Competitive solubilization of naphthalene and pyrene in various micellar systems

Cosolubilization of polycyclic aromatic hydrocarbons (PAHs) (naphthalene and pyrene) has been studied in surfactant systems of varying nature of their head-group viz. nonionic: Brij30 and Brij56, cationic: DDEAB and CTAB and anionic: SDS. Solubilization capacity of micelles was quantified in terms of molar solubilization ratio, the micelle-water partition coefficient, the first stepwise association constant and average number of solubilizate molecules per micelle determined by employing spectrophotometric and tensiometric techniques. Solubilization capacity of all the surfactant systems was generally higher for naphthalene than pyrene and followed the order: nonionics>cationics>anionic surfactant. Solubility of naphthalene decreased during cosolubilization in all surfactant systems studied while the solubility of pyrene decreased only in Brij30 and Brij56 surfactant systems due to competitive solubilization of PAHs for the same solubilization site. The solubility of pyrene, however, enhanced in presence of naphthalene in CTAB, DDEAB and SDS surfactant systems owing to increase in core volume of the micelles by the palisade layer solubilization of naphthalene. The results of this study can provide valuable information on the selection of particular surfactant systems for selective separation of naphthalene and pyrene from their mixture relevant to surfactant enhanced remediation (SER) technology at the contaminated sites.