Preparation of pH-Responsive Oil-in-Water Microemulsion Using a Full-Bio-Based Surfactant Containing a Dynamic Covalent Bond

A novel pH-responsive full-bio-based surfactant (Ca-S) containing a dynamic covalent bond is synthesized using renewable cashew phenol, 5-chloro-2-furanaldehyde, and taurine. The structure of Ca-S is characterized by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (NMR) analysis. Limonene containing oil-in-water (O/W) microemulsions are prepared on the basis of the Ca-S surfactant and are applied to the remediation of oil-contaminated soil under low-energy conditions at ambient temperature. These results show that Ca-S presents lower cytotoxicity against the A549 cell line. The microemulsions feature low interfacial tension and fast response characteristics, along with an optimal pH responsiveness. The microemulsions that undergo rapid and complete phase separation separate into distinct oil and water phases within 5 s in acidic media (pH < 4). In addition, the microemulsion significantly reduces the oil content to below 4%. The microemulsions hold broad application prospects in soil remediation.