We bought nanosized cobalt oxide and Fe2O3 powders but has aggregrated, how can we return it to nanosize ? What solvent should we sonicate it in?
it was a mistake to buy the powders. This should be done only when you want to use them dry or when manufacturer gives a procedure to redisperse them in solvents you need effectively. The problem is, you get the powders in highly aggregated/agglomerated form only. Mostly during storage material keeps on forming strong interparticle bonds. Instead of buying powders you should have bought nanoparticles stabilized in dispersion.
In addition to solvent you can also consider the method for dispersion. In some cases you need to input a lot of energy in order to disperse the particles properly, for example using a sonication probe. However, the sonication procedure might infleunce particle properties and promote dissolution, especially if you input a lot of energy.
See this paper for more info:
http://www.tandfonline.com/doi/abs/10.1080/10937404.2015.1074969#.Vw06ffmLS70
I usually do that using ethanol. I prepared suspensions of particle concentration of 0.025 wt.% and sonicated for 8 hours. I have prepared SiC nanoparticles, Si nanoparticle and iron oxide nanoparticles. when I spray them I found sometime single particle deposition. However, that may not indicate full dispersion, but for my application it is acceptable enough.
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