Surface Area and Pore Volume of Adsorbent

Example 1 Surface Area and Pore Volume of Adsorbent A... 

In addition to the pore structure, the most striking features of these novel materials are the large BET surface area and pore volume, which make this family of materials excellent adsorbents in many applications [16]. 

Unlike the thermal and hydrothermal stabilities, the mechanical stability seems less dependent on the nature of mesoporous materials. All materials gradually collapse with the increase of pressure, accompanied with the decrease of surface area and pore volume. Recent studies show that cubic SBA-1 and MCM-48 are more mechanically stable than hexagonal mesoporous materials such as MCM-41 and SBA-15. Hydrolysis of Si-O-Si bonds by water adsorbed onto the silanol groups under compression was found as the main reason for mechanical instability. Organically functionahzed materials are more hydrophobic than unmodified counterparts, and thus show enhanced mechanical stability due to the water repelling ability. " ... 

Adsorbent is characterized by its specihc surface area and pore volume, which are evenly distributed axially and radially in the column. (This assumption is equivalent to the assumption of column homogeneity.)... 

For the ACs the data are representative of the samples after heat-treatment at all three temperatures since during their fabrication these materials have already been treated at temperatures in excess of 850°C. However, for the alumina and clay samples the surface areas and pore volumes are shown after treatment at each temperature as these materials undergo various phase transitions that lead to sintering of the samples and shifts in their relative pore size distributions with heat-treatment. The particle size was determined from the corresponding MIP curve for the powder raw material. The Sbet in the case of microporous ACs should be considered as an apparent surface area due to the micropore filling mechanism associated with these materials [15]. The external area and micropore volumes were calculated from the slope and intercept of the t-plots of the corresponding isotherms. The total pore volume was taken as the amount of gas adsorbed at a relative pressure of 0.96 on the desorption isotherm, equivalent to a pore diameter of 50 nm. The mesopore volume was calculated from the difference in the total pore volume and the micropore volume. 

Table 1 shows the values for specific surface area, Sbet and volume of N2 adsorbed at P/P°=0.98, Vad, of the pillared samples and the raw material. All the pillared samples show a more developed porosity than the raw material (montmorillonite). The specific surface area and pore volume increase in all the pillared samples, but the increase is greater in the Al/La-pillared samples than in the Al-pillared sample. The increase in specific surface area was consistent with the expansion of the structure observed by XRD. The Al-Wy sample had a Sbet of 195 mVg while the AlLa-Wy-100 had a value of 349 m /g. 

The objective of this research work was to use the surface fractal theory to analyze the adsorbent from industrial sludge at various conditions. Effects of activated temperature, activated time and activated agent on the specific surface area and pore volume surface of adsorbents were investigated. 

Activated carbons are produced with a wide range of properties and physical forms, which leads to their use in numerous applications (Table 1). For example, their high internal surface area and pore volume are pertinent to their being employed as adsorbents, catalysts, or catalyst supports in gas and liquid phase processes for purification and chemical recovery. General information on the manufacture, properties, and applications of conventional activated carbons can be found in Porosity in Carbons, edited by John Patrick [I],... 

To follow the environmental law and to remove small but sometimes persistent concentrations of pollutants activated carbons seem to be the media of choice. They are relatively inexpensive, easily to obtain, and owing to their enormously high surface area and pore volume, they are able to remove and retain even traces of air and water pollutants. Activated carbons, due to their unique surface chemistry act not only as adsorbents but also as catalysts for oxidation of inorganic and organic species. Moreover, their surface can be modified and tailored toward desired applications. 

Activated carbons or carbon fibers are the most common materials nsed as adsorbents and catalysts. They are employed widely in both liquid and gaseous phases. This universality is due not only to their high surface area and high volume of pores, but also to the variety of chemical properties of their surfaces. Although for physical adsorption the porous structure is the most important feature, for reactive adsorption and catalysis the chemical environment plays an important role, provided that the structure is developed sufficiently for dispersion of active chemical species and for accommodation of molecules to be adsorbed or to undergo a targeted chemical reaction. 

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