Agenda de l'ENS de Lyon

The capture of polluting gases such as CO₂ and SO₂ presents a significant challenge in mitigating the environmental impact of human activities. To address this challenge, we propose the development of new materials based on reactive ionic liquids (ILs) as absorbents, with low environmental impact and cost-effectiveness. ILs are non-volatile compounds with a melting temperature below 100°C, capable of dissolving a wide range of substances due to their versatile cation-anion combinations. With unique properties like low flammability, high conductivity, and thermal stability, ILs hold promise for various applications, including gas absorption. The wide range of possible combinations of cations and anions allow for the design of a multitude of ionic solvents with tunable properties. A novel family of ILs comprising carboxylate anions and phosphonium cations for the selective separation of CO₂ and SO₂ has been developed and prepared. Through rigorous experimental and computational analyses, we investigated their physicochemical properties, thermal behavior, and microscopic structure. They notably displayed promising thermal stability and a large liquid window. It was possible to distinguish the microscopic structure of the ILs based on the substituents of the carboxylate anions. [P4,4,4,4][TetrazC1COO] appeared as an outlier with peculiar anion-anion correlations. Measurements of gas absorption as a function of temperature and partial pressure revealed the crucial role of carboxylate anion basicity in CO2 capture capacity, but not in SO₂ capture. The pKa of corresponding carboxylic acids in water of each carboxylate anion was nonetheless determinant for the reversibility of SO2 capture, and crucial for achieving high selectivity over CO₂. The related thermodynamics properties were carefully studied and interpreted based on the equilibrium constants and Henry's law constants, obtained from the absorption isotherm fittings, and ab initio simulations. Exploratory projects were carried out to consider other potential applications of these ILs and their mixtures in electrochemistry due to their high electrochemical stability, but also as plastic crystals. These studies pave the way for understanding the properties of these ILs, guiding future research in this field.