In addition, the N2 adsorption on porous solids occurs in
ascending order to the pore size, i.e., pores with smaller diameters
are filled first than those, which have larger diameters [38]. This
fact justifies the large amount of N2 adsorbed at low pressure
ratios. According to the IUPAC (International Union of Pure and
Applied Chemistry), materials composed essentially of micropores
exhibit a isotherm profile of type I, which is also known as
Langmuir isotherm [39]. This isotherm shows an almost vertical
branch at low pressure regions, due to the easiness of N2
adsorption by micropores [38]. At higher pressure ratios, it can
be observed that there is an increasing in the amount of N2
adsorbed, which is related to the presence of mesopores in the
material, evidenced by the presence of hysteresis. In this region,
the isotherm behaves as one of type II. Similar behaviors were
described by other researchers, who used ZnCl2 as activating agent
in the synthesis of ACs [16,24].