamental role played by GO size, in this review, we summarize the main methods employed to reduce and homogenize in nanometric scale the lateral dimensions of graphene oxide produced by chemical exfoliation of graphite, as well as post-synthesis separation techniques to uniform the size. We also discuss the implication of the small size in cancer treatment by exploiting GO nanocarriers as an effective theranostic tool.

Synthesis of High-Quality Graphene Oxide Made By a Novel One-Step Electrochemical Exfoliation of Natural Graphite Flakes Based on a 3D-Printed Reactor

Since its discovery in 2004, Graphene has been widely study for different applications, noticeable for electrochemical energy devices, due to its excellent properties as a barrier material, electrical conductivity or high surface area. However, it is still an expensive material since it cannot be produced in a large scale. Graphene based materials such as Graphene oxide (GO) or Reduced Graphene Oxide (rGO) also present similar properties than Graphene and can be produce in a more economical way [1]. However, traditional method to produce GO, Hummer’s method, which base on chemical exfoliation of graphite, is a long and tedious process which requires the use of strong oxidants and hazardous chemicals leading environmental pollution that cannot be repaired [2,3]. Recently, electrochemical exfoliation of graphite to produce GO has attracted more and more attention due its environmental protection, low price, easy process and high efficiency [4-7]. Since natural graphite is mostly in the form of flakes and its tiny size is not conducive to its direct use in electrochemical exfoliation, currently, electrochemical exfoliation is mostly made of graphite foil, graphite rod and other graphite processed products. These materials are obtained by using processes such as chemical, thermodynamic, and mechanical compression, leading in physical or chemical changes that alter their original properties or structure. There are also some attempts to use natural graphite flakes for electrochemical exfoliation [8,9]. However, this makes electrochemical exfoliation require more voltage, longer time and less yield. In this work, we present novel design reactor to perform electrochemical exfoliation using natural graphite flakes as raw materials. By using ammonium sulphate as electrolyte, electrochemical exfoliation of natural graphite flakes can be done at low voltage with short time. This achievement also enables the comparison of electrochemical exfoliation products with different raw materials (graphite foil and natural graphite flakes) at the same exfoliation voltage and the same exfoliation time. We explored the properties of the product by raman spectroscopy, ultraviolet–visible spectroscopy (UV-VIS), fourier-transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), four-probe method and contact angle measurement. We have found that by combining natural graphite flakes with the reactor, the product obtained is significantly different from the exfoliated product based on graphite foil, achieving better oxidation, better dispersion in deionized water, more defects and greater yield. In addition, the special structure of the reactor allows the exfoliation time to be controlled, and we also compare the products obtained at different exfoliation times. The Exfoliated Graphene Oxide (EGO) obtained it has been used as a filler material in proton exchange membranes for hydrogen fuel cells as well as a support material for electrocalyst to enhance the kinetics for the reactions which take place in these fuel cells.

Magnetic and optical properties of perovskite-graphene nanocomposites LaFeO3-rGO: Experimental and DFT calculations

We present an experimental and theoretical study of the perovskite-graphene nanocomposites LaFeO3 – rGO, where we demonstrate a easy way to prepare this compound using citrate auto-compulsion method, starting from corresponding metal nitrate and graphene oxide solution. The Hummer’s method was used to prepare graphene oxide by chemical exfoliation of graphite. The structural characterization has been performed using XRD, FT-IR and scanning electron microscope (SEM) to analyze the morphology of the sample, FT-IR, whereas the magnetic properties has been studied using VSM measurements. Furthermore, ab-initio calculations has been performed based on the Density Functional Theory (DFT), where for a better description of the electronic and magnetic properties, the Hubbard correction was considered over the General Gradient Approximation (GGA + U).

