Precise Pore Structure Regulation of an Oxalate-Functionalized Metal–Organic Framework for Efficient Carbon Dioxide Sieving with High Capacity

Adsorptive separation of carbon dioxide from methane is a crucial process for natural gas and biogas upgrading. Designing porous materials with both high CO2 uptake capacity and high selectivity remains challenging. Herein, we realized the efficient sieving of CH4 from CO2, with a high adsorption capacity (4.54 mmol/g at 298 K and 5 bar), by an oxalate-functionalized metal–organic framework ZU-301a decorated by high-density oxalate anions and hydrophobic methyls. Specifically, ZU-301a featuring a regularly layered three-dimensional configuration was obtained by the facile post-treatment of the previous material ZU-301 with the spiral pore structure. ZU-301a exhibited improved porosity and narrower pore size via the precise configuration regulation, leading to a 69% increase in CO2 adsorption capacity at 298 K and 5 bar. Breakthrough experiments further confirmed the superior separation ability of ZU-301a for CO2/CH4 separation under various temperature conditions. A dual-bed six-step vacuum pressure swing adsorption (VPSA) simulation process was designed, and 99.59% high purity CO2 as well as a high CO2 recovery rate (98.01%) was obtained from a CO2/CH4 (50/50) mixture. Additionally, DFT calculations revealed that the strong binding of CO2 is mainly due to the electrostatic interactions with C(δ+) on the CO2 molecules and with O(δ–) on oxalic acid. These findings not only demonstrate an efficient configuration regulation strategy to build ultramicroporous metal–organic frameworks but also suggest a potential use of the CO2 VPSA process for natural gas and biogas upgrading.