Bi-functionalized ionic liquid-grafted mesoporous alumina: Synthesis, characterization and CO2/N2 selectivity

Abstract In this work, short-chain bi-functionalized ionic liquid (IL) was grafted onto mesoporous alumina (MA) for ideal CO2/N2 selectivity. First, bi-functionalized IL 1-(2-carboxymethyl)-3-methoxyethyl-imidazolium bromide ([CmMOEim][Br]) with ether and carboxyl group was successfully synthesized and the initial decomposition temperature is 165 °C. Then low-cost hydroxyl-MA (MA-OH) was obtained from ordered MA (OMA) with the assist of 30 wt% H2O2 solution to prepare [CmMOEim][Br]-grafted MA with different molar ratios of [CmMOEim][Br] and MA-OH via facile chemical reaction without the introduction of alkoxysilanes. MA-OH material presents slit-like structure and more hydroxyl groups compared to OMA sample before hydroxylation. Crystal structure and morphology of grafted material remains unchanged after grafting process. [CmMOEim][Br] is successfully grafted onto MA-OH via the chemical link of carboxyl group on IL and hydroxyl group on MA-OH. Finally, CO2 and N2 capture capacities of different materials were separately evaluated at 0.1 MPa and 25 °C. With the increase of IL dosage, CO2 capture capacity of the grafting material first enhances and then decreases while N2 capture capacity gradually falls owing to the high CO2 affinity of [CmMOEim][Br]. Wherein, [CmMOEim][Br]-grafted MA-0.15 exhibits the optimum CO2 capture capacity of 45.3 cm3/g at 25 °C and ambient pressure. The ideal CO2/N2 selectivity of [CmMOEim][Br]-grafted MA can reach up to 30 based on single-component adsorption isotherms, which is higher than that of [CmMOEim][Br] and MA-OH. Furthermore, CO2 capture capacity, morphology and structure of [CmMOEim][Br]-grafted MA maintain well even after ten cycles.