Ionic liquids as passive monitors of an atmosphere rich in mercury

An ionic liquid (IL) is a compound at dynamical equilibrium in which at any time more than 99.99% of it is shifted toward the ionic rather than the molecular species. ILs have raised considerable attention during the past few years due to their extremely low vapor pressure, good electrolytic properties and wide electrochemical window. Also, they remain liquid at a wide range of temperature. ILs are able to dissolve some non polar chemical species as well as some very polar ones. Their main applications have been so far in environmental chemistry and can be considered as environmental friendly solvents. Mercury is a naturally occurring element that is found in the atmosphere, generally present in three forms: elemental (Hg⁰), oxidized, and particulate-bounded. It is a very toxic element and its assessment in the environment is highly desired, however due to its volatility is an element difficult to detect by conventional sampling methods. This paper presents the results of a research on mercury binding using ILs. The following ILs were tested: 1-butyl-3-methyl- imidazolium-hexafluorophosphate [BMIM][PF₆] and 1-butyl-3-methyl- imidazolium thiocyanate [BMIM] [SCN]. Known amounts of ILs were introduced, in the form of bulk or thin coating layer, to a 70 mL glass tube with a known amount of metallic Hg and sealed with a PTFE® cap. The concentration of Hg in the IL was measured after 12 weeks of exposure. Total Hg determination was performed by particle X-ray emission (PIXE). Changes in the spectroscopic properties due to the Hg binding were followed by Raman and infrared (IR) spectroscopy. The sorption efficiency for the ILs under different experimental conditions is discussed.