Porous molecular solids

If a Type I isotherm exhibits a nearly constant adsorption at high relative pressure, the micropore volume is given by the amount adsorbed (converted to a liquid volume) in the plateau region, since the mesopore volume and the external surface are both relatively small. In the more usual case where the Type I isotherm has a finite slope at high relative pressures, both the external area and the micropore volume can be evaluated by the a,-method provided that a standard isotherm on a suitable non-porous reference solid is available. Alternatively, the nonane pre-adsorption method may be used in appropriate cases to separate the processes of micropore filling and surface coverage. At present, however, there is no reliable procedure for the computation of micropore size distribution from a single isotherm but if the size extends down to micropores of molecular dimensions, adsorptive molecules of selected size can be employed as molecular probes. 

The solubility of contaminants in subsurface water is controlled by (1) the molecular properties of the contaminant, (2) the porous media solid phase composition, and (3) the chemistry of the aqueous solution. The presence of potential cosolvents or other chemicals in water also affects contaminant solubility. A number of relevant examples selected from the literature are presented here to illustrate various solubility and dissolution processes. 

Various nanoscale architecture can be designed, including solid spheres, hollow spheres, tubes, porous particles, solid particles, and branched structures (Table 2).To achieve such nanostructures, different fabrication methods are used depending on the types of material. The methods used for nanoscale assembly include molecular self-assembly, bioaggregation, nanomanipulation, photochemical patterning, molecular imprinting, layer-by-layer electrsostatic deposition, and vapor deposition. 

D.H.T. Spencer, The use of molecular probes in the characterization of carbonaceous materials, in R.L. Bond (Ed.), Porous Carbon Solids. Academic Press, New York, NY, 1967, pp. 87-154. 

High selectivity and difficulty of separation from products are two quintessential characteristics of soluble catalysts. Attempts to retain the catalyst selectivity and alleviate the separation (and corrosion) problems have resulted in the preparation of catalysts consisting of molecular species bonded to solid supports, The common supports are organic polymers and porous inorganic solids, which are discussed in turn in the next two sections. 

When fluids can seep through pores, interacting mechanically with the solid skeleton, the material is composed of more than one constituent thus we need to use a mixture theory in which we could clearly make out each part filled by different constituents on a scale which is rather large in comparison with molecular dimensions so we put forward a new continuum theory of an immiscible mixture consisting both of a continuum with ellipsoidal microstructure (the porous elastic solid) and of two classical media (see, also, the conservative case examined by Giovine (2000)). In accordance with Biot (1956), we consider virtual mass effects due to diffusion we also introduce the microinertia associated with the rates of change of the constituents local densities, as well as the one due to the deformation of the pores close to their boundaries. 

Sozzani. P. Comotti. 4. Simonutti, R. Meersmann, T. Logan, J. W. A porous crystalline molecular solid explored by hyperpolarized xenon. Angew. Chem.. Int. Ed. 2002. 39. 2695-2699. 

Fluids, molecular solids, and porous materials received more and more attention in the last few years. This is due to the continuous development of models and calculation methods (Stepanov et al. 2000 Paiziev 2000) supplying the possibility of a more accurate interpretation... 

Several groups, including ours, have obtained some success in developing porous organic molecular solids. A recent review article by Atwood and Barbour has summarized the current progress in engineering void space in organic van der Waals crystals, particularly for calixarene-based crystals. In this context, it is very important to briefly discuss the term porosity and its proper use. A recent feature article by Barbour has described three different kinds of porosity conventional porosity, virtual... 

Zeolite molecular sieves are crystalline, porous inorganic solids, typically aluminosilicates, with channel diameters ranging from 0.3 to 1.2 nm and beyond, and crystal sizes typically between 0.5 and 5 /im. If species are selectively adsorbed into the well-defined channel systems of zeolites, the sensor response can be made selective for those species, while larger molecules are only adsorbed on the outer surface of the sensor membrane. Furthermore, many zeolites show ion exchange capability which introduces numerous possibilities for intrapore modifications. 

Adsorption may in principle occur at all surfaces its magnitude is particularly noticeable when porous solids, which have a high surface area, such as silica gel or charcoal are contacted with gases or liquids. Adsorption processes may involve either simple uni-molecular adsorbate layers or multilayers the forces which bind the adsorbate to the surface may be physical or chemical in nature. 

Gel permeation chromatography, exclusion chromatography. gel filtration chromatography. A technique for separating the components of a mixture according to molecular volume differences. A porous solid phase (a polymer, molecular sieve) is used which can physically entrap small molecules in the pores whilst large molecules pass down the column more rapidly. A solvent pressure up to 1000 psi may be used. 

We have considered briefly the important macroscopic description of a solid adsorbent, namely, its speciflc surface area, its possible fractal nature, and if porous, its pore size distribution. In addition, it is important to know as much as possible about the microscopic structure of the surface, and contemporary surface spectroscopic and diffraction techniques, discussed in Chapter VIII, provide a good deal of such information (see also Refs. 55 and 56 for short general reviews, and the monograph by Somoijai [57]). Scanning tunneling microscopy (STM) and atomic force microscopy (AFT) are now widely used to obtain the structure of surfaces and of adsorbed layers on a molecular scale (see Chapter VIII, Section XVIII-2B, and Ref. 58). On a less informative and more statistical basis are site energy distributions (Section XVII-14) there is also the somewhat laige-scale type of structure due to surface imperfections and dislocations (Section VII-4D and Fig. XVIII-14). 

As a general rule, adsorbates above their critical temperatures do not give multilayer type isotherms. In such a situation, a porous absorbent behaves like any other, unless the pores are of molecular size, and at this point the distinction between adsorption and absorption dims. Below the critical temperature, multilayer formation is possible and capillary condensation can occur. These two aspects of the behavior of porous solids are discussed briefly in this section. Some lUPAC (International Union of Pure and Applied Chemistry) recommendations for the characterization of porous solids are given in Ref. 178. 

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