Highly reversible CO2 capture using amino acid functionalized ionic liquids immobilized on mesoporous silica

• Amino acid functionalized ionic liquids immobilized on silica were synthesized.
• Moderate binding energy facilitates fast and reversible CO2 adsorption–desorption.
• CO2 adsorption capacity increased with increasing adsorption energy of CO2.
• Lysine with highest degree of band gap exhibited the best CO2 adsorption capacity.

Amino acid functionalized 1-methyl-3-ethyl-imidazolium based ionic liquid (IL) supported on ordered mesoporous silica (OMS-IL (AA)) were prepared via grafting method and were applied as solid sorbent for CO2 adsorption–desorption. Four different kinds of amino acids (AA), including lysine (Lys), glycine (Gly), alanine (Ala), and proline (Pro) were selected in order to prepare different OMS-IL (AA) adsorbents. The developed solid adsorbents were characterized by using 29Si-NMR, FT-IR, TGA, BET, SEM, TEM, and elemental analysis. The CO2 adsorption–desorption studies were carried out using the thermogravimetric method with temperature swing assistance of the adsorbed CO2. Evaluation of CO2 adsorption nature revealed that the adsorbents show fast kinetics, moderate chemisorption and easy desorption. Among the synthesized OMS-IL (AA), OMS-IL (Lys) showed the best CO2 adsorptive performance corresponding to 0.61 mmol/g at 25 °C. The energy requirements for activation, adsorption and desorption are estimated by using different methods to meet its energy criteria. Further, the approach has been made to discuss the activity of selected amino acids, their effective loading, kinetics, and adsorption capacities in detail. DFT studies reveals that the energy required for CO2 adsorption on IL (Lys) is high enough for CO2 uptake (=−0.98 eV). According to experiment and DFT calculations, a worthy correlation is identified between CO2 adsorption capacity, adsorption energy, and the orbital localization, which determines the basic role of ILs over support to adsorbed CO2 efficiently.

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