Structural Factors Determining Thermal Stability Limits of Ionic Liquid/MOF Composites: Imidazolium Ionic Liquids Combined with CuBTC and ZIF-8

Abstract

Twenty-nine different imidazolium ionic liquids (ILs) were combined with two different metal−organic frameworks (MOFs), ZIF-8 and CuBTC, and the resulting IL/MOF composites were characterized in detail by combining X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer−Emmett−Teller (BET), and Fourier transform infrared (FTIR) spectroscopy. Characterization data illustrated that MOFs remained structurally intact upon combining them with ILs. Thermogravimetric analysis performed on IL/MOF composites showed that most of the composites have lower thermal stabilities compared to the bulk ILs and pristine MOFs, whereas composites with ILs having a functional group in their anions showed thermal stability limits higher than those of bulk ILs. The derivative onset temperatures representing the maximum tolerable temperatures of the composites were analyzed based on the structural differences in MOFs and ILs, such as the changes in the alkyl chain length, methylation on the C2 site, and functionalization of the cation and the size/electronic changes on the anion. Data illustrated that the maximum tolerable temperatures of IL/MOF composites decrease with an increase in the alkyl chain length on the IL's imidazolium ring. Substitution of the alkyl group with functionalized groups in the IL's imidazolium ring also led to a decrease in the maximum tolerable temperatures of the composites. Whereas, fluorination of the anion resulted in an increase in the thermal stability limits of the corresponding IL/MOF composites. Furthermore, ILs having a dicyanamide, acetate, and phosphate anion also showed an increase in their maximum tolerable temperatures when combined with CuBTC compared to their bulk counterparts. Moreover, simple structural descriptors for each cation and anion were defined by means of the density functional theory (DFT) calculations and used in the quantitative structure−property relationship (QSPR) analysis to correlate the maximum tolerable temperatures of IL/MOF composites to the IL's cation and anion structure. Results presented in this study will provide a guideline for the selection of proper IL−MOF pairs according to the application temperature of IL/MOF composites in various fields.

Sodium Ion Conductivity in Superionic IL-Impregnated Metal-Organic Frameworks: Enhancing Stability Through Structural Disorder

“…This is a small decrease, and the high thermal stability of the composite remains suitable for applications in electrochemical energy storage devices. In good agreement with the IR peak shifts, the lower decomposition temperature for S-IL@MOF is attributed to the immobilizing interaction between IL molecules and the MOF framework 44,45 . Consistent with this result, DSC profiles ( Fig.…”

“…Both BET surface area and pore volume ( Fig. S2 and Table S1) of ZIF-8 decreased significantly after S-IL confinement (from 1297.3 m 2 g −1 and 0.641 cc STP g −1 respectively in ZIF-8, to 7.29 m 2 g −1 and 0.006 cc STP g −1 respectively in S-IL@ZIF-8), indicating that the S-IL solution occupies the pores in ZIF-8 43,44 . Since the thermal stability limit of such composites determines the potential application of the electrolytes in the desired operation conditions, thermogravimetric analysis was conducted and the corresponding decomposition temperatures were measured ( Fig.…”

Core-Shell Graphitic Carbon Nitride/Zinc Phytate as a Novel Efficient Flame Retardant for Fire Safety and Smoke Suppression in Epoxy Resin

“…The absorption peaks at 1404, 1253 and 1146 cm −1 were associated to the stretching vibration of C-O, P=O and P-O bonds, respectively [20]. Moreover, the characteristic bands of Zn salt were detected at 550 cm −1 [21]. This result could be verified by SEM and TEM analysis.…”

Comparison of the ionic conductivity properties of microporous and mesoporous MOFs infiltrated with a Na-ion containing IL mixture

“…This reduction in thermal stability is consistent with other IL@ZIF-8 composites and is attributed to the IL/MOF interactions. [37][38][39][40][41] After incorporation of the NaIL solution, the BET surface area of the samples decreased significantly from 1864.4 m 2 g -1 to 8.3 m 2 g -1 for NaIL@ZIF-8micro and from 1298.0 m 2 g -1 for NaIL@ZIF-8meso to 18.5 m 2 g -1 ( Table 1). This suggests the microand mesopores are no longer accessible.…”