Providing all of humanity with sufficient clean drinking water is a Herculean task. This is especially true in desert areas. The problem is also likely to get worse in the future. Because climate change is causing many regions on earth to become increasingly drier. In addition, the distribution of rainfall changes. In some regions it tends to rain less, but then all the more heavily. A few years ago, researchers therefore developed a system to extract valuable drinking water even from dry desert air. They used so-called organometallic materials for this. These formed a porous framework structure with numerous small cavities. The individual water molecules then got caught in these. Subsequently, the abundant heat from the sun in the desert was used to initially allow the water to evaporate. Cooling fins then provided the necessary condensation to guide the cool water into the tank container.
X-ray crystallography brought valuable insights to light
In this way, a prototype built at the time filtered around three liters of drinking water from the air per day. This would be enough to provide at least one human with it. However, the development of water catching technology was largely based on the principle of trial and error. So far, the researchers have not been able to explain why the molecules stuck to certain organometallic materials better than others. This has