Porous structure total pore volume

If we assume a quasi-cylinder pore structure of the electrode material as in Fig. 1, an average effective pore radius r can be evaluated from the relationship r = 2V/A, where V is the total pore volume, and A is the total pore surface that can also be determined using the DFT method (see also [5]). Then the migration coefficients determined as shown in Fig. 5 can be plotted vs. the pr2 product - see, e.g., Fig. 7 for five electrodes, which were made of various porous carbons produced by Skeleton Technologies. 

The performance of a catalyst in industrial usage is likely to be determined by its pore structure, that is to say, by its total pore volume and its pore size distribution. In cases where the active phase is mounted on a porous support, its pore characteristics may affect the accessibility of the active phase to the reactants, as well as other features of the catalyst s performance. For these and other reasons it is important to have agreed and reliable procedures for the measurement of these and related quantities progress in this direction is surveyed in Section 11.1.4.7. 

Prepared iroin rayon several activated caiixm fibers (ACF) with difibient pore structure were used to remove Ci(VI) and/or Cr(lll) species fiom solutions. The a oiption experiments were carried out to determine the influence of ACF/solution contact time, pH, temperature, initial Cr(VI) and Ciflll) concentration on the efficiency of chromium ions removal by ACF. It was found that for ACF with total pore volume more than 0.4cm Vg the porous texture has no great importance for the amount of chromium retained. For all non-oxidized ACF the amounts of Cr species adsorbed and Cr(VI) reduced to Ciflll) after 48 h of ACF/solution contact are very close. At the beginning phase of ACF/solution contact the latent period of CtfVI) to Cr(III) reduction was observed. Oxidized ACF has lower adsorption capacity to Cr(VI) species and higher to Ctflll) ions in respect to non-oxidized ACF. The increase of initial CifVI) concentration increases the chromium species removal but the increase of pH and temperature decreases it. 

Pore Size Distribution. The pore structure is sometimes interpreted as a characteristic pore size, which is sometimes ambiguously called porosity. More generally, pore structure is characterized by a pore size distribution, characteristic of the sample of the porous medium. The pore size distribution/ ) is usually defined as the probability density function of the pore volume distribution with a corresponding characteristic pore size 6. More specifically, the pore size distribution function at 5 is the fraction of the total pore volume that has a characteristic pore size in the range of 5 and 5 + dd. Mathematically, the pore size distribution function can be expressed as... 

The morphologic characterization of the immobilized enzyme is important to correlate the biocatalyst performance with porous structure parameters. BET analysis, which is usually based on N2 isothermal adsorption at 77 K, allows determining the solid-specific surface area, total pore volume, pore size distribution, and mean pore diameter. It is not recommended for solids with a low specific surface area (<5 m g ). Table 2 shows the specific smface area, mean pore diameter, and total pore volume determined by BET for the pure sol-gel silica matrix having TEOS as the precursor and the same matrix with the encapsulated CGTase. 

Precipitation of the growing polymer from the initial solution of styrene and DVB in an inert diluent during crosshnking copolymerization results in the formation of a two-phase heterogeneous network, in which one phase is presented hy the highly crosshnked and rigid polymer, while the rejected diluent forms another phase. After removing the diluent, permanent voids remain in the copolymer beads. The total pore volume, and the inner surface area, S, are the major characteristics of the porous structure these are intimately related to pore size and pore size distribution. These parameters determine the practical apphcation frelds of the polymeric adsorbent resins therefore, a precise quantitative characterization of resin porosity becomes an important task. 

The relevance of the pore structure on the drug release rate from porous matrices is shown in table 2 and figure 2m For a wettable polymer such as the acrylic, the reduction in total pore volume caused by any process,... 

Upon addition of the ionomer the total pore volume increases, due to the formation of an additional intergranular porous structure. At the same time the... 

Pores are found in many solids and the term porosity is often used quite arbitrarily to describe many different properties of such materials. Occasionally, it is used to indicate the mere presence of pores in a material, sometimes as a measure for the size of the pores, and often as a measure for the amount of pores present in a material. The latter is closest to its physical definition. The porosity of a material is defined as the ratio between the pore volume of a particle and its total volume (pore volume + volume of solid) [1]. A certain porosity is a common feature of most heterogeneous catalysts. The pores are either formed by voids between small aggregated particles (textural porosity) or they are intrinsic structural features of the materials (structural porosity). According to the IUPAC notation, porous materials are classified with respect to their sizes into three groups microporous, mesoporous, and macroporous materials [2], Microporous materials have pores with diameters < 2 nm, mesoporous materials have pore diameters between 2 and 50 nm, and macroporous materials have pore diameters > 50 nm. Nowadays, some authors use the term nanoporosity which, however, has no clear definition but is typically used in combination with nanotechnology and nanochemistry for materials with pore sizes in the nanometer range, i.e., 0.1 to 100 nm. Nanoporous could thus mean everything from microporous to macroporous. 

In summary, textural parameters that are essential for the catalysts performance were prepared from variable combinations of CTAB/NH4OH/ H20 in the presence of co-surfactants, i.e. acetone and the light alcohols (MeOH, EtOH, PrOH). The resuts indicate that the porous structure of the materials thus obtained are maintained along the distinct TEOS and CTAB concentration ratios, even with the influence of diverse co-surfactants. Then, the textural properties of the mesoporosus MSS, measured by N2 adsorption, indicate a reproducibility of the textural properties, i.e. pore volume, mean pore size distribution and total surface area (Figure 15.8). 

---