Graphene oxide (GO) sheets have been synthesized at
lab scale using highly efficient Hoffman and Hummer’s method. The protocol followed
to synthesize GO nano sheets is discussed thoroughly in this article with color
change indications at divergent steps of synthesis procedure. All the chemicals
were used without any prior processing.
1. Materials and methods:
Lab scale synthesis of fine graphene oxide (GO) is a
four to five day simple procedure in which temperature conditions, amount of
chemicals used and color change are the main points to be considered. Different
instruments and chemicals used in the whole procedure are given in table 1 and
2 respectively.
Table.1. Instruments used in the synthesis of graphene oxide sheets
Table.2. Chemicals used in the synthesis of graphene oxide (GO)
The first and foremost factor affecting the quality
of synthesized graphene oxide is temperature, as it differs remarkably at
various points. Secondly, amount and ratio of graphite powder and potassium
permanganate is considerably the other most promising factor in the synthesis
process and perhaps the most sensitive factor point of the reaction. The present
research work is based on efficient synthesis and characterization of graphene
oxide.
The ratio of graphite powder and KMnO4 used in this protocol is 1:6 grams respectively, which is the only appropriate amount of both chemicals to synthesize GO sheets. To begin the reaction, six grams of graphite, in a fine powdered form, along with three grams of NaNO3 were mixed in 250 mL of concentrated H2SO4 at ice bath conditions, keeping the temperature below 4oC. This mixture was kept on stirring using mechanical stirrer and left for two to three hours, until and unless the color of the mixture turned black. Potassium permanganate was grinded in powdered form before to add in aforementioned mixture, at ice bath conditions keeping the temperature of the reaction system at 0oC, to avoid any explosions which would be resulted by heat produced during this step. A weighed amount of 18 grams of potassium permanganate was added pinch by pinch to the reaction mixture, which changes the black color mixture to dark blackish green. Afterwards, the reaction flask was shifted to magnetic hot plate and left at stirring for three days at 30 to 35oC, which turned the greenish homogenous mixture to brownish thick slurry, followed by the addition of 100 mL of distilled water drop by drop. Addition of water abruptly increases the temperature of the reaction system and at the same time converted the color of the from green to hazel brown which is the indicating point of graphene oxide synthesis. Hydrogen peroxide is ultimately added to stop the reaction and then left overnight after adding 10% hydrochloric acid, to let the synthesized product to settle down at the bottom. The upper liquid is discarded and finally synthesized graphene oxide is first separated and then washed with mixture of methanol and ethanol using centrifuge machine at 6000 rpm, until the pH of graphene oxide solution reached at 7. Electric oven was preheated at 60oC, prior to keep the GO oxide solution in it for drying. At the end thin sheets of graphene oxide has been collected from oven. Figure 1 shows different steps of graphene oxide synthesis and the color change at each step.
The synthesized product
was subjected to morphological and elemental analysis to characterize the
efficiency and features of the synthesized GO sheets.
2.1 Elemental analysis:
The synthesized product was employed to elemental
analysis to confirm the permutation of graphite into graphene oxide. The X-ray
diffraction technique was used for this purpose. For sample preparation
graphene oxide sheet was grinded using minute amount of ethanol which resulted
in fine to get the fine sample. the grinded sample was then tipped on a glass slide
for final analysis.
The obtained XRD pattern of GO is shown in figure 2,
which shows sharp peaks at specific 2-theta values. Sharpness of peaks in XRD
pattern indicates the purity of the produced graphene oxide. The peaks at
2-theta values of 10.80o, 17.51o, 26.52o and
48.44o with miller indices of (001), (010), (101), and (110) confirm
the successful production graphene oxide. The presence of high intensity sharp
peak at 2-theta value of 10.80o and the absence of specific peak at
2-theta value of 13.5o corresponds to the conspicuous conversion of
graphite into graphene oxide.
2.3 Morphological characterization:
Scanning electron microscope was used to analyze the
morphology of the fabricated sheets. For this purpose sample was prepared
sonicating the GO sheet in methanol to get a thick solution and then carbon
tape was used to form slurry on its surface, which was then subjected to
scanning electron microscope for further analysis at different resolutions.
Figure 3 (a) and (b) shows the obtained results of SEM analysis. A layered 2D
structure of GO sheets can be seen clearly in the given images of figure 3. The
results of SEM image show a considerably porous structure of synthesized
graphene oxide sheets. The presences of sufficient oxygenated species are indicated
in the given image by the stacked layers and a little bit of thickness, which
also indicates the puffiness graphene oxide. The oxygen containing functional
groups, which include hydroxyl group, epoxy group, carbonyl group and
carboxylic group, are present on the surface as well as among interfacial
layers of GO. These groups are actually responsible for the porosity in the
structure of graphene oxide structure and also an indication of successful
conversion of graphite to graphene oxide.
0 Comments