I am using carbon dots synthesized from citric acid and glycine. The problem I am facing is the precipitation of the carbon dot solution after 2 days of dialysis. Is there any idea to optimize the time of dialysis or the volume of the carbon dots solution in the dialysis tube or maybe any other parameter which I am not aware of.
Dialysis membrane pore size: 500 to 1000 dalton.
Dear Abhishek Pathak..
In my opinion, precipitation may be due to the less solubility of pure CDs. Initially the crude product contains some molecular intermediates and/or ions along with CDs, which might stabilize the CDs dispersion. As the dialysis progress, these molecular intermediates will be replaced with water molecules and only CDs will remain finally.
Less solubility may be due to the presence of less polar and/or less number of functional groups on the surface.
Adjust the pH and check whether the precipitate becomes soluble or you can try dispersing it in other solvents
In addition to Rajkumar Bandi, I would like to add the following text.
Purification of CQD by dialysis is to remove residual precursors (if your are synthesizing CQD by bottom up method) or small molecular byproducts. A total of ~12 h of dialysis with occasional change of water (or whatever aqueous solution you are using for dialysis) is sufficient.
Dear Rajkumar,
As far as the solubility of pure CD is concerned, the CD solution was homogenous and having sufficient -OH groups on its surface which explain its hydrophilic nature. Dialysis at different pH levels has been tried but the results were more or less the same. I thought of using different solvent but the application of the synthesized CD is to carry out cell imaging and if I use organic solvents such as ethanol or toluene, it may end up in cell lysis.
Dear Saptarishi,
I agree with you but the problem is that how can we ensure the correct time for dialysis.
Different samples required different spans of dialysis.
The literature survey briefs up the dialysis time to be 2 days using 0.5 to 1 Kda MWCO membrane (with slight variation).
I believe this should not be treated as standard protocol.
I would appreciate it if you can provide a conceptual detailing on the dialysis time to obtain the pure CD.
PS: Thank you all for coming up with great logical implications.
Dear Saptarishi,
Could you please elaborate that how the fluorescence of the water (outside membrane of course) correlates with the purity of CD sample.
It's great to know that you actually have a customized HPLC method to purify CD. Please do share the doi of your paper.
Dear Abhishek Pathak
The crude product initially contains several molecular intermediates and/or ions in addition to CDs, which can help to stabilize CD dispersion. These molecular intermediates will be substituted with water molecules as dialysis progresses, leaving only CDs.
How can CQDs be purified if dialysis is not possible to purify carbon quantum dots?
Saptarshi Mandal
Sir, Can you please suggest to me which particular membrane will be useful?
I already use Himedia LA411, which was a failure. Looking for 500-1000 Da MCO membrane. Which membrane should I use?
You may see Article Are carbon dots worth the tremendous attention it is getting...
You may use dialysis membranes from Sigma Aldrich or Spectrum Labs within appropriate MWCO. Himedia LA411 have MWCO of 12-14 KDa which is usually larger for carbon dots..
Hi sir i am also facing problem in dialysis. Is your membrane gives the accurate results.
I am not getting TEM images of C dots even I did dialysis in 1000 Da MWCO(Sigma Aldrich). Surprisingly, I can see some fluorescence of the solution (carbon dot in water).
Dialysis helps in the purification of Carbon dots. Dialysis tubing with 1 Kda MWCO helps cut down the ionic impurities substantially. You might have to optimize the TEM imaging parameters such as voltage, magnification, and so forth.
What parameters have you defined for TEM image acquisition?
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