Enhanced CO2 adsorption performance by crystal defect method of multi-level pore Mg-MOF-74 using organic acids

Metal-organic frameworks (MOFs) are popular crystalline materials owing to their high porosity, tunable pore structure, and large surface area. By introducing a carboxylic acid to compete with 2,5-dihydroxyterephthalic acid for magnesium ions in solution, a crystal defect method was used to prepare multi-level pore Mg-MOF-74 with an unregular framework structure of Mg-MOF-74 in this paper. In the prepared samples, the adsorption amounts varied in descending order with various carboxylic acid species: Mg-MOF-74-Propionic acid (37.95 cm 3 /g STP) > Mg-MOF-74 (15.46 cm 3 /g STP) > Mg-MOF-74-Acetic acid (9.19 cm 3 /g STP) > Mg-MOF-74-Formic acid (7.81 cm 3 /g STP). At 1.5 kPa, the CO 2 adsorption of 2,5-dihydroxyterephthalic acid and propionic acid with a ratio of 2:1 can reach 2.78 cm 3 /g STP (standard temperature and pressure) with the comparison to 0.47 cm 3 /g STP of pristine Mg-MOF-74. Under atmospheric pressure, the adsorption capacity of modified Mg-MOF-74 can reach 37.95 cm 3 /g STP, equivalent to 2.45 times of the original Mg-MOF-74.