(320aa) Study on Zeta-Potential of Adsorbent in Aqueous Solution - Activated Carbon Adsorption System

It was examined how absorption was related to zeta-potential, adversely what kind of affect zeta-potential gave to electrical properties of adsorbent surface for absorption in particular. The zeta-potential for the phenol showed minimum at the pKa. On the other hand, there were a local minima value in the vicinity of pH6.5 and a minimum pH 8.5 for p-hydroxybenzoic acid. It is thought that there are two kinds of processes of H+ dissociating from carboxyl group and H+ dissociating from phenol-related hydroxyl group. Amount adsorbed at equilibrium decreased with increase of pH. The molecular species was adsorbed easily and adversely dissociation species decreases, because of promoting the dissociation of a weakly acidic electrolyte in solution decreases with increase in the pH. It is because the ion that wears the negative charge gathers in surroundings of the activated carbon particle by the concentration of ion species in solution increasing when the pH increases, and the absolute value of the zeta-potential was larger. Oppositely, the zeta-potential approaches zero because of increase of the concentration of molecular species and that of the ionic species that wears the negative charge when the amount of adsorption is large.