Organic aerogels

Another focus was put on the melamine-formaldehyde system. Through a microemulsion templating sol-gel route [237], thermal conductivities of the samples slightly below 0.025 Wm K have been obtained [238]. Most recently, polyimide aerogels have been developed by NASA s Glenn Research 

Center the most attractive mechanical strong gels can reach up to 500 times stronger than the conventional aerogel with the similar low thermal conductivity 

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Figure 8. Multiscale organization of carbon aerogels imaged by TEM. Example of the Ca(OH)2 based organic aerogel (Resorcinol/Catalyst - 45) heated at 1050°C.

Pekala RW. Organic aerogels from the polycondensation of resorcinol with formaldehyde J. Mat. Sci. 1989 3221-7. 

Pekala RW and F.M. Kong FM. A synthetic route to organic aerogels-mechanism, structure, and properties. Revue de physique appliquee. ColloqueC4, tome 24, avril 1989. 

Organic aerogels, 1 750-752 Organically modified layered silicate (OMLS), 20 306, 307, 308 Organic archaeological materials,... 

Organic Materials. The sol-gel chemistry of organic materials is similar to that of inorganic materials. The first organic aerogel was prepared by the aqueous polyconclensation of resorcinol with formaldehyde using sodium carbonate as a base catalyst. 

Using alkoxides as precursors, carbon dioxide as tile drying agent, and a semicontinuous process the diying procedure became safer and faster. Introduction of organic aerogels. 

The recent developments in science and technology require a more exact control of structure/ nanotexture and properties of various materials, including carbon materials. In order to meet the requirements for carbon materials, various novel carbonization processes have been proposed. In relation to electrochemistry, the following processes have to be mentioned template method, polymer blend method, defluorination of fluorinated hydrocarbons, and carbonization of organic aerogels [99],... 

Aerojet has made organic aerogels with densities of 0.1-0.2 g/mL3 for use in insulators and capacitors.252 Transparent macroporous monoliths have also been made by polymerization of trimethylolpropanetrimethacrylate using toluene, ethyl formate, and other liquids as poro-gens.253 Poly(alkyl methacrylates) have good resistance to outdoor weathering and can be used in windows. 

The physicochemical surface properties of Cr-, Fe-, Co-, Ni-, and Cu-doped monolithic organic aerogels and their carbonized and steam-activated derivatives were also studied [42-44]. These samples were prepared by adding chromium nitrate or metal acetates to an initial mixture with an R/F molar ratio of 0.5 and an R/W molar ratio of 0.13. The amount of metal added was that required to yield 1 wt% of the metal in the initial solution. 

The surface morphology and pore texture of these metal-doped organic aerogels depended on the nature of the metal used, essentially because of... 

Carbnrization of the Mo-doped organic aerogel yielded a higher percentage of carbide phase with better dispersion than that of carbnrization of the Mo-doped carbon aerogel. 

Cn-doped monolithic organic aerogels were prepared by sol-gel polymerization of a resorcinol derivative containing an ion-exchange moiety with binding sites for metal ions with the aim of determining their structure [23,24] and electrochemical [26] and transport properties [25]. Thus, the potassium salt of... 

XPS stndy of the Cu-doped organic aerogel showed that both carboxyl and hydroxyl groups of the polymer repeat unit were involved in the chelation of Cu ions. After carbonization, the Cu-doped carbon aerogel contained 0.5 wt% K and... 

Similarly, Pt catalysts supported on carbon aerogels were used in the combustion reaction of toluene, o-xylene, and m-xylene [41,67]. Carbon aerogels were obtained by carbonization of an organic aerogel at 773 and 1273 K. Both samples were mesoporous, and their microporosity was equally accessible to N2 and CO2 at 77 and 273 K, respectively. Pt was deposited on both carbon aerogels by an incipient wetness technique using an aqueous solution of [Pt(NH3)4]Cl2. The supported catalysts thus obtained were pretreated in different atmospheres to obtain different mean Pt particle sizes. 

These authors used the term metal-doped carbon aerogels both in the title and throughout the text, although they were not in fact carbon aerogels because the organic aerogels were not carbonized, with the exception of that with Mn. The model compound chosen for the study was sodium j)tira-chlorobenzoate (pCBA). 

The Mn-doped organic aerogel enhanced ozone transformation into OH radicals, whereas Co- and Ti-doped organic aerogels were not active in this process. The mechanism operating with the Mn-doped organic aerogel was based on oxidation-reduction reactions on Mn surface-active sites ... 

In this process, oxidation of Mn(II) to Mn(III) and Mn(IV) resulted in the transformation of O3 into OH radicals. This capacity decreased with longer exposure, due to irreversible oxidation of Mn(II) to higher oxidation states. The pCBA oxidation rate increased in the presence of Mn-doped activated carbon aerogel compared to the Mn-doped organic aerogel, which the authors attributed mainly to the increase in surface basicity. The efficiency of the Mn-doped activated carbon aerogel to transform O3 into OH radicals was greater than that... 

Carbon aerogels were first synthesized by Pekala in 1989 through pyrolysis of organic aerogels [28,29]. They display three-dimensional random close-packed monolithic structure [30,31] of slightly overlapping carbon spheres (3 to 30 nm)... 

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