Pore structure aerogel

The aerogel-prepared metal oxide nanoparticles constitute a new class of porous inorganic materials because of their unique morphological features such as crystal shape, pore structure, high pore volume, and surface areas. Also, it is possible to load catalytic metals such as Fe or Cu at very high dispersions on these oxide supports and hence the nanocrystalline oxide materials can also function as unusual catalyst supports. Furthermore, these oxides can be tailored for desired Lewis base/Lewis acid strengths by incorporation of thin layers of other oxide materials or by preparation of mixed metal oxides. 

The pore structure of two types of catalyst support material were studied 7-alumina and silica aerogel. The alumina samples were commercial catalyst supports made in 1/8 inch diameter pellet form by Harshaw Chemical. Silica aerogels were prepared from silica gels synthesized by a two step acid/base catalyzed procedure employing TE0S with a water to silicon ratio equal to 3.7 [17] and ammonium hydroxide concentration of 0.005 M (sample A) or 0.01 M... 

Highly porous carbons can be produced from a variety of natural and synthetic precursors [11, 12]. Relatively inexpensive activated carbons are useful adsorbents, but generally their surface and pore structures are exceedingly complex [11, 13]. However, it is now possible to prepare a number of more uniform carbonaceous adsorbents. For example, molecular sieve carbons (MSCs) are available with narrow distributions of ultramicropores, which exhibit well-defined molecular selectivity [11], and carbon nanotubes, aerogels, and membranes are also amongst the most interesting advanced materials for research and development [12, 14]. 

BET adsorption and desorption is usually performed with liquid N2 and is a widespread technique for determining the specific surface area of porous materials [28]. In fact, only surfaces that are accessible to the N2 molecules are detected. The Kelvin equation correlates the curvature of the liquid surface with the applied partial pressure and pore size distributions can be derived [29]. However, this method is successful only for pore structures below about 20 nm. Thus, in aerogels with typical pore sizes in the 1—100 nm range, only a fraction of the total available pore space is detected. For an aerogel with a den-... 

Effect of heat treatment on pore structure parameters of carbon aerogels. Courtesy of Prof. Y. Yamada of Fukui Univ. 

Figure 8.1 An architectural model (left) and transmission electron micrograph (right) of an aerogel showing the nanostructured network and pore structure. (Left panel reproduced with permission from D. R. Rolison and B. Dunn, J. Mater. Chem. 2001, 11, 963. Copyright 2001 Royal Society of Chemistry. Right panel reproduced with permission from M. L. Anderson et al., Adv. Eng. Mater. 2000, 2, 481. Copyright 2000 Wiley-VCH.)...

In contrast, aerogels do not have an ordered pore structure or a narrow distribution of pores. While many see beauty in order, the disordered structure of aerogels may have significant advantages in terms of function (3, 4). Thus, because the pore size... 

The motivation for preparing conductive aerogels stems from the desire to be able to transport electrons through the nanostmcture (solid network). When coupled to the high surface area and interconnected pore structure, this architecture enables ions or molecules to be transmitted to the surface where they can be reduced or oxidized by the conductive network. For this reason, such materials are being explored for charge storage and electrocatalytic applications. 

The liquid is then removed by heating the gel in an autoclave to above the critical point, then releasing the pressure. In this way a liquid-vapor interface never forms, so surface tension forces never have an opportunity to collapse the pore structure. This method of production, while effective, is sufficiently expensive to have greatly inhibited significant commercial development of silica aerogels. 

Nanopore Structure Analysis. - MRI has provided direct visualization of gaseous xenon and methane in the void spaces of aerogels, offering unique information and insights into the pore structure and molecular diffusivities of occluded sorbates. Pore structure and sorption properties of silica aerogels... 

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