Docusate Ionic Liquids: Effect of Cation on Water Solubility and Solvent Extraction Behavior

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Ionic liquids (ILs) are salts that are liquid at ambient temperatures, offering tunable properties for various applications.
• Docusate (dioctyl sulfosuccinate or DOSS) anion-based ILs are explored for their potential in liquid-liquid extraction.
• Phosphonium cations functionalized with ester, carboxylic acid, or ethylene glycol groups are investigated in combination with the DOSS anion.

Purpose of the Study:

• To synthesize and characterize novel phosphonium docusate ionic liquids.
• To investigate the phase behavior and metal extraction capabilities of these ionic liquids, particularly focusing on thermomorphic properties.
• To evaluate the potential of these ILs for separating critical metal pairs relevant to recycling.

Main Methods:

• Synthesis of phosphonium ionic liquids with the docusate anion.
• Determination of water miscibility and phase behavior (lower critical solution temperature).
• Screening of metal ion extraction for divalent and trivalent metals.
• Separation studies of Sm/Co and La/Ni pairs and investigation of extraction mechanisms.

Main Results:

• Most synthesized docusate ionic liquids were immiscible with water, except for [P444E3][DOSS].
• [P444E3][DOSS] exhibited lower critical solution temperature phase behavior, forming a homogeneous phase below 19°C, enabling fast homogeneous liquid-liquid extraction.
• Initial screening showed varying metal extraction efficiencies for different docusate ILs.
• [P444E3][DOSS] demonstrated effectiveness in separating Sm/Co and La/Ni pairs, relevant for recycling applications.

Conclusions:

• The docusate anion can be incorporated into phosphonium ionic liquids to create tunable extraction media.
• [P444E3][DOSS] is a promising thermomorphic ionic liquid for efficient and selective metal extraction and separation.
• This study highlights the potential of docusate-based ionic liquids for critical metal recovery and recycling processes.