The Theoretical Calculation For CO₂ Capture Using Hydroxypyridine-based Ionic Liquids And Its Immobilization On Molecular Sieve MCM-41

The emission of carbon dioxide?CO₂?has received worldwide attention because of its implication in climate change.CO₂ capture by ionic liquids?ILs?as a potential alternative method has been widely studied.In our study,a series of new hydroxypyridine-based ILs are synthesized and applied in CO₂ capture through chemical absorption,in which one IL,i.e.,tetrabutylphosphonium 2-hydroxypyridine?[P4444][2-Op]?shows a viscosity as low as 193 cP with an absorption capacity as high as 1.20 mol CO₂/mol IL.Because the traditional anion-CO₂ absorption mechanism cannot provide an explanation for the influences of cation and temperature on CO₂ absorption capacity,herein,a novel cation-participated absorption mechanism based on the proton transfer is proposed to explain the high absorption capacity and the existence of a turning point of absorption capacity with the increase of temperature for the capture of CO₂ using [P4444][n-Op]?n=2,3,4?ILs.Also,the relationship between the viscosity of IL and the linear interaction energy is proposed for the first time,which can guide how to design and synthesize ILs with low viscosity.Quantum chemistry calculation,which is based on the comprehensive analysis of dipole moment,cation-anion interaction energy and surface electrostatic potential,indicates that the different viscosities of hydroxypyridine-based ILs and the changes after CO₂ absorption are mainly resulted from the different distribution of charge in the ILs.In order to solve the problem of the slow rate of CO₂ absorption by ILs,the hydroxypyridine-based ILs were loaded in the mesoporous molecular sieve MCM-41.It was found that the adsorption of composite material after loaded with quick adsorption rates,high adsorption capacity,as well as good cycle stability.In addition,the synergistic effect appeared in the progress of CO₂ adsorption when load percentage of IL was in a certain range.In order to explore the influence of loading to adsorption at the molecular level,the MCM-41 molecular sieve and cluster model were built.The interaction between ILs with MCM-41 molecular sieve surface was studied to explain the two quality loss arising from the thermogravimetric experiment corresponding to the free-ILs in the hole and the bound-ILs loaded in the hole wall.In addition,by comparing the charge distribution of adsorption sites in composites before and after loaded,we found that the synergistic effect due to induced polarization,thus greatly enhance the adsorption capacity of the material.This study provides a spark of inspiration for the design and synthesize of the CO₂ capture materials.