Khizar hayat Khan

What do you mean by 'dispersed fully'? What is your expectation here?

Take a look at this webinar (registration required):

Dispersion and nanotechnology

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat

Have a look at this paper, it may help in your experiments

Article Dispersion and Aggregation of Graphene Oxide in Aqueous Media

It will also depend on the thickness of your material. You will always have some deposits of graphene oxide at the bottom part of your flask. If you want to increase your dispersion in water, maybe you can PEGylate it or functionalize it with some surfactant, however, the surface of your GO will not be available any longer.

Dear Khizar hayat Khan, according to your description, that GO does not a high oxidation degree, which is why that cannot be dispersed in water easily. In fact, the dispersibility of GO is predominantly determined by its oxidation degree (C/O Ratio). Several factors can lead to the chemical reduction of GO and deteriorating its hydrophilicity ranging from improper drying temperature to long storage conditions. High-quality GO possesses a high oxidation degree, is light brown, and is readily dispersed upon the addition of water without any further sonication. Since your GO cannot be dispersed in water easily, that has been most likely reduced as a result of improper or long storage conditions. Hence, I highly recommend you synthesize GO according to the following article (Tour's Method) which is so straightforward.

Article Improved synthesis of graphene oxide. ACS Nano 4:4806-4814

Besides, I have optimized the synthesis conditions and thoroughly described them in the following article. I assure you that the obtained GO using this procedure is highly hydrophilic. (Note: the temperature of the drying step is so crucial.)

Article Self-assembled graphene-based microfibers with eclectic opti...

Dispersion of a highly oxidized GO looks like the attached photo.

Best,

Dear Mahdi Ghamsari , I agree with you, however, graphite oxide will show you aswell high degree of oxidation (close to 30% measured by XPS) and it will be deposit. It is a mixture of parameters, where the oxidation, thickness and size influence the final dispersion and stability. In my experience, the separation step is one of the most importants. Additionally, sonication could lead to a reduction of your graphene oxide sheets due to the energy produced. I would not recommend to soniicate it, as the material should be easily redispersed in water without any problem.

Dear Adrian Esteban Arranz , I agree with you as well. But among all of the involving factors, I consider the oxidation degree as the most determinant one in getting a good dispersion. It is mostly the main problem in a lot of cases that unintentional reduction of GO leads to low hydrophilicity and dispersibility. Sometimes, inproper drying of freshly prepared GO gives rise to a bunch of crosslinked nanosheets with low oxidation degree that are incapable of making a stable dispersion. As I stated before, try to synthesize GO yourself using Tour's method and centrifuge it at low speed to separate multilayer GO nanosheets from single and bilayer ones after purification. Besides, short sonication with an ultrasonic bath might be useful for further exfolation, but long and severe sonication can reduce GO.

Best,