Synthesis and Applications of High Quality Graphene Made By a Novel Electrochemical Exfoliation of Natural Graphite Flakes

Since its discovery in 2004, Graphene has been widely study for different applications, noticeable for electrochemical energy devices, due to its excellent properties as a barrier material, electrical conductivity or high surface area. However, it is still an expensive material since it cannot be produced in a large scale. Graphene based materials such as Graphene oxide (GO) or Reduced Graphene Oxide (rGO) also present similar properties than Graphene and can be produce in a more economical way [1]. However, traditional method to produce GO, Hummer’s method, which base on chemical exfoliation of graphite, is a long and tedious process which requires the use of strong oxidants and hazardous chemicals leading environmental pollution that cannot be repaired [2,3]. Recently, electrochemical exfoliation of graphite to produce GO has attracted more and more attention due its environmental protection, low price, easy process and high efficiency [4-7]. Since natural graphite is mostly in the form of flakes and its tiny size is not conducive to its direct use in electrochemical exfoliation, currently, electrochemical exfoliation is mostly made of graphite foil, graphite rod and other graphite processed products. These materials are obtained by using processes such as chemical, thermodynamic, and mechanical compression, leading in physical or chemical changes that alter their original properties or structure. There are also some attempts to use natural graphite flakes for electrochemical exfoliation [8,9]. However, this makes electrochemical exfoliation require more voltage, longer time and less yield. In this work, we present novel design reactor to perform electrochemical exfoliation using natural graphite flakes as raw materials. By using ammonium sulphate as electrolyte, electrochemical exfoliation of natural graphite flakes can be done at low voltage with short time. This achievement also enables the comparison of electrochemical exfoliation products with different raw materials (graphite foil and natural graphite flakes) at the same exfoliation voltage and the same exfoliation time. We explored the properties of the product by raman spectroscopy, ultraviolet–visible spectroscopy (UV-VIS), fourier-transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), four-probe method and contact angle measurement. We have found that by combining natural graphite flakes with the reactor, the product obtained is significantly different from the exfoliated product based on graphite foil, achieving better oxidation, better dispersion in deionized water, more defects and greater yield. In addition, the special structure of the reactor allows the exfoliation time to be controlled, and we also compare the products obtained at different exfoliation times. The Exfoliated Graphene Oxide (EGO) obtained it has been used as a filler material in proton exchange membranes for hydrogen fuel cells as well as a support material for electrocalyst to enhance the kinetics for the reactions which take place in these fuel cells.

Influence of Oxidation Degree of Graphene Oxide on the Shear Rheology of Poly(ethylene glycol) Suspensions

This work studies the influence of the concentration and oxidation degree on the rheological behavior of graphene oxide (GO) nanosheets dispersed on polyethylene glycol (PEG). The rheological characterization was fulfilled in shear flow through rotational rheometry measurements, in steady, transient and oscillatory regimes. Graphene oxide was prepared by chemical exfoliation of graphite using the modified Hummers method. The morphological and structural characteristics originating from the synthesis were analyzed by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. It is shown that higher oxidation times increase the functional groups, which leads to a higher dispersion and exfoliation of GO sheets in the PEG. Moreover, the addition of GO in a PEG solution results in significant growth of the suspension viscosity, and a change of the fluid behavior from Newtonian to pseudoplastic. This effect is related to the concentration and oxidation level of the obtained GO particles. The results obtained aim to contribute towards the understanding of the interactions between the GO and the polymeric liquid matrix, and their influence on the suspension rheological behavior.

