Influence of Surface Oxides of Activated Carbons on the Adsorption of Surface-active Reagents

Abstract

The adsorption of surface-active reagents on activated carbons has been studied in order to clarify the effects of surface oxide of activated carbon on the adsorption of surface-active reagents.
Poly(oxyethylene)nonylphenyl ether (PO), octadecyltrimethylammonium chloride (OT) and sodium dodecylbenzenesulfonate (DB) were used after purification as nonionic, cationic and anionic surface-active reagents, respectively. Activated carbons with different amounts of acidic and basic surface oxides were prepared by evacuating an original activated carbon, having 1.34 meclig of acidic surface oxide, at various temperatures.
The surface oxides of activated carbon exhibited no effect on the adsorption of PO (Fig.2). The adsorption by the van der Waals force was dominant in the adsorption of PO. The increase in adsorption of OT due to the dissociation of strong acidic surface oxide was found above pH 4 (Fig.4). Therefore, the electrostatic force between dissociated strong acidic surface oxide and OT cation contributes to the adsorption of OT as well as the van der Waals force. The agreement between the amount of strong acidic surface oxides (Table 2) and the increase in the amount of adsorption of OT (Fig.5) reveals that each strong acidic surface oxide captures one OT molecule at nearly neutral pH. In the case of DB, the presence of acidic surface oxides suppressed the adsorption of DB by electrostatic repulsion (Fig.6).
The activated carbon outgassecl at high temperature adsorbed an additional amount of DB in an acidic region (Fig.7). This increase in the amount of adsorption seems to be due to the interaction between basic surface oxide and DB anion.