Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed micelles composed of a photoresponsive surfactant and a conventional non-ionic surfactant

• A photoresponsive mixed surfactant system was built to solubilize PAHs.
• Reversible surfactant-enhanced remediation based on this system was explicated.
• Nonideal interaction between the photoresponsive surfactant AZTMA and Tween80 was proved.
• Solubilization-release cycle of PAHs by AZTMA–Tween80 mixed micelles was achieved.

Surfactant-enhanced remediation is a powerful technology for soil clean-up. However, some drawbacks, such as its high cost and the secondary contamination caused by flushing agents, have hampered this technology and its commercial application has been largely limited to North American and European countries. The aim of this work is to introduce a novel reversible solubilization system composed of the photoresponsive surfactant 4-butylazobenzene-4′-(oxyethyl)trimethylammonium bromide (AZTMA) and the commercial non-ionic surfactant Tween80 for the solubilization of organic contaminants. The solubilization behavior of the AZTMA/Tween80 surfactant system toward polycyclic aromatic hydrocarbons (PAHs) has been studied. Critical micelle concentration (CMC) values indicate that the mixed system has a synergism in mixed micelle formation, and that the interaction parameter (β) is −2.85 when the mole ratio is 2:8. AZTMA is also predicted to be low biologic toxicity by the CMC and surface tension. The synergistic effect on molar solubilization ratio (MSR) and micelle-phase/aqueous-phase partition coefficient Kmc values is related to the composition and concentration of the mixed system and follows the order pyrene > phenanthrene > acenaphthene, and these parameters are much higher than those for the single surfactants. After irradiation with UV light, more than 65% of the PAHs could be separated from the mixed micelles, and the cumulative release efficiencies of selected PAHs are consistent with the results of solubilization experiments. All of these features demonstrate that mixed AZTMA/Tween80 should be preferable to single surfactants for soil remediation, avoiding the issues associated with chemical flushing agents and decreasing remediation costs.

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