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

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.