Since we are using strong acids during the synthesis (be it Hummers, modified Hummers, Marcano etc.), you will always end up with a highly acidic first product. You cannot rely only on dialysis for getting a clean final product; instead you need to apply post-synthesis processing, which usually translates into a tedious and prolonged cleaning via filtration, using alternate washing of HCl, ethanol, and water. For details you can take a look at my article " Graphite Oxide Post-Synthesis Processing Protocols" (DOI: 10.13140/RG.2.1.2452.9041) - you can download it from my profile. Or, of course, you can also look elsewhere.

Conference Paper Graphite Oxide Post-Synthesis Processing Protocols

The pKa value of GO is 4.3 due to the presence of phenolic and carboxylate groups, are attached during the oxidation process. Hence, the aqueous GO solution will be always acidic.

When you treat with a mild base means you partially deprotonate the GO. 

Check this paper for further reading

dx.doi.org/10.1021/jz300236w | J. Phys. Chem. Lett. 2012, 3, 867−872

Try ultra-filtration on ceramic membranes, it is much more effective and quicker...

How much sulphuric acid per gram of graphite do You use? All of it should be removed from GO suspension.

Thank you all for your constructive and helpful suggestions. appreciate it. 

Tomasz Ciach, can you offer a couple of examples/links for the proper ceramics? Thanks in advance!

You can explore these links, it may help you.

http://www.instanano.com/nanomaterial-synthesis/carbon-nanomaterial/synthesis-graphene-oxide-hummers-method/

http://www.instanano.com/nanomaterial-synthesis/carbon-nanomaterial/graphene-oxide-washing/