An environmentally stable supramolecular biosolvent: Characterization and study of its potential for the elimination of polar toxic substances in water

Abstract

Supramolecular solvents (SUPRASs), which are nanostructured liquids made up of non-covalent self-assembled amphiphilic aggregates, are highly promising for the development of engineered green solutions for elimination/reduction of toxic substances in water. However, the reversible and dynamic character of these aggregates have so far prevented the development of cost-effective and scalable strategies. Here, bioSUPRASs made up of non-dynamic assemblies were synthesized from the acid-induced coacervation of rhamnolipids (RLs). These bioamphiphiles contain multiple –COOH and –OH groups, which resulted in RL assemblies with a high intermolecular cohesive force. The synthesis occurred spontaneously, at concentrations of hydrochloric acid as low as 0.01 M, and it took place with high atom-economy (more than 99% of the RL was incorporated into the bioSUPRAS) and under energy-saving conditions (e.g. room temperature). The bioSUPRAS, made up of RL (80 ± 4%, w/w) and water (27 ± 2%, w/w), was environmentally stable, which allowed their direct application to water bodies. This feature, along with the high concentration of RL in the bioSUPRAS (∼840 g L−1) and the mixed-mode mechanisms offered for solute solubilisation, enabled its application to the efficient extraction of highly water-soluble toxic substances (recoveries for ionic dyes were in the range ∼70–100% at fractional bioSUPRAS phase volumes between 0.008 and 0.018). This research shows that highly stable bioSUPRASs can be produced by proper selection of amphiphiles, which should enable the eco-efficient and cost-effective elimination of toxic substances from water bodies.