Environmentally friendly preparation of exfoliated graphite

Asghar, Hafiz Muhammad Anwaar; Hussain, Sabir; Sattar, H.; Brown, N. W.; Roberts, Edward P.L.

doi:10.1016/j.jiec.2013.09.014

Cited by 29 publications

(22 citation statements)

References 19 publications

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“…The resulting intercalation compound, known as graphite bisulfate, consists of carbon layers with HSO 4 -radical ions and H 2 SO 4 molecules between the layers. This compound is commonly prepared by direct chemical interaction of graphite with a mixture of concentrated sulfuric acid [34] and an oxidizing agent (e.g., nitric acid [34], potassium permanganate, hydrogen peroxide [34], ozone [35], etc.). Similarly, nitric acid can be intercalated [36], with potassium permanganate as an oxidizing agent [37,38].…”

Section: Structure Of Exfoliated Graphitementioning

confidence: 99%

“…However, unlike sulfuric acid, nitric acid can be intercalated without the presence of an oxidizing agent if the concentration of the nitric acid is very high, as in the case of fuming nitric acid. Another method that is effective for the intercalation of sulfuric acid involves electrolysis [34], which is advantageous in that it requires sulfuric acid that is dilute [34]. The residual acidity present in the EG is not desirable for structural applications such as those typically associated with flexible graphite.…”

Section: Structure Of Exfoliated Graphitementioning

confidence: 99%

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A review of exfoliated graphite

2015

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Exfoliated graphite (EG) refers to graphite that has a degree of separation of a substantial portion of the carbon layers in the graphite. Graphite nanoplatelet (GNP) is commonly prepared by mechanical agitation of EG. The EG exhibits clinginess, due to its cellular structure, but GNP does not. The clinginess allows the formation of EG compacts and flexible graphite sheet without a binder. The exfoliation typically involves intercalation, followed by heating. Upon heating, the intercalate vaporizes and/or decomposes into smaller molecules, thus causing expansion and cell formation. The sliding of the carbon layers relative to one another enables the cell wall to stretch. The exfoliation process is accompanied by intercalate desorption, so that only a small portion of the intercalate remains after exfoliation. The most widely used intercalate is sulfuric acid. The higher concentration of residue in unwashed EG causes the relative dielectric constant (50 Hz) of the EG to be 360 (higher than 120 for KOH-activated GNP), compared to the value of 38 for the water-washed case. An EG compact is obtained by the compression of EG at a pressure lower than that used for the fabrication of flexible graphite. Compared to flexible graphite, EG compacts are mechanically weak, but they exhibit viscous character, outof-plane electrical/thermal conductivity and liquid permeability. The viscous character (flexural loss tangent up to 35 for the solid part of the compact) stems from the sliding of the carbon layers relative to one another, with the ease of the sliding enhanced by the exfoliation process.

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Section: Structure Of Exfoliated Graphitementioning

confidence: 99%

Section: Structure Of Exfoliated Graphitementioning

confidence: 99%

A review of exfoliated graphite

2015

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“…For successful exfoliation, overcoming the Van der Waals attractions between the adjacent layers is necessary [3]. Even though mechanical methods had demonstrated to be effective to exfoliate stacked materials [4,20], chemical methods are preferred, its major disadvantage is the use of concentrated sulfuric acid or sulfur trioxide (SO 3 ) [9] and strong oxidizing agents as: nitric acid, potassium permanganate, and hydrogen peroxide [4,16,21], where the discharge of acid waste and its treatment have been pointed out to be troublesome [9]. This opens a window of opportunity for methods that are environmentally friendly, such as the one proposed herein.…”

Section: Introductionmentioning

confidence: 99%

A Green Method for Graphite Exfoliation Using a Mechanochemical Route

Estrada-Guel

Hernandez

Martínez-Sánchez

2015

Materials Characterization

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In the present work, we proposed a method to manufacture exfoliated graphene. This method is low cost and environmentally friendly by mechanochemical means and avoids the use of highly corrosive and dangerous reagents. Our raw material consists of natural graphite and sodium carbonate. The mix is milled followed by a citric acid treatment used as defoliation agents. The mixture consists of an equiatomic mix of graphite and sodium carbonate that is processed in a high-energy ball mill. The milled and raw mixtures are leached with an aqueous acid solution, hot refluxed, washed, and overnight dried. Observed morphological and chemical evidence exhibits a notable reduction of particle size with an important increased level of defoliation that improved the surface area values.

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“…The graphite material was mixed with dilute sulfuric acid solution to obtain a paste containing 50% w=w graphite, and was placed in the anode compartment. The electrodes were connected to a DC power supply and a current of 0.9 A (corresponding to a current density of 2.3 mA cm À2 ) was supplied during the electrochemical synthesis for a period of 60 min (Asghar et al, 2012). The thickness of the graphite paste was maintained at 10 mm.…”

Section: Electrochemical Intercalationmentioning

confidence: 99%

Potential Graphite Materials for the Synthesis of GICs

Asghar

Hussain

Sattar

et al. 2014

Chemical Engineering Communications

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The potential of various graphite materials including Chinese flake graphite, Madagascan flake graphite, natural vein graphite, recycled vein graphite, and synthetic graphite for the preparation of -bisulfate was investigated through electrochemical intercalation method. All the graphite materials were characterized using laser particle size analyzer, SEM analysis, XRD analysis, and X-ray EDS elemental analysis. Chinese flake and Madagascan flake graphite materials were found to be capable of synthesizing GIC-bisulfate through electrochemical intercalation. Natural vein, recycled vein, and synthetic graphite materials did not show any evidence of forming GIC-bisulfate. The formation of GIC-bisulfate was verified through XRD results. Thermal exfoliation volume was observed as an indicator of GIC-bisulfate when the electrochemically treated material was exposed to a sudden thermal shock at a temperature of 850 C.

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Environmentally friendly preparation of exfoliated graphite

Cited by 29 publications

References 19 publications

A review of exfoliated graphite

A review of exfoliated graphite

A Green Method for Graphite Exfoliation Using a Mechanochemical Route

Potential Graphite Materials for the Synthesis of GICs

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