A Robust Ultramicroporous Aluminum-Based Metal─Organic Framework for Efficient Deep Removal of Trace Ammonia from Air

Effective removal of trace ammonia (NH₃) is essential to mitigate its adverse effects on human health and the environment. However, capturing NH₃ at ultra-low concentrations remains challenging due to its weak interactions with conventional adsorbents. In this study, a novel ultramicroporous aluminum-based metal-organic framework, MIL-120, with 1D channels (5.4 Å × 4.7 Å) densely functionalized with µ₂-OH groups is synthesized as a highly efficient adsorbent for NH₃ capture from polluted air. MIL-120 exhibits a high static NH₃ uptake of 7.8 mmol g^-1 at 298 K and 1 bar. Under trace conditions (100 ppm NH₃), dynamic breakthrough experiments reveal a notable adsorption capacity of 0.68 mmol g^-1, demonstrating a significant performance advantage over similar adsorbents. In situ FTIR spectroscopy combined with density functional theory (DFT) calculations confirms that the enhanced NH₃ affinity arises from a synergistic effect between ultramicropore confinement and strong hydrogen bonding at µ₂-OH sites. This work highlights MIL-120 as a promising candidate for trace NH₃ capture and provides critical insights for the rational design of next-generation MOF-based air purification materials.