Name: Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies (Video) | JoVE Journal
Uploaded: 2015-11-05T14:00:00.000+00:00
Duration: 10 min 23 s
Description: Learn to synthesize 3D graphene aerogels using sol-gel chemistry with tunable density, surface area, and pore size. This method produces monolithic carbon materials for energy storage and catalysis applications.

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5 minutes

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release LLNL-JRNL-667016.

1. Resorcinol-formaldehyde (RF) Derived Graphene Aerogels
<ol>
	<li>Na2CO3 catalyzed carbon aerogel (11% solids, cRF)
	<ol>
		<li>In a 40 ml scintillation vial, add deionized water (7.1 ml) to resorcinol (0.625 g, 5.68 mmol) and mix on a vortex for 1 min. Crush large resorcinol pieces to powder using a mortar and pestle prior to water addition. Note that they may not completely dissolve until the next step.</li>
		<li>Add 37% formaldehyde solution (0.900 g, 11.4 mmol) to the resorcinol slurry and vortex for 1 min.</li>
		<li>Add sodium carbonate (0.003 g, 0.028 mmol) to the reaction mixture and vortex for 1 min.</li>
		<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket) which define the shape of the resulting solid part.</li>
		<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
		<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically we perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.</li>
	</ol>
	</li>
	<li>Acetic acid catalyzed carbon aerogel (AARF)17
	<ol>
		<li>In a 40 ml scintillation vial, add deionized water (15 ml) to resorcinol (12.3 g, 0.112 mol) and mix on a vortex for 1 min. Crush large resorcinol pieces to powder using a mortar and pestle prior to water addition. Note that they may not completely dissolve until the next step.</li>
		<li>Add 37% formaldehyde solution (17.9 g, 0.224 mol) to the resorcinol slurry and vortex for 1 min.</li>
		<li>Add glacial acetic acid (0.44 g, 0.007 mol) to the reaction mixture and vortex for 1 min.</li>
		<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket), which define the shape of the resulting solid part.</li>
		<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
		<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically we perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.</li>
	</ol>
	</li>
	<li>Carbon Additives to the RF precursor solution (CNT, GO)
	<ol>
		<li>Carbon nanotube/RF composite11
		<ol>
			<li>Suspend 1 wt% single-walled carbon nano-tubes in deionized water and thoroughly disperse using an ultrasonic bath (sonic power 90 W, frequency 40 kHz).</li>
			<li>Add resorcinol (1.235 g, 11.2 mmol), formaldehyde (1.791 g, 22.1 mmol), and sodium carbonate catalyst (5.95 mg, 0.056 mmol) to 1.5 g of the CNT dispersion.</li>
			<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket), which define the shape of the resulting solid part.</li>
			<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
			<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.&#160;</li>
		</ol>
		</li>
		<li>Graphene oxide/RF composite12
		<ol>
			<li>Suspend 1 wt% graphene oxide (GO, 300-800 nm diameter) in deionized water and thoroughly disperse using an ultrasonic bath (sonic power 90 W, frequency 40 kHz).</li>
			<li>Add resorcinol (1.235 g, 11.2 mmol), formaldehyde (1.791 g, 22.1 mmol, 37% solution) and sodium carbonate catalyst (5.95 mg, 0.056 mmol) to 1.5 g of the GO dispersion.</li>
			<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket) which define the shape of the resulting solid part.</li>
			<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
			<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Drying
	<ol>
		<li>Supercritical CO2
		<ol>
			<li>Prepare washed samples for drying with supercritical CO2 by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Load acetone-exchanged samples into a supercritical drying apparatus, filled with acetone and with circulating coolant at 12-15 &#176;C.</li>
			<li>Seal supercritical dryer and exchange with liquid CO2 until no acetone remains (4-24 hr depending on sample size, density, pore morphology, etc.).</li>
			<li>Shut off CO2 supply and raise temperature of circulating coolant to 55 &#176;C, while maintaining pressure in the supercritical dryer between 1,200-1,600 psi (80-110 bar). Hold at 55 &#176;C for 1 hr.</li>
			<li>Slowly vent CO2 (2-12 hr) while maintaining temperature of circulating coolant at 55 &#176;C. Remove samples.&#160;</li>
		</ol>
		</li>
		<li>Ambient drying (Xerogel)
		<ol>
