The effect of solution pH on bentazon uptake onto SFHAC was
examined at different pH ranges from pH 2 to 12 and is illustrated
in Fig. 6. The figure shows the amount adsorbed by SFHAC
decreases with increasing the solution pH. At the initial pH the
adsorbed amount was 25.75 mg/g then gradually increases with
increasing pH until pH 5 (33.62 mg/g) afterwards decreases and
finally at pH 12 it reduces to 8.72 mg/g. Actually, the interaction
between the SFHAC adsorbent and bentazon was mainly regulated
by the dissociation constant (pKa) value of the bentazon and the pH
point-of-zero charge (pHPZC) of the adsorbent