Temperature-Responsive Xylene Isomer Separation via Biomimetic Window Confinement and Defect-Engineered Nanospace in Metal–Organic Frameworks

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.