An Efficient Water Saving Step During the Production of Graphene Oxide via Chemical Exfoliation of Graphite

Abstract Since its first systematic study in 2004, graphene and their derivatives has treated as one of the most exotic materials for the scientific community, and its exceptional physical properties have produced huge research articles. Herein, we are reporting a sustainable route to neutralize the highly acidic graphene oxide (GO) solution obtained through chemical exfoliations of graphite. To achieve this, we have used 1N Ba(OH)2 solution to maintain/neutralize pH of acidic GO solution. By adding this step to Hummer’s and related methods we could save at least 10L distilled water for each 2g of pure GO productions in short time compared to other methods

Mechanochemical Organic Functionalization of Graphite Produces Tunable Coatings of Carbon Fibers by Multilayered Graphite Microparticles

The properties of carbon fiber reinforced composites depend on the adhesion of fibers to the polymer matrix. The improvement of interfacial properties in carbon fiber containing composite materials was extensively studied by introducing water-soluble derivative of graphene, graphene oxide and linkers molecules that were dispersed in the fiber sizing onto the surface of individual carbon fibers. Here we report mechano-chemical synthesis of a series of functionalized multilayer graphite micro particles able to modify carbon fibers simply dipped to their suspensions in various solvents, including water. The known mechanoactivated chemical exfoliation of graphite by maleic anhydride and maleimide was expanded to hexadecylmaleimide and 1,6-dimaleimidohexane. The new materials were characterized by SEM imaging, X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), powder X-Ray Diffractometry (XRD), nitrogen adsorption isotherm surface analysis, and Diffuse Light Scattering (DLS). The coatings produced on both sized and unsized carbon fibers are resistant to ultrasonication. The pH-dependent dispersibility in water and particle size, relatively high surface area, presence of the thiol-reactive maleimide group in the material cross-linked with 1,6-dimaleimidohexane are the welcome properties f

Exploiting the chemistry of redox active compounds to enhance the capacitance of reduced graphene oxide

The restacking of graphene sheets leading to poor electrical conductivity and reduced surface area strongly affects the capacitance properties of reduced graphene oxide (RGO). Many strategies employed to mitigate the restacking issue include the introduction of spacer materials between the graphene layers, hetero atom doping, compositing with metal oxides, etc. Herein, we report the enhancement of the capacitance properties of RGO by the addition of a small amount of redox active compounds, such as benzoquinone, KI, and NaI in the electrolyte. RGO is prepared by chemical exfoliation of graphite followed by a hydrothermal reduction in the presence of a small amount of hydrazine hydrate. The quality of prepared RGO is examined by microscopic and Raman spectroscopic studies. X-ray photoelectron spectroscopic studies reveal doping of 1.97 atomic weight % of nitrogen in RGO. The specific capacitance values of 105, 244, 322 and 414 F g−1 at a current density of 2 A g−1 are obtained for RGO in 0.25 M H2SO4 and 0.25 M H2SO4 containing 0.05 M of NaI, KI and benzoquinone, respectively. The enhancement in the specific capacitance of RGO is attributed to the reversible redox reaction of the additives. Interestingly, the mechanism of charge storage of RGO in NaI and KI containing electrolytes is different. Owing to rather slow kinetics of redox reaction of electrolyte additives, the rate performance of RGO has slightly compromised in redox active electrolytes.

Liquid-phase exfoliation of fluorinated graphite to produce high-quality graphene sheets

Chemical exfoliation of graphite as a facile method is used to synthesize graphene sheets on a large scale. However, the preparation process including oxidation of graphite and reduction of graphene oxide causes many defects and unnecessary oxygen-containing groups in obtained graphene sheets. In this study, a simple and facile method is proposed to create graphene starting from fluorinated graphite (FGi). Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy were employed to analyze the components and structure of the graphene sheets. The results showed that large and flat graphene sheets with the polycrystalline structure were obtained by the chemical exfoliation of FGi. The F/C ratio can be facilely tuned just by adjusting the refluxing time, and the ratio is almost not decreased when reaction time is more than 8 h. Furthermore, the electrical conductivity and electrochemical properties of the as-prepared graphene have been systematically investigated and exhibited regularity with a variation of the F/C ratio.

