Synthesis and Characterization of –NH 2 Functionalized MOF UiO-66: Comparing Adsorption of CO 2 , CH 4 , N 2 , C 2 H 4 , C 2 H 6 , C 3 H 6 , and C 3 H 8 at Different Temperatures with Mixture Behavior Predictions

Metal–organic frameworks UiO-66 (UiO, Universitet I Oslo) and UiO-66-NH2 (Zr6O4(OH)4(BDC-NH2)6) were successfully synthesized using a solvothermal method. The morphology of the resulting materials was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption at 77 K. Pure component adsorption isotherms were measured for CO2, CH4, N2, C2H4, C2H6, C3H6, and C3H8 by microgravimetric analysis, at 303, 323, and 343 K. The average isosteric heat of adsorption for the above-mentioned gases compared favorably to values reported in the literature. The modification with –NH2 on the UiO-66 structure leads to greater surface heterogeneity, which increases the potential for static adsorbent–adsorbate interaction with respect to guest adsorbate gases interacting with the active sites of the structure. Several well-known adsorption isotherms including Langmuir, Sips, Toth, and dual-site Langmuir were used to model the experimental pure component isotherms. Binary mixture predictions were made using the dual-site extended Langmuir model. The results suggest that UiO-66 is a promising material for potential hydrocarbon: paraffin–olefin separations with C2H6/C2H4 selectivity predictions of about 3.5 and 2 for UiO-66 and UiO-66-NH2, respectively. The C3H6/C3H8 selectivity is predicted to be 8.5–4.5 for UiO-66 and about 0.65 for UiO-66-NH2. Additionally, C3H8 adsorption was observed to be greater on UiO-66-NH2, compared with the unmodified material.