Adsorption density/isotherm linearity range

Nitrogen adsorption-desorption isotherms measured at 77 K with a Micromeritics ASAP 2000 instrument were used to obtain values of the specific surface area, Sbet, estimated from a linear section of adsorption isotherm, taking five points from 0.05-0.2 p/p range, and pore volume VpN2, determined from the amount adsorbed at p/po of about 0.98. Bulk density, pb, was determined from mercury porosimetry data afforded by Micromeritics Auto Pore 9220. The later quantity was used to calculate the total pore volume = VpN2 + Vmacropores using the expression Vt = l/pb-l/ps [7], where ps is skeletal density, taken equal to 2.2 g cm", i.e. density of amorphous silica obtained by the sol-gel method [8]. 

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