Freeze-drying is probably the best way to separate the aqueous phase from the copper Nanoparticles. The working principle is based on freezing the solution and then reducing the surrounding pressure as to allow the frozen liquid to sublimate directly from the solid phase to the gas phase (without transitioning to its liquid phase).

It is a well-established technique, but you would need access to freeze-drying equipment.

Hi Akshaya,

Copper particles could be separated by dialisys also. For example, the copper particles could be kept in a  dialysis bag and then the solution filtered 

by a filter assembly with a 0.2 um naylon

membrane. Please see the attached article that may help.

Good luck!

Luiza

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I have tried freeze drying but after drying I kept it in a desiccator it went back to the liquid form. 

Dear Akshaya, this is very strange, after freeze drying there shouldn't be any liquid left!

Centrifuge your sample and discard the supernatant  Repeat the process 2-3 times and then dry the sample in oven. But drying temperature should be chosen carefully depending on the stability of the sample.

Centrifuge the copper colloid. Time and speed of your centrifugation will be depended on the particle size of your sample. Repeat the centrifugation for number of times with subsequent washing for removal of solvents and other impurities and dry it in vacuum dryer or desiccator. Please keep in mind, that rapid centrifugation also leads to oriented attachment of your particles and makes also clusters and aggreagates.

Centrifugation is the best choice.

You can convert copper nanoparticles from solution to powder form by lyophilization process.