Ultrastable Hydrogen-Bonded Organic Framework for Efficient CO₂/CH₄ Separation in Humid Environments

Selective CO₂ removal during methane purification is critical for energy-efficient utilization. The development of porous adsorbents integrating ultrahigh structural stability, excellent separation capability, and moisture resistance represents a desirable yet challenging objective for upgrading natural gas. Unlike conventional synthesis strategies for hydrogen‑bonded organic frameworks (HOFs) that utilize strong hydrogen-bonding groups such as carboxylic acid groups and 2,4-diaminotriazine, this study employs aldehyde functionalities to construct a novel HOF (HFPTP-HOF) with exceptional moisture resistance and ultrahigh stability. At 298 K and 1 atm, the material exhibits an IAST selectivity of 18.61 for equimolar CO₂/CH₄ mixtures, representing the highest values among reported HOF materials. Dynamic breakthrough experiments confirm its ability to produce 99.99% pure CH₄. More notably, the HOF adopts a distinctive interlayer stacking structure formed by synergistic interligand multiple C-H⋯O hydrogen bonding and interdigitation. This interlayer stacking architecture imparts remarkable stability to HFPTP-HOF by encapsulating the hydrogen bonds responsible for framework formation within a hydrophobic barrier, which allows it to retain structural integrity even when immersed in 12 M hydrochloric acid at 50°C, 20 M sodium hydroxide at 100°C or boiling water for 7 days. To our knowledge, this stability exceeds those of all reported HOFs. In addition, within the HOF's pore channels, aldehyde groups and hydrophobic benzene rings are distributed on opposite sides of the pores. This spatial arrangement effectively prevents water molecule clustering within the pores, enabling HFPTP-HOF to maintain outstanding CO₂/CH₄ separation performance even under 90% RH. Overall, this work provides new insights into the design and synthesis of HOFs that combine ultrahigh stability with exceptional humidity‑resistant separation efficiency.