Adsorption of Organic Compounds on Surface-Modified Activated Carbons in Aqueous Solution

Abstract

Influence of surface chemical properties on adsorption of organic compounds on activated carbons in the aqueous solution was investigated. In order to detect the large influence, activated carbons with large different chemical properties and with little change in pore-size distribution were prepared by oxidation treatment with nitric acid or by reduction treatment with hydrogen. The adsorption behaviors of nonionic, anionic, and cationic compounds on these surface-modified activated carbons were examined and the following results were obtained.(1) The adsorbability of nonionic and anionic compounds decreased with an increase in surface acidity of the activated carbons.(2) The adsorbability of cationic compound decreased in the low acidity range but the adsorbability increased in the high acidity range.(3) The influence of surface acidity on adsorption increased with an increase in the solution pH.(4) The hydration water around the surface acidic groups disturbs a hydrophobicmolecule contact the hydrophobic surface of activated carbon, consequently decreases the adsorption.(5) The acidic groups on activated carbon surface dissociate into anions in high pH, the surface anion groups depress the adsorption of anionic compounds by electrostatic repulsions and promote the adsorption of cationic compounds by electrostatic attractions.