Preparation of Graphitic Oxide

A rapid,
relatively safe method  has been developed  for preparing graphitic oxide from graphite in what is essentially an anhydrous
mixture  of  sulfuric acid, sodium  nitrate and potassium  permanganate.
The preparation of  graphitic  oxide by methods described  in  the literature  is time consuming and hazardous.
Introduction
Graphitic oxide, sometimes called graphitic acid,
has  been known  for  almost  a  century.  It-was
first prepared  by  Brodie2  in  1859  by  repeated
treatment  of  Ceylon  graphite with  an  oxidation
mixture  consisting of  potassium  chlorate and fum-
ing nitric acid.  Since then, many other procedures
have  been devised  for forming  graphitic  oxide,
nearly  all  dependent upon  strong  oxidizing mix-
tures  containing  one  or  more  concentrated  acids
and oxidizing material~.~-s
The methods most  commonly used  at the pres-
ent time  are the  original Brodie  synthesis and one
described  by Staudenmaier,6  in which  the graphite
is oxidized in concentrated sulfuric and nitric acids
with potassium  chlorate. Recent  workers  in  the
field  such  as Hofmann  and  Frenzels  and  Hamdi7
using  the Staudenmaier method found  the process
time  consuming  and  hazardous.  The  Stauden-
niaier-Hofmann-Hamdi  method  involved  the  ad-
dition  of  potassium  chlorate  to  a mixture  of  con-
centrated  sulfuric  acid, concentrated  (63%)  nitric
acid  and  graphite.  The  potassium  chlorate  was
stirred slowly and carefully into the mixture over a
period  of  one  week  with  cooling.  The  chlorine
dioxide evolved was removed  with  an  inert  gas
such  as carbon  dioxide  or  nitrogen.  The process
required more  than 10 g. of  potassium  chlorate for
each gram of  treated graphite and explosion was a
constant hazard.
In the present method,8  the oxidation of  graphite
to  graphitic  oxide  is  accomplished  by  treating
graphite with  essentially a water-free  mixture  of
concentrated  sulfuric  acid,  sodium  nitrate  and
potassium  permanganate.  The  entire  process  re-
quires  less  than  two hours for completion  at tem-
peratures  below 45'  and can be carried  out  safely
providing reasonable  care is maintained in observ-
ing the temperature limitations.
Experimental
The  graphitic oxide  was prepared  by  stirring  100 g.  of
powdered flake graphite (Dixon's  8635, 325 mesh) and 50 g.
of  sodium  nitrate into 2.3 liters of  66'  Be technical sulfuric
acid.  The ingredients were mixed  in a  15-liter battery jar
that had been cooled  to 0'  in an  ice-bath as a  safety measure.
While maintaining vigorous  agitation,  300  g. of  potassium
permanganate was  added  to the  suspension.  The  rate of
(1)  This research conducted under National Lead Company Fellow-
ship at the Mellon  Institute of  Industrial Research.
(2)  B. Brodie, Phil.  Trans.. 149, 249  (1869).
(3)  B. R. Brown  and 0. W. Storey, Trans.  Amur. Elcclrochcm.  Soc.,
(4)  G. Charpy, Compf.  rend., 148, 920 (1909).
(6)  U. Hofmann and  A.  Frenzel,  Bct., 898,  1248  (1930).
(6)  L.  Staudenmaler,  ibid.,  31,  1481 (1898);  81,  1394  (1899);  88,
(7)  H. Hamdi, Kolloid  Briheffc, 64,  654  (1943).
(8)  W. S. Hummers, U.  S  Patent No. 2,798,878  (1967).
69,129  (1928).
a824  (1900).
addition was controlled carefully to yevent the  temperature
of  the suspension from exceeding 20  .
The ice-bath was  then  removed  and  the  temperature  of
the suspension brought to 35 f  3O, where it was maintained
for  30  minutes.  As  the  reaction progressed,  the mixture
gradually thickened with  a  diminishing  in  effervescence.
At  the end  of  20 minutes,  the mixture  became  pasty with
evolution  of  only  a small  amount  of  gas.  The paste was
brownish grey in color.
At the end  of  30 minutes,  4.6 liters  of  water  was  slowly
stirred  into  the paste,  causing violent effervescence and an
increase in  temperature  to  98'.  The  diluted  suspension,
now brown in color, was maintained  at  this temperature for
15 minutes.  The  suspension was  then further  diluted  to
approximately  14 liters with  warm water  and  treated with
37,  hydrogen peroxide to reduce  the residual permanganate
and manganese  dioxide  to  colorless soluble manganese  sul-
fate.  Upon  treatment  with  the  peroxide,  the  suspension
turned bright  yellow.  The suspension was filtered resulting
in a yellow-brown  filter  cake.  The filtering was conducted
while  the  suspension was  still warm  to  avoid precipitation
of  the slightly soluble salt  of  mellitic  acid8  formed as a  side
reaction.
After washing  the yellowish-brown filter cake three times
with a  total of  14  liters of  warm water,  the graphitic  oxide
residue was dispersed in 32 liters of  water to approximately
0.570  solids.  The remaining  salt impurities  were removed
by treating with  resinous anion and cation exchangers.  The
dry form of  graphitic oxide was obtained  by centrifugation
followed by  dehydration  at 40"  over phosphorus pentoxide
zn vacuo.
Results
The effectiveness of  the oxidation method can be
judged  by  the proportion  of  graphitic oxide in  the
product or  by  its  carbon  to  oxygen  ratio.  Well
reacted  samples of  graphitic oxide will have a  car-
bon  to oxygen atomic ratio  lying between  2.1  and
2.9.  Also the color of  the product when suspended
in water may be used  as criterion for  the degree of
oxidation  of  the graphite.  The product richest  in
graphitic  oxide  will  have  a  bright  yellow  color
whereas poorer  samples with  higher  carbon-to-
oxygen ratios will have a green to black hue.
An analysis of  the dried graphitic oxide prepared
by the present method  is compared  in Table I with
a  sample made  by  the  Staudenmaier  procedure.
The  present synthesis resulted  in  approximately
188  g.  of  graphitic  oxide  containing  23%  water
and 2% ash.  The carbon  and hydrogen  were de-
termined by the combustion of  graphitic oxide with
cupric oxide.Q l1
TABLE  I  Carbon-
to-
oxxen
% by weight atomic
Method  Carbon  Owaen  Water  Ash  ratio  .-
Acid-permanga-
nate-nitrate  47.06  27.97 22.99  1.98  2.25
Staudenmaier  52.11  23.99 22.22  1.90  2.89
HOUSTON,  TEXAS
(9)  B.  Juettner, THIS  JOURNAL,  59, 208 (1937).
(10)  W. A. Selvis and W. C. Ratliff, Trans. Amer. Elcclrochcm. SOC.,
(11)  H. Tbiele, 2. onorg.  allpcm. Chrm., 190, 145  (1930).
1'7,  121 (1920).5169