Tailoring Pore Environment of Metal–Organic Framework via In Situ Ligand Reaction Strategy to Boost CH 4 /N 2 Separation

Low-concentration coalbed gases are vital energy resources, but more significant amounts of N2 severely limit the efficient utilization of their primary component CH4. Due to their similar physicochemical properties, separating CH4 from N2 remains highly challenging. Adsorption using porous materials has emerged as a promising approach for CH4/N2 separation. Herein, we developed an in situ ligand reaction strategy to engineer the pore shape and chemical environment of a copper-based metal–organic framework (NUC-201Cu), achieving efficient CH4/N2 mixture separation. Structural characterization elucidated the successful modulation of pore geometry and in situ conversion of CN groups into tetrazole groups during the one-spot MOF synthesis process. The single-component adsorption isotherm of NUC-201Cu exhibits a high CH4 adsorption capacity of 36.4 cm3/g at 298 K and 1 bar, surpassing most reported MOFs for CH4/N2 separation. Theoretical calculations unveiled that the suitable pore geometry and polarized tetrazole groups optimized pore environments to establish preferential interactions with CH4 via C–H···N hydrogen bonds. In situ time-dependent infrared spectroscopy further confirmed the strong host–guest interaction between the framework and CH4. Breakthrough experiments verified the exceptional CH4/N2 separation performance of NUC-201Cu under different dynamic separation processes. This research establishes an in situ ligand reaction strategy to optimize the pore adsorption environment for effective separation of CH4/N2.