Tailoring Superhydrophobic Ultramicropores in Covalent Organic Frameworks for Humidity-Resistant Methane Purification

Efficient purification of methane from raw natural gas under humid conditions remains challenging because water adsorption often degrades the separation performance and structural stability of porous adsorbents. Here we report a topology- and stacking-guided molecular design strategy that integrates ultramicropore engineering with pore-surface fluorination to construct superhydrophobic covalent organic frameworks (COFs) for humidity-resistant methane purification. Two isoreticular fluorinated COFs, TF-COF and NF-COF, were constructed by rationally controlling framework topology and interlayer stacking, generating well-defined ultramicropores for size-selective discrimination of C1-C3 hydrocarbons. Fluorination simultaneously enhances pore-wall hydrophobicity and strengthens host-guest interactions, creating a confined adsorption environment that promotes hydrocarbon recognition while effectively suppressing competitive water adsorption. As a result, NF-COF exhibits a propane uptake of 99.4 cm3 g-1 and an exceptional C3H8/CH4 IAST selectivity of 251.7 at 298 K. Dynamic breakthrough experiments further demonstrate efficient methane purification under both dry and highly humid conditions, with the separation performance fully retained at 97% relative humidity owing to its superhydrophobic surface. Theoretical calculations reveal that densely distributed fluorine atoms generate synergistic pore confinement and multiple C-H···F van der Waals interactions, simultaneously maximizing adsorption capacity and molecular discrimination. These findings establish fluorinated superhydrophobic COFs as a robust platform for energy-efficient natural gas upgrading under industrially relevant humid conditions.