Preparation of Carbon Aerogels

R/C ratio RF mass concentration (RF wt%) Linear shrinkage (%) Mass loss (%) References 

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Perez-CabaUero F, Peikolainen A.-L, Uibu M, Kuusik R, Volobujeva O, Koel M (2008) Preparation of carbon aerogels from 5-methylresorcinol-formaldehyde gels. Micropor Mesopor Mat 108 230-236. 

Wu, D., Fu, R-, 2008. Requirements of organic gels for a successfiil ambient pressure drying preparation of carbon aerogels. 

It is less well known, but certainly no less important, that even with carbon dioxide as a drying agent, the supercritical drying conditions can also affect the properties of a product. Eor example, in the preparation of titania aerogels, temperature, pressure, the use of either Hquid or supercritical CO2, and the drying duration have all been shown to affect the surface area, pore volume, and pore size distributions of both the as-dried and calcined materials (34,35). The specific effect of using either Hquid or supercritical CO2 is shown in Eigure 3 as an iHustration (36). 

Other materials that can be used for preparation of rigid aerogels are carbon [44] and aluminium oxide [45]. 

The effect of carbon aerogel pore texture and method of preparation of the supported Pt catalysts on their activity has recently been reported [85]. Two different Pt precursors were used H2[PtCl6] and [Pt(NH3)4](OH)2. For a given Pt precursor, the pore texture of carbon aerogels used had no influence in Pt surface area and ORR activity. The best ORR specific activity was obtained with catalysts prepared with H2[PtCl6]. By contrast, the activity of catalysts prepared from [Pt(NH3)4](OH)2 was low, despite the fact that the Pt dispersion value reached was the highest. These authors [85] indicate that this is probably due to the particle size effect on ORR activity, with a smaller Pt particle size showing a lower activity. 

Mesopores of carbon aerogels have possibility for reaction field and thereby carbon aerogels can be applied as template for production of new materials. Thus, carbon aerogels were used as a template for the preparation of highly crystalline zeolites (ZSM-5 and Y) with uniform mesoporous channels [162,163]. 

Shimoyama, Y, Ogata, Y, Ishibashi, R., and Iwai, Y., Drying processes for preparation of titania aerogel using supercritical carbon dioxide, Chemical Engineering Research and Design, 88, 1427-1431, 2010. 

Tang Q, Wang T (2005) Preparation of silica aerogel from rice hull ash by supercritical carbon dioxide drying. 

Bryning et al. [25] have reported the preparation of carbon nanotube aerogels, reinforced with polyvinyl alcohol. These materials conduct and have structural integrity, and show promise for sensing applications. 

Table 36.1. Types and characteristics of carbon aerogels prepared with different organic sources...

Scheme 2. Preparation of carbon structures in silica aerogels...

Li, J., Wang, X., Huang, Q., Gamboa, S., Sebastian, P.J., 2006. Studies on preparation and performances of carbon aerogel electrodes for the application of supercapacitor. Journal of Power Sources 158 (1), 784—788. 

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