You can follow the following paper-

http://www.tandfonline.com/doi/abs/10.1080/02678292.2014.949888

As an update, I have filtered the solution through a 0.22 microns membrane and everything seems to go straight through. The papers I have read suggested that the black precipitate should be filtered out after passing through the membrane. Please give some suggestion of what next steps I should be taking.

The papers that I have mentioned are:

http://onlinelibrary.wiley.com/doi/10.1002/adma.200902825/abstract

http://pubs.rsc.org/en/Content/ArticleLanding/2011/CC/c1cc11122a#!divAbstract

http://onlinelibrary.wiley.com/doi/10.1002/adfm.201203771/abstract 

Sir,

After filtration to know the difference btwn these two materials I.e. GQDs and rGO, you prefer having a look under UV-Cabinet by keeping these samples herein. You will notice a main difference if GQDs are formed then they will give fluorescence otherwise its rGO. And the protocol you are using is preferred and correct. You must centrifuge the sample before going for dialysis to prevent agglomeration. 

Thank you, Anupma Thakur.  To make sure that I understand you correctly: I have to centrifuge the black solution and then collect the supernatant for dyalysis. Is that correct?

Also, could you describe the dialysis process that you mentioned?

Thanks 

Ok Sir,

Just collect the supernatant, fill the dialysis bag with the supernatant. Taking an outer chamber and fill it with the solvent you had used before. Now dip the dialysis bag into the outer chamber and keep this setup under stirring condition for 12-24 hrs. 

 Hello Jimmy Lam

You can follow attached article. Hope you can find something from this article to solve your problems.

Thanks 

Md Nafiujjaman

Hello Jimmy Lam

Follow attached paper. It help me to synthesis GQDs.