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

Abstract Effective removal of trace ammonia (NH ₃ ) is essential to mitigate its adverse effects on human health and the environment. However, capturing NH ₃ 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 µ ₂ ‐OH groups is synthesized as a highly efficient adsorbent for NH ₃ capture from polluted air. MIL‐120 exhibits a high static NH ₃ uptake of 7.8 mmol g ⁻¹ at 298 K and 1 bar. Under trace conditions (100 ppm NH ₃ ), 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 NH ₃ affinity arises from a synergistic effect between ultramicropore confinement and strong hydrogen bonding at µ ₂ ‐OH sites. This work highlights MIL‐120 as a promising candidate for trace NH ₃ capture and provides critical insights for the rational design of next‐generation MOF‐based air purification materials.