Tribochemical formation of high aspect ratio graphitic structures via platinum nanoparticle catalysts

The cost effective and scalable production of nanoscale graphitic structures, such as graphene, has been a design challenge for researchers across a wide variety of disciplines. Commonly used in industry and laboratory settings alike, mechanical and chemical exfoliation of graphite are among the most prominent methods of creating these useful 2-D formations. By utilizing a tribometer to generate precise, controllable mechanical force, the exfoliation of a polycrystalline graphite rod was achieved via tribochemical means at a sliding interface with a platinum nanoparticle catalyst. The deposited graphitic material caused a measurable decrease in friction at the interface, due to graphite's lubricity, and atomic force microscopy measurements consistently verified the presence of 1–3 layer carbon structures for a short time period. Additional surface analysis was performed within the wear track using energy dispersive X-ray spectroscopy to characterize the catalytic effect of the platinum on the graphite. Methods, such as the one described herein, are a step towards simple and greener methodologies to produce graphene.

Chitosan Nanocomposites with Graphene-Based Filler

This study evaluates the properties of chitosan (CS) membranes modified with different percentages (0.5%, 3%, and 5% w/w) of a graphene-based material. Graphene oxide (GO) and reduced graphene oxide (RGO) were obtained by the chemical exfoliation of graphite and thermal reduction. Then, they were characterized by electrical conductivity measurements, FESEM, XRD, AFM, and Raman spectroscopy. The composites’ morphology was evaluated by FESEM. The degree of swelling over a 48 h period and mass loss behavior in phosphate-buffered saline solution for up to 70 days were also studied. The hydrophilicity of the CS and CS/graphene nanocomposites was examined by water contact angle. The graphene materials showed small stacks (6-8 sheets) with low defect density and nanoscale thickness (1.3-5.9 nm). The dispersion of the graphene material in the CS matrix significantly decreased the degree of swelling (460%) but did not modify the hydrolytic degradation process and the hydrophilicity of membranes.

A general strategy for direct synthesis of reduced graphene oxide by chemical exfoliation of graphite

In this work, a first stage of synthesis to obtain reduced graphene oxide (rGO) using an efficient chemical exfoliation method from graphite was studied. An ammonium hydroxide and a nitric-sulfuric acid mixture were used for in situ oxidation and partial-reduction of graphite. Flakes with a thickness of 3 nm were observed by using AFM, suggesting the presence of ten or less graphene layers. The average C/O atomic percentage ratio obtained was 4.27, which is similar to those results obtained by conventional reduction processes associated with using hydrazine. In addition, a graphitic nitrogen functionalization was observed during the proposed process. Besides that, the precursor of rGO suspension obtained remained stable for six months. Therefore, the present study showed a less aggressive and dangerous chemistry route in order to rGO production than others previously reported works.

High degree reduction and restoration of graphene oxide on SiO2 at low temperature via remote Cu-assisted plasma treatment

A high throughput synthesis method of graphene has been required for a long time to apply graphene to industrial applications. Of the various synthesis methods, the chemical exfoliation of graphite via graphene oxide (GO) is advantageous as far as productivity is concerned; however, the quality of the graphene produced by this method is far inferior to that synthesized by other methods, such as chemical vapor deposition on metals. Developing an effective reduction and restoration method for GO on dielectric substrates has been therefore a key issue. Here, we present a method for changing GO deposited on a dielectric substrate into high crystallinity graphene at 550 °C; this method uses CH4/H2 plasma and a Cu catalyst. We found that Cu remotely catalyzed the high degree reduction and restoration of GO on SiO2 and the effect ranged over at least 8 mm. With this method, field-effect transistor devices can be fabricated without any post treatment such as a transfer process. This plasma treatment increased electron and hole mobilities of GO to 480 cm2 V−1 s−1 and 460 cm2 V−1 s−1 respectively; these values were more than 50 times greater than that of conventional reduced GO. Furthermore, the on-site conversion ensured that the shape of the GO sheets remained unchanged after the treatment. This plasma treatment realizes the high throughput synthesis of a desired shaped graphene on any substrate without any residue and damage being caused by the transfer process; as such, it expands the potential applicability of graphene.

