Competitive solubilization of 4,4′-dibromodiphenyl ether, naphthalene, and pyrene mixtures in Triton X series surfactant micelles: The effect of hydrophilic chains

• Synergism for naphthalene/pyrene became stronger as POE chain length increased.
• Synergism for BDE-15/pyrene became stronger as POE chain length increased.
• Inhibition occurred for BDE-15/naphthalene in TX-305 and TX-405 surfactant systems.
• Halogen bonding probably formed between BDE-15 and ether groups of surfactants.

The present study investigated the solubilization and cosolubilization of 4,4′-dibromodiphenyl ether, naphthalene, and pyrene in a series of Triton X surfactant systems with different polyethylene oxide chain lengths. Cosolubilization effects were quantified in terms of molar solubilization ratio, micelle-water partition coefficient, and synergistic/inhibitive ratio. During cosolubilization, a stronger synergism was observed for naphthalene/pyrene and 4,4′-dibromodiphenyl ether/pyrene when the polyethylene oxide chain length increased. In contrast, inhibition was observed for 4,4′-dibromodiphenyl ether/naphthalene in Triton X-305 and Triton X-405 surfactant systems, indicating that 4,4′-dibromodiphenyl ether probably had a partitioning behavior similar to naphthalene which led to an appreciable amount of 4,4′-dibromodiphenyl ether in the palisade layer. This assumption was supported by 1H NMR and FTIR data showing that: (i) the protons on the outer hydrophilic chain of each surfactant did not undergo any upfield shifts, and the upfield shifts that occurred on the innermost ethoxylate group gradually disappeared as the polyethylene oxide chain length increased; (ii) the C–Br stretching and torsional frequencies of 4,4′-dibromodiphenyl ether decreased slightly as Triton X-100 monomers were added. The results of this study provide valuable information on the interactions between solutes and surfactant hydrophilic chains that may improve the remediation of PBDEs- and PAHs-contaminated soils and non-aqueous phase liquids (NAPLs) treated with surfactant enhanced remediation (SER) technology.

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