Researchers from the University of Limerick, Maynooth University, and Chinese institutions have detailed the water adsorption mechanism and atmospheric water harvesting performance of a hydrolytically stable metal-organic framework, according to a peer-reviewed study published in Nature Communications on August 7, 2026.
The study evaluated two bnn-topology rod building block (RBB) metal-organic frameworks with the formula M2F2(tzba)(bpy)2, where tzba represents 4-(1H-tetrazol-5-yl)benzoate and M is either cobalt or nickel. These frameworks, designated bnn-1-Co and the previously reported bnn-1-Ni, are built using an RBB made of three bridging moieties: fluoride, carboxylate, and tetrazolate.
Testing showed that bnn-1-Ni delivers material-level atmospheric water harvesting performance driven by an uptake threshold below 20% relative humidity, minimal hysteresis, fast loading kinetics, and a regeneration temperature of 60 °C or lower. Under simulated temperature swing conditions, the material demonstrated cycling stability over more than 100 cycles and achieved a projected gravimetric water productivity of 0.3044 wt% min−1, or 4.38 kg−1 kg−1 d−1.
Using single-crystal X-ray diffraction and density functional theory calculations, the researchers observed water loading at the molecular level. The analysis revealed that the first water molecule binds to a site with multiple hydrogen bonds, showing an adsorption energy of −75 kJ mol−1. This initial molecule anchors the formation of subsequent water layers, which exhibit an average adsorption energy of −59 kJ mol−1.
The cobalt counterpart, bnn-1-Co, showed lower hydrolytic stability than bnn-1-Ni. The authors attributed this difference to stronger Ni-N/O/F coordination bonds compared to corresponding Co-N/O/F bonds.
Computational facilities and support for the research were provided by the Irish Centre for High-End Computing. Grant funding supported researchers through Research Ireland, Enterprise Ireland, and the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement number 847402.
