10.1039/c4ta04367g
Advancement in liquid exfoliation of graphite through simultaneously oxidizing and ultrasonicating
Graphite powder (Micro 0850) was provided by Asbury Carbons Pty Ltd. Potassium permanganate, sulphuric acid (95-98%) and phosphoric acid (85 wt%) were purchased from Sigma-Aldrich. Hydrogen peroxide (30 wt%) was bought from Chem-Supply. 
KMnO4 (0.4 g) was dissolved in a mixture of concentrated H2SO4 (6.0 g) and H3PO4 (26.0 g). Graphite powder (0.1 g) was added into the mixture and stirred for 1 min. Then the mixture was immediately covered and placed into an ultrasonic bath (200 W and 42 kHz) for simultaneous oxidization and ultrasonication (oxidi-sonication). A cooler was connected with the bath to prevent heat build-up. During the oxidi-sonication, graphite flakes could exfoliate and split into graphene sheets; meanwhile, they were oxidized by Mn2O7 that was created by 2KMnO4 (s) + H2SO4 (aq) - Mn2O7 (l) K2SO4 + H2O. The reaction can be terminated anytime by moving the mixture out of the bath and then adding 120 g water slowly, followed by vacuum filtrating and washing three times with water and hydrogen peroxide for removal of ions and acids. The prepared sheets should be stored in solvents such as water or acetone for the following film fabrication. For characterization in need of powder samples, the sheets were dried in an air-ventilated oven at 60 degC and then in a vacuum oven at 100 degC for 4 hours to remove crystalline water. Although we started with 0.1 g graphite, the product was weighed to be 0.105 g; the slight increment would be caused by the O element added by the oxidi-sonication and also likely due to the combined water.
sulphuric acid
95-98%
%
phosphoric acid
85 wt%
wt%
Hydrogen peroxide
30 wt%
wt%
KMnO4
dissolved
0.4 g
g
H2SO4
6.0 g
g
H3PO4
26.0 g
g
Graphite powder
added
0.1 g
g
mixture
stirred
1 min
min
n ultrasonic bath
200 W
W
n ultrasonic bath
42 kHz
kHz
water
adding
120 g
g
water and hydrogen peroxide
washing
three times
times
sheets
dried
60 degC and then in a vacuum oven at 100 degC
degC
sheets
dried
4 hours
hours
graphite
0.1 g
g
product
weighed
0.105 g
g