Installing Methyl Group Guards in a Metal–Organic Framework Featuring Multiple N/O Active Sites for Efficient C₂H₂/CO₂ Separation under Moist Conditions

C2H2/CO2 separation is still a challenging task due to their very close physical properties. Metal–organic frameworks (MOFs) with accessible N/O active sites exhibit excellent affinities to capture C2H2 from the C2H2/CO2 mixture; however, their performance is usually affected by moisture impurities. To address this matter, a new methylated MOF (TUTQ-1Ni) featuring multiple N/O active sites was successfully constructed. TUTQ-1Ni exhibited a record high C2H2/CO2 uptake ratio of 4.1 and top tier C2H2/CO2 selectivity (11.4) among the reported hydrophobic adsorbents. Single crystal X-ray diffraction studies combined with theoretical calculations indicated that multiple N/O sites provided strong and multiple attractive interactions for C2H2 over CO2. Breakthrough experiments demonstrated that TUTQ-1Ni efficiently separated C2H2/CO2 mixtures, affording a high separation factor of 7.4. Benefiting from the high density of methyl groups, the C2H2/CO2 separation performance of TUTQ-1Ni was even maintained at a high relative humidity of 85%.