Temperature-Responsive Xylene Isomer Separation via Biomimetic Window Confinement and Defect-Engineered Nanospace in...

Biological channels achieve remarkable selectivity by amplifying subtle molecular differences through nanoscale confinement and steric gating. Inspired by this principle, we investigate the zirconium fumarate framework MOF-801, whose triangular pore windows act as biomimetic steric filters that preferentially accommodate para-xylene (PX) over its meta- (MX) and ortho- (OX) isomers. To further enhance the separation performance, we introduced structural defects that enlarge the internal nanospace while preserving the selective gating effect of the windows. The resulting material, MOF-801-132AA, delivers high liquid-phase separation performance, achieving a PX/OX selectivity of 103.9 at room temperature and a PX uptake of 243.8 mg g^-1, as determined from vapor adsorption measurements. MOF-801-132AA also exhibits a temperature-dependent selectivity inversion with the preferential order shifting from PX > MX > OX at 25-60 °C to OX > MX > PX above 160 °C. This unusual dynamic behavior is validated by liquid-batch adsorption, vapor-phase sorption, and breakthrough experiments. Single-crystal electron diffraction reveals preferential PX localization in the octahedral cages, while molecular simulations attribute the inversion to the interplay of window-blocking effects, isomer packing configurations, and defect-induced nanospace enlargement. Together, these results illustrate how defect-modulated nanospace and window confinement can be combined to enable the adsorption-based separation of structurally similar isomer mixtures.