Functionalization of Ti3C2 MXene with cholinium amino acid ionic liquids for enhanced CO2 adsorption performance

The 2D structure and unique properties of MXenes have attracted significant research interest. In this study, Ti₃C₂ MXene was functionalized with cholinium amino acid ionic liquids ([Cho][AA]s) to synthesize IL@Ti₃C₂ MXene, aiming to expand interlayer spacing, enhance surface functionality, and improve CO₂ adsorption performance. The modification effectively increased the interlayer spacing, facilitating superior adsorption properties compared to pristine Ti₃C₂ MXene. The IL@Ti₃C₂ MXene composites were characterized using X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Raman Spectroscopy, Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDX), and Brunauer-Emmett-Teller (BET) surface area analysis, while CO₂ adsorption was evaluated via Quartz Crystal Microbalance (QCM) at 288.15-308.15 K and pressures up to 1 bar. Adsorption isotherms followed the Langmuir model, suggesting a predominant chemisorption mechanism involving amine functionalities. At 298.15 K and 1 bar, Ti₃C₂ MXene exhibited a CO₂ adsorption capacity of 1.95 mmol/g, while IL@Ti₃C₂ MXene composites displayed enhanced adsorption: [Cho][Arg]@Ti₃C₂ (3.25 mmol/g), [Cho][His]@Ti₃C₂ (2.92 mmol/g), and [Cho][Tyr]@Ti₃C₂ (2.64 mmol/g). These improvements were resulted from electrostatic interactions, hydrogen bonding, Lewis acid-base interactions, and interlayer expansion. The exothermic nature of adsorption, confirmed by negative enthalpy (ΔH) values, indicates an energetically favorable process.