Re: How to get SiO2 paticles from ethanol suspension ?

From: Yung-Jen Lin (yjlin_at_ttu.edu.tw)
Date: 10/18/04 

Date: 17 Oct 2004 23:42:20 -0700

Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<416FEAE2.4436735F@hate.spam.net>...
> Yung-Jen Lin wrote:
> >
> > I made silica particles from TEOS (tetra-ethyl orthosilicate), which
> > was dissolved in plenty of ethanol and gelled by adding ammonia water.
> > The silica particles are spherical with < ~ 0.3 micrometer in diameter
> > and could suspend in ethanol for a long time. Previously, I was
> > patient enough to wait for 2-3 weeks to let it settled to the bottom
> > of the beaker. Then, I syringed away the clear solution in the upper
> > part and dried the bottom part in an oven to get the solid particles.
> > Recently, I have a strong feeling that there must be a better way. So,
> > I try.
> > Centrifuging is certainly a good way. Unfortunately, the machine is
> > broken at this moment.
> > Filtration is also possible. But it is quite slow because the
> > particles are so small. The filter membrane needs to have small
> > openings.
> > Adjusting the pH by adding nitric acid in order to manipulate the
> > electrical double layer and coagulate. But this seems not woking,
> > maybe because of the low dielectric constant of ethanol.
> > The last method occurs to me is to add some kind of polymer or
> > surfactant. But I do not have any idea of which kind.
> >
> > Does anyone have similar experience? What is the best way to get those
> > silica spheres out of ethanol? Thanks.
>
> Can you rotovap the suspension?
>
> Depends on the volume being processed. Adding benzene (not in the
> US!) or toluene and azeotroping out water and ethanol with a
> Dean-Stark trap (with a stop***) could be nice. The much lower
> density and viscosity of the organic solvent will facilitate isolation
> by settling, centrifugation, or filtration. Benzene freeze-dries
> exceptionally well. Will your particulates come along for the ride in
> the vapor stream?
>
> Benzene is mildy leukemogenic with chronic exposure. Good lab hygiene
> is implicit.
>
> A second possiblity is to have a low density low dielectric constant
> solvent miscible with ethanol like ether or perhaps cyclohexane. That
> should dump out the denser microspheres. On any large scale you would
> have to recycle solvent.

Thank you, Uncle Al. I will try rotavap. Using another organic solvent
in the process seems to cause more troubles.