Modified hummers method Graphene Oxide – Single & Few Layer, a variety of platelet sizes, high oxygen content, & freeze dried to preserve solubility
Reduced Graphene Oxide
Graphene Oxide Gel
Graphene Oxide Dispersions
Graphene Oxide (GO) and RGO come in powder form. We can also provide them as a dispersion, or a spin coated film. Our GO products are well suited to Ink Jet, 3D, and other printing applications. Please call us to discuss your needs.
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GO’s synthesis methods have been known for decades. Originally called graphite oxide, it is a compound of carbon, oxygen, and hydrogen in variable ratios. It is synthesized by exfoliating graphite with strong oxidizers, rinsed repeatedly until the the rinse water is PH neutral and then freeze dried to preserve solubility. Many companies try to reduce the rinsing or skip the freeze drying but they are critical to success in using the product. The bulk product is a brownish/yellowish solid material that retains the layer structure of graphite but with a much larger and irregular spacing. GO doesn’t require post production functionalization as it consists of graphene sheets with hydroxyl, carboxyl, & epoxide groups. It is highly soluble in Di water, NMP, DMF, THF, Ethanol, and other solvents that behave like water. GO can be reduced using several methods such as laser, microwave, electrochemically, hydrazine vapor treatment, or by annealing at temperatures from 250-400C in a forming gas (95% argon, 5% hydrogen) environment yielding the intrinsically high electrical and thermal conductivity of graphene.
Molecular Structure of Graphene Oxide
GO’s molecular structure is shown below. The functional groups are present on the edges of the flakes and on the top and bottom which helps impart GO with legendary solubility compared to most nanoscale particles. No surfactants are needed when dispersing into typical solvents such as Di Water, NMP, DMF, THF, DCB, or Ethanol.
Graphene Oxide Applications
Graphene Oxide has numerous applications due to its high solubility and the ability to reduce it to neat graphene. This overcomes the well known dispersion problems with other nanomaterials enabling you to get the full benefits of nanoscale additives such as improved mechanical properties as well as enhanced conductivity.
Reduced Graphene Oxide
RGO first undergoes the typical synthesis process and then it is reduced which removes most of the surface functional groups as well as restores the molecular structure to one much closer to pristine graphene than GO.
There are a number of ways reduction can be achieved and is typically a chemical, thermal or electrochemical process. Some of these techniques are able to produce very high quality rGO, similar to pristine graphene, but can be complex or time consuming to carry out.
Common graphene reduction techniques are:
Treating GO with hydrazine hydrate and maintaining the solution at 100c for 24 hours
Exposing GO to hydrogen plasma for a few seconds
Exposing GO to another form of strong pulse light, such as those produced by xenon flashtubes
Heating GO in distilled water at varying degrees for different lengths of time
Directly heating GO to very high levels in a furnace
Directly heating GO in a microwave
At 400C in a forming has atmosphere 95% argon, 5% hydrogen
Chemical reduction is a highly scalable method, unfortunately the reduced GO produced often has resulted in relatively poor yields in terms of surface area and electronic conductivity. Thermally reducing GO at temperatures of 1000℃ or more creates rGO that has been shown to have a very high surface area but the annealing process damages the structure of the GO when pressure between builds up and carbon dioxide is released. During reduction, there is a substantial reduction in the mass of the GO (figures around 30% have been mentioned) which creates imperfections and voids in the structure and interferes with its unique properties.
Electrochemical reduction of GO is a method that has been shown to produce very high quality RGO, almost identical in terms of structure to pristine graphene.
Once RGO has been produced, it can be selectively functionalized thus enabling its use in different applications. By treating RGO with other chemicals or by creating new compounds when combining RGO with other two dimensional materials, we can engineer the surface chemistry of the compound to the specific application.
Graphene Oxide Paper
Graphene Oxide Paper is relatively easy to make with vacuum filtration. GO is known to disperse very easily due to the type and amount of functional groups on its surface. To make GO paper, researchers typically disperse the GO in a solvent such as water or an organic solvent and then using a 0.2um membrane filter, they pour the GO solution through a vacuum filtration apparatus and the membrane keeps the particles on top while the solvent is collected below. When dry, the membrane can be removed leaving a free standing GO paper product. RGO paper can be made by similar methods but will require surfactants to stabilize it so it may be desirable to make the GO paper and then reduce it instead of adding surfactants.