Can ultra-sonication be considered as an effective method/treatment in order to increase the specific surface area of carbon powders (e.g. carbon nanotubes, graphene nanoplatelets, etc)?
Generally speaking, the answer is yes, but the effect may be low. Because agglomeration still means porosity, so the surface area should not decrease too much by this effect. But I agree with Khosro that the effect may be lost upon drying in normal conditions. For keeping the particles in a non-agglomerated state, I recommand freeze-drying, which will lead to an extremely low-density powder of highest surface area.
Alain
if you really want to increase the surface area of nanocarbon material, you may consider the drying condition (after ultrasonication). Actually i got improved surface area by controlling the drying environment.
Hi Nikolaos, as Khosro said, sonication can separate aggregated carbon nanomaterials, but you will have to include detergents like SDS to keep them separated after the sonication.
Generally speaking, the answer is yes, but the effect may be low. Because agglomeration still means porosity, so the surface area should not decrease too much by this effect. But I agree with Khosro that the effect may be lost upon drying in normal conditions. For keeping the particles in a non-agglomerated state, I recommand freeze-drying, which will lead to an extremely low-density powder of highest surface area.
Alain
Ultrasonication in air induces defects and oxygenated moieties on carbon surfaces the extent of which depends on operational parameters like time, power etc. DOI: 10.1021/jp2057699
I agree with Alain. It could increase the specific surface area. However, the most effective way of surface area increasing is keeping the micropores within the carbon powders. The specific surface area is strongly depends on presence of the micropores. Depending on particle size of the carbon particles, interstital pores formed between agglomerated particles will vary micro to meso region. So, if you use very fine particles of the carbon and ultrasonic them you may succeed.
This problem is closely related to the instability of anisotropic surfaces and interfaces under capillary, electrostatic, and elastostatic and dynamics forces, which was put into the sound theoretical basis by Ogurtani and his coworkers in recent years.[1-3] First of all, the stored elastic energy in elastic bodies can be released spontaneously ( i.e., positive rate of internal entropy production) in solids by generating surface ripples and undulations, which are counteracted by capillary forces! There is an optimal surface undulation wave vector KM=3(normalized with respect to the characteristic length), which has the maximum growth rate. Similarly, the upper bond of the instability range is KB=4, and below ,which long wave instability regime just starts to developed.[2] This limiting wave length is about 19 nm for 4.3 GPa in Ge/Si system. The critical length depends on the surface Helmholtz free energy density of the thin film linearly and it is also inverse quadratic function of the applied stress intensity.
Unfortunately, the ultrasonic wave length in graphite is in the range of about 106 nm. Therefore the surface undulations induced by the ultrasonic stresses are completely in the long wave instability range, and they can not sustain any stable surface morphology, they rather result surface cracks and finally catastrophic failure by decimation. Of course this also increases the surface area by fragmentation!!!!!
Dear All, many thanks for your answers & i really appreciate your correspondence. I am actually ultra-sonicating carbon powders dispersed in a acetone solution and then dry them at room temperature.
Hi Nikolaos, are you adding anything to your acetone ultrasonication solution that will prevent the carbon nanopowder constituents from reassuming their aggregated state upon drying?
Dear Steingrimur, i have not added any substance in the acetone solution. What could be added to be sure keeping the powder to a non-agglomerated state upon drying?
Hi Nikolaos, people usually uses SDS or deoxycholate and sonication to separate carbon nanomaterials. But that is in aqueous solutions. When you dry those solutions, you will have high concentrations of detergents, but the carbon material will be dispersed.
You will have to check how soluble these detergents are in acetone before you dry the mixture.
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