			<li>Prepare washed samples for drying under ambient conditions by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Place acetone-exchanged samples on a clean surface (e.g., Teflon block). To slow the rate of solvent evaporation to prevent cracking and uneven shrinking, cover the sample with an inverted beaker of sufficient volume to provide plenty of headspace.</li>
			<li>Allow solvent to evaporate for (24-72 hr).&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Carbonization
	<ol>
		<li>Perform carbonization of the dried foams at 1,050 &#176;C under N2 atmosphere. Ramp from RT at a rate of 5 &#176;C/min, and hold at 1,050 &#176;C for 3 hr. Note that thin samples may need to be placed between two sheets of graphite paper (or other temperature stable, non-reactive material) with weight on top to prevent curling and &#8220;potato chipping.&#8221;</li>
	</ol>
	</li>
	<li>Activation
	<ol>
		<li>Activate an AARF carbon foam part (2 cm &#215; 3 cm &#215; 4 mm, 1.2 g) to generate 3D nanographene (3D-NG) under flowing CO2 (10 sccm) at 950 &#176;C for 5 hr.7</li>
	</ol>
	</li>
</ol>
2. Graphene Oxide Derived Graphene Macro Assemblies
<ol>
	<li>NH4OH catalyzed GO assembly
	<ol>
		<li>In a 40 ml scintillation vial, add deionized water (20 ml) to 400 mg single layer graphene oxide (GO, 300-800 nm diameter). Thoroughly disperse using an ultrasonic bath (sonic power 90 W, frequency 40 kHz) O/N.</li>
		<li>Add concentrated NH4OH solution (0.211 ml per g GO suspension).</li>
		<li>Transfer into glass molds that can be sealed airtight (e.g., vial or glass slides that are separated by a silicone gasket which defines the shape of the resulting solid part).</li>
		<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
		<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.&#160;</li>
	</ol>
	</li>
	<li>Drying
	<ol>
		<li>Supercritical CO2
		<ol>
			<li>Prepare washed samples for drying with supercritical CO2 by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Load acetone-exchanged samples into a supercritical drying apparatus, filled with acetone and with circulating coolant at 12-15 &#176;C.</li>
			<li>Seal supercritical dryer and exchange with liquid CO2 until no acetone remains (4-24 hr depending on sample size, density, pore morphology, etc.). Complete exchange is indicated by cessation of acetone drips at the exhaust valve of the supercritical dryer.</li>
			<li>Shut off CO2 supply and raise temperature of circulating coolant to 55 &#176;C, while maintaining pressure in the supercritical dryer between 1,200-1,600 psi (80-110 bar). Hold at 55 &#176;C for 1 hr.</li>
			<li>Slowly vent CO2 (2-12 hr) while maintaining temperature of circulating coolant at 55 &#176;C. Remove samples.&#160;</li>
		</ol>
		</li>
		<li>Ambient drying (xerogel) 
		Note that thin samples may need to be placed between two sheets of Teflon (or other non-stick material) with weight on top to prevent curling and &#8220;potato chipping.&#8221;
		<ol>
			<li>Prepare washed samples for drying under ambient conditions by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Place acetone-exchanged samples on a clean surface (e.g., Teflon block). To slow the rate of solvent evaporation to prevent cracking and uneven shrinking, cover the sample with an inverted beaker of sufficient volume to provide plenty of headspace.</li>
			<li>Allow solvent to evaporate for (24-72 hr).&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Carbonization
	<ol>
		<li>Perform carbonization of the dried foams at 1,050 &#176;C under N2 atmosphere. Ramp from RT at a rate of 5 &#176;C/min, and hold at 1,050 &#176;C for 3 hr. Note that thin samples may need to be placed between two sheets of graphite paper (or other temperature stable, non-reactive material) with weight on top to prevent curling and &#8220;potato chipping.&#8221;</li>
		<li>Thermal anneal for highly crystalline GMA. Perform additional thermal annealing of carbonized foams at temperatures up to 2,500 &#176;C under He atmosphere. Ramp from RT at a rate of 100 &#176;C/min, and hold at elevated temperature for 1 hr.&#160;</li>
	</ol>
	</li>
	<li>Post-carbonization functionalization
	<ol>
		<li>Non-covalent anthraquinone functionalization (AQ-GMA)
		<ol>
			<li>Prepare a 3 mM solution of anthraquinone (AQ) in dry EtOH. Heat in a sealed vial at 75 &#176;C to ensure complete dissolution.</li>
			<li>Add hot AQ solution to GMA sample (~2 ml/mg of sample). Soak in a sealed vial for 2 hr at 75 &#176;C.</li>
