Construction of molecular fans in metal-organic framework to overcome diffusion resistance for trace benzene capture

Molecular size-matched pores of adsorbents provide strong adsorptive forces for benzene, but high diffusion resistance. Overcoming the diffusion resistance within molecular size-matched pores is essential to efficient capture of trace benzene from indoor air or industrial exhaust gas, but challenging. Herein, we report a stable Fe-based metal-organic framework (ZJU-701) featuring hierarchical micropores (5.8 ± 0.9, 10.2 ± 2.3, and 21.2 ± 1.4 Å) and molecular fans with 1,4-naphthylene as rotors between micropores. ZJU-701 shows adsorption rate constant of 5.84 × 10⁻³ min⁻¹ and adsorption capacity of 2.05 mmol g⁻¹ for benzene at P/P₀ = 0.001 and 298 K, surpassing other benchmark adsorbents. Strikingly, ZJU-701 exhibits only 10.1% loss of dynamic adsorption capacity for trace benzene as the gas velocity increases from 0.03 to 0.12 m·s⁻¹, much lower than other benchmark adsorbents (30.6% ~ 76.9%). The rapid adsorption of benzene is attributed to the rotational motion of molecular fans in ZJU-701, verified by in-situ Infrared/Raman Spectroscopy and solid-state NMR. This work highlights a dynamic pore-engineering strategy with molecular fans to alleviate diffusion resistance within molecular size-matched pores and balance adsorption rate and capacity for trace gas capture.