Synergistic size-sieving and van der Waals adsorption for the efficient separation of cis/trans-1,2-dimethylcyclohexane

UiO-66-CH 3 achieves cis/trans-1,2-DMCH separation with α = 3.55. • Methylation reshapes UiO-66 pores to enhance molecular shape matching. • Van der Waals surface engineering magnifies cis/trans differences in cycloalkanes. • UiO-66-CH 3 retains 94% regeneration efficiency after five cycles. In the field of chemical and fine chemical industries, cis/trans-1,2-dimethylcyclohexane (cis/trans-1,2-DMCH) isomers serve as vital cycloalkane intermediates, yet their efficient separation remains a formidable challenge due to their highly similar physicochemical properties. Here, zirconium-based UiO-66 was employed as a platform to construct UiO-66, UiO-66-CH 3 , and UiO-66-(CH 3 ) 2 via a ligand methylation strategy, systematically regulating pore microenvironments for shape-selective separation. Notably, UiO-66-CH 3 exhibited the highest cis/trans selectivity (α = 3.55) and the widest breakthrough separation window (Δ t  = 1500 min), outperforming the pristine and over-methylated counterparts. Characterizations and molecular simulations revealed that moderate methyl introduction enhanced framework-analyte interaction energies, which were predominantly governed by van der Waals forces. Furthermore, probability density distributions elucidated that the more compact cis-1,2-DMCH approached the methyl-functionalized pore walls more closely, forming multi-site, short-range contacts that led to higher loading and more pronounced van der Waals stabilization. Overall, this work demonstrates that tailoring MOF pore microenvironments via mild ligand methylation can effectively amplify subtle molecular conformation differences without relying on strong chemical interactions, offering a promising paradigm for designing advanced adsorbents for challenging isomer separations. Ligand methylation optimizes UiO-66's van der Waals field and geometric confinement, enabling efficient cis/trans-1,2-DMCH separation by perfectly matching the compact cis-conformation while rejecting the spatially hindered trans-isomer. Download: Download high-res image (166KB) Download: Download full-size image