			<li>Remove excess AQ solution from vial and allow sample to dry at 75 &#176;C O/N&#160;(vial cap off).&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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<li>Pekala, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Organic+aerogels+from+the+polycondensation+of+resorcinol+with+formaldehyde%5BTitle%5D)+AND+%22J.+Mater.+Sci%22%5BJournal%5D)">Organic aerogels from the polycondensation of resorcinol with formaldehyde.</a> J. Mater. Sci. 24 (9), 3221-3227 (1989).</li>
<li>Biener, J., Dasgupta, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Macroscopic+3D+nanographene+with+dynamically+tunable+bulk+properties%5BTitle%5D)+AND+%22Adv.+Mater%22%5BJournal%5D)">Macroscopic 3D nanographene with dynamically tunable bulk properties.</a> Adv. Mater. 24 (37), 5083-5087 (2012).</li>
<li>Worsley, M. A., Olson, T. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High+Surface+Area%2C+sp+2-Cross-Linked+Three-Dimensional+Graphene+Monoliths%5BTitle%5D)+AND+%22J+Phys.+Chem.+Lett%22%5BJournal%5D)">High Surface Area, sp 2-Cross-Linked Three-Dimensional Graphene Monoliths.</a> J Phys. Chem. Lett. 2 (8), 921-925 (2011).</li>
<li>Worsley, M. A., Kucheyev, S. O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mechanically+robust+3D+graphene+macroassembly+with+high+surface+area%5BTitle%5D)+AND+%22Chem+Commun%22%5BJournal%5D)">Mechanically robust 3D graphene macroassembly with high surface area.</a> Chem Commun. 48 (67), 8428-8430 (2012).</li>
<li>Biener, J., Stadermann, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Advanced+carbon+aerogels+for+energy+applications%5BTitle%5D)+AND+%22Energ.+Environ.+Sci%22%5BJournal%5D)">Advanced carbon aerogels for energy applications.</a> Energ. Environ. Sci. 4 (3), 656-667 (2011).</li>
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<li>Worsley, M. A., Pauzauskie, P. J., Olson, T. Y., Biener, J., Satcher, J. H., Baumann, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Synthesis+of+graphene+aerogel+with+high+electrical+conductivity%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">Synthesis of graphene aerogel with high electrical conductivity.</a> J. Am. Chem. Soc. 132 (40), 14067-14069 (2010).</li>
<li>Fu, R., Baumann, T. F., Cronin, S., Dresselhaus, G., Dresselhaus, M. S., Satcher, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Formation+of+Graphitic+Structures+in+Cobalt-+and+Nickel-Doped+Carbon+Aerogels%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Formation of Graphitic Structures in Cobalt- and Nickel-Doped Carbon Aerogels.</a> Langmuir. 21 (7), 2647-2651 (2005).</li>
<li>Worsley, M. A., Pham, T. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Synthesis+and+Characterization+of+Highly+Crystalline+Graphene+Aerogels%5BTitle%5D)+AND+%22ACS+Nano%22%5BJournal%5D)">Synthesis and Characterization of Highly Crystalline Graphene Aerogels.</a> ACS Nano. 8 (10), 11013-11022 (2014).</li>
<li>Campbell, P. G., Merrill, M. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Battery%2Fsupercapacitor+hybrid+via+non-covalent+functionalization+of+graphene+macro-assemblies%5BTitle%5D)+AND+%22J.+Mater.+Chem.+A%22%5BJournal%5D)">Battery/supercapacitor hybrid via non-covalent functionalization of graphene macro-assemblies.</a> J. Mater. Chem. A. 2, 17764-17770 (2014).</li>
<li>Worsley, M. A., Charnvanichborikarn, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Toward+Macroscale%2C+Isotropic+Carbons+with+Graphene-Sheet-Like+Electrical+and+Mechanical+Properties%5BTitle%5D)+AND+%22Adv.+Funct.+Mater%22%5BJournal%5D)">Toward Macroscale, Isotropic Carbons with Graphene-Sheet-Like Electrical and Mechanical Properties.</a> Adv. Funct. Mater. 24 (27), 4259-4264 (2014).</li>
<li>Baumann, T. F., Worsley, M. A., Han, T. Y. -J., Satcher, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High+surface+area+carbon+aerogel+monoliths+with+hierarchical+porosity%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">High surface area carbon aerogel monoliths with hierarchical porosity.</a> J. Non-Cryst. Solids. 354 (29), 3513-3515 (2008).</li>
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<li>Braff, W. A., Bazant, M. Z., Buie, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Membrane-less+hydrogen+bromine+flow+battery%5BTitle%5D)+AND+%22Nat.+Comms%22%5BJournal%5D)">Membrane-less hydrogen bromine flow battery.</a> Nat. Comms. 4, 1-6 (2013).</li>
<li>Zhu, C., Han, T. Y., Duoss, E. B., Golobic, A. M., Kuntz, J. D., Spadaccini, C. M., Worsley, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Highly+compressible+3D+periodic+graphene+aerogel+microlattices%5BTitle%5D)+AND+%22Nat+Comms%22%5BJournal%5D)">Highly compressible 3D periodic graphene aerogel microlattices.</a> Nat Comms. 6, (2015).</li>
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The authors have nothing to disclose.

