Effects of gemini surfactant CG12-3-12, rhamnolipid and triton X-100 on solubility enhancement of PAHs: A comparative study

Effects of cationic Gemini Surfactant (CG12-3-12), anionic biosurfactant (rhamnolipid), and the traditional non-ionic surfactant (TX-100) on solubility enhancement of two typical PAHs: phenanthrene and pyrene were systematically investigated. The effects of individual surfactant and their mixture on the solubilization of PAHs were discussed in detail through comparing their critical micelle concentration (CMC), molar solubilization ratio (MSR) and standard free energy ΔGs⁰ of solubilization. The effects of three surfactants on solubilization followed the order of: CG12-3-12> rhamnolipid> TX-100. When comparing TX-100/CG12-3-12 and TX-100/rhamnolipid with individual ones, it can be observed that there was a better solubility enhancement for PAHs in mixed surfactant system, which exhibited a synergistic effect. However, the mixed solutions did not follow an ideal mixture. There was a larger negative deviation of the experimental CMCexp than ideal critical micelle concentration (CMCmi) in TX-100/CG12-3-12 system. It can be found that TX-100 and rhamnolipid mixed system was easier to form mixed micelles than TX-100 and CG12-3-12 mixed system through Gibbs free energy of solubilization (ΔGm⁰). The TX-100/rhamnolipid mixed system showed better synergistic solubilization capacity than TX-100/CG12-3-12 mixed system. The results can provide a scientific basis for repairing the hydrophobic organic matter pollution environment.