Purification or contamination? The effect of sorbents on ionic liquids

摘要

Commonly used for purification, alumina and silica are found to contaminate ionic liquids with particles; these particles cannot be removed easily and can have a non-negligible impact on the electrochemical, spectroscopic and physical properties of an ionic liquid, including its nucleation and crystallisation kinetics. The popularity of ionic liquids (ILs) as solvents and electrolytes has risen greatly over the last twenty years. Two properties that make ILs especially appealing, in some cases, are low or non-existent freezing points and negligible vapour pressures. It is these two properties, however, that make ILs difficult to purify by traditional crystallisation and distillation techniques. For this reason, sorbents such as activated carbon, alumina and silica are commonly used, and have proven useful in the removal of organic and/or coloured impurities. The assumption that sorbents are easily and completely removed is so widespread that, in most cases, very little experimental detail is given regarding their use, or the techniques employed for their removal. Recently, evidence has arisen that alumina is left behind as a trace level contaminant in certain ILs.