Effect of the Porous Structure and the Presence of Amino Groups on Selective Adsorption of Methane, Ethane, and Carbon Dioxide on Zirconium-based UiO-66 Structures

UiO-66 and NH2-UiO-66 materials with different porosity (microporous and mesoporous) prepared by solvothermal and microwave synthesis were compared in methane, ethane, and CO2 adsorption for the first time. Both microporous samples with or without amino groups exhibit significantly higher methane, ethane, and carbon dioxide uptakes (up to 30 %) compared to the corresponding mesoporous materials. Highest uptake of ethane and methane (6.75 mmol/g and 3.59 mmol/g at 20 atm, respectively) and carbon dioxide (13.89 mmol/g at 30 atm) were obtained on microporous micro-UiO-66 sample, while on its amino-functionalized microporous analog micro-NH2-UiO-66 the uptake values for all 3 mentioned gases are somewhat lower (4.46 mmol/g of ethane, 2.44 mmol/g of methane at 20 atm and 6.96 mmol/g of carbon dioxide at 30 atm). Adsorption of both hydrocarbons and carbon dioxide decreases in the following order: micro-UiO-66 > meso-UiO-66 > micro-NH2-UiO-66 > meso-NH2-UiO-66. The ideal selectivity and IAST selectivity were calculated for the first time for these materials. The maximum ideal selectivity was obtained for the micro-UiO-66 sample (3.17 : 1 for C2H6/CH4 at 5 atm). The best IAST selectivity was found for the micro-UiO-66 sample (7.94 : 1 for C2H6/CH4 at 15 atm), i.e. UiO-66 is a good candidate for natural gas separation. The presence of amino groups significantly enhances the IAST selectivity for the carbon dioxide/methane pair.