Hi there,

As I under stood from your question that you have used Modified Hummers method to synthesize GO. Hence the solution what you get after oxidation is a combination of GO powders in dil. sulphuric acid and the contamination are Mg, , Na, those are used as solvent and oxidizing agents respectively. So first of all you filter that solution, followed by 200 ml of 30 % HCl washing. In this step all the metal ions will be converted to the corresponding chloride salts.  Then you wash with distilled water for for several times to remove the chloride contamination. To check the complete removal of chloride ions take the drop of the filtrate and add it to silver nitrate solution if no white color appears then it is clear that all the chlorides are removed. Finally you wash with 200 ml of ethanol to get the dry brown color GO powder. Also see the attached paper that will give you a clear idea about the washing step given in the experimental section. Hope this will help you. Cheers. 

Usully, GO can be washed using HCl and DI water with vacuum filtration.

When the degree of oxidation of GO is high, GO present very good hydrophilicity, vacuum filtration may could not drew water out from GO suspension. In this condition, we used centrifuge to remove the acid solution.

What's more, we also used dialysis to purify GO.

After graphite oxidation You have to remove potasium, manganium and sulphuric acid. Final concentration of impurities depends on the application of graphite oxide. First, depending on the graphite flakes You used, try filtration (bigger flakes) or centrifugation. For final cleaning You can use membranes – dialysis. If You plan to produce larger quantities of GO, crossflow filtration on nanofiltration membranes does the job. Sonication is rather used to separate flakes from each-other. We don't use HCl

Avoid the filtration step! Perform centrifugation and use diluted HCl. 

I agree with other friend  and i'm suggest use diluted HCl at first step then in next step use centrifugation.

depending on the lateral size and oxidation degree of lamellae, during filtration you might observe the formation of a hydrogel or, generally speaking, an extremely viscous slurry, thus dramatically increasing the difficulties related to work-up. See also: 

Article A novel approach to prevent graphene oxide re-aggregation du...

Article A rapid and eco-friendly route to synthesize graphene-doped ...

Data Synthesis and self-assembly of a PEGylated-graphene aerogel

Article Synthesis of a Fluorinated Graphene Oxide-Silica Nanohybrid:...

We use dilute HCl washing step,vacuum filtration and ultrasonication. Another approach we observed that the effect of electrophoresis of GO without supporting electrolyte  can separate GO.

If it is after deposition, a possibility will be using annealing on your samples, but it depends also from your substrate. You can find more information in this review:

"Graphene oxide: from fundamentals to applications" (http://dx.doi.org/10.1088/0953-8984/27/1/013002). I hope it helps.

thank you for all the answer.. i want to ask. 

is it the production after washing is powder or solution?

Hi there,

As I under stood from your question that you have used Modified Hummers method to synthesize GO. Hence the solution what you get after oxidation is a combination of GO powders in dil. sulphuric acid and the contamination are Mg, , Na, those are used as solvent and oxidizing agents respectively. So first of all you filter that solution, followed by 200 ml of 30 % HCl washing. In this step all the metal ions will be converted to the corresponding chloride salts.  Then you wash with distilled water for for several times to remove the chloride contamination. To check the complete removal of chloride ions take the drop of the filtrate and add it to silver nitrate solution if no white color appears then it is clear that all the chlorides are removed. Finally you wash with 200 ml of ethanol to get the dry brown color GO powder. Also see the attached paper that will give you a clear idea about the washing step given in the experimental section. Hope this will help you. Cheers. 

This link will surely help you,

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

ultrasonic

I agree with

Andrea Maio

@ Yashabanta Narayan Singhbabu please, is there another method to test

the Chloride Ions removal using another thing than Silver Nitrate?

I recommend Dheeraj's answer

Best Regards

What kind of filter paper or membranes is used to filter off and rinse the graphene oxide please?

I have tried with PTFE membranes and filtered under vacuum, but it did not work.

Normal, cellulose filter papers do not work either, since the solution is acidic and the filter paper literally 'melts' once it is in contact with the acidic solution.

@Maria PTFE should work, it resists to acids but it maybe too slow if the filter pores are small. If you want to use the regular cellulose filter papers, first dilute GO solution by adding a lot of DI water then allow it to sediment several hours/days depending on your GO sheets size. Later, get rid of the acidic solution above and filter the GO solution settled down. Because of GO gelatin behavior, its washing through filtration is too tedious, thus either sedimentation or centrifugation is preferred.

Zineb Benzait Many thanks for your suggestion. What kind of PTFE? I used a PTFE membrane/disc filter, placed in a buchner funnel and vacuum filtered it. The mixture managed to pass through. I was thinking of using the PTFE syringe filters, however it would take ages to finish.

Maria Magro Actually I used 0.22 um PTFE membrane filters not for GO washing but for the preparation of GO free-standing films as a lot of researches do. The process is slow and takes 24-72 h (depending on sheets size) to filter only 20 ml diluted solution (has around 20 mg GO), thus it may not be practical for GO purification unless you produced only a small quantity.

For your problem (the mixture passes through), if you used the PTFE with the mentioned pores size (0.22 um), it means that it is not due to the filter paper type but to its diameter. The paper should be smaller in diameter than the base of Buchner (but it must cover all the holes) and should sit flat on the bottom of the funnel with no creases or folds (i.e. not folded up at the edges). Before starting, it is also useful to moisten the filter paper with a little water to adhere the paper to the funnel so your solution will not escape. check this file or more practical information concerning filtration:

www.chem.ucalgary.ca/courses/351/laboratory/filtration.pdf

If you want to finish quickly the washing/purification step, just use the centrifugation method. But if you don't have a centrifuge, diluting GO solution by adding a lot of DI water then allowing it to sediment maybe more practical than filtering directly the first strong acidic solution.

By the way, there is a group who proposed to use tap water instead of DI water just in the first washing cycle, because dissolved ferric salts in tap water reverse the colloidal suspension of GO and help it to aggregate faster, the sediment was then dried and powdered then introduced to the washing cycle of HCl, ethanol and DI water, which minimized the filter clogging due to GO gel-like behavior. Here is the article which mentioned this method Conference Paper Graphite Oxide Post-Synthesis Processing Protocols

and here is a video explaining it: https://www.youtube.com/watch?v=HICuva__6Q4

Besides, some groups mentioned the use of dialysis membrane which maybe practical (no efforts), just put your GO inside the dialysis membrane/tube and dip it in DI water for a week (with regular water changing (either using an automatic system or manually).

Zineb Benzait Thank you so much for your detailed answers!

Novel methods for fast purification of as-prepared GO without pre-treatment was developed using commercially available hollow-fibre dialyzer (Phylther-1.7 m2). The dialyzer can be used several times in a crossflow filtration or dialysis process in the designed systems without deteriorating. The concentrations of impurities in GO suspension were monitored during purification process by measuring the ionic conductivity of the GO suspension