Aerogel porous

Apart from obvious dry cleaning applications, potential applications of C02-based microemulsions include (i) printed circuit board cleaning, (ii) extraction of contaminants from soils, (Hi) cleaning of polymers, foams, aerogels, porous ceramics, and laser optics, (iv) regeneration of activated carbon beds or catalysts, and (v) the separation of dyestuffs from textiles. 

Natural fractals such as clouds, polymers, aerogels, porous media, dendrites, colloidal aggregates, cracks, fractured surfaces of solids, etc., possess only statistical self-similarity, which, furthermore, takes place only in a restricted range of sizes in space [1,4,16]. It has heen shown experimentally for solid polymers [22] that this range is from several angstroms to several tens of angstroms. 

Gel permeation chromatography (GPC) Technique that separates substances according to their molecular size and shape. Three classes of stationary phases are used aerogels (porous glass), xerogels (crosslinked dextran), and xerogel-aerogels (polystyrene). 

Fig. XVII-29. Nitrogen isotherms the volume adsorbed is plotted on an arbitrary scale. The upper scale shows pore radii corresponding to various relative pressures. Samples A, Oulton catalyst B, bone char number 452 C, activated charcoal F, Alumina catalyst F12 G, porous glass S, silica aerogel. (From Ref. 196).

Tamon H, Ishizaka H, Mikami M, Okazaki M. Porous structure of organic and carbone aerogels synthesized by sol-gel polycondensation of resorcinol with formaldehyde. Carbon 1997 35 791-6... 

Aerogels are highly porous materials where the pore sizes are truly on a molecular level, less than 50 nm in diameter. This gives a material with the highest known internal surface area per unit weight. The surface area of 1 oz. is equal to 10 football fields, over 1000 m in 1 g. 

Porous materials can be either open-pored such as a common sponge, or closed-pored such as the bubble-wrap packaging. Aerogels are open-pored materials such that unbonded material can move from one pore to another. 

Porous chalcogenide aerogels is another broad class of non-oxidic framework that prepared by template-free routes [71-73]. These materials possess a continuous nanostructured chalcogenide framework that is penetrated by a random network of nanopore channels. Because these high surface area structures are random and not exhibit long-range pore periodicity, such systems are outside of the scope of this review and will not be covered further. 

These porous solids obviously have very high surface areas, and they lend themselves naturally to service in catalysis. Palladium catalysts supported on alumina aerogels have been used successfully to remove CO and NO from automobile exhausts,13 and a V205/Ti02 aerogel is itself a catalyst for the selective reduction of NO to N2 and water by gaseous ammonia.14... 

The sulfate promoted transition metal oxides focussed considerable attention in recent years due to attractive catalytic properties. Most of the research carried out to date centered on sulfated zirconias,1 5 not surprisingly perhaps, as they exhibit the highest surface acidity (Ho <-16.04) among the members of this family of materials and appear to be able to initiate isomerization reactions in temperatures as low as 298 K. Far less interest attracted sulfated porous titanias, mainly owing to a lower surface acidity,6 although it may be a useful property in many catalytic situations. Thus closer inspection of the preparation procedures for sulfated titanias may be of interest, in particular as the reports on preparation and properties of these materials are scarce and we are not familiar with any work dealing with titania-sulfate aerogels. 

---