Abstract
The adsorption equilibria of benzene derivatives (phenol, benzoic acid, nitrobenzene, and aniline), 1-hexanol, 1-butanol, 1-heptanoic acid, and valeric acid on carbon black in aqueous solutions were studied. The carbon black used as the adsorbent was Electronic Conductive Carbon Black (Lion Akzo Co.) treated with nitric acid (B) or hydrogen (C). The surface acidity of carbon black B was large, but that of carbon black C, small. The adsorption isotherms were in good agreement with the Freundlich-type isotherm. The amounts of organic compounds adsorbed increased with decreasing solubility in water. The amount of phenol adsorbed was very large and its solubility, large. To investigate the influence of the ionization of phenol, the amounts of phenol, benzoic acid, and aniline adsorbed on modified carbon blacks were measured for their solutions varying widely in pH. The amounts of phenol and benzoic acid adsorbed on carbon black C decreased with increasing pH, but the amount of aniline adsorbed onto it decreased with decreasing pH. Thus, the amount of phenol, benzoic acid, and aniline adsorbed decrease with an increase in the amount of adsorbate ionized. The pKa value of phenol was larger than those of other organic compounds. Consequently, it is thought that phenol is adsorbed specifically owing to its large pKa. The adsorption character of an organic compound can be predicted on the basis of its solubility and pKa.
