New findings on porous organometallic materials (MOFs) improve water extraction at low humidity. In this way, systems can be built that filter clean drinking water from dry desert air.
Berlin, Germany). In many regions of the world there is hardly any clean drinking water. Science is therefore still looking for new ways of obtaining water. Among other things, a new surface coating made of polymers was recently presented, which makes it possible to extract water from the air by condensation without additional energy at realistic humidity.
Scientist the Humboldt University of Berlin (HU Berlin) have now in the trade magazine Science new findings on porous organometallic materials (MOFS) published. These play a key role in extracting water from desert air, because water molecules get caught particularly well in their tiny cavities. The study that has now been published provides details on the molecular-chemical processes that take place and can therefore help to further optimize the materials.
Porous framework structure
In MOFs, organic substances and metals together form a porous framework structure, which, thanks to its many tiny cavities, has a large internal surface. MOFs based on aluminum therefore make it possible to trap water in the cavities at a humidity of just 20 percent. Then the warmth of the sun ensures that the harvested water is pressed out of the MOF. In this way, clean drinking water can be obtained without additional energy.
Many researchers therefore see MOFs as a key technology for supplying people in arid areas with water. However, research has not yet been able to fully explain how the water molecules get caught in the MOFs.
X-ray crystallography examines cavities
The scientists around Prof. Dr. Joachim Sauer and Prof. Dr. Laura Gagliardi therefore used quantum chemical calculations and X-ray crystallography to investigate the cavities in the MOFs at the atomic level. They were able to determine why the water molecules in the air collect in the organometallic framework.
The first water molecules combine with the organic substances in the MOF. Further water molecules then combine with the molecules that have already been captured in a much better process. This creates clusters in the cavities that grow together to form a network. It is crucial in this process that the first water molecules are not too strongly bonded to the MOF, otherwise it will be difficult to press them out later on the material.
New organometallic materials
On the basis of their new knowledge, the researchers then developed MOFs in which the water molecules can form clusters without bonding firmly to the organic matter. “The development of water-absorbing materials has so far been based on the principle of trial and error. Since we now understand how the molecular evolution of water structures in organometallic materials works, we can optimize them in a targeted manner at the atomic level, ”explains Prof. Dr. Joachim Sauer.
Because water molecules behave differently depending on the humidity and outside temperature, the scientists can now create MOFs that are optimized for certain environmental conditions. MOFs can also be used in cooler areas.
Science, doi: 10.1126/science.abj0890