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-NH 2 (Zr 6 O 4 (OH) 4 (BDC-NH 2 ) 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 N 2 adsorption at 77 K. Pure component adsorption isotherms were measured for CO 2, CH 4, N 2, C 2 H 4, C 2 H 6, C 3 H 6, and C 3 H 8 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 –NH 2 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 C 2 H 6 /C 2 H 4 selectivity predictions of about 3.5 and 2 for UiO-66 and UiO-66-NH 2, respectively. The C 3 H 6 /C 3 H 8 selectivity is predicted to be 8.5–4.5 for UiO-66 and about 0.65 for UiO-66-NH 2 . Additionally, C 3 H 8 adsorption was observed to be greater on UiO-66-NH 2, compared with the unmodified material.