It is important to note that the procedures outlined here are only representative. Many adjustments are possible to tune materials for a specific application. For example, varying the starting material concentrations, while keeping resorcinol/formaldehyde (RF) ratio constant, can have an impact on the final material density. Catalyst loading can alter pore morphology, as a higher loading in the RF procedure leads to smaller primary particles and vice-versa. Activation time can play a role as well; at shorter activation t...

Since the isolation of graphene in 2004,1 interest in harnessing its unique properties has led to intense effort directed toward assembling graphene into three-dimensional, monolithic structures that retain the properties of individual graphene sheets.2-5 These efforts have been hampered by the fact that graphene itself is expensive and time consuming to produce and tends to aggregate in solution, which limits the scalability of materials based on graphene building blocks. Additionally, graphene assemblies are typically comprised of physical cross-linking interactions (e.g., van der Walls forces) between the individual graphene sheets, which are much less conductive and mechanically robust than chemical bond cross-links. Lawrence Livermore National Laboratory has been involved in the development of novel porous, low-density carbon materials since the 1980s.6 Several strategies have been identified to fabricate mass-producible graphene-based monolithic bulk materials from both low-cost polymer-derived carbon foams, which are called graphene aerogels (GAs),7 as well as by direct cross-linking of graphene oxide (GO) sheets, which are called graphene macro-assemblies (GMAs).8,9 These ultrahigh surface area bulk materials have high electrical and thermal conductivities, exceptional mechanical strength and elasticity, and tunable pore morphologies. GAs and GMAs have found utility in numerous applications including electrode materials in supercapacitors and rechargeable batteries, advanced catalyst supports, adsorbents, thermal insulation, sensors, and desalinization.10
The synthesis of graphene aerogels begins with sol-gel polymerization of an aqueous solution of resorcinol and formaldehyde to generate highly cross-linked organic gels. These gels are washed with water and acetone, then dried using supercritical CO2 and pyrolyzed in an inert atmosphere to give carbon aerogels with relatively low surface area and pore volume. Carbon aerogels are activated by controlled removal of carbon atoms under mild oxidizing condition (e.g., CO2) to form a cross-linked material composed of both amorphous carbon and graphite nanoplatelets, with higher surface area and open pore morphology.7 A unique advantage of the sol-gel synthesis is that GAs can be fabricated in a variety of forms, including monoliths and thin films, depending on the needs of the application. Carbon nanotubes11 and/or graphene sheets12 can be integrated into GAs by including these additives in the sol-gel precursor solution. This generates composite structures in which the additive becomes a part of the primary carbon network structure. Additionally, the GA framework can be functionalized after carbonization/activation either through modification of the aerogel surface or through the deposition of materials, for example catalyst nanoparticles, onto the framework structure.13
Graphene macro-assemblies (GMAs) are prepared by directly cross-linking suspended graphene oxide (GO) sheets, taking advantage of their inherent chemical functionality.9 GO sheets contain a variety of functional groups, including epoxide and hydroxide moieties, that can serve as chemical cross-linking sites. As in the GA preparation, assembled GMAs are supercritically dried to preserve the porous network, then pyrolized to reduce the chemical cross-links into conductive carbon bridges that provide structural support for the assembly. Due to the covalent carbon bridges between graphene sheets, GMAs have electrical conductivities and mechanical stiffness that are orders of magnitude higher than graphene assemblies formed with physical cross-linking. Additionally, GMAs have surface areas approaching the theoretical value of a single graphene sheet. Post-synthetic thermal treatment at elevated temperatures (&#62;1,050 &#176;C) can significantly improve the crystallinity of GMAs, leading to even higher conductivities and Young&#8217;s moduli as well as better thermal oxidation resistance.14 Post-synthetic chemical treatment of GMAs with redox-active organic molecules such as anthraquinone can enhance charge storage capacity in supercapacitor applications.15
The tunable material properties of GAs and GMAs are, in part, a result of carefully varying synthetic conditions such as reagent and catalyst concentrations, cure time and temperature, drying conditions, and carbonization/activation processes.16 This detailed video protocol aims to resolve ambiguities in the published methods, and to guide researchers attempting to reproduce the materials and conditions.

