Yes the washing stage is the most difficult part of synthesizing GO. First, to get good result out of the wash, it is better if your synthesis method is improved Hummers, instead of Hummers or Modified Hummers. Read this article in case you didn't : D. C. Marcano , D. V. Kosynkin , J. M. Berlin , A. Sinitskii , Z. Sun, A. Slesarev , L. B. Alemany , W. Lu , J. M. Tour , ACS Nano 2010 , 4 ,4806 . Now to answer your question, since the maximum speed of your centrifuge is 5,000RPM, then you better use it at lower speed such as 500RPM for 30min to remove unwanted graphite and other large particles that precipitate, and keep the supernatant (the solution) for further wash.  The supernatant contains your GO and acidic staff, so wash it many times with enough distilled water by waiting until it precipitates naturally (by itself). Here keep the solid precipitate and remove the supernatant each time, to obtain a pH approx. =6 and above. Actually, this will take longer time. But if you manage to get ultra high centrifuge, run it in two stage: 1st run  it at 500rpm, and keep the supernatant; 2nd run it at 40,000rpm and keep the the precipitate.

Actuaaly filtering is the main problem......if there is any method then please suggest...it would be very helpful bcoz the filtering taking more than usual

centrifugation is the good method to wash, but what i am doing is first one or two times i washed with water in filter paper after second wash i am using centrifugation for further washing, usually i am discarding the supernatant but the rpm is very important if u have done with low rpm then u r GO may be present in the supernatant so use high rpm, atleast more than 4000rpm.

But I am guessing when u centrifuge it the unreacted graphite and graphene oxide will be settle at bottom. When u use 2 gms of graphite in the recipe you get a lot of brown sticky material. Is all of that graphene oxide or unreacted graphite? Isn't the GO supposed to stay in suspension unlike the graphite when you resonicate it? Is that the way to go to separate them? I mean in that case your supenatant would have the GO?

hari sir the amount of yield (GO) is depends upon our oxidation process,we will not get good yield from normal hummers method and modified hummers method , so if we prepare GO through these methods during centrifugation we will get more unreacted graphite at the bottom. improved hummers method is better to get good dispersion we can reduce the unreacted graphite from the GO.

Dear Hari,

The fine graphite powder was separated from large particles using a mesh. A different concentration of sodium dodecylbenzene sulphonate (SDBS) solutions was

prepared in millipore water, stirring it overnight. Graphite powder was dispersed in the SDBS solutions (in 25 ml cylindrical vials), followed by sonication for half an hour. The dispersed solution was left undisturbed for 24 h for the formation of unstable aggregates. After that, it was centrifuged for 90 minutes at 500 rpm. 15 ml, from the top of the vial was used after decantation.

You need not use filtration

I am totally agree with @p. Gnanaprakasam. When you're dealing with the process of purifying GO (washing with distilled water), you need a high speed centrifuge. I used 5000rpm and there's still GO left in the discarded supernatant. Plus, when u sonicate GO to make a GO dispersion, you need even higher rpm since 5000rpm won't do.

Centrifugation can basically solve the mentioned problem with a two-step approach. Step 1: at low speed centrifugation (500-1000 rpm), remove graphite flakes and multilayered GO, keep the supernant. Step 2: using high speed centrifiguration (10000 -12000 rpm), discard supernant. You can repeat Step 2 for 3-5 times with washing by distilled water or Milli-Q water. A about three-day dialysis can further be employed, if you want highly pure GO.

It is a common problem in GO synthesis by Hummers method. a possible way that I use is to transfer your synthesized suspension in separating funnel of 250 ml or of bigger capacity. Bigger the surface faster will be the setting down, and keep it aside for two days; after two days the bottom will be filled of GO suspension, now separate this layer from top layer by transferring the GO suspension slowly without mixing the upper one with lower layer in another separating funnel. Now if you want to wash it to make it Cl and Mn free, you can follow the same method or else you can proceed for Centrifuge, to collect the paste of GO you need to centrifuge it minimum at 9000 RPM for 15-20 min. and then you can convert it into powder form by evaporating the water.

in other way You can choose a dialysis membrane and just fill it, close the membrane at ends and leave it in a beaker containing warm water. Leave it for stirring. the benefit is that, you do not need to take care of washing and and use your time for other research work. You can also purchase a purify dialysis kit from sigma.In starting of reaction add some HCl (0.5-1M) .Hope answer will be helpful.

After extensivelly washing with HCl 1 mM, 1 g of GO can be dispersed in 200 mL of H2O with 2 mL of 27% amonium solution. Then centrifugation at 3500 rpm will result in a well dispersed GO in water.

I have prepared GO for the first time and I am unable to find clearwashing instructions using centrifuge, can someone please guide me? What speed is to be used and for how long?

P.S.-Max speed of my centrifuge if 5000rpm

Hope to hear back...

Yes the washing stage is the most difficult part of synthesizing GO. First, to get good result out of the wash, it is better if your synthesis method is improved Hummers, instead of Hummers or Modified Hummers. Read this article in case you didn't : D. C. Marcano , D. V. Kosynkin , J. M. Berlin , A. Sinitskii , Z. Sun, A. Slesarev , L. B. Alemany , W. Lu , J. M. Tour , ACS Nano 2010 , 4 ,4806 . Now to answer your question, since the maximum speed of your centrifuge is 5,000RPM, then you better use it at lower speed such as 500RPM for 30min to remove unwanted graphite and other large particles that precipitate, and keep the supernatant (the solution) for further wash.  The supernatant contains your GO and acidic staff, so wash it many times with enough distilled water by waiting until it precipitates naturally (by itself). Here keep the solid precipitate and remove the supernatant each time, to obtain a pH approx. =6 and above. Actually, this will take longer time. But if you manage to get ultra high centrifuge, run it in two stage: 1st run  it at 500rpm, and keep the supernatant; 2nd run it at 40,000rpm and keep the the precipitate.

 good answer Fatima Ahmad

I recommend Gizaw's answer

Best Regards

i am using centrifuge at 5000 rpm to separate the GO and material is sticked at the bottom how can i remove it easily

If centrifuge available at lab can only go up to around 3500 rpm, does it make sense that step 2 is carried out 3500 rpm but for a longer time?

Thanks for the information, I will definitely try these steps.

yes you can increase the time span but still some material will remain at this lower speed

Dear Zunair Arslan

You mean that some impurities can remain?

some of your material will also sustain in liquid at lower speed

Why is the rpm commonly used rather than g force? I am trying to decide on what rpm to use to separate the graphene oxide from the mixture, however, in literature only rpm is mentioned, and never the g force.

I know that g force depends a lot on the rotor (and consequently the volume used).