Gallate-based metal–organic frameworks for the selective removal of trace ammonia via hydrogen bond engineering

Ammonia (NH₃) is a prevalent indoor pollutant, particularly in semiconductor cleanrooms, where it is essential to adhere to stringent regulations that maintain concentration levels below parts per million (ppm). The development of sustainable adsorbents exhibiting high selectivity and adsorption capacity for NH₃ at low partial pressures constitutes a critical yet challenging endeavor within this field. Herein, we introduce a class of isostructural gallate-based metal–organic frameworks (M−GA MOFs, M = Co, Mg, and Mn) endowed with abundant hydrogen bond donors within the pore channels. Notably, the Co-GA MOF exhibits an exceptionally high NH₃ uptake of 3 mmol g⁻¹ at an ultralow pressure of 0.001 mbar, surpassing all previously reported MOFs. Density-functional theory (DFT), independent gradient model based on Hirshfeld partition (IGMH), and quantum theory of atoms in molecules (QTAIM) analyses reveal the presence of strong O-H···N and N-H···O hydrogen bonds between NH₃ and the MOF framework. These interactions, combined with van der Waals forces, contributed to exceptional NH₃ selectivity over CO₂ and N₂, with selectivity exceeding 10⁴ for NH₃/CO₂ = 0.1 %:99.9 %. Breakthrough experiments validate the exceptional removal performance of Co-GA MOFs for trace amounts of NH₃, with a breakthrough point observed at 14 d g⁻¹ for a concentration of 10 ppm NH₃. This work not only advances our understanding of ultralow-pressure gas separation mechanisms but also offers a scalable solution for efficient separation and purification of trace contaminants in environmentally relevant settings.