Characterization of adsorbent-adsorbate interaction mechanisms on activated carbons

Adsorption is governed by the physicochemical properties of the adsorbent surface, the nature of the adsorbate and medium conditions. A complete understanding of the adsorption mechanisms will allow better utilization of this phenomenon. The primary objective of this research is to characterize the adsorbate-adsorbent interaction mechanisms on activated carbons. This was accomplished by characterizing the surface properties of activated carbons, and studying the specific and non-specific interactions of surfaces with two basic drugs. The effects of pH and ionic strength on fluoxetine adsorption were also examined.; Surface characterizations were attempted by Boehm titration, isoperibol calorimetry, pH-drift, FTIR, and XPS. Boehm titration was used to quantitatively determine the amounts of surface acidic and basic groups, which showed that these activated carbons are greatly different in the amounts of surface acidic and basic groups. Oxidation with H₂O₂ increased surface acidic groups and decreased specific surface areas. The heats of wetting in water and heats of neutralization with NaOH were measured using isoperibol calorimetry. The heat of wetting study indicated that all polar functional groups acted as adsorption sites for water.; Adsorption of procaine and fluoxetine by activated carbons was studied in vitro using a rotating bottle method. The adsorption mechanisms of these two drugs on the various surfaces were evaluated by correlating their adsorption capacities with the relative percentages of the various oxygen-containing surface functionalilities. For both drugs, the relative percentages of non-specific capacity were linearly correlated with the relative percentages of hydrocarbon, which indicated that the carbon basal plane acted as the hydrophobic interaction site. The adsorption studies showed that the primary adsorption sites for procaine are surface COOH and -OH. The surface COOH and C=O groups are the primary adsorption sites for fluoxetine. The adsorption capacities of Darco KB-B for fluoxetine increased with increasing pH from 4.5 to 8.4, with no significant change below pH 4.5. The adsorption capacities also increased with increasing ionic strength. The anion effect on the adsorption capacity of fluoxetine followed the order: $ClO-4>NO-3$ > Br− > Cl−.