This figure shows the structure of hydrolytically stable and highly porous Cr-soc-MOF-1, which can capture twice its weight in adsorbed water. Image: Prof. Mohamed Eddaoudi (KAUST).Material chemists in Saudi Arabia have developed a superporous solid known as a metal-organic framework (MOF), made up of a patchwork of metal ions and organic linkers, that can suck up to 200% its own weight in atmospheric moisture. The material, reported in a paper in Chem, could be used for regulating humidity levels, particularly in confined environments such as aircraft cabins and air-conditioned buildings.
"I am not surprised that MOFs surpass existing solids in their water capacity uptake," says senior author Mohamed Eddaoudi at the King Abdullah University of Science and Technology (KAUST). "MOFs' modularity, ultra-high surface areas and large pore volumes, combined with the ability to control the pore surface functionality and pore size and shape, place MOFs as prospective candidates for energy-efficient and cost-effective humidity-control systems."
Permanently porous superabsorbent materials that possess a combination of hydrolytic stability (stable in water) and significant water uptake are challenging to make because most porous solids are either too dense or too reactive with water. Eddaoudi and his collaborators overcame this problem with their synthesis of Cr-soc-MOF-1, a MOF comprising chromium (Cr) ions linked together by carboxylate-based organic ligands that create well-defined cages and channels where water can collect. The chromium ions are held in place by carboxylate moieties in a bidentate fashion, forming a rigid hexacarboxylate oxo-trinuclear chromium(III) cluster, which provides the resultant Cr-soc-MOF-1 adsorbent with the required hydrolytic stability.
The researchers tested Cr-soc-MOF-1's water adsorption properties and found that its water uptake increases gradually up to a relative humidity of 55%, before speeding up between 60% and 75% relative humidity. As this point, the MOF reaches its maximum capacity, where it can capture nearly twice its weight in adsorbed water (1.95 g/g). Markedly, Cr-soc-MOF-1 maintained its structural integrity and performance over more than 100 water vapor adsorption-desorption cycles.
Now the researchers have a material that can readily regulate humidity by absorbing and releasing water, they are engaged in collaborative work to develop a humidity-control device.
"In 20 years we went from a folklore that MOFs are not stable and are just pretty structures to MOFs with unprecedented hydrolytic stability and exceptional properties relevant to energy security and environmental sustainability," Eddaoudi says. "There is no doubt in my mind that the future of MOFs is bright, and the only limitation will be the scientist's imagination on where MOFs can be deployed effectively and efficiently."
This story is adapted from material from Cell Press, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.