A green aluminum-based metal organic framework outperforms its polymorph with MIL-53 type topology in o-xylene purification

Investigation of structure–property relationships for xylene separation using polymorphic metal–organic frameworks (MOFs) as adsorbent is highly desirable but the practice remains a vacancy. Herein, we report a comprehensive performance comparison between two polymorphic aluminum-based MOFs (MIL-53-TDC and CAU-23) for selective adsorption of o-xylene (OX) over m-xylene (MX) and p-xylene (PX) in liquid phase. Although containing the same chemical compositions and similar 1D channels, MIL-53-TDC and CAU-23 exhibit distinct pore geometries (square shape VS pseudo-square shape) and pore sizes (8.5 Å VS 6.8 Å). It was found that CAU-23 exhibited much higher OX uptake (1.90 mmol g−1) and selectivity (αOX/PX: 10.4; αOX/MX: 7.6) in liquid-phase competitive adsorption in comparison to MIL-53-TDC. The enhancement of OX preference by the efficient pore confinement in the narrow channel of CAU-23 was confirmed by the theoretical calculations. By virtue of the multiple hydrogen bonding interactions in the confined environment, CAU-23 exhibited excellent preferential OX uptake over other isomers in liquid phase, outperforming most of the reported sorbents. Further, the continuous adsorption–desorption experiments as well as recycling experiments demonstrated exceptional separation performance of CAU-23 under dynamic conditions. Therefore, the excellent separation performance combined with the facile green low-cost synthesis suggest an impressive potential of CAU-23 for practical application.