Simple synthesis of graphene nanocomposites MgO–rGO and Fe2O3–rGO for multifunctional applications

Hummer’s method was used to prepare graphene oxide (GO) by chemical exfoliation of graphite. Simple precipitation method was used for the preparation of hybrid nanocomposites MgO–rGO and Fe2O3–rGO. A 0.3 Molar of corresponding metal nitrate solution and GO solution are used for the preparation process. XRD, FT-IR, and XPS were used to characterize the prepared nanocomposites. The reduction of GO into reduced rGO in the formed nanocomposites was confirmed. Morphological characterization showed the formation of needle-shaped nanocrystals of MgO successfully grown on graphene nanosheet with average crystallite size 8.4 nm. Hematite nanocomposite Fe2O3–rGO forms rod-shaped crystals with average crystallite size 27.5 nm. The saturation magnetization observed for Fe2O3–rGO is less than reported value for the pure Fe2O3 nanoparticles. Thermal properties of as-prepared hybrid nanocomposites MgO–rGO and Fe2O3–rGO showed thermal stability of the prepared nanocomposite over long range of temperature.

One-pot synthesis of TiO2/graphene nanocomposites for excellent visible light photocatalysis based on chemical exfoliation method

Facile electron-hole recombination and the broad band gap are two major bottlenecks of titanium dioxide (TiO2) applied in visible-light photocatalysis. Hybridization of TiO2 with graphene is a promising strategy to alleviate these drawbacks. In this paper, we demonstrate a novel technique to synthesize TiO2/graphene nanocomposites without the use of graphene oxide (GO). Graphene dispersion was obtained through the chemical exfoliation of graphite in titanium tetra-n-butoxide by ultrasonication. The dispersion was directly used for the sol-gel reaction in the presence of different catalysts, affording TiO2/graphene nanocomposites featured with several advantages: i) the formation of a TiO2 nano layer that uniformly and thinly covered graphene sheets, ii) a trace amount of defects on graphene sheets, iii) a significant extension of the absorption edge into the visible light region, and iv) a dramatic suppression of electron-hole recombination. When tested for methylene blue decomposition under visible light, our nanocomposites exhibited the photocatalytic activity 15 and 5 times greater than that of TiO2-P25 and a conventional GO-based nanocomposite, respectively.

Influence of reduction time of catalyst on methanol synthesis via CO 2 hydrogenation using Cu–Zn/N-rGO investigated by in situ XANES

Abstract N-doped reduced graphene oxide (N-rGO) was synthesized as a support for the Cu–Zn/N-rGO catalyst by the chemical exfoliation of graphite using hydrazine as a reducing agent. 10%CuZn/N-rGO was prepared via an incipient wetness impregnation and was used as a catalyst for methanol synthesis from CO 2 hydrogenation reaction. The influence of the catalytic reduction time was investigated by in situ X-ray absorption near-edge spectroscopy (XANES). Interestingly, the optimum holding time, that is, 90 min, for a 350 ° C-reduction achieved excellent methanol productivity (591 mg MeOH /g cat /h) at a reaction temperature and pressure of 250 ° C and 15 bar, respectively.

3D graphene from CO2 and K as an excellent counter electrode for dye-sensitized solar cells

3D graphene, which was synthesized directly from CO2 via its exothermic reaction with liquid K, exhibited excellent performance as a counter electrode for a dye-sensitized solar cell (DSSC). The DSSC has achieved a high power conversion efficiency of 8.25%, which is 10 times larger than that (0.74%) of a DSSC with a counter electrode of the regular graphene synthesized via chemical exfoliation of graphite. The efficiency is even higher than that (7.73%) of a dye-sensitized solar cell with an expensive standard Pt counter electrode. This work provides a novel approach to utilize a greenhouse gas for DSSCs.