Exceptional capture of methane at low pressure by an iron-based metal-organic framework

The selective capture of methane (CH₄) at low concentrations and its separation from N₂ are extremely challenging owing to the weak host-guest interactions between CH₄ molecules and any sorbent material. Here, we report the exceptional adsorption of CH₄ at low pressure and the efficient separation of CH₄/N₂ by MFM-300(Fe). MFM-300(Fe) shows a very high uptake for CH₄ of 0.85 mmol g^-1 at 1 mbar and 298 K and a record CH₄/N₂ selectivity of 45 for porous solids, representing a new benchmark for CH₄ capture and CH₄/N₂ separation. The excellent separation of CH₄/N₂ by MFM-300(Fe) has been confirmed by dynamic breakthrough experiments. In situ neutron powder diffraction, and solid-state nuclear magnetic resonance and diffuse reflectance infrared Fourier transform spectroscopies, coupled with modelling, reveal a unique and strong binding of CH₄ molecules involving Fe-OH⋯CH₄ and C⋯phenyl ring interactions within the pores of MFM-300(Fe), thus promoting the exceptional adsorption of CH₄ at low pressure.