solvent : use Distilled/deionized water (if your CQDs are Citric acid/urea/l-cystein etc) based. such CQDs have hydrophilic nature and they show aggregation in organic solvents. But if your CQDs are based on organic precursors (di-amino benzene, thiobenzoic acid, etc), which are organic precursors, hence those CQDs are best dispersed in methanol or ethanol. To make the sample, Place the TEM grid on cellulose filter paper in a glass petri dish (plastic dish has too much charge), then drop cast your solution. all the extra solution will be absorbed by filter paper, then cover the top of TEM grid with other filter paper (to avoid the dust deposition) and place it in the oven at 70 degrees overnight, to completely remove the solvent.

Dilution factor: you can keep the concentration of solution around 0.05-0.5 wt%. but in any case, it should not exceed 1% by weight. At higher concentrations, the CQDs make a uniform film, hence difficult to see the individual CQDs.

Best Regards.

well , thank you vey much for taking your time to response. I have prepared gqd not cqd, will there be any difference? precursor is citric acid, and for other precursor is glucose. somewhere I read, for graphene quantum dot with this precursor they have used ethanol as solvent for some characterization..now bit confused.

graphene quantum dots are derived from graphene oxide via cutting (top down approach). Citric acid and glucose etc make CQDs... and for this type of CQDs, you can use water as a solvent.

I have followed top down approach to prepare graphene quantum dots, well, many thanks.

Water is a good diluent for citric acid based carbon dot. Add a very dilute solution on TEM grid and dry it at room temperature. You may further dry it in a vacuum desiccator. (I will never recommendnd to drying carbon dot in oven).

You may also need to check the perplexity in nomenclature associated with carbon dots.

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