On Wed, Mar 28, 2012 at 1:48 PM, m d <2md...
> This method looks promising to make functionalized graphene in bulk
> "Researchers placed graphite and frozen carbon dioxide in a ball miller,
> which is a canister filled
> with stainless steel balls. The canister was turned for two days and the
> mechanical force produced
> flakes of graphite with edges essentially opened up to chemical
> interaction by carboxylic acid
> formed during the milling.
> The carboxylated edges make the graphite soluble in a class of solvents
> called protic solvents,
> which include water and methanol, and another class called polar aprotic
> solvents, which includes
> dimethyl sulfoxide.
> Once dispersed in a solvent, the flakes separate into graphene naonsheets
> of five or fewer layers.
> To test whether the material would work in direct formation of molded
> objects for electronic
> applications, samples were compressed into pellets. In a comparison, these
> pellets were 688 times
> better at conducting electricity than pellets yielded from the acid
> oxidation of graphite.
> After heating the pellets at 900 degrees Celsius for two hours, the edges
> of the ball-mill–derived
> sheets were decarboxylated, that is, the edges of the nanosheets became
> linked with strong hydrogen
> bonding to neighboring sheets, remaining cohesive. The compressed
> acid-oxidation pellet shattered
> during heating.
> To form large-area graphene nanosheet films, a solution of solvent and the
> graphene nanosheets was cast on silicon wafers 3.5 centimeters by 5
> centimeters, and heated to 900
> degrees Celsius. Again, the heat decarboxylated the edges, which then
> bonded with edges of
> neighboring pieces. The researchers say this process is limited only by
> the size of the wafer. The
> electrical conductivity of the resultant large-area films, even at a high
> optical transmittance, was
> still much higher than that of their counterparts from the acid oxidation.
> By using ammonia or sulfur trioxide as substitutes for dry ice and by
> using different solvents, “you
> can customize the edges for different applications,” Baek said. “You can
> customize for electronics,
> supercapacitors, metal-free catalysts to replace platinum in fuel cells.
> You can customize the edges
> to assemble in two-dimensional and three-dimensional structures."
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