Table 1 also shows the pHPZC values obtained. AC is relatively
acidic, compared to the other materials. This shows that
there are larger amounts of oxygen-containing surface groups on
NORIT C-GRAN, as confirmed by TPD (as a result of the phosphoric
acid activation of this commercial sample). A neutral surface was
observed on CNT, since there was no significant amount of surface
groups, as shown in Fig. 3. pHPZC for the xerogel was slightly lower
than that of CNT.