Thesis (Ph.D.)--Chulalongkorn University, 2008

Surfactant-modified adsorbents have been widely used for industrial and environmental applications. Surfactant aggregates adsorbed at the solid/liquid interface are capable of solubilizing organic solutes due to the partition of organic solute from the aqueous phase known as adsolubilization. The surfactants used in this study were linker-based surfactant system and extended surfactant which has propylene oxide group of intermediate polarity, inserted between head and tail of the surfactant molecule. The impact of linker-based and extended surfactant properties on admicelle formation and organic solute adsolubilization were evaluated through adsorption and adsolubilization and solubilization studies on positively charged aluminum oxide surface. While linker-based systems achieved a higher maximum adsorption than extended surfactants, the extended surfactants reached maximum adsorption at a lower aqueous surfactant concentration. The three organic solutes with varying the degree of polarity from high to low value including phenylethanol, styrene, and ethylcyclohexane were evaluated in solubilization and adsolubilization studies. The results are summarized by the extent of solute solubilization into micelle and admicelle, as captured through micellar partition coefficient, (Kmic) and admicellar partition coefficient (Kadm). The extended-surfactant-based micelle and admicelle system showed greater solubilization capacity than the linker-based system. For the high polarity solute (phenylethanol), the presence of propylene oxide group (PO) has a greater effect than the number of PO groups or the tail length, while for the low polarity solute (ethylcyclohexane) as the number of POs groups and the tail length increased, the adsolubilization capacity also increased. These results thus provide insights into linker-based and extended-surfactant-based admicellar systems and highlight the differences observed from admicelles based on conventional surfactant system. The comparison of adsolubilization capacity (Kadm) was lower than solubilization capacity (Kmic) due to the tighter packing density observed in the surface admicelles may have squeezed out the area where enhanced solubilization was experienced in micelles. The extended-based surfactant system demonstrated solubilization and adsolubilization enhancement and significantly lower desorption potential compared to the linker-based surfactant and conventional surfactant system. Thus, the surface modification by extended surfactants shows particular promise for treatment of groundwater and wastewater contaminated with organic solutes