<table><tbody><tr><td>Single Layer Graphene Oxide</td><td>Cheap Tubes</td><td>n/a</td><td>300-800&amp;#160;nm XY dimensions</td></tr><tr><td>single wall carbon nano tubes (SWCNTs)</td><td>Carbon Solutions</td><td>P2-SWNT</td><td></td></tr><tr><td>resorcinol</td><td>Aldrich</td><td>398047-500G</td><td></td></tr><tr><td>37% formaldehyde solution in water</td><td>Aldrich</td><td>252549</td><td></td></tr><tr><td>acetic acid</td><td>Aldrich</td><td>320099</td><td></td></tr><tr><td>ammonium hydroxide solution 28-30% NH&lt;sub&gt;3&lt;/sub&gt; basis</td><td>Aldrich</td><td>320145</td><td></td></tr><tr><td>sodium carbonate</td><td>Aldrich</td><td>791768</td><td></td></tr><tr><td>anthraquinone</td><td>Aldrich</td><td>a90004</td><td></td></tr><tr><td>Polaron supercritical dryer</td><td>Electron Microscopy Sciences</td><td>EMS 3100</td><td>this is a representative model, any critical point dryer compatible with acetone should work</td></tr></tbody></table>

synthesis and functionalization of 3d nano-graphene materials: graphene aerogels and graphene macro assemblies

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

The evolution of material composition and morphology during fabrication can be tracked in various ways including X-ray diffraction, Raman and NMR spectroscopy, electron microscopy, and porosimetry. For example, in the synthesis, pyrolysis, and CO2 activation of GAs, the conversion was followed by X-ray diffraction (XRD) (Figure 1E). The absence of the stacking-related (002) diffraction peak in the XRD pattern after activation (blue trace) indicates the transition from a structure containing gr...

