Good answer by Sajjad.Also, based on the content of chemical functionalization of the graphene sheets ,the three carbonaceous materials have different  dispersion and conductivity properties .Graphene oxide quantum dots shows  low conductivity  and high solubility in comparison with the other two materials.

Dear Ayesha Saleem,

Graphene quantum dots (GQDs) represent single-layer to tens of layers of graphene of a size less than 30 nm and it is mainly composed of carbon. GQDs treatment via a strong oxidizer leads to production of  graphene oxide quantum dots which contain  hydroxyl and carboxylic acid functional groups in other word it is composed of carbon, oxygen, and hydrogen.reduced graphene oxide quantum dots is perty much the same structure but its oxygen, and hydrogen content stand some where between GQDs and graphene oxide quantum dots based on the reduction procedure.

Good answer by Sajjad.Also, based on the content of chemical functionalization of the graphene sheets ,the three carbonaceous materials have different  dispersion and conductivity properties .Graphene oxide quantum dots shows  low conductivity  and high solubility in comparison with the other two materials.

Very good answers so far but you can also think about how they were created. For example if you use a top-down approach (let’s say e-beam lithography) on CVD graphene and graphene oxide you will get graphene quantum dots and graphene oxide quantum dots, respectively. If you oxidize the former you’ll end up with graphene oxide quantum dots while the reduction of the latter will give you reduced graphene oxide quantum dots. Similar thing will happen with the bottom-up approach.

but my question is what is the difference between graphene oxide and graphene quantum dots. how can we conclude it with TEM images

Here you are all referring to the same materials resulting from the down-sizing of graphene oxide and/or graphitic materials to sizes (typically 1-10 nm) which consequently impart the phenomenon of quantum confinement. The 'oxide' and reduced terminologies are just what people use to refer to when surface groups (OH, COOH) are more than the others. In reduced GQDs, OHs, COOHs are depleted. In the GOQDs, these groups are more etc. Note, these groups may also affect the surface states of the GQDs, hence optical and chemical properties. So it makes sense to know the difference after all. Thank you!