Synthesis And Properties Of A Series Of Pure Inorganic Ionic Liquids Based On Polyoxometalates

Ionic liquids（ILs）are widely used in many fields such as catalysis,extraction,and electrochemistry because of their low saturated vapor pressure and melting point,high ionic conductivity,and wide electrochemical window.The cations of ionic liquids currently reported are mostly organic cations,and there are relatively few reports on ionic liquids composed of inorganic cations.In this paper,a series of rare earth salts based on Ti-substituted Keggin tungstophosphoric acid were synthesized.It was found that the series of compounds behaved as a liquid with very good fluidity in the range of4°C to 65°C,and exhibited ionic liquid behavior.We have performed a series of characterizations on the composition,structure and properties of the series of pure inorganic ionic liquids through ICP,IR,PXRD,TG and other methods.The main innovations are as following:1.A series of pure inorganic ionic liquids KLn H₃PTi₂W₁₀O₄₀·x H₂O[Ln=La（1）,Ce（2）,Pr（3）,Nd（4）,Sm（5）,Eu（6）,Er（7）,Yb（8）]were synthesized using lanthanide metal salts and titanium-substituted Keggin type polyoxometalates,through inductively coupled plasma atomic emission spectroscopy（ICP）,thermogravimetric analysis（TG）,infrared spectroscopy（IR）,powder X-ray diffraction（PXRD）,etc.have determined their composition,crystallinity and water content.2.The changes in the state of their lost（gained）water and the influence of water on their compositions and states are investigated.A small amount of water is an indispensable component in the composition of the ionic liquids.After completely losing water,they become transparent solids.Adding a proper amount of water can regain fluids with good fluidity.IR and PXRD spectra analysis show that the structures of the ionic liquids don’t change significantly before and after water is obtained or lost.The series of ionic liquids and water are immiscible into two phases at room temperature,and they are miscible into a homogeneous phase after heating,showing the upper critical solution temperature（UCST）phase behavior.3.The conductivity and electrochemical properties（CV）of the series of ionic liquids were systematically studied.The conductivity of this series of ionic liquids at room temperature was investigated,and their conductivity was higher than 10 m S cm^-1.Take Ce-containing ionic liquid 2 as an example to study the effect of temperature on its electrical conductivity.When the temperature rises from room temperature to 65°C,its electrical conductivity gradually increases from 13.3 m S cm^-1 to 22.6 m S cm^-1,But when the temperature rises from 65°C to 90°C,the conductivity decreases significantly.The cyclic voltammetry curves of ionic liquids are studied,and the electrochemical window is between 1.6～1.9 V.