Washing of GO is not directly related to morphology of the GO. Very efficient washing is need to separate GO from the by product of the reaction and the un-exfoliated graphite, presence of which modify the properties and stability of the GO. like from XRD you can get multiple peaks and so on for other characterizations.

You can follow the steps to purify GO:

The yellow solution was first centrifuged and the precipitates are collected for washing by mixture of DI water and 37% HCl (9:1 volume ratio). Then the collected pest like materials were mixed with the solution for purification by applying centrifugal force on it. When the slurry brownish yellow layer floats on the solution in the centrifuge tube, by adding DI water repeatedly to make the pH to 7. After achieving pH 7 the slurry layer of pure GO was collected in a fresh beaker, and dried in room temperature into vacuum desiccator.

after 4-5 washing the material fails to be separated completely and pH sticks at 4 in spite of washing with ultra pure water. what could be the reason behind that? what is the preferred rmp for the centrifugation GO without defecting the layers?

4-5 times washing is not sufficient. You need to wash at least 7-8 times by dilute HCl, then wash it by de-ionized water for another 4-5 times, then check the pH, if it becomes 7. then collect the slurry layer from the solution, do not collect the precipitate from centrifuge tube.

It is  necessary to  wash  GO onsecutively for several times with hydrochloric acid, ethanol  and distilled water until the pH of washing becomes 7 .The final washings  must performed with distilled water.

It is best to collect  GO by filtration under vacuum .Sometimes exfoliated  GO is separated using centrifuge at 4000-6000 rpm after removing   settle un-exfoliated graphite by decanting process.

No clear  relationship between washing and morphological properties.Exicisting of impurities can affected FTIR spectra ,electrical and  optical properties.  

Hi Huma,

Steady pH could be well an intrinsic pH of your GO, if you have more protonogenic groups there.

Is it a must to bring pH to 7 or simply 5-6 is enough to proceed further as GO itself has acidic groups and is acidic in nature.

Unless neutralised, you would not be able to bring it to 7.

Take a look at this paper which compares washing methods for GO post-synthesis:

I have tried the modified Hummers' method (for the first time) and thought of neutralising the diluted sulfuric acid before starting the filtration and centrifugation steps. I am not sure if this makes any sense, but at least the amount of water needed to wash the GO is reduced.

However, it still takes a lot of time to filter off the GO, and even centrifuge and wash it.

Dear Hassan Alshamsi Does washing with HCl solution always come with gas releasing? since I added it to suspension and it beacame fizzy. how much time does it take to be safe to centrifuge?

Zahra Yari Ghale What was the concentration of the HCl solution? I usually add 10% of HCl, the volume I still have to figure out, but I never noticed any effervescence. Effervescence should only be noted when 30% hydrogen peroxide is added. This is why you should add it (ideally) drop-wise.

Dear Maria Magro

I used 10%, too. actually a lot of bubbles produced while adding DI water and H2O2, in a way that even one day later its surface had been covered by permanent bubbles...and then after adding HCl it got fizzy for about one hour.

Dear Zahra Yari Ghale ,

I think you have excess/unreacted H2O2, therefore when you add the HCl it reacts with the peroxide to release Cl2. If you manage to smell the gas it should resemble that of bleach, or else do a simple test with damp blue litmus which should turn red and then white.

Yes dear Maria Magro you are right. I could smell Cl2...

But I did the synthesis based on a recorded procedure in an article. In your book, how can I avoid using excess components? For example using a titration method to estimate the amount of H2O2, H2SO4 and so on.

Dear Zahra Yari Ghale ,

I think you can limit the amount of H2O2 by adding drop-wise whilst stirring the mixture and take note of the colour change of the mixture. It should change from a very dark brown/black to an orange/yellow colour. If you continue adding the peroxide and the mixture does not get lighter in colour, than it means that all of the Mn2+ has been oxidised and that the peroxide being added is in excess (not reacting).

With regards to H2SO4, I guess you can only eliminate it by doing several washings with DI water. There are several methods that you can use, in fact, I am still optimising this step!

I hope this helps :)

Dear Maria Magro

thank you so much for your valuable advice. Apparently I should fix it by practicing.

Best regards

Dear Zahra Yari Ghale ,

You're welcome :)

Dear Maria Magro Zahra Yari Ghale

kindly help me in synthesizing by modified hummers method as I have tried a lot but there is only color change in one step.

Dear Hameem,

What is the colour change that you are seeing? Can you please specify what reagents you are using and methodology?

Mam I have used 10g NaNO3, 20g graphite powder, 30 KMnO4,80ml sulphuric acid, 300 ml DI water, 150 ml H2O2. Color obtained was brown when I used KMnO4 and when I stopped oxidation it turned to black. But I cannot see any other color. Kindly tell me what steps should I follow

Dear Hameem,

If you are adding de-ionised water to stop the reaction, make sure that you add the water in small volumes. Since the reaction mixture involves concentrated sulfuric acid, an exothermic reaction is produced with water which might alter your oxidised graphite. I would add a small volume at a time and wait for the temperature of the mixture to decrease before adding another portion of water. I hope this helps.