Boiling point of organic ligands will be very low compared to Quantum Dots, can these organic ligands be removed by heating the film. Then what are the ways to do surface passivization if ligands are removed.
Boiling will likely cause aggregation. A possibility is to centrifuge the particles at fast rotations (>10000 rpm) and wash them several times to remove the ligands. The uncapped particles will be less stable and will aggregate with time.
In general there is not easy way of keeping the particles stable without some form of functionalization. Two main approaches is electrostatic and steric stabilization. For electrostatic it's typically citrate or other ligands. Steric involves capping with some polymer (typically PVK) or coating with inert SiO2 shell. It's all dependent on the final aim.
donot remove ligand, excange them
use for example S2-, dilute Na2S in DMF (0.1-0.5% in weight) , mix this solution with the QD in hexane and sonicate to induce phase transfer
trash the clear part and save the polar part, readd hexane to fusrther clear, the polar part and once settle remove it
trhen add ethanol to precipiate the particle, centrifuge and redispersed the fomed pellet in DMF
alternatively solid state ligand exchange work well, dip for 1min a film of QD in short ligand solution (EDT, S2-, Cl-) in ethnaol a,d then rince in pure ethanol
Can you provide me some sources to understand this ligand exchange process clearly( I am new to chemistry concepts).
Does this ligand exchange process effects the spectral properties of colloidal quantum dots? Can we theoretically calculate the amount of spectral shift caused by these ligands.
Thank You.
On general basis ligand exchange toxard short ligand leads to a small redshift
however for HgSe, the main effect is to change doping and change the relative ration on inter vs intraband absorption
for procedure regarding ligand exchange
solid state ligand exchange
A film of HgSe nanocrystal capped with dodecanethiol ligand is deposited by dropcasting a solution of nanocrystal dispersed into a 9:1 hexane octane mixture. Meanwhile Na2S or NaSH solid is mixed with ethanol at 0.5% in weight. The solution is sonicated to obtain clear solution. The nanocrystal film is dipped in this solution for 30s and rinsed in pure ethanol. The film is finally dried using Ar flow.
liquid ligand exchange
A few mg of Na2S are dissolved in 2mL of N-methylformamide. The solution is sonicated for 2min. In a test tube 1mL of the previous solution is introduced with 3mL of HgSe QD dispersed in hexane. The solution is strongly stirred and further sonicated. A phase transfer of the nanoparticle occurred and the polar phase turns dark. The non-polar phase is then clean three times by adding hexane and let the solution settled. The clear top phase is trashed each time. Finally 3mL of ethanol are added and the tube is centrifuged at 3000 rpm for 3min. the liquid is trashed and the formed pellet is dried under nitrogen flow, before getting redispersed into fresh N methyl formamide.
Sir One last question, How do you make sure sure that controlled doping of n=2 is made during ligand exchange process.
According to your paper : "Lhuillier, Emmanuel, et al. "Infrared Photodetection Based on Colloidal Quantum-Dot Films with High Mobility and Optical Absorption up to THz."Nano letters 16.2 (2016): 1282-1286"
Thanking You,
you do not
doping depend on size and surface chemistry
big qd are doped with way more than 2 electrons, even if it was not clear by the time of the NL paper
if you do not take to you ligand exchange you may loose all the doping
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