Ammonia Hydration in a Cu(II)-Pyrazolate Framework for Efficient Trace Capture

Ammonia (NH₃) emissions from industrial and agricultural activities pose severe environmental and health issues. Trace NH₃ capture typically relies on chemisorption at Lewis acid sites or physisorption on porous adsorbents but usually suffers from irreversible binding, energy-intensive regeneration, and structural degradation. In this work, for the first time, we demonstrate a new hydration pathway as a promising solution. In a Cu(II)-pyrazolate framework, BUT-64(H₂O), the bridging water molecules between adjacent Cu(II) ions serve as Brønsted acid sites to hydrate ammonia, achieving a remarkable NH₃ packing density of 0.27 g cm⁻³ at 0.1 kPa and an adsorption capacity of 1.51 mmol g⁻¹ for 1000 ppm NH₃ under 80% relative humidity, among the leading adsorbents. The reversible hydration mechanism combines enhanced NH₃ affinity with facile regeneration and mitigated moisture co-adsorption, overcoming the inherent trade-off. The remarkable alkaline stability of this material also highlights its potential as an energy-efficient sorbent for trace NH₃ capture.