I have synthesized oleic acid capped PbS quantum dots with absorption maxima of 950 nm (around 3nm size) and I am trying to do ligand exchange with other shorter carboxylic ligands such as myristic acid, decanoic acid or octanoic acid. I want to use a solution base ligand exchange. I'm wondering what is the best way to do this? I mean what concentrations of new ligand solution and PbS nanoparticles to use? How much time to mix them? and What is the mechanism for that?
Dear Hadi, You may try the solution based method or just disperse the quantum dots in the new ligand (about 5 mg/ml) and stir continuously at lower or RT overnight (or for 1 day). So if you insist on using the QDs already in OLA then you should know the concentration of the dots and relate that to the advised concentration for solid dots. This is one of the techniques, many others can be found in literature (publications) including the ones below.
S. Ananthakumar et al. Solar Energy 106 (2014) 151–158
P.Kalimuthu et al. Materials Chemistry and Physics 122 (2010) 380–385
Dear Hadi,
ligand is possible if you want them water soluble using thiolated ligand. as you are telling about sort chain functionalized alkanes u need high temperature. instead of using OA have u tried using these short chains. try these i thing it may work out. as there are reports of synthesis of QDs using these acids. if u want water soluble then try mercaptodecanoic acid.
If you plan to exchange ligands with similar head groups (here carboxylic acid), thus with similar affinity, you really need to flood you sample with the new ligands, with relatively high concentration, for long period of times, many times.
Look at: ACS Nano, 2010, 4 (2), pp 869–878 (here the replace OLA with oleylamine).
Each exchange step will occur according to a diffusive equilibrium, where you might exchange 80% during the first round, than 80% of what remains in the second round, and so on. You can monitor the removal of OLA through its C=C bond (FTIR), as the other acids you're using don't contain double bonds. However, the steric forces induced by the C=C and the long chain of OLA are what makes the particles stable in non-polar solvents. I cannot guarantee that your new ligands will prevent precipitation.
Good luck
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