Organogels based on aromatic amino acids with appended long-chain fatty acids for sustainable oil spill recovery and environmental remediation

Abstract

Various organogelator molecules based on fatty-acid-appended amino acids have been synthesized via amide coupling between an aromatic amino acid (L-phenylglycine/L-phenylalanine) and fatty acid (palmitic acid/lauric acid), and their organogelation abilities have been tested in various organic solvents, including simple hydrocarbons, aromatic solvents, and oils, namely, kerosene and diesel. Palmitic-acid-appended L-phenylalanine (C₁₅-Phe) and L-phenylglycine (C₁₅-Phg) undergo stable organogelation in organic solvents including iso-octane, heptane, hexane, cyclohexane, methylcyclohexane, petroleum ether, kerosene and diesel. However, lauric-acid-appended L-phenylglycine (C₁₁-Phg) and L-phenylalanine (C₁₁-Phe) undergo transient organogelation and clear solution formation under the same conditions, respectively. Interestingly, the minimum gelation concentration of the organogelator C₁₅-Phg has been estimated to be lower than that of the organogelator C₁₅-Phe. Moreover, C₁₅-Phg organogels in all hydrocarbon solvents show a helical nanofibrillar morphology; however, C₁₅-Phe shows a nanobelt-like straight fibrillar morphology, except in isooctane. C₁₁-Phg also shows a helical nanofibrillar ribbon-like morphology. Powder XRD and FT-IR studies revealed the involvement of π–π stacking, hydrogen bonding and van der Waals interactions in their gel states. The organogels of C₁₅-Phg in diesel and kerosene show thixotropic behaviour. The thermal stabilities of the C₁₅-Phg organogels have been found to be greater than those of C₁₅-Phe. A phase-selective gelation study has been performed in a diesel–water mixture for C₁₅-Phg, in which the gel layer could be easily separated to recover the oils, demonstrating the promising applicability of C₁₅-Phg in oil spill recovery from marine and aquatic water. This study showcases the green and sustainable development of oil spill recovery and environmental remediation by using simple chemistry to save marine and aquatic life.