[smf]

I have synthesised some gold nanoparticles (100-200nm) but am having a very difficult time removing them from their growth solution which contains DMF and PVP.

I tried centrifuging and even at low speeds the gold sticks to the centrifuge tube walls

I have tried diluting also in water and centrifuging and still no luck

the nanoparticles are fairly concentrated/ high yield.

Are there any tips on removing DMF/PVP.

The simpler the method the better, please

Thanks

[wildfyr]

Are they ligated with anything that would prefer water or organic solvent? Can you do a liquid/liquid extraction and get them to prefer one phase?

And PVP=polyvinyl pyrrolidone right?

One last question: Why can't you decant the supernatant while the gold sticks to the walls after centrifuging?

DMF can, with difficulty, be removed with vacuum. Its usually better to extract it. PVP is insoluble in acetone and ether, but precipitating it seems like asking for aggregation issues with the gold particles, especially since I assume the PVP is the stabilizing "ligand" for the particles.

[Enthalpy]

Could PVP (if it's the polymer) be destroyed to ease its removal? Like, cut in small debris?

[smf]

Are they ligated with anything that would prefer water or organic solvent? Can you do a liquid/liquid extraction and get them to prefer one phase?

And PVP=polyvinyl pyrrolidone right?

One last question: Why can't you decant the supernatant while the gold sticks to the walls after centrifuging?

DMF can, with difficulty, be removed with vacuum. Its usually better to extract it. PVP is insoluble in acetone and ether, but precipitating it seems like asking for aggregation issues with the gold particles, especially since I assume the PVP is the stabilizing "ligand" for the particles.

Thank you, I took your advice and removed the supernatant while the gold stuck to the walls and then just sonicated for a very long time. I have TEM later so I am hopeful that this will work. I have read online that liquid/liquid extraction would work to remove dmf but practically speaking would have little experience with doing so. My gold nanoparticles are not capped as far as I'm aware of the method so I am not sure how liquid-liquid extraction would work with them.

(I'm mostly a physicist/inorganic chemist with limited knowledge of organic chem!!)

Thanks again!

[wildfyr]

Liquid liquid extraction is just when you take two immiscible solvents (like chloroform and water) and separate the compounds in a mixture based on which solvent they prefer. In this case a little trial and error in choosing the organic phase would probably be necessary.
From my minor experience synthesizing nanoparticles, I think they are capped with PVP.

Enthalpy,
Unfortunately that would be very difficult. PVP is a free radically polymerized polymer so it is held together by C-C bonds. Quite drastic measures would need to be taken to break these bonds.

[Corribus]

Gold particles are notorious for sticking to tube walls, especially plastic. You say your gold particles are "not capped" but they must be capped with something, else they'd just clump together even without centrifugation. Have you tried any stabilizers, like citrate?

You may also try glass centrifuge tubes, since adsorption of gold to glass is weaker than to most plastics, as I understand.

[Enthalpy]

[Breaking the polymer] would be very difficult. PVP is a free radically polymerized polymer so it is held together by C-C bonds. Quite drastic measures would need to be taken to break these bonds.

I was thinking at drastic means, yes, because gold is quite inert (or at least solid gold is). Things like ozone or hot nitrogen oxides, that completely burn the PVP and DMF - reactive and diluted enough that the reaction proceeds at a temperature where gold doesn't get sintered.

What about a good dose of ionizing rays, in the presence of an oxidizer? At some point the polymer will be broken. This polymer doesn't look very resistant to ionizing rays. Reticulated polyethylene (heatshrink sleeves for electric cabling) is produced by irradiation and is affordable.

But for sure, I didn't understand what an acceptable final state is. Nanopowder in air? Or rather, a suspension in a different liquid?

[wildfyr]

Enthalpy,
If you totally destroy all the PVP, then suddenly the gold nanoparticles are not capped, and they will Ostwald ripen to reduce surface energy. Either polymers like PVP or PEG, or small coordinating molecules like citric acid or alkyl amines are used to stabilize nanoparticles against such aggregation behavior. They simply arent stable when "naked."

I'm sure she wants them to be suspended in either water or a volatile organic.

Corribus, I'm fairly sure the polyvinylpyrrolidone is the lingand/capping agent. Examples are plentiful in the literature https://www.sciencedirect.com/science/article/pii/S0167577X11006070

Sarah,
Perhaps you could change the "solubility"/aggregation/sticking behavior by doing a ligand exchange with something like dodecanethiol or dodecylamine if your centrifugation is unsuccessful.

[Enthalpy]

Thanks wildfyr, +.