pH is a very important parameter..., higher pH value may result better dispersion..

Have you centrifuged the GO?

No moayeri sir i centrifuged after completion of reduction process and i dried it in an oven at 50 c after that i weighed 0.0005g/ml and re dispersed using ultrasonicator that is all. The former one was stable i did the same procedure for the later sample also but it is not dispersed well .

The factors controlling the dispersion of rGO is 1) its degree of reduction, and (2) the pH of its dispersion since they determine the surface properties of rGO and the stable dispersion is achieved when surface polarity and surface potential of rGO is adjusted to the right values suitable for each dispersion medium. I think your first sample degree of reduction is different then your other sampels and hence you cannot disperse them as before (see the attached reference).

Oh ok sir now i understand what i did , thanks for your information i hope the paper will be very useful.

pH is a very important parameter..., higher pH value may result better dispersion..

In fact you cannot disperse graphene in water you shoud use another less polar solvents. The simplest way to disperse graphene in water is to convert them in graphene oxide. You should read a very interesting review to better undestand all the graphene feactures on colloidal solutions "Solvated graphenes: an emerging class of functional soft materials: Adv. Mater. 2013, 25, 13-30"

I tried to disprse few layer graphene in water an year ago and it was not well-dispersed; I tried chloroform and then acetone and ethanol. With my experience flg dispreses well with ethanol!

Hello.

Thank you for your query. To me please re-look following -

1. The problem in reproducing is either you had using different GO as reducing source in the reactions. You make elemental analysis to clarify it. TO REPRODUCE such experiments, one must trust elemental analysis and we must use GO with same composition of C, O , N and S at least. The settling down in later case means we have less polar functional groups to keep rGO suspended in water.

2. Water may not be best to disperse rGO with very higher C to O ratio. In that case, Please try NMP, DMF, DCM etc solvents. Your suspension in NMP will be stable for months since we have done it.

Also, take precaution to keep GO inert. because if you make a GO and keep in air or unsealed vessel for weeks, the chemical composition of powder immediately changes. So, be aware of it.

Thanks, Vineet

Mr.vineet so we have DMF to wash the GO means it will take short time to wash the materials.?.why?

Hi Sadha sir, Thanks for your query. I am sorry if I may not have understand your query very efficiently But, I think -

DMF is a good solvent for dispersing because it has an interactive effect with GO or Graphene. I may not know if some one has used it as a washing agent but there are several paper in which authors have demonstrating its nature to form stable dispersion and also used for exfoliating via sanitation.

Perfect Paper for reference -

http://www.nature.com/nnano/journal/v3/n9/abs/nnano.2008.215.html

PS: The query was "What are the factors affecting the dispersion of graphene in water?" (NOT for washing)

Good Luck,

Vineet

graphene is hydrophobic in nature, thus it explains why graphene will never dispersed well in water