Pore Environment Engineering in Al-MOFs Enables Thermodynamic–Kinetic Synergy for High-Resolution Chromatographic Separation

Aluminum-based metal-organic frameworks (Al-MOFs) are recognized as promising materials for chromatographic separation, but achieving an optimal thermodynamic-kinetic balance for the separation of aromatic isomers remains challenging. Herein, we demonstrated a ligand functionalization strategy to tune the pore environment and separation performance of <b><i>frl</i></b>-topology Al-MOFs. By the introduction of methoxy (OMe) and cyclopentyloxy (OCp) groups into the parent Al-L-H framework, three isostructural materials (Al-L-H, Al-L-OMe, and Al-L-OCp) were obtained. The introduction of alkoxy side chains reduced porosity and modulated host-guest interactions. Mechanistic analyses revealed that OMe substitution simultaneously weakened adsorption strength and enhanced molecular diffusion, achieving an optimal thermodynamic-kinetic balance. Thus, Al-L-OMe exhibited the highest separation efficiency among the three MOFs, with a resolution of 13.74 for <i>p</i>-xylene and <i>o</i>-xylene, surpassing most reported MOF-based stationary phases. This study provides a fundamental understanding of how pore environment engineering through ligand design can harmonize thermodynamic and kinetic effects, offering an effective route toward high-performance stationary phases.