The for 0.5 gr graphite, 32 ml

The modified Hummers method was used for preparing graphene oxide from
natural flake graphite.  In this method,
first the graphite sheets are extended and converted into graphite oxide in the
presence of high concentrations of oxidizing agents. This process is
accompanied by an increase in interlayer spacing, which, of course, depends on
the amount of oxidation and sintering. Briefly, the flake graphite was added to
solution of sulfuric acid in ice bath. The proportion of acid to graphite should
be 1:46; however, in this research for 0.5 gr graphite, 32 ml sulfuric acid was
used. The obtained solution was subjected to magnetic stirrer for stirring in
400 rpm in 1 hour. In this step the pore structure of the 3d graphene was
determined. If the stirring time continues, the graphite sheets will fractionalize
more. Consequently, the synthesized 3d graphene with 3 hour stirring GO has
more porosity than the 3d graphene which obtains from 1 hour stirring graphene
oxide. In this study, the 3d graphene which synthesized by 3 hours stirring GO
referred as 3dGO3 and the 3d graphene which synthesized by 1 hour stirring GO
referred as 3dGO1. While the mixture got colder, 0.5 gr NaNO3 was
introduced to the solution. In the next step, required oxygen for better
reduction was provided by KMnO4 in the proportion of 1:6 to graphite
(3 gr). The KMnO4 should be added slowly under the stirring
condition and after 15 minute the solution color changed to dark green. After
reaching to the room temperature, the solution was heated up to 35 °C for 1 hour under stirring condition. This heating up
helped the reduction process to place the carboxylate group between the graphene
sheets.

In the next step, 40 cc DI water was gradually introduced to the solution
and then heated up to 90 °C under stirring in 30 min, which the mixture color changed to dark brown.
The quality of graphene sheets is closely related to the way which droplets of
DI water were added to the mixture. Thus, the more gradually droplets were added,
the higher quality graphene sheets will be synthesized. Afterwards, 100 cc DI
water was added to the mixture for two reasons; first, diluted the solution,
second, to assured the reduction completion. The end point of the reduction
happened when the color of mixture changed to light orange. To reduce remain
KMnO4 for terminating the reduction, 5 cc H2O2
was introduced to the solution. For purification the filtered GO was washed by
10% HCl solution to remove salts and furthermore, washed again by 100 cc DI
water. The PH of GO should be increased for enhancing the stability; hence, the
filtered GO was rinsed in more than three days. The filtered graphene oxide was
carved from filter paper when PH of the solution reached to 5. Using ultrasonic
bath for scattering the graphene sheets it is also required.

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