area of microporous materials it is easy to apply and is widely
accepted. To the calculations of the BET surface areas, denoted as
SBET, the same relative pressure p/p0 range of nitrogen isotherms
(0.05–0.2) was applied for all samples, where for liquid nitrogen at
77 K, p0 = 762
±
2 Torr. Within this partial pressure region the linearity
of 1/(V[(p0/p)−1]) versus p/p0 plot was satisfactory (R greater
than 0.997), where V is the volume of gas adsorbed at a relative
pressure of p/p0.
The total pore volume, Vp, was estimated from N2 adsorption
data as volume of liquid N2 at p/p0 equal to 0.99. The external
surface area, SE, was calculated with the use of the t-plot method.
CO2 adsorption at 273 K at subatmospheric pressures is used
to determine the volume of narrow microporosity. This method
is an adequate technique to complement the characterization of
porosity by N2 adsorption at 77 K, which is of special relevance for
the characterization of ACs with narrow porosity not accessible to
N2 at 77 K.