The N2 adsorption/desorption isotherms of the SSH activated
carbons measured at 77 K are depicted in Fig. 2. As can be seen, all
isotherms display an abrupt increase in adsorbed volume at a low
relative pressure. This is characteristic of type I isotherm that
represents microporous structure according to the classification of
International Union of Pure and Applied Chemistry (IUPAC) [24]. As
the relative pressure increases, all samples show increase of
nitrogen uptake, suggesting the existence of mesoporous structure.
When the relative pressure is greater than 0.4, an apparent
desorption hysteresis loop appears on the isotherms of S-3-
550 and S-3-650, confirming the high volume fraction of mesopore
in these two samples. Similar phenomenon has been observed by
Chang et al. [22] when they activated the hydrothermally obtained
carbon colloid nanospheres by ZnCl2. The enhancement of
mesoporous structure can be ascribed to the micropore coalescence
at higher ZnCl2/SSH ratio due to high release of volatile
matters from the precursor during activation.