I am doing a synthesis of gold nanoparticles preparation method by Brust et al. , to study its size variations by temperature control, and I have a question in one of the synthesis steps of the method: The DT-Au NPs are dispersed in toluene and precipitated by methanol to remove the excess DT and TOAB. Does that mean freely moving DT can be dissolved in methanol but it's a poor solvent for DT-Au NPs? Is that why they are being precipitated?
A paper relevant for my question is attached. Please refer to the experimental section of it.
here's my analysis on what I read (your answer is at the bottom but I have shared my thoughts from start till end in case it helps):
up until adding sodium borohydride the gold is in solution in its oxidized state (orange solution).
Once the sodium borohydride is introduced into the solution the solution turns black, sodium borohydride is a reducing agent and will reduce the gold from the dissolved solution state into its solid Au0. (I have not personally worked with Au nanoparticles in organic solvent but I think the Au NP may be formed in the organic toluene phase hence the lack of color as would be expected due to plasmon effect in aqueous solution)
DT, the capping agent is in solution, is also inside the solution to control the size of the nanoparticles
the solution of NPs and its clusters is rotovap'ed/heat treated to remove all solvents.
This is where your answer is at:
the black solid is dissolved into 30ml toluene 300ml methanol to dissolve excess DT and TOAB.
Dodecanethiol is soluble in methanol and toluene
TOAB from memory is soluble in toluene and not so much in methanol
DT capped AuNP is *hydrophobic and will also be partly soluble (or at lease dispersable) in toluene but considering only 30ml is used, you will most likely reach your solubility limit of DT-Au NP in the toluene phase hence the pricipitate of your DT-Au NP particles in methanol.
*DT-Au NP = hydrophobic because the thiol end is the part that binds to the gold nanoparticles and only the carbon chain is exposed
here's my analysis on what I read (your answer is at the bottom but I have shared my thoughts from start till end in case it helps):
up until adding sodium borohydride the gold is in solution in its oxidized state (orange solution).
Once the sodium borohydride is introduced into the solution the solution turns black, sodium borohydride is a reducing agent and will reduce the gold from the dissolved solution state into its solid Au0. (I have not personally worked with Au nanoparticles in organic solvent but I think the Au NP may be formed in the organic toluene phase hence the lack of color as would be expected due to plasmon effect in aqueous solution)
DT, the capping agent is in solution, is also inside the solution to control the size of the nanoparticles
the solution of NPs and its clusters is rotovap'ed/heat treated to remove all solvents.
This is where your answer is at:
the black solid is dissolved into 30ml toluene 300ml methanol to dissolve excess DT and TOAB.
Dodecanethiol is soluble in methanol and toluene
TOAB from memory is soluble in toluene and not so much in methanol
DT capped AuNP is *hydrophobic and will also be partly soluble (or at lease dispersable) in toluene but considering only 30ml is used, you will most likely reach your solubility limit of DT-Au NP in the toluene phase hence the pricipitate of your DT-Au NP particles in methanol.
*DT-Au NP = hydrophobic because the thiol end is the part that binds to the gold nanoparticles and only the carbon chain is exposed
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