Solubilization capabilities of mixtures of cationic Gemini surfactant with conventional cationic, nonionic and anionic surfactants towards polycyclic aromatic hydrocarbons

Solubilization capabilities of equimolar mixed micellar solutions of Gemini surfactant, C16H33N+(CH3)2(CH2)5N+(CH3)2 C16H33 2Br− (G) with cetylpyridinium chloride (CPC), sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and Brij56 towards polycyclic aromatic hydrocarbons (PAHs), viz pyrene and anthracene are studied spectophotometerically at 25 °C and then compared. The results showed that irrespective of the surfactant type, the solubility of PAHs increases linearly with increasing surfactant concentration, as a consequence of association between the PAH and micelles. Solubilization capacity has been quantified in terms of molar solubilization ratio (MSR), micelle-water partition coefficient (Km), ratio of binding constant (K1) between the micelle and PAH to the aggregation number (N) of surfactant solution and free energy of solubilization (ΔGs0) of PAHs. Equimolar binary surfactant mixtures showed higher solubilization capacity than their respective individual surfactants except G-CPC wherein the values were intermediate between the two. The mixed micellization parameters viz interaction parameter, β, micellar mole fraction within the mixed micelle, Xi, and activity coefficients, fi, were evaluated using Rubingh approach. The values of Xi were then employed to evaluate solubilization efficiency of mixed micelles using Regular solution approach (RSA). In addition experimental micelle-water partition coefficients of hydrocarbons have been compared with those predicted theoretically by geometric mean equation for mixed Gemini-conventional surfactant systems. Such mixed systems promise to improve the performance of surfactant enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.