Credit: © 2009 ACS

Metal–organic frameworks (MOFs) — porous materials consisting of metal ions or clusters linked by organic ligands — are widely studied for applications that involve adsorbing guest molecules. Hydrothermal stability is a critical property of MOFs, which would allow advantageous processing conditions and the possibility of their regeneration. Now, a team led by Richard Willis and John Low from the UOP Research Center in Illinois have developed1 a theoretical method for screening MOFs for hydrothermal stability that agrees well with the results of their high-throughput stability tests.

They model the reaction between water and a ligand–metal cluster — with a simplified organic ligand — using density functional theory and calculate reaction activation energies. The validity of the model was confirmed by comparing calculated values with the hydrothermal stability of various related MOFs. This was measured experimentally using a high-capacity reactor that consisted of 48 parallel heaters. Their stability was determined using X-ray diffraction to measure structural changes on exposure to a carrier gas loaded with various concentrations of water at different temperatures.

The observed trends highlight the importance of ligand–metal bond strength to hydrothermal stability. The results show how this theoretical method could be used to 'virtually' screen a large number of MOFs, selecting those most likely to be hydrothermally stable for further study.