Surface Area from the Isotherm

As hinted at in the previous section, if one can determine the amount of material in one monolayer of adsorbate, then the surface area can be calculated from this. One simply needs to know what the average cross-sectional area of the adsorbate molecule. The calculation is then rather simple. If is the number of moles of adsorbate in a monolayer and a the cross-sectional area of the adsorbate molecule, then the surface area, Aj, is given by [Pg.14]

The adsorption is a high-energy adsorption, such as on silica. [Pg.14]

The latter condition must be adjusted depending upon the adsorbate-adsorbent combinations. The BET equation is [Pg.15]

By plotting the quantity on the left of this equation versus PIP one can add the slope and intercept of this plot to obtain C and thus substitute this into either the slope or intercept expression to obtain n. The plot should be taken over the 0.05-0.35 PIP range as mentioned above. Beyond these values the linearity of the plot breaks down. (The sequence to derive this is to invert both sides of Eq. (2) and then multiply both sides by PIP. One might wonder why the latter operation was performed.) The most common adsorptive used is nitrogen and the value used for a is 16.2x10 ° m. [Pg.15]

Another method to determine the surface area comes from / theory. The values obtained by this method (as analyzed by Condon [13]) seem to agree with some other methods, such as the absolute method of Harkins and Jura [14] and the conclusions by Kaganer [15, 16], It also consistent with X-ray analysis for some porous samples. For a non-porous, single energy surface the following equation holds according to / theory [17] [Pg.15]

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