Exceptional Packing Density of Ammonia in a Dual-Functionalized Metal-Organic Framework

We report the reversible adsorption of ammonia (NH3) up to 9.9 mmol g(-1) in a robust Al-based metal-organic framework, MFM-303(Al), which is functionalized with free carboxylic acid and hydroxyl groups. The unique pore environment decorated with these acidic sites results in an exceptional packing density of NH3 at 293 K (0.801 g cm(-3)) comparable to that of solid NH3 at 193 K (0.817 g cm(-3)). In situ synchrotron X-ray diffraction and inelastic neutron scattering reveal the critical role of free -COOH and -OH groups in immobilizing NH3 molecules. Breakthrough experiments confirm the excellent performance of MFM-303(Al) for the capture of NH3 at low concentrations under both dry and wet conditions.

Automated summary

In this study, a robust Al-based metal-organic framework, MFM-303(Al), was reported to show reversible adsorption of ammonia up to 9.9 mmol g(-1), attributed to the presence of free carboxylic acid and hydroxyl groups. The acidic sites within the framework played a critical role in immobilizing NH3 molecules, resulting in exceptional packing density. Breakthrough experiments demonstrated the excellent performance of MFM-303(Al) in capturing NH3 at low concentrations under both dry and wet conditions.