Hello,
I am preparing GO using hummers method as follows:
Briefly, 69 mL of concentrated H2SO4 was slowly
added to a mixture of graphite powder (3 g, 1 wt equivalent) and
NaNO3 (1.5 g, 0.5 wt equivalent) in a 500 mL beaker. The mixture
was cooled down to 0 ◦C in an ice bath and stirred for 1 h. Then,
KMnO4 (9.0 g, 3 wt equivalent) was slowly added in portions to
keep the reaction temperature below 20 ◦C. The beaker was then
placed in a 35 ◦C water bath and the solution was stirred for ∼1 h
to form a thick paste to which ultra-pure DI water (138 mL) was
added slowly, which produced a large 98 ◦C exotherm; maintained
atthis temperature for 15 min. Then, a mixture of DI water (420 mL)
and 30% H2O2 (10 mL) were added, producing another exotherm at
below 20 ◦C. Finally, the solution was filtered to obtain the precipitate.
i followed these instructions very closely, especially maintaining the temp, i got the green color after adding kmno4 and brown after adding water, however i was unable to get the bright yellow color on adding hydrogen peroxide, instead i got a dirty greenish brown color (pic attached). I did see yellow bubbles on adding h202 but the color of the whole solution does not change to yellow.../
My questions what does the color change to yellow indicate? If I am not getting it which step could the mistake be in?
Thanx Dr. Khosro, I did get a dark green color after adding kmno4, doesnt appearance of dark green color indicate oxidation?
hi friends, i think , H3PO4 is for improved hummers but NANO3 is for hummers methods, and it dosent change to yellow color, dark green is corrected. i ask a question: What happens when you add concentrated sulfuric acid to sodium nitrate? i wanna to know saftey points. i did improved hummers method.
Avideh,
The yellow color on adding h202 is due to the excess kmno4 salts and is hence seen in both methods.
Sodium nitrate acts as a secondary oxidizing agent and the safety concern in my opinion is the production of toxic no2 gas later in the process, just do it in a fume hood and you'll be fine....
through centrifugation, the graphite black can be separated from your GO.
the GO can be collected,
the graphite black is in the bottum of centrifuge tube.
Dr. Chen,
After filtration I just wash the GO cake with DI water by centrifugation at 5000rpm for 3-4 hours (till pH becomes neutral),and I change the water every 30 mins. and then the residue is dried and tested for GO, this residue I believe is a mix of GO and the unreacted graphite, what changes can I make to the centrifuge step to remove the graphite (speed, time)?
p.s- please note the max speed of my centrifuge is 5000rpm.
Many thanks.
to remove the unreacted graphite particles, the best method is washing with ethanol. there two things you can do.
First, for most of case, the solvents is water, so you can adding ethanol into GO solution, for example ethanol: water = 50:50. the aim of adding ethanol is to make the graphite particles more easy settling.
Second, centrifugarationfor a short time, then the clean GO in the above column is collected; the graphite particles in bottum are collected into another beaker.
speed 5000rpm is enough!!!
for the question: "You have a picture titled 75 wt%, that is the kind of film I want, but 75 wt% mean u added 75g GO in 25g solvent, that seems way too high, please confirm the conc you used."
We add 75%weight of GO dissovled in NMP, and the other 25% is PANI LB in NMP.
I think that the main problem came from the concentration of H2o2 you used in the reaction, which is responsible for giving this yellowish color. I've got the same problem when I was preparing graphene so you should fresh h2o2 and double dis. water.
wish the best of luck and let me know what is happened with you?
Albert
I have same problem. I used modified hummers method. The mixture turned green instead of yellow. Any help would be appreciated.
Check if the H2O2 used is 30% by volume. If it is 60% and you need 10 mL, just take 5 mL of H2O2 and add 5 mL of DI to prepare 30%
Dear Fatima
to talk into your count, the yellowish colour means complete oxygenation process with high probability so that in your case the oxygenation process didn't complete. all what you need to give time to your reaction, or maintain it a sufficient temperature.
Please use Modified Hummer's Method. You will get desired results.
Regards
Hi there
I had the same problem while synthesizing graphene oxide. I know this question has been asked several years ago, but I am about to share with my experience about preparing graphene oxide, I hope it works for all those researchers who face this challenge and see this page. The problem of your procedure is that you applied low temperature while adding H2O2. You must pour it when the temperature of mixture is high, around 45 to 98, depending on the application predicted to the GO product. Actually the logic behind adding water before adding H2O2 is to rise the temperature of mixture, but unfortunately you kept T below 20 degrees of centigrade. So the next time you need to put the mixture into a high T water bath if you want to get GO and brownish yellow color.
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