The effect of pH for the adsorption of RB19 onto DAHbentonite
at 20 8C is shown in Fig. 1. It can be seen that the
adsorption of RB19 was pH-dependent. The results show that
the amount of adsorbed dye onto DAH-bentonite decreases as
the pH increases from 1.5 to 7 and after pH 7, a small increase in
adsorption is observed. This situation can be related to the
surface charge of the adsorbent. DAH-bentonite has negatively
charged adsorption sites, but it is positively charged at low pH
values. Therefore the electrostatic interactions between negatively
charged –SO3
groups in the dye molecule and the
positively charged adsorbent increase. As a result, the amount of
dye molecules onto the modified bentonite increases at lower
pH values.