Hi Harfiz,

The graphene oxide aqueous solution is usually of yellowish to brown color. However, if the graphene oxide got somewhat reduced, its color will become black, always with degenerated solubility as well. Therefore,

1. a) Take a Raman spectra of your black product, and notice if the ratio of Id/Ig is significantly improved, which indicates the level of your oxidation. See http://pubs.acs.org/doi/full/10.1021/am506435u  Figure 1 for detailed description.

 b) take a TEM and notice if the graphene layers has been sufficiently exfoliated. See http://www.sciencedirect.com/science/article/pii/S1385894714016313 Figure S1 for detailed information.

2. I don't think 98 degree in strong oxidant will reduce your samples, but if you dry your samples at this temperature it does turn black.

3. Yellowish to brown color when dispersed in water.

Thanks Xin Zhou for that valuable information. Great articles indeed! tqvm!~

Dear Xin,I think that the link for  1 b) is might not right. I didnt see any TEM discussion in that article.

i am getting yellow colour of the final solution after 1 day is it symbol of graphene oxide formation ???

Me too, but after several washing (wash, centrifuge repetitively) i found that the yellow colour turns darker and eventually black-ish. As the pH changes to 7 (neutral) the colour turn to black (but not completely black). It more to brownish black.

After washing with HCl and DI water, the color will change to brown and gel like structure.

the color of pure graphene oxide is brown and if your product is not brown than it means graphene oxide is not formed.

@Harfiz can you please give me the paper you used as reference to make GO,,,what is the final color of GO