I am having problems in making completely dried QDs films. It always remains sticky. I think it is because of the excess organic ligands (Palmitic acid, TOP, Oleic acid). I purified the QDs by precipitating from hexane using ethanol four or six times. But I couldn't completely get rid off the excess organic ligands.
I am looking for some kind of ligand exchange procedures with other long alkyl chain ligands.
Chloride S-benzylthiuronium( BTC ) forms with carboxylic acids and sulfonic acids and their salts, hardly soluble, well crystallizing salts in aqueous ethyl alcohol, water. Mix the aqueous solution of BTC with quantum dots. Look will be a sticky layer or not. If not, wash the new salt with hexane. Experiment.
Best regards.
I think some scientists have used plasma to get rid of surface organic liquids from PbS QDs.
QDs surface modification strategies rely heavily on ligand exchange method like ion exchange resin.
Gowar,
You are quite correct - hydrogen peroxide plasmas, formed at low pressure, have indeed been used to both sterilize and clean inorganic surfaces. There are commercial firms offering this type of service.
As for removing the excess organic ligands without ligand exchange procedure:
You can try acetone induced precipitation (adding 1 or 2 parts acetone into the hexane or chloroform solution of the QD particles), and this operation will remove some of the physically adsorbed organics on particle surface.
You can also try vacuum annealing (300 or 400 Celsius degree, 1 or 2 hours), and this will remove some of the chemically bonded (such as covalently bonded) organics on particle surface.
Chengpeng Jiang,
could you refer any reading materials or references regarding the methods you mentioned?
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