Micropore surface area from mercury porosimetry

Both deBoer s t-method and Brunauer s MP method are based on the assumption that the BET measured surface area is valid for micropores. Shields and Lowell, using this same assumption, have proposed a method for the determination of the micropore surface area using mercury porosimetric data. The surface area of micropores is determined as the difference between the BET surface area and that obtained from mercury porosimetry (see Section 11.5). Since mercury porosimetry is capable of measuring pore sizes only as small as approximately 18 A radius, this technique affords a means of calculating the surface area of all... 

Samples BET Surface Area (m. g" ) MIcroporous Volume from f-plot (cm. g ) Mesoporous Volume (V at P/Po=0.96 - Microp. Vol.) (cm. g- ) Macroporous Volume from mercury porosimetry (cm. g" )... 

The different pore volumes of the carbons and their corresponding activated carbons are compiled in Table I the micropore volume has been deduced from Nj (77 K) and CO2 (273 K) adsorption isotherms by use of DR equation (ref. 5) and the meso and macropore volume from mercury porosimetry. Table 1 also shows the Nj surface area deduced from BET equation and the CO2 surface area from DRK equation (ref. 5). Impiortant features related with these data are ... 

The pore size distribution (see Fig. 3) can be obtained from the mercury porosimetry data and the t-plot from N2 adsorption isotherms, using an active carbon with a very low surface area as a reference [13]. It was observed that the volumes of mercury intruded were very small. As a consequence, the volumes of meso (the largest ones) and macropores are low. Thus, the samples studied are mainly microporous, as already mentioned in the N2 and CO2 adsorption isotherm results. 

The average pore size of modem analytical HPLC packings is 100 A range 60-120 A. Figure 5 shows the internal surface area versus pore diameter for four commercial 5 im silicas with pore sizes ranging from 60 to 120 A as determined by mercury porosimetry (33). This technique can measure pore diameters down to 30 A, which is the upper limit of the size range for micropores. Note that the data in Figure 5 are biased toward the smallest pore sizes, which... 

In order to characterize the structure of RF and carbon xerogels, a combination of nitrogen adsorption (for micro- and meso-pores) and mercury porosimetry (for pore diameters from 7.5 to 150 nm) was used to obtain the BET surface area and pore volume (microporous and total) helium and mercury pycnometry were applied to determine the skeletal and bulk density. 

Porosity and pore-size distributions were determined by gas adsorption and immersion calorimetry, with the measurement of helium and bulk densities. Volumes of micropores were calculated using the Dubinin-Radushkevich (DR) equation (Section 4.2.3) to interpret the adsorption isotherms of N2 (77 K), CO2 (273 K) and n-C4H o (273 K). Volumes of mesopores were evaluated by subtracting the total volume of micropores from the amount of nitrogen adsorbed at p/p° = 0.95. The two density values for each carbon were used to calculate the volume of the carbon skeleton and the total volume of pores (including the inter-particle space in monolithic disks). Immersion calorimetry of the carbon into liquids with different molecular dimensions (dichloromethane 0.33 run benzene 0.37 nm and 2,2-dimethylbutane 0.56 nm) permits the calculation of the surface area accessible to such liquids and subsequent micropore size distributions. The adsorption of methane has been carried out at 298 K in a VTI high-pressure volumetric adsorption system. Additional techniques such as mercury porosimetry and scanning electron microscopy (SEM) have also been used for the characterization of the carbons. 

The commercial sample, spherical bead activated carbon, was supplied by Kureha Chemical Industry. This activated carbon is referred to as Kureha carbon, which has a total micropore volume of 0.56 cm g" and a BET surface area of 1300 m g . The detailed textural properties of Kureha carbon are reported elsewhere [9]. The pore size distribution was evaluated in terms of the simulation of the density hmctional theory (DFT) using the isotherm data of nitrogen adsorption at 77 K and relative pressures up to 0.2. Only micropores contribute to the total pore volume and surface area. This was further confirmed by mercury intrusion porosimetry, no significantly additional porosity was observed in the pore size range from 2 nm to 100 pm. So, the investigated adsorbent is a purely microporous material and its pore size distribution covers the range from 0.4 to 1.9 nm [9]. 

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