Adding any anti- solvent like EtOH will help to precipitate the silica nanoparticles. Moreover, you can use centrifugation.

Adding any anti- solvent like EtOH will help to precipitate the silica nanoparticles. Moreover, you can use centrifugation.

You can try adding some salt to your solution of nanoparticles. But as Sagar suggested it would be better to use centrifugation since the salt-induced precipitation may not be reversible.

Thank you Sagar and Philips, Indeed I need a method to prepare large amounts so it is better to get a preciptate rather than a colloidal solution.

I have actually tried your suggestions before, but the strange thing that some times the method which gives me usually milky appearance give me precipitate !!!! so I can separate it easelly

You need to reduce the surfactants (if you are using any) or co-solvent (if you are using any). Good luck.

Thank you Halina, so what will they effect?

Also a change in pH, which will cause either a sticking to the container walls or an agglomeration effect.

Use Ethanole , and centrifugation for example 8000 rpm/8 min ..