Studies on the thermal stability and exothermic behaviour of imidazolium-based ionic liquid binary mixture

Due to their numerous properties as an advanced or specialized material, ionic liquids (ILs) have found an increasingly wide utilization in many fields. Moreover, mixtures of ILs can further improve their correlative properties. Therefore, it is significant that the thermal stability and exothermic behaviour of IL binary mixtures were studied. In this work, two typical representative imidazole ILs ([BMIM]BF4 and BMIM[NO3]) were selected, and their binary mixture thermal stability and thermal decomposition process of visualization were investigated by simultaneous thermogravimetric analyser (STA). Furthermore, their binary mixture exothermic behaviour and decomposition products were obtained by differential scanning calorimetry (DSC) and thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR), respectively. The compound mode of imidazolium-based IL binary mixtures was divided into three categories: the molar fraction (7:3, 1:1, and 3:7) of parent pure ILs. We found that TG curves trend of IL binary mixtures was consistent with their parent pure ILs. Compared with TG curves, DSC curves of IL mixtures demonstrated that the behaviours of heat absorption and heat release at greater than 700.0 K in mixtures were different from their parent pure ILs. According to the infrared spectrum of gas products, the oxygen-containing functional group in BMIM[NO3] is likely to have some influence on the second-stage decomposition of sample 1#. Systematic thermal analysis results provided a significant reference for the exothermic behaviours and thermal degradation process of imidazolium-based ionic liquid binary mixture and a feasible research route for further investigations into the thermal decomposition characteristics of IL mixtures.