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

In this work, short-chain bi-functionalized ionic liquid (IL) was grafted onto mesoporous alumina (MA) for ideal CO 2 /N 2 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% H 2 O 2 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, CO 2 and N 2 capture capacities of different materials were separately evaluated at 0.1 MPa and 25 °C. With the increase of IL dosage, CO 2 capture capacity of the grafting material first enhances and then decreases while N 2 capture capacity gradually falls owing to the high CO 2 affinity of [CmMOEim][Br]. Wherein, [CmMOEim][Br]-grafted MA-0.15 exhibits the optimum CO 2 capture capacity of 45.3 cm 3 /g at 25 °C and ambient pressure. The ideal CO 2 /N 2 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, CO 2 capture capacity, morphology and structure of [CmMOEim][Br]-grafted MA maintain well even after ten cycles.