Classification of pores

Dubinin [13,14] classified pores into three categories, the boundary limits being modified slightly by lUPAC  

Mikhail and Robens [15] extended this classification to include 

---

Classification of pore sizes micropores, mesopores and macropores... 

The pore systems of solids are of many different kinds. The individual pores may vary greatly both in size and in shape within a given solid, and between one solid and another. A feature of especial interest for many purposes is the width w of the pores, e.g. the diameter of a cylindrical pore, or the distance between the sides of a slit-shaped pore. A convenient classification of pores according to their average width originally proposed by Dubinin and now officially adopted by the International Union of Pure and Applied Chemistry is summarized in Table 1.4. 

Table 16-4 shows the IUPAC classification of pores by size. Micropores are small enough that a molecule is attracted to both of the opposing walls forming the pore. The potential energy functions for these walls superimpose to create a deep well, and strong adsorption results. Hysteresis is generally not observed. (However, water vapor adsorbed in the micropores of activated carbon shows a large hysteresis loop, and the desorption branch is sometimes used with the Kelvin equation to determine the pore size distribution.) Capillary condensation occurs in mesopores and a hysteresis loop is typically found. Macropores form important paths for molecules to diffuse into a par-... 

The classification of pores according to their size (Rodriguez-Reinoso and Linares-Solano, 1989)... 

Until now we have mainly treated adsorption onto non-porous surfaces. In reality, most industrial and many natural materials are porous Textiles, paper, bricks, sand, porous rocks, food products, zeolites etc. We start our discussion with a classification of pores according to their size, which is recommended by IUPAC ... 

The classification of pores is also based on the difference in the types of molecular interactions controlling adsorption in the different groups. That is, in micropores, the overlapping surface forces of opposing pore walls are predominant in mesopores, surface forces and capillary forces are significant, while for the macropores, the contribution of the pore walls to surface forces is very small [15,19],... 

The upper limit of 2.0 nm for the micropore width was put forward as part of the IUPAC classification of pore size [4]. It now seems likely that there arc two different microporc filling mechanisms, which may operate at p/p° below the onset of capillary condensation the first, occurring at low p/p°, involves the entry... 

A feature of special interest for many purposes is the width of pores, e.g., the diameter of a cylindrical pore, or the distance between the sides of a slit-shaped pore. A convenient classification of pores according to their... 

The classification of pores according to their size, proposed by Dubinin, has been adopted by IUPAC (127, 128) the classifications are macropores (d > 2000-4000 A), mesopores (30-32 A < d < 2000-4000 A), supermicropores (12-14 A < d < 30-32 A), and micropores (d < 12-14 A). This classification system has proved useful and is used in the study of amorphous silica having different structural characteristics (4). 

A classification of pores based on pore sizes was proposed by the International Union for Pure and Applied Chemistry (lUPAC). As illustrated in Fig. 1, pores are usually classified into three classes macropores (>50 nm), mesopores (2-50 nm) and micropores (<2 nm) [1], Micropores can be further divided into supermicropores (with a size of 0.7-2 nm) and ultramicropores (<0.7 nm in size), Since nanotechnology attracted the attention of many scientists recently, the pore structure has been required to be controlled closely, a part of which will be explained in Section 5. Wlten scientists wanted to express that they are controlling pores in the nanometer scale, some of them preferred to call the smallest pores nano-sized pores, instead of micro/mesopores. 

Attaining an economic space-time yield (Equation 2.1-3) requires a sufficient number of active centers.This is achieved by having a large internal surface area in the form of pores. Table 2.1-6 lists the standard classification of pores according to their diameter. Methods for determining the pore size distribution and the mean pore diameter are mercury porosimetry and the BET method (see Section 2.1.3.3) [Kast 1988, Wijngaar-den 1998]. 

TABLE 5.3 Classification of pore formation in carbon materials... 

To satisfy the first requirement, the porous solid must have small pore size with a reasonable porosity. This suggests that a good solid must have a combination of two pore ranges the micropore range and the macropore range. The classification of pore size as recommended by lUPAC (Sing et al., 1985) is often used to delineate the range of pore size... 

Regarding joint ESC and lUPAC classifications of pores, ESC nanopores (d< 100 nm) can be divided into three types. The first one is narrow nanopores at R<1 nm (5 , Table 5.6) corresponding to micropores in the lUPAC classification of pores. The second is nanopores of middle sizes at 1 [Pg.626]

Estimation of the mesh size ( (Canal and Peppas 1989, Wallace and Rosenblatt 2003), assuming uniform hydrogel structure at a protein volume fraction Vj O.OS, gives =20-25 nm. This value is in the nanopore (in LSC classification of pores) range and mnch lower than the average pore diameter d. The difference between the d and values is due to structural nonuniformity of the CG hydrogel composed of thin pore walls (v2 =0.6-0.8 and <2-3 nm) and broad micro/macropores filled by water (V2,s 0). Consequently, the pore walls can be impermeable for proteins and other macromolecules. 

It is worthwhile to mention that Dubinin classification of pores in active carbons is not entirely arbitrary because it takes into account differences in the behavior of molecules adsorbed in micro- and mesopores. Although adsorption-desorption hysteresis is characteristic of mesopores, it has also been observed in the case of micropores at low relative pressures." This has been attributed to inelastic distortion of some micropores, resulting in trapping of the adsorbate molecules. Consequently, the accessibility of the micropore system has been found to be increased after a number of adsorption-desorption cycles. ... 

---