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

The flexible soul gel synthesis route enables materials to be produced with tunable density, surface area, and pore size, which can be cast into a variety of forms, including monoliths and thin films. The synthesis begins by combining a catalyst with the precursor solution and allowing the mixture to cure at moderate temperature. This produces a fully cross-linked monolithic gel with solvent trapped in the pore structure.Cure time and temperature can be used to control the morphology of the material produced. As a second step, the wet gel is dried using super critical CO2 to preserve the nano structure. The material is now an arrow gel.Next, the arrow gel is heated to high temperature in an inert atmosphere in order to carbonize it, removing oxygen containing functional groups and converting the chemical crosslinks to conductive SP two bonds. The resulting materials are chemically and mechanically robust analytical tools such as scanning electron microscopy are used to characterize morphology and measure surface area and poor size distribution. Post synthetic surface treatment can be used to enhance desired properties such as charge storage capacity.Carbon air gels were invented at Lawrence Livermore National Laboratory in the 1980s, and we've continued to develop ultra high service area low density materials. The soul gel synthesis you're going to see today is highly flexible, allowing us to develop materials to meet the unique needs of research that happens here at Livermore. The main advantage of this technique over existing methods to produce low density, high surface area carbon materials is that we can produce monolithic materials that are fully cross-linked with SP two carbon bonds.These carbon bonds produce a material that is highly electrically conductive and has very good mechanical properties all without the use of binders or conductive fillers. This methodology allows for exquisite control over density, surface area, pore size, and volume. It can be used to produce materials for various applications, including battery and supercapacitor electrodes, supports fer, nanoparticles and other catalysts, as well as ultra strong and lightweight structural materials.To synthesize an acetic acid, catalyzed carbon aero gel begin by crushing 112 millimoles of resorcinol into a powder and adding it to a 40 milliliter scintillation vial. Then add 15 milliliters of deionized water and vortex this mixture for one minute. Next, add the suspension to 224 millimoles of a 37%formaldehyde solution and vortex to mixture for another minute.The resource and all should be fully dissolved by this point. Finally, add seven millimoles of glacial is acidic acid and vortex. Again, this solution is now ready to be cured and dried to create an RF and graphene oxide or geo composite.First, use an ultrasonic bath to create a one weight percent suspension of graphene oxide in the ionized water. Next, take 11.2 millimoles of RESORCINOL and add it to 1.5 grams of the graphene oxide suspension. 22.1 millimoles of a 37%formaldehyde solution and 56 micromoles of sodium carbonate catalyst.This composite is now ready for curing and drying. To begin synthesis of ammonium hydroxide catalyzed, go assembly, add 20 milliliters of deionized water to 400 milligrams of single layer. Go in a 40 milliliter scintillation vial and vortex for one minute.Use an ultrasonic bath to thoroughly disperse the mixture. Complete dispersion may take up to 24 hours. A properly dispersed suspension should not flow When the vial is inverted, add 0.211 milliliters of concentrated ammonium hydroxide per gram of geo suspension.Then transfer the geo suspension with catalyst into a glass mold and seal it tightly. Place it in the oven at 80 degrees Celsius and cure for 72 hours. Remove the sennett liquid from the vial and replace with DI water.Then wash it in a water bath to remove the residual materials. Replace the water bath twice at 12 hour intervals. Then remove the excess water and transfer the sample from the water bath to an acetone bath.Replacing with fresh acetone twice after 12 hour intervals. After washing, load the sample into a super critical drying apparatus that is filled with acetone and circulating coolant between 12 and 15 degrees Celsius. Next, seal the dryer and exchange the acetone completely with liquid carbon dioxide.When no more acetone drips from the dryer exhaust, shut off the carbon dioxide supply. Raise the coolant temperature to 55 degrees Celsius while maintaining a pressure between 1200 and 1600 PS.I hold the coolant temperature at 55 degrees Celsius for one hour. Then slowly vent the carbon dioxide over two to 12 hours while holding the coolant temperature at 55 degrees Celsius.Remove the samples once the carbon dioxide has completely vented. Once graphene arrow gels are appropriately cured and dried, load large samples into a boat or similar container and place disc shaped samples between two sheets of carbon paper with weight on top to prevent curling. Move them into an inert atmosphere to be carbonized.Increase the temperature at a rate of five degrees Celsius per minute until 1050 degrees Celsius is reached, and then hold the reaction at 1050 degrees Celsius for three hours. To obtain highly crystalline graphene micro assemblies increase the temperature at a rate of 100 degrees Celsius per minute and hold the foam at 2, 500 degrees Celsius for one hour. Once the foam is carbonized, it can be functionalized with redox active quinone.To enhance charge storage capacity, first, prepare a three millimolar solution of anthraquinone in anhydrous ethanol, and heat the solution in a sealed vial at 75 degrees Celsius. To dissolve the anthraquinone, add the heated quinone solution to the graphene macro assembly at two milliliters. For every milligram of material in a sealed vial, soak the macro assembly for two hours at 75 degrees Celsius, then decant the excess solution from the vial and leave the vial uncapped at 75 degrees Celsius overnight to dry the material.Tracking the morphology and evolution of the material composition can be accomplished utilizing a variety of analytic methods, scanning electron microscopy and transmission electron microscopy are used to examine material morphology while the results of x-ray diffraction and ramen analysis are consistent with a graphene like material. Poor asymmetry is used to determine poor volume and poor size distribution. Solid state nuclear magnetic resonance or NMR is used to follow the transformation of graphene oxide into graphene macro assemblies.Comparing carbon 13 NMR Spectra, a significant reduction of peaks corresponding to epoxide and hydroxyl functionality is seen post curing while the presence of an atic peak appears after carbonization. Proton NMR highlights the elimination of methylene and Methoxy Modi. These eliminations suggest that the SP three hybridized carbon crosslinks become thermally converted to conductive.SP two hybridized carbon junctions during carbonization, post synthetic functionalization with quinone is verified by Thermo Gravimetric analysis. Mass loss is consistent with 10 to 14 weight percent loading, and the increase in temperature compared with bulk quinone indicates diffusion limited desorption kinetics. The enhanced charge storage capacity is measured by cyclic vol telemetry, which indicates a nearly threefold increase even at very high rates.Using this procedure as a general guideline, additives such as carbon nanotubes or graphene oxide or reaction concentrations can be changed in order to tailor the material properties to your specific needs. After watching this video, you should have a good understanding of how to synthesize high surface area graphene aerogels, starting with simple, inexpensive precursors.

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Research

JoVE Journal

Engineering

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Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

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