Researchers at Germany’s Fraunhofer Institute of Solar Energy Systems have developed highly-porous metal organic frameworks (MOFs) that can be applied in a thin layer to efficiently absorb large quantities of water vapor.
MOFs, as determined by research published in RSC Advances, are three-dimensional porous structures consisting of metallic clusters and organic linkers adept at absorbing water vapor.
“MOFs can be put together arbitrarily like Lego bricks and outperform every previously known class of material in terms of flexibility,” Stefan Henninger, Ph.D., head of the Sorption Materials Group at the Initiative for Science in Europe (ISE), said in a recent press release. “The materials are porous and have interior surfaces which can add up to 4,000 square meters per gram. This is sufficient space for the water vapor to be able to adsorb and accumulate.”
MOFs have the largest inner surface area of any known material, and when applied as a thin layer to structures or systems, can dramatically improve heat conductivity. Because of this, MOFs have huge implications in a variety of products that involve heat transfer and are predicted to be of use in such diverse industries as chemical manufacturing, gas and liquid detectors, medical technology and more.
After developing MOFs and determining their usefulness, the next challenge for researchers was finding a way to apply MOF technology not as a powder – the form MOFs are usually available in – but as a layer, which would maximize surface area and be significantly easier to incorporate into structures than loose granules. After subsequent research and testing, the researchers were able to determine a way to apply MOFs in a thin layer, a significant breakthrough in the technology. When applied thus, the MOFs require no other auxiliary layers, and range from 50-150 micrometers, a good thickness for cooling and heating.
“In the past, the material has been used in loose grain configuration as a filling between e.g. lamella heat exchangers,” Henninger said. “Now we have developed two patented processes in which we can apply different MOFs or other adsorbents directly onto the heat exchanger structures. This not only increases the cooling or heating efficiency of the system but also makes the unit much more compact.”
One of these processes involves direct crystallization of MOFs onto metals, while the other involves binder-based coatings used on materials like ceramic. In both processes, to apply MOFs upon a device, a material is submerged in a fluid consisting of its “essential components.” Because of this, the temperature required for crystallization occurs only on the surface of the device, producing minimal waste. Thus, MOFs require only a simple “dipping” process to be applied.
“The MOF layer grows directly on the component at a rate of up to 50 micrometers per hour. This is significantly faster than before,” Henninger said.
This finding could have huge implications in not only industrial cooling and heating technologies, but also medical and consumer products. For example, Henninger predicts that MOFs could be layered on surgical equipment to reduce bacterial content, or on plastic dinnerware to limit stains.
“Due to the enormous flexibility of MOFs and our manufacturing process, a variety of applications is possible,” Henninger said. “We can apply the desired structure quickly to almost any component. In principle, our technology could be beneficial for every process in which material or heat transfer plays a role.”
– Melanie Abeygunawardana