1) 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.

Note：

• no Carbon particle is on the wall, Very important !!! 
• Keep stirring for 4 hours, in order to react enoughly.

2)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.

Note：

• Keep stirring for 4 hours, in order to react enoughly.

3) The beaker was then placed in a 35 ◦C water bath and the solution was stirred for ∼2 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 30 min.

Note：

• at least 4-6 hours, in 35 ◦C water bath, and yellow product can be obtained.

4) Later, 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.

Note：

• .if the carbon particles unreacted, you can remove it through the method in the picture 1
• testtube used
• furthermore, you can prepared it into film flexbile.

That looks really weird. Iam no expert in XRD, but you should have either a single peak around 10-15 from the GO, a peak around 32 from the graphite or a combination of those. Your preperation looks a bit wierd to me as well. Ive been working mostly with the Hummers method, so I doent undertand why you would ad your oxidizing agent before adding your acids. The sulfuric acid will make the graphite swell and make the oxidation go easier. If you do it the other way around you will get a very local and strong heating of your graphite which might result in complete oxidation (burning) of the graphite. Additionally, I would never use tap water. It is full of all kinds of strange things which you might not get rid of again. I would suggest that you just filter the GO after the oxidation and the wash it by centrifugation.

Dr. Petersen I tried the hummers method as follows

Step 1: Mix 2g of graphite + 1g NaNO3 with 50ml H2S04 in an ice bath for 30 minutes under vigorous stirring.

Step 2: Add 7g of KMNO4 to the mixture slowly, after addition remove from icebath and let it stir overnight, the mixture gradually become pasty and the color changes to brown,

Now my problem is with step 2, after adding kmno4 i let it stir overnight but there is no color change atall, my mixture is still purple(pic attached) and not pasty, what could be the reason?

This XRD spectrum actually looks like a mix of graphite, graphite intercalated with sulphuric acid (wide diffraction peak between 20 and 30 degrees) and the oxidation product (10-20 degrees range). I suppose your product is not fully oxidized at should contain a lot of sulfur- you can check it by elemental analysis (CHN+S). The latter will also indicate an approximate oxidation degree.

You can seen an example of GO preparation by Hummers method with elemental and XRD analyses in the attached paper.

Using Hummers method you have to be very careful with hydrolysis stage. At first add a small quantity of cold water. Only after the exotherm effect you may add the water excess. Otherwise a sudden increase in the temperature may decompose GO even with explosive exfoliation. It is more safe to use modified Hummers with addition of phosphoric acid complexing the most reactive species.

See: http://pubs.acs.org/doi/abs/10.1021/nn1006368

add about 250ml dist.H2O very slowly as it is highly exothermic and leave it about 30 mins. then add 30ml H2O2 30% the colour will then changed .....

try and be in contact .....

B.W

Hello,

The original Tour's work suggests the XRD peak of GO should be at around 9 degree. However, in yours GO XRD look for RGO . In this sense yours graphite is not fully exfoliated because in yours XRD GO peak is far away from own position... any way yours graphite was burned and sunstainitally reduced to RGO at the time of addition of H2O2. In this respect, probably you got black particles more... compare to white/yellowish. Any way, try to do again ...best of luck.

GO obtained by Hummers method can be black or brownish, more strongly coloured than those prepared using Staudenmeier or Brodie methods. The position of XRD peak depends on the presence of water or polar solvents and d002 interlayer distance may change by several angstroms. However, in  "pure" GO its XRD peak should be rather narrow, sometimes accompanied by less intensive unintercalated graphite peak.

Thank you for all the valuable feedback!

I have been reading about tours and hummers method for GO prep and there are some stark differences between the two, it would be great if you experienced folks could provide some insight to these differences,

1) In hummers method, maintaining 0C when adding kmno4 is stated to be very vital as oxidation of graphite will only occur at very low temp, however tours method does not mention the use of 0C, does that not result in incomplete oxidation?

2) After adding kmno4 some methods mention stirring at rtp, whereas others mention 60C, again this is a big difference in temp as rtp is usally less than 20. What is the role of temperature in this stirring step?

3) Exactly when does the color change occur from purple to brown? Tours method metions this color change after adding kmno4 and stirring overnight, whereas hummers mentiod the color change after adding water.

Addition of permanganate is added at 0 C because you want to avoid over heating and is originaly mostly for safety reasons, but S. Eigler have shown that a higher quality GO can be obtained by keeping the temperature at zero during the entire oxidation. The color should change when the permanganate have reacted. 

Oh and another things, I noticed that you doent use very much sulfuric acid compared to what I use. For that amount of graphite I would use 92 ml koncentrated sulfuric acid. 

Cheers, gl 

Thanx for all the suggestions guys, really helpful! However, i have hit another roadblock, I started the whole thing again, was very careful with the temp and got the nice dark green color after adding kmno4, let it stir overnight at 50C, added water slowly and then h202 but didnt get any color change to brown/yellow atall, the solution stayed dark green.

I am repeating it but I would like to know what the mistake was, my guess is 50C was too high temp and could have resulted in reduction again, perhaps 30C is more suitable...

What do you experienced people think could be the reason?

Hi Fatima

Just to provide a brief answer to you query of color change

Hummer's method Color change

Once you remove the reaction vessel from the ice bath and bring it to room temperature (above 30C) there will be some effervescence and this is the time when the color changes to browinsh grey and slowly the effervescence will dissappear. THis should not take more than 30 - 60 mins. After addition of DI water and H2O2 there will be violent effervescence and the solution will be brown.

Tour's Method

After the addition of KMnO4 the temperature should be around 40C (exothermic). Heat it to 50C for 12h and there should be a gradual color change.

