Adsorption, nanoporous materials zeolites

In the past two decades, 129Xe NMR has been employed as a useful technique for the characterization of the internal void space of nanoporous materials. In particular, the xenon chemical shift has been demonstrated to be very sensitive to the local environment of the nuclei and to depend strongly on the pore size and also on the pressure [4—6], Assuming a macroscopic inhomogeneity resulting from a distribution of adsorption site concentrations, 129Xe NMR spectra of xenon in zeolites have been calculated, and properties such as line widths, shapes as well as their dependence on xenon pressure can be reproduced qualitatively. A fully quantitative analysis, however, remains difficult due to the different contributions to the xenon line shift. (See Chapter 5.3 for a more detailed description of Xe spectroscopy for the characterization of porous media.)... 

The attachment of molecules to the surface of a solid by adsorption is a broad subject. This chapter is focused on the adsorption of gases in high-capacity solid adsorbents such as active carbon or zeolites. These commercial adsorbents owe their enormous capacity to an extensive network of nanopores of various shapes (cylinders, slits) with specific volumes in the range from 100 to 1000 cm kg . Applications of adsorption exploit the ability of nanoporous materials to adsorb one component of a gas preferentially. For example, the preferential adsorption of nitrogen from air passed through an adsorption column packed with zeolite creates a product stream of nearly pure oxygen. 

Zeolites are erystaUine nanoporous materials with uniform nanosized pores (<1 nm) (Fig. 9.3). Selective permeation in zeolite membranes is based on molecular sieving and selective adsorption. Zeolite membranes have drawn attention as suitable membranes for DH applications due to their high thermal and chemical stability. When supported (Fig. 9.3), zeolite-based membranes also offer excellent mechanical strength, which is an important feature for DH applications. The permeation of single compounds in zeolitic membranes depends on the kinetic diameter of the molecule and size selectivity and they exhibit moderate selectivities to hydrogen. 

The past two decades have shown an explosion in the development of new nanoporous materials mesoporous molecular sieves, zeolites, pillared clays, sol-gel-derived metal oxides, and new carbon materials (carbon molecular sieves, super-activated carbon, activated carbon fibers, carbon nanotubes, and graphite nanofibers). The adsorption properties for most of these new materials remain largely unexplored. 

Molecular probes have already been used to characterize nanoporous materials, in term of pore size determination (gas adsorption) or surface chemistry investigation (use of polar probe molecules) [5]. In this paper, we describe a new methodology based on liquid chromatography in order to characterize the two kinds of mesopores discussed above. The results obtained so far on a highly dealuminated (Y, Zeolyst CBV780) and non-dealuminated (Y, Zeolyst CBV300) zeolites are reported. 

Compared with the traditional adsorbent such as activated carbon, zeolites, and silica gel, electrospun nanoflbers are good candidates for heavy metal ion adsorption due to its large surface area, tailored pore structure, good interconnectivity of pores, and potential to incorporate active chemistry or functionality on nanoscale [62,63]. Moreover, recycle is of great importance in the field of water treatment taking this aspect into consideration, the nanofiber-based adsorbents are more suitable compared with powdered nanoporous materials. 

Solvation behavior can be effectively predicted using electronic structure methods coupled with solvation methods, for example, the combination of continuum solvation methods such as COSMO with DFT as implemented in DMoF of Accelrys Materials Studio. An attractive alternative is statistical-mechanical 3D-RISM-KH molecular theory of solvation that predicts, from the first principles, the solvation structure and thermodynamics of solvated macromolecules with full molecular detail at the level of molecular simulation. In particular, this is illustrated here on the adsorption of bitumen fragments on zeolite nanoparticles. Furthermore, we have shown that the self-consistent field combinations of the KS-DFT and the OFE method with 3D-RISM-KH can predict electronic and solvation structure, and properties of various macromolecules in solution in a wide range of solvent composition and thermodynamic conditions. This includes the electronic structure, geometry optimization, reaction modeling with transition states, spectroscopic properties, adsorption strength and arrangement, supramolecular self-assembly,"and other effects for macromolecular systems in pure solvents, solvent mixtures, electrolyte solutions, " ionic liquids, and simple and complex solvents confined in nanoporous materials. Currently, the self-consistent field KS-DFT/3D-RISM-KH multiscale method is available only in the ADF software. 

This chapter discusses the fundamental principles for designing nanoporous adsorbents and recent progress in new sorbent materials. For sorbent design, detail discussion is given on both fundamental interaction forces and the effects of pore size and geometry on adsorption. A summary discussion is made on recent progress on the following types of materials as sorbents activated carbon, activated alumina, silica gel, MCM-41, zeolites, n -complexation sorbents, carbon nano tubes, heteropoly compounds, and pillared clays. 2001 Academic Press. 

In the case of alkane cracking, dispersion forces between the alkane molecules and the siliceous walls of the zeolites and perhaps other nanoporous crystalline and ordered materials are possibly the most important interactions for stabilizing adsorption in the cavities, since the proton affinity of alkanes is low [104] and the electrostatic interactions between the alkane and the adsorbent are negligible [97],... 

The different mechanisms that operate in the separation of gases have been previously described in Section 10.4.1. In pervaporation, the transport mechanism can be described by an adsorption-diffusion mechanism [74,114] similar to one for polymeric membranes [115]. However, it is necessary to consider that the specific interactions between the permeating component and the zeolitic material are different in zeolites. Moreover, the diffusion through the ordered zeolite nanopores is different than in the dense organic matrix. 

A series of CP syntheses on a nanometer scale fall into the category of template syntheses and are based primarily on adsorption of monomers within nanoporous templates. The concept is relatively simple Include the monomer of a well characterized CP, such as P(Py), within the pores of commercially available or easily synthesizable nanoporous matrices made of relatively inert material such as commercial polycarbonate or alumina membranes, or zeolites, then polymerize it chemically via introduction of an oxidant, or electrochemically. For the electrochemical polymerization, an electrical connection is made by metallizing the membrane pores and one side of the membrane. The result is conductive nanofibrils , of quaint scientific interest if not, at least from presently available knowledge, of immediate practical utility. 

Zeolites are crystalline nanoporous inorganic materials formed by TO tetrahedra (T=Si, Al, P, etc.), which show widespread applications in many industrial processes such as catalysis, adsorption, and separation [1-3]. In the 1940s, Barrer and Milton opened up the avenue to the synthesis of zeolites. Since then, there have been considerable efforts in the synthesis of new zeolite materials. Up to Jun. 2013, 206 types of zeolite materials have been identified by the Structure Commission of the International Zeolite Association (IZA), each of which has been named with a three-letter code [4]. Table 1 presents the new framework types approved since the 16th International Zeolite Conference (IZC-16) in 2010. 

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