https://web.iitd.ac.in/~arunku/files/CEL311_Y13/Adsorption%20Theory%20to%20practice_Dabrowski.pdf

Adsorption — from theory to practice

We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas‐liquid (capillary condensation), layering, liquid‐liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid‐liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.

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Phase separation in confined systems

The classification of adsorption hysteresis loops recommended by the IUPAC in 1984 was based on experimental observations and the application of classical principles of pore filling (notably the use of the Kelvin equation for mesopore analysis). Recent molecular simulation and density functional (DFT) studies of the physisorption of gases by model pore structures have greatly improved our understanding of the mechanisms of hysteresis and it is therefore timely to revisit the IUPAC recommendations. In this review, we conclude that there is no immediate need to change the IUPAC classification of physisorption isotherms and hysteresis loops. However, in the light of recent advances, we are able to offer a revised checklist for the analysis of nitrogen isotherms on nanoporous solids: this includes a carefully regulated application of DFT in place of a classical procedure such as the well-known Barrett-Joyner-Halenda (BJH) method.

https://journals.sagepub.com/doi/pdf/10.1260/0263617053499032

Physisorption Hysteresis Loops and the Characterization of Nanoporous Materials

Porosity plays a clearly important role in geology. It controls fluid storage in aquifers, oil and gas fields and geothermal systems, and the extent and connectivity of the pore structure control fluid flow and transport through geological formations, as well as the relationship between the properties of individual minerals and the bulk properties of the rock. In order to quantify the relationships between porosity, storage, transport and rock properties, however, the pore structure must be measured and quantitatively described. The overall importance of porosity, at least with respect to the use of rocks as building stone was recognized by TS Hunt in his “Chemical and Geological Essays” (1875, reviewed by JD Dana 1875) who noted:

> “Other things being equal, it may properly be said that the value of a stone for building purposes is inversely as its porosity or absorbing power.”

In a Geological Survey report prepared for the U.S. Atomic Energy Commission, Manger (1963) summarized porosity and bulk density measurements for sedimentary rocks. He tabulated more than 900 items of porosity and bulk density data for sedimentary rocks with up to 2,109 porosity determinations per item. Amongst these he summarized several early studies, including those of Schwarz (1870–1871), Cook (1878), Wheeler (1896), Buckley (1898), Gary (1898), Moore (1904), Fuller (1906), Sorby (1908), Hirschwald (1912), Grubenmann et al. (1915), and Kessler (1919), many of which were concerned with rocks and clays of commercial utility. There have, of course, been many more such determinations since that time.

There are a large number of methods for quantifying porosity, and an increasingly complex idea of what it means to do so. Manger (1963) listed the techniques by which the porosity determinations he summarized were made. He separated these into seven methods for …

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Characterization and Analysis of Porosity and Pore Structures

We present a review of experimental, theoretical, and molecular simulation studies of confinement effects on freezing and melting We consider both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) The most commonly used molecular simulation, theoretical and experimental methods are first presented We also provide a brief description of the most widely used porous materials The current state of knowledge on the effects of confinement on structure and freezing temperature, and the appearance of new surface-driven and confinement-driven phases are then discussed We also address how confinement affects the glass transition

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Effects of confinement on freezing and melting.

A new simple and rapid method to determine pore size distributions is described which employs a simple nuclear magnetic resonance (NMR) apparatus. The method exploits the depression of the melting point of a crystalline solid confined within a pore, which is dependent on the pore diameter. The melting point distribution is determined by analyzing the NMR signal as a function of temperature. The technique is demonstrated by application to porous silicas and is shown to give pore size distributions comparable to those obtained by the conventional gas desorption method for pore sizes in the range 5 to 50 nm.

Characterization of porous solids by NMR.

The characterization of porous solids by NMR.

A Stray Field Magnetic Resonance Imaging Study of the Drying of Sodium Silicate Films.

Broad-line magnetic resonance imaging has been used to monitor water transport in beds of industrial grade zeolite 4A. Diffusion profiles as a function of time have been obtained for a series of temperatures in the range 20--70 \ifmmode^\circ\else\textdegree\fi{}C. The dynamics is observed to be strongly non-Fickian. A model based on coupled diffusion equations for the vapor in the interparticle space and water within the particles has been developed and shown to be in good agreement with experiment. Values for the intraparticle water diffusion coefficient and the interparticle vapor diffusion coefficient, which can be obtained from the model, and their respective temperature dependencies are in good agreement with other published results.

E.G. Smith

Papers

Characterization of porous solids by NMR.

The characterization of porous solids by NMR.

A Stray Field Magnetic Resonance Imaging Study of the Drying of Sodium Silicate Films.

Water diffusion in zeolite-4-a beds measured by broad-line magnetic-resonance-imaging

NMR studies of electrophoretic mobility in surfactant systems