If you still see purple then my advise would be get some fresh KMnO4 and try.

Now I was not sure what did you mean by stir the KMnO4 mixture with one hand and add acid. Bad Idea - stir is using a magnetic stirrer only. Maybe you have chunks of KMnO4 unreacted. 

Hope these tips help :)

Dr. Ammu,

You mentioned in hummers method there will be color change to brown upon adding h202, I did get this color change(dirty brown), however in lit mentions there should be a color change to bright yellow, so I am a bit confused...

Attached is a pic of the color change I got...

Looking forward to hear back...

Hi,

Miss Fatima

First of all this is very nice you have tried again GO synthesis by another method. Any way, in this XRD there is two kind of domains one is exfoliated counterpart having plenty of oxygen containing groups. Another is exfoliated one but do not pertain/hold sufficient number of  oxygen functionalities (exactly we can say the peak at around 25 two theta degree refer the RGO? So now you have mixture of GO and RGO.

Second, the peak at around 9 degree refer the good exfoliation of graphite which has more number of oxygen functional groups ( due to large lattice spacing). Which indicates that shift of 2 theta to lower angle. However, unfortunately in yours system the other impurity (means RGO) also. Probably, you will get rid of RGO in next synthesis just take care of few things (i) try to maintain proper stirring of GO slurry ... acidic mixture of (C+ H2SO4 + NaNO3+ KMnO4) mostly it happens after some time..during the synthesis... magnetic stirrer stuck in the slurry (due to the highly viscous nature of slurry) and some part of graphite is remain unreacted or partially reacted , second sonication part which is must necessary for GO exfoliation (try to do proper sonication of GO). Moreover, at the time of synthesis please try to not change this sequence, first, should add DD water then H2O2.

Dr. Rahul,

Thank you for the detailed reply, I have some follow up questions if time permits...

1) You mentioned the peak at around 25 corresponds to rGO, if it corresponded to graphite it is understandable as maybe all the graphite did not get oxidized, but I dont understand how rGO can be formed as I did not perform any reduction treatment.

2) You mentioned viscosity of the slurry, this is one thing i have never achieved... my mixture never becomes gel like even after stirring for 24 hours at 50C it still seems rather liquidy, does this mean the process is not complete?

3) You mentioned sonication for GO exfoliation, I was not aware that sonication is necessary, I just filter the solution, wash the filtrate with 5% HCL and DI water using centrifuge at 5000rpm (max speed of my centrifuge) for 3 hours until pH becomes neutral. Could you please provide some details of how to sonicate to obtain pure GO?

Thank you very much.

Hi,

Miss Fatima just please see GO synthesis in my some published works in researchgate such as:

https://www.researchgate.net/publication/261638202_Rapid_Electrochemical_Synthesis_of_Hydrogenated_Graphene_Oxide_Using_Ni_Nanoparticles

Regards

Rahul Krishna

Article Rapid Electrochemical Synthesis of Hydrogenated Graphene Oxi...

HI,

The above mail was related to the XRD of GO which shows single phase.

Regarding of RGO which I have wrote please do not confuse from oxidation and reduction. This refer that more and less exfoliation of graphite.

You have used 50 C temperature the degree of dissolved oxygen inside of system is less compare to low temperature. However, this is very complicated topic for me how to explain all things in one mail...but in future I can try to say some more in detail. For more under standing just please read my one answer in researchgate 

https://www.researchgate.net/post/why_the_yellow-brown_colour_of_the_prepared_graphene_oxide_by_modified_Hummers_method_turns_to_dark_brown_after_washing_with_water#view=549f4caad4c118f50a8b46bc

Q. Why the yellow-brown colour of the prepared graphene oxide by modified Hummers method turns to dark brown after washing with water?

Answer by Rahul Krishna: 

Hi,

First of all, at the time of synthesis the acidic mixture contains lots of MnSO4 impurity. The color of this specie is pale pink ( especially, in case of tetrahydrate ). So, initially due to this GO looks more bright and faded white. After the continuous rinsing this impurity get rid of along with some labile oxygen functional groups. Moreover, at the time of washing dissolved oxygen of the system (either in acidic water or between in the layers of GO) also deprive/reduces. Due to this some how crystallographic lattice spacing (001) also decreases as compare to original exfoliated system after adding of water.... simply means reduction process happen which finally led the color change as per pi conjugation and chromophore theory"

Regarding of ultrasonication during the process (means before the complete filtration) it is an important step. However, normally it is not mentioning in GO synthesis. Any way, please try to make the sonication of GO dispersion after filtration in one big beaker for at least 30 + 30 min.

1) 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.

Note：

• no Carbon particle is on the wall, Very important !!! 
• Keep stirring for 4 hours, in order to react enoughly.

2)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.

Note：

• Keep stirring for 4 hours, in order to react enoughly.

3) The beaker was then placed in a 35 ◦C water bath and the solution was stirred for ∼2 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 30 min.

Note：

• at least 4-6 hours, in 35 ◦C water bath, and yellow product can be obtained.

4) Later, 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.

Note：

• .if the carbon particles unreacted, you can remove it through the method in the picture 1
• testtube used
• furthermore, you can prepared it into film flexbile.

 Hello.

I used Tour method and after adding H2O2, solution turn to yellow from dark brown. From the paper, it showed that oxidation of graphite flakes occur which mean Graphite Oxide form. Washing with 5% HCl and water then dilute with 400mL DI, stir and sonicate. The result characterized using FTIR and no C-OH, C-O-C, C-OH observed. Just one obvious peak (1635cm-1 attributes C=O) (most paper mentioned around 17++) was observed. Why it happened?

Fatima Ahmad..please follow the Video Synthesis Graphene Oxide by Tour Method..