Nitrogen Sorption Measurements

The BET surface area and pore structures of the RF and carbon aerogels with different R/C ratios and RF mass concentrations are shown in Table 36.3. The surface area of carbon aerogels increases dramatically after pyrolysis, which is due to the creation of micropores as a result of evaporative loss of organic moieties. It is also shown that the micropore area of carbon aerogels decreases with the increase in density [60]. 

Sample series R/C ratio RF mass concentration (%) Density (kg/m ) BET surface area (m /g) Micropore area (m /g) Average pore diameter (nm) 

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As discussed above, hysteresis loops can appear in sorption isotherms as result of different adsorption and desorption mechanisms arising in single pores. A porous material is usually built up of interconnected pores of irregular size and geometry. Even if the adsorption mechanism is reversible, hysteresis can still occur because of network effects which are now widely accepted as being a percolation problem [21, 81] associated with specific pore connectivities. Percolation theory for the description of connectivity-related phenomena was first introduced by Broad-bent et al. [88]. Following this approach, Seaton [89] has proposed a method for the determination of connectivity parameters from nitrogen sorption measurements. 

Nitrogen sorption measurements were performed on a Quantachrome Autosorb 6B (Quantachrome Corporation, Boynton Beach, FL, USA). All samples were degassed at 423 K before measurement for at least 12 hours at 1 O 5 Pa. Mercury-porosimetrie has been measured on a Porosimeter 2000 (Carlo Erba Instruments) Scanning electron micrographs were recorded using a Zeiss DSM 962 (Zeiss, Oberkochen, Germany). The samples were deposited on a sample holder with an adhesive carbon foil and sputtered with gold. 

Nitrogen sorption measurements were performed by use of a Sorptomatic 1900 Turbo apparatus by Carlo Erba Instruments. All samples were degassed at 393 K before measurement for at least 24 hours at 10 mbar. The mercury porosimetry measurements were carried out on a Porosimeter 2000 apparatus by Carlo Erba Instruments. A contact angle of 141.3° for Hg was used. The samples were degassed at 393 K before measurement for 24 h. SEM of the porous glass membranes was carried out on a Phillips ESEM XL 30 PEG microscope. 

Table 1 gives some representative synthesis conditions, gel times, and architectural features of the resulting gels determined by small-angle X-ray scattering and nitrogen sorption measurements. 

Micropore volume, total and external surface data of the modified and parent zeolites determined by nitrogen sorption measurements are reported on Table 2 Micropore volumes decrease by more than 1/3 following modification of H-Y, whatever the grafting agent or the Si/Al ratio. Moreover, the modification of the amino- into 4-methoxybenzamido function further reduces the micropore accessibility. This could indicate an anchorage of the organic chain inside micropore system. 

Different n-alkoxysilanes with increasing hydrophobicity were employed as silica precursors. The porosity parameters as determined by nitrogen sorption measurements are summarised in table 2. 

Results of nitrogen sorption measurements on Vacac-doped gels. 

Liu, H. and Seaton, N. (1994). Determination of the connectivity of porous solids from nitrogen sorption measurements. III. Sohds containing large mesopores. Chem. Eng. Sci., 49, 1869-78. 

In view of possible commercial applications of rice husk silicas, e.g. as catalyst supports, their surface areas and porosities are important properties. Nitrogen sorption measurements of the three differently treated rice husk silicas show that these are porous materials with moderately large surface areas. The surface areas are, in detail 73 m /g for the calcined material, 75 mVg in the case of the material oxidized by Fenton s reagent and 51 m /g for the rice husks treated with Caro s acid. As the shapes of the ad- and desorption isotherms reveal (Fig. 3), pores ranging from micro- up to macropores are present. 

Fig. 1.6 Comparison of TEM images and nitrogen sorption measurements for SBA-15 template and the nitrogen-doped carbon replica. (Reproduced with permission Ref [33] Copyright 2010, John Wiley Sons Ltd)...

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