Effect of anionic-nonionic-mixed surfactant micelles on solubilization of PAHs

The solubility enhancement of phenanthrene (Phe), fluoranthene (FLT), and benzo[a]pyrene (BaP) in water by the single anionic surfactant sodium dodecyl sulfate (SDS), single nonionic surfactant Triton X-100 (TX100), and mixed surfactant solution (SDS-TX100) with varying proportions and the synergism mechanism were investigated in detail. Solubilization of phenanthrene was greatly enhanced either by SDS or by TX100. The sequence of solubilization for different mixed-surfactant solutions or surfactant solutions was SDS-TX100 (1:9, liquid mass ratio) > TX100 > SDS-TX100 (2:8) > SDS-TX100 (3:7) > SDS-TX100 (4:6) > SDS-TX100 (1:1) > SDS-TX100 (7:3) > SDS when the concentrations were above their critical micelle concentration (CMC). The composite surfactant SDS-TX100 (1.9) had better solubilization capacity than any single surfactant, which is attributed to the lower CMC of the mixed surfactant solution and the increase of the molar solubilization ratio (MSR) of the solution. The linear relationship between the solubility values of three targets polycyclic aromatic hydrocarbons (PAHs) and the polarities of the microenvironments of pyrene with SDS-TX100 mixtures has been demonstrated, with a linear regression coefficient of 0.7331, 0.7658, and 0.8669, respectively. The optimum mixed micelles of the anionic and nonionic surfactants (SDS-TX100; 1:9) had lower polarity and higher aggregation number This indicated that more PAHs were transferred into the mixed micelles of the anionic and nonionic surfactants.