Commercial powdered natural graphite (from Alfa Aesar) was
used as our starting material. The commercial graphite has a
particle size of 70 mm with a purity of 99.99995% and a density of
2.25 g/cm3. Graphite was oxidized following the Staudenmaier
method to form graphite oxide (GO). In this method, graphite (5 g)
was first mixed with sulfuric acid (87.5 ml) and nitric acid (45 ml)
and stirred. When graphite was uniformly dispersed, potassium
chlorate (55 g) was added slowly and stirred for over 96 h. After the
completion of oxidizing reaction, the mixture was added into
deionized water and then filtered. The GO was repeatedly rinsed
and redispersed in a 5% solution of HCl for three times. It was then
washed continually with deionized water until the pH of the
filtrate was neutral [22]. The GO slurry was dried and pulverized.
Potassium stays in the GO even after several times of washing.
Therefore multiple washing cycles used in conjunction with bath
ultrasonication in fresh ethanol are needed for the removal of
residual potassium [23]. After this the GO was dried and pulverized
again. Finally, the GO was heated to 1050 8C and held in the furnace
for 30 s to form graphene.