Pore Dubinin classification

Table 9.2 illustrates a convenient classification of porous solids by the characteristic sizes of their pores. This classification was originally proposed by Dubinin [114], and in 1972 it was officially adopted by International Union of Pure and Applied Chemistry (IUPAC) [7,53,58],... 

The individual pores in heterogeneous catalysts and in other porous technical substances may vary greatly, both in size and in shape. An important quantity is the width of the pores, e.g. the diameter of a cylindrical pore, or the distance between the sides of a slit-shaped pore. A classification of pores according to their average width was originally proposed by Dubinin [4] and has now been officially adopted by the International Union of Pure and Applied Chemistry [5]. 

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. ... 

Three groups of pores of different width, tv, were defined by Dubinin [9]. The classification, which was adopted in a revised form by the lUPAC [10], is as follows in micropores tv< 2nm in mesopores w 2-50nm in macropores IV > 50 nm. It also expedient [11] to subdivide the micropores into ultramicropores (iv < 1 nm) and supermicropores (iv 1—2 nm). However, all these dimensions are somewhat arbitrary and imprecise because the stages of pore filhng are dependent on the gas-solid system as well as the pore geometry [11]. Similarly, there is no precise definition of the currently popular term nanopore, which is often applied to a pore in the supermicropore or narrow mesopore range. 

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). 

Active carbons are associated with pores starting from less than a nanometer to several thousand nanometers. Dubinin proposed a classification of the pores that has now been adopted by the International Union of Pure and Applied Chemistry (lUPAC). This classification is based on their width (w), which represents the distance between the walls of a slit-shaped pore or the radius of a cylindrical pore. The pores are divided into three groups the micropores, the mesopores (transitional pores), and the macropores. 

Carbons may have closed and open pores with a large variety of dimensions from a few angstroms to several microns. In terms of structure, the pores in active carbons are divided into three basic classes [64, 67) macropores, transitional pores, and micropores. Pores are formed during the production of carbon (pyrolysis of its precursors), or can be formed by other means such as oxidation by O2, air, CO2, or H2O [64]. According to Dubinin s classification [64, 67], the radius of a macropore is in the range 500—20000 A, and its surface area can vary from 0.5 to 2 m g . ... 

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