See the attached paper for the typical synthesis routine. Check the right amount of the used chemicals: sulfuric acid (H2SO4, 98%), phosphoric acid (H3PO4, 85%), potassium permanganate (KMnO4, 99.9%), hydrogen peroxide (H2O2, 30%), and hydrogen chloride (HCl, 37%). Oxidation of graphite is carried out by mixing H2SO4:H3PO4 (320:80 mL), graphite flakes, and KMnO4 (18 g) using a magnetic stirrer. After adding all the materials slowly, the one-pot mixture is left for stirring for 3 days to allow the oxidation of graphite. The color of the mixture changes from dark purplish green to dark brown. Later, H2O2 solution is added to stop the oxidation process, and the color of the mixture should change to bright yellow, indicating a high oxidation level of graphite.

You can replace sodium nitrate with sodium nitrite. See the attached paper for the water soluble synthesis.

http://www.e-journals.in/PDF/V1N3/500-507.pdf

Moreover, you can actually improve the synthesis by completely excluding NaNO3 (and thus avoiding the generation of the toxic gases NO2 and N2O4). Take a look.

http://www.ludiserv.com/zenos/docu/Improves%20Synthesis%20of%20graphite%20oxide.pdf

See the attached paper for the typical synthesis routine. Check the right amount of the used chemicals: sulfuric acid (H2SO4, 98%), phosphoric acid (H3PO4, 85%), potassium permanganate (KMnO4, 99.9%), hydrogen peroxide (H2O2, 30%), and hydrogen chloride (HCl, 37%). Oxidation of graphite is carried out by mixing H2SO4:H3PO4 (320:80 mL), graphite flakes, and KMnO4 (18 g) using a magnetic stirrer. After adding all the materials slowly, the one-pot mixture is left for stirring for 3 days to allow the oxidation of graphite. The color of the mixture changes from dark purplish green to dark brown. Later, H2O2 solution is added to stop the oxidation process, and the color of the mixture should change to bright yellow, indicating a high oxidation level of graphite.

The amount of precursors used in the above-mentioned paper has already proved highly efficient for getting a quality product. Therefore, I guess it is safe to assume that any tangible deviation from this working recipe will affect the final result. But if you really want to gain a useful personal experience in this field, I would strongly suggest trying different routes and comparing the obtained results. The same is also true about the oxidation time.

I want to work on GO synthesis by hummers or modified hummers or improved, I reviewed some papers but each paper reported something ( oxidation time is 1/4/6 h or 3 days or 5 days , some papers used oil bath or ice bath ) any body can help me how can trust them and the which is the best paper is under your experimental?

dear Mr Nazanin

based on my experince, i used ice bath when stired sulfuric acid, graphite and NaNO3 for 4 hour while KMnO4 was added slowly. and then i removed the ice bath and continued stirring for 24 hours in the temperature 40 C. after that i added 200 ml aquades, stirring it for 1 hour and then added H202

I used this conversation and thanks

Hi, why did you use phosphoric acid? I use just H2SO4.

Hi  Lita nur Azizah

addition of NaNO3 during synthesis decreased  number of layers were reduced and interlayer distances were increased to a minor extent. The decrease in number of layers was most prominent for the 45micron particle size graphite precursor

What if we don't use H3PO4 or NaNO3 in the method ? what will be the effect,

The below paper may answer your question in a great way :  

Chowdhury et al. "Role of graphite precursor and sodium nitrate in graphite oxide synthesis." RSC Advances 4.29 (2014): 15138-15145.

Good luck with your research! 

Following this discussion, but it raised a few questions:

Do the Hummer's method and modified Hummer's method make sure that all of the graphite reacts with the volume and mass ratios that are shown in the protocol/s?

My worry is that not all of the graphite powder or flakes react, so the work-up procedure becomes tedious, especially in the separation steps. What if some graphite is left unreacted once the reaction is quenched? How would you separate (physically) the unreacted graphite from graphene oxide?

Again, with the above-mentioned methods I am assuming that all of the graphite is reacted (i.e. graphite is the limiting reagent).

I wanted to know why only NaNO3 is used in modified hummers method and if it causes reduction in number of layers and increase spacing then why KMnO4 is used as catalyst i.e oxidizer

The paper that Ms Mina Sabzevari (by Chowdury) mentioned above should help.