From Phase Change Materials to Green Solvents: Hydrophobic Low Viscous Fatty Acid–Based Deep Eutectic Solvents

Abstract

Inspired by the use of fatty acids in development of low temperature latent heat storage materials, novel low viscous and hydrophobic deep eutectic solvents (DESs) based exclusively on fatty acids are herein proposed as sustainable solvents. Three DESs were prepared by exclusively combining fatty acids, namely octanoic acid (C 8 ), nonanoic acid (C 9 ), decanoic acid (C 10 ), and dodecanoic acid (C 12 ), which can simultaneously act as hydrogen bond donors and acceptors. The obtained fatty acid-based DESs were analyzed in order to check their structures, purities, and proportions. Water stability was also carefully evaluated through 1 H NMR. Fatty-acid DESs melting point diagrams were determined by visual observation. Good agreement was obtained between the experimental eutectic point and that predicted by considering an ideal system of two individually melting compounds. Important solvent thermophysical properties, such as density and viscosity of the dried and water-saturated DESs, were measured. Finally, the removal of bisphenol A, a persistent micropollutant present in aqueous environments illustrates the potential of binary and ternary fatty acid-based DESs as extraction solvents. All prepared DESs showed good ability to extract bisphenol A from water with extraction efficiencies up to 92%.

Quest for Green‐Solvent Design: From Hydrophilic to Hydrophobic (Deep) Eutectic Solvents

“…Furthermore, the hydrophobic (D)ESs could be successfully recovered and recycled using selected hydrophilic DESs. Persistent micropollutants, such as pesticides from the neonicotinoids family and bisphenol‐A (a plasticizer present in water bottles and simultaneously acting as an endocrine disruptor), were successfully extracted using all natural hydrophobic (D)ESs with extraction efficiencies around 70 % and more than 90 %, respectively. Recently, Dietz et al .…”

“… Comparison of densities at 25 °C using different families of hydrophobic (D)ESs. Data taken from Refs .…”

“…Data taken from Refs. . Bars correspond to solubility of water in hydrophobic (D)ESs and points to viscosity data of pure hydrophobic (D)ESs.…”

“…Other hydrophobic ESs based on lidocaine and decanoic acid at several molar ratios were also proposed . Other sustainable hydrophobic ESs composed of two compounds from the same family (i.e., long‐chain fatty acids) were also proposed . In these hydrophobic ESs, both acids can act as HBA and as HBD.…”

“…Moreover, they found that a hydrogel formed when the sodium‐based (D)ES came into contact with water. The presence of the sodium ions seems to play a decisive role in the formation of the hydrogel as in a previous work no gel was formed as the (D)ES consisted of two carboxylic acids with a long alkyl chain that were completely immiscible with water. In the former case, instead of two mutually immiscible liquid phases a hydrogel was obtained.…”