Preparation and ion transport properties of NaY zeolite–ionic liquid composites

The physicochemical properties of protic ionic liquids (IL)–zeolite (Z) composites were investigated. H-3 methylimidazolium bis(trifluoromethanesulfonyl) imide (TFSI)/NaY zeolite composites with different IL/Z weight ratios were prepared and characterized. X-ray diffraction and FT-Raman measurements show the formation of NaTFSI during the preparation procedure which indicates that an ion exchange reaction is taking place during the composite preparation method. N2 physisorption shows that the zeolite pores are completely filled when IL/Z ratio is between 0.2 and 0.5. The water adsorption capacity of the samples decreased with IL/Z ratio. The conductivity of the composite pellets increased with temperature and ionic liquid loading, however significant enhancement was detected once the IL/Z weight ratio was higher than a threshold value (∼0.5). Moreover, theoretical calculations were performed using the Effective Medium Theory in order to understand the effect of IL/Z ratio on conductivity. In qualitative agreement with the experimental data, the model shows a sharp increase of the conductivity right above a critical threshold value for the ionic liquid/zeolite mass ratio, followed by a more moderate increase at higher loadings.