The graphene layers are held by weak van der Waals' force, this should be comparable to the force holding solvent particles. Why doesn't graphite dissolve in organic solvent and separate into graphene layers?
2$\begingroup$ An individual van der Waal's bond is weak but graphite sheets have zillions of such bonds, hence overall there is a strong attraction between the individual sheets. $\endgroup$– MaxWJul 10, 2018 at 13:57
2$\begingroup$ That said, you may separate layers all right, but it does not mean that graphite would dissolve. $\endgroup$– Ivan NeretinJul 10, 2018 at 14:07
5$\begingroup$ You don't need to go to graphite. Already tetracene (four C6-rings) is only soluble in boiling benzene, and not very well. pi-stacking makes quite strong bonds. en.wikipedia.org/wiki/Stacking_(chemistry) $\endgroup$– KarlJul 10, 2018 at 18:12
1$\begingroup$ @Karl According to NIST's compilation, pyrene dissolves at 295.35 K up to 13.47 mol% in THF (doi.org/10.1063/1.4775402 or digital.library.unt.edu/ark:/67531/metadc152456/m2/1/high_res_d/… p. 013105-179, left column). Not terrific, but not none. Here, en.wikipedia.org/wiki/Coronene coronene is claimed to dissolve well in ordinary organic solvents. While I agree with the big picture (the more C, the more difficult, e.g. some of the perylene dyes) I want to point out that occasionally there are some compounds not that dead precipitates (e.g., helicenes). $\endgroup$– ButtonwoodJun 23, 2020 at 17:39
1$\begingroup$ @Buttonwood From that wp article on Coronene : Centimeter-long crystals can be grown from a supersaturated solution of the molecules in toluene (ca. 2.5 mg/ml). Not what I would call "well soluble". ymmv ;-) 1mmol/L (.3g) in chloroform even much less. $\endgroup$– KarlJun 23, 2020 at 17:46
While you cannot directly make a suspension or dispersion of graphene nano-platelets from graphite, it is possible to perform very similar process, called exfoliation, on graphite oxide, as graphite oxide has functional groups decorating it that reduce the functional strength of the van der Waal's forces between layers.
The exfoliation process can create a dispersion of graphene nanoplatelets in an organic environment, however, outside energy is often (if not always) necessary to promote the exfoliation of the individual layers. Most often, this energy is provided by sonicating the solution.
A very quick search of suggests that this method has been shown to work using NMP, DMF, THF, and ethelyne glycol. (see Paredes, Villar-Rodil, Martínez-Alonso, and Tascón, 2008 for more info)
Because lots of weak interactions lead to large attractive forces
The reason why graphite (or graphene) won't dissolve in common solvents isn't to do with the nature of the chemical forces holding the layers together: it has more to do with the sheer number of such weak forces in each small flake of the substance.
Each hexagon has only dispersion forces to bind it into a solid crystal. Compare to benzene which has just a single carbon hexagon. Those forces between hexagons mean that benzene crystallises at around 6 C. Disrupt them even slightly (by adding a methyl group to give toluene) and the solid doesn't form until you have cooled the substance about 100 degrees. The forces are weak, but notable in their effect. Benzene is soluble or miscible with many organic solvents because you only have to disrupt single benzene-benzene interactions to get a solution.
So why are layers of graphite not soluble? The same forces that makes benzene crystallize at such a high temperature are present but, in each tiny flake, there are millions of hexagons in the same plane. When even a microscopically tine such flake interacts with another flake the total force between them will be millions of times stronger than the forces between benzene molecules. That is a lot of attractive force to overcome if you want to get a flake into solution. You can't overcome the hexagon-hexagon interactions one by one as you do for benzene, you have to disrupt the whole sheet all at once and that is monumentally harder than doing one hexagon at a time.