Making aerogels and cryogels, etching titanium dioxide
So when it comes to materials that are both very light and have lots of surface area, aerogels and cryogels hold the tops spots. Aerogel is made using
supercritical carbon dioxide to remove the solvent from a gel whereas cryogels are made by simply freeze drying the gels. Cryogels are a little more
dense but if done right, they can actually outpreform aerogels in some cases. For example, carbon/graphite aerogels. If you try and make a super
lightweight gel, you'll end up with something that has lots of surface area, but isn't very conductive. However, if you make a more dense gel, and
etch away some of the carbon, you end up with a foam that has lots of surface area, is lightweight, but is also much more conductive.
I've been spending a lot of time reading about the various kinds of gels but the ones that got me the most interested were the inorganic, non silica
aerogels. Turns out you can make aerogels out of pretty much any transition metal. Normally they use epoxides to act as the geling agent but I've read
a few papers that show that things like pyridine can also work as a gelling agent.
The plan, is to see if I can make a titanium dioxide aerogel from titanium isoproproxide and pyridine, replace the water with alcohol, then freeze dry
it to produce a cryogel. Because I'm going the cryogel route, I was thinking about etching it to lighten it up a bit. Though I'm not sure what would
work as a suitable etchant for titanium dioxide. For carbon aerogels, the best thing to use is molten sodium hydroxide under argon. I wonder if nitric
acid would work for the titanium gel. Would certainly be easier to use and I could dilute it as needed to adjust how fast the etching goes. But I'm
not sure if it'll etch properly.
Thoughts? Has anyone worked with cryogel/aerogels before? Has anyone tried gelifiying transition metal oxides?
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