Methyl-Functionalized Al-Based MOF ZJU-620(Al): A Potential Physisorbent for Carbon Dioxide Capture

Developing Al-based metal-organic frameworks (MOFs) with moisture-resistance ability is a challenge for carbon dioxide (CO₂) capture. Methyl-functionalized Al-based MOF ZJU-620(Al), with excellent chemical-thermal stability and specific surface area of 1347 m²/g, observed here, is a potential adsorbent for CO₂ capture with good recyclability and large capacity up to 4.25 mmol/g at 298 K and 1 atm. CO₂ molecules are largely trapped on two types of sites. One (site I) is near the AlO₆ clusters, and another (site II) is between two parallel benzene rings with a distance of 6.64 Å. ZJU-620(Al) can be used for CO₂/N₂ (15/85) separation with the excellent selectivity up to 107.20 at 273 K and 31.93 at 298 K, and the separation factor of 13.68. It is also with excellent moisture-resistance ability due to 5% breakthrough time (outlet concentration reached the 5% of inlet concentration) without reduction at 80% relative humidity than under dry conditions. Water molecules occupy a small amount of CO₂ adsorption site I, but they almost do not occupy the CO₂ adsorption site II due to hydrophobic methyl-functional ligands. Moreover, CO₂ can be adsorbed on the ZJU-620(Al) surface through C═O···H binding of water molecules with high affinity. Thus, ZJU-620(Al) is a candidate adsorbent for CO₂ capture and separation especially under humidity conditions.