What is the best way to clean the quartz cells using for the UV-vis and PL measurements of quantum dots, such as CIS/ZnS, CdZnSe/ZnS, etc. We usually prepare the quantum dots using 1-Dodecanethiol (DDT), 1-Octadecene (ODE), Oleic acid (OA), and Oleylamine. Subsequently, the prepared quantum dots are centrifuging with ethanol and also with acetone. Finally, the residue is re-dispersed in chloroform.
For the measurements, we fill the quartz cell with chloroform and then we put few drops of the quantum dots solution. What is the the best way to clean the quartz cells from quantum dots.
Usually the specific quantum dots can be easily removed from the quartz cell (cuvette) if you wash it many times with toluene or chloroform (i.e. with a solute with similar polarity as that of the intrinsic polarity of the QDs along with their ligands). The problem starts if you let the solute to evaporate so that the dots get aggregated on the walls of the cell. A way to remove the aggregates is to use an ultrasonic bath. After this procedure you can try to perform a PL measurement and check if there are any residues.
Another process that you can follow is to wash the quartz cell with a very dilute solution of an acid like HNO3, but this may damage the cell.
Unfortunately I have not a plasma cleaner but as Dr Celzard mentions it is the best way to clean your cuvettes, if you have one.
If you want to be sure that any organic substance has to be removed totally from quartz, you should use a plasma cleaner, have a look there : http://www.plasma.de/en/index.html
It is totally safe for quartz, and no organic substance can survive the treatment, which is a kind of low-temperature burning in oxygen.
Alain
Usually the specific quantum dots can be easily removed from the quartz cell (cuvette) if you wash it many times with toluene or chloroform (i.e. with a solute with similar polarity as that of the intrinsic polarity of the QDs along with their ligands). The problem starts if you let the solute to evaporate so that the dots get aggregated on the walls of the cell. A way to remove the aggregates is to use an ultrasonic bath. After this procedure you can try to perform a PL measurement and check if there are any residues.
Another process that you can follow is to wash the quartz cell with a very dilute solution of an acid like HNO3, but this may damage the cell.
Unfortunately I have not a plasma cleaner but as Dr Celzard mentions it is the best way to clean your cuvettes, if you have one.
Unfortunately, we do not have plasma cleaner in our lab.
Nikolaos, I tried the ultrasonic bath before but I found it harmful for the quartz cells over the time as it will week the materials gluing their walls and get them easy to break parts. I do not recommend this technique at all. regarding solvents, can you please explain this sentence and give me some example to make it clear for me:"(i.e. with a solute with similar polarity as that of the intrinsic polarity of the QDs along with their ligands)"
As Nikolaos said, rinsing with chloroform (or whatever solvent you have used to disperse the QDs) right after use, followed by rinsing with ethanol or acetone, and finally DI-water is a good practice. However, if the QD dispersion was allowed to dry out, then follow the same procedure but then place the cuvettes in a bath of dilute nitric acid for a few hours, and then rinse extensively with DI-water to wash away the acid. In both cases, it is a good idea to finally dry them overnight in an oven.
Dear Abu,
QDs have an intrinsic polarity due to the inequalities of surface and volume charges, which are mainly attributed to the higher percentage of surface defects comparing to the defects on the volume of the QDs (CuInS2 QDs contain a lot of defects as being a trimer compound). So, in order to make the QDs solable to a certain solvent, the QDs need to obtain the same polarity with the solvent. This is possible to be achieved by attaching ligand molecules on their surface. So, the total polarity (or net polarity) of the QDs is the sum of the intrinsic polarity of the QD along with the polarity of the ligand molecules. That is why the QDs are not solable in all solvents but only to specific solvents. If you use a solvent with different polarity of the polarity of the QDs it will be very difficult to replenish them from the walls. That is why you need to use the same solvent in which the QDs were primary dispersed. Of course if the QDs are damaged and the ligand molecules have been destroyed then their polarity will have change and you will have to experiment with different solvents. I hope that the paper that I send you will help you (even though it is refered to CdSe QDs the basic idea is the same for CuInS2/ZnS QDs).
http://scitation.aip.org/content/aip/journal/apl/91/24/10.1063/1.2822399
@ Nikolaos
QDs are insoluble in organic solvents except specific ones, like e.g. acids for sulfides.
If it would be possible under mild conditions, dissolving the QDs would be the first choice.
Further, it is a 2 sided story. In principle they should be removed by solvents, e.g. aqueous, which more strongly interact with quartz than with the QDs, however, mostly a second solvent is needed to easily remove the layer of solvent wetting the quartz in first place if this is immiscible with the first.
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