Hydrophobic Porous Liquids with Controlled Cavity Size and Physico‐Chemical Properties

Abstract

Abstract Developing greener hydrometallurgical processes implies offering alternatives to conventional solvents used for liquid‐liquid extraction (LLE) of metals. In this context, it is proposed to substitute the organic phase by a hydrophobic silica‐based porous liquid (PL). Two different sulfonated hollow silica particles (HSPs) are modified with various polyethoxylated fatty amines (EthAs) forming a canopy that provides both the targeted hydrophobicity and liquefying properties. This study shows that these properties can be tuned by varying the number of ethylene oxide units in the EthA: middle‐range molecular weight EthAs allow obtaining a liquid at room temperature, while too short or too long EthA leads to solid particles. Viscosity is also impacted by the density and size of the silica spheres: less viscous PLs are obtained with small low‐density spheres, while for larger spheres (c.a. 200 nm) the density has a less significant impact on viscosity. According to this approach, hydrophobic PLs are successfully synthesized. When contacted with an aqueous phase, the most hydrophobic PLs obtained allow a subsequent phase separation. Preliminary extraction tests on three rare earth elements have further shown that functionalization of the PL is necessary to observe metal extraction.

Keywords

• hydrophobicity
• nanoscale ionic materials
• porous liquids
• hollow silica spheres
• solvent extraction