I have synthesized graphene quantum dots in high concentration sulfuric acid. After synthesizing, I tried dialysis with 1000 da dialysis bag, but most of the particles could pass the bag pores. Does any body have any facile chemical or physical solution to separate graphene quantum dots from sulfuric acid solution?
Erfan Salahinejad
I tried centrifuge for 30 minutes and 10,000 rpm. But there was no separation. I guess the particles are solved in solution.
Method 1:
I used 0.22 um corning PES filter membrane to filter water soluble GQDs, followed by freeze drying of this filter solution, again do the 0.22 um filtration. This obtained solution having highly conc. Solution of GQDs. In each filtration your removing most of salts fomed in Neutralization as well as the particles size above 0.22 um size. Followed, by dialysis of this obtained filter solution with 1000 or 2000 Da dialysis bags, u can get pure GQDs size less than 10 nm.
Method 2:
If you want to get the all GQDs. then add DMSO or DMF solvents to this water soluble GQDs (2:1 v/v ratio, DMF: water GQDs), you will get white precipate of GQDs with salts (sodium sulphate, if you add NaOH for Neutralization). You can just do either decantation or precipitation then collect semi solid/powered GQDs solution. Then add acetone/isopropanol/ethanol which have low boiling points solvents (need to select GQD insoluble solvents) to remove DMF and water content in this wet product. Repeat this step 3 times and remove all the impurities. After, one day you can get powered GQDs.
By using 0.22 um filter membrane and freeze drying of solution, you can remove most of the sodium sulphate salts and unreacted impurities.
By using DMSO/DMF solvents, you can get white precipate (sodium salts) and black ppt (GQDs).
Method 3:
You can also try column or flash chromatography with water and Acetonitrile (80:30) as a solvents ratio, to purify this GQDs.
From your question it seems you didn't neutralized your GQDs solution before Dialysis. IF so then you should make it neutral (pH=7), as the dialysis may degrade in acidic medium.
Also roughly 1000 Da refers to 1.3 to 1.5 nm pore size. thus certainly you will loose GQDs smaller then these, so its bit better if you use 500 Da.
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