It is always to better to cook your food to sell. Then only, you will come to know what proportion to use for what taste using ingredients. Remember the things:
You may purchase the GO nano-powder and applied. In order to improve your research outlook, it will be necessary to synthesize your GO and play around the turnable features. You can also conduct comparative studies with commercial GO and yours to estimate the efficiency. Who knows, the cost factor may be lower.
I suggest you to prepare it yourself, as the technique doesn't require any expensive instrument or expensive chemicals and above all, the process is well explained in many papers. For instance the original paper by Hummer himself.
Caveat: Please take care of the neutralization step that is a bit tricky (my advise is add a lot of water to the acidified solution let the powders settle for 12 h and carefully extract the sediments by discarding the water, repeat the process until your litmus paper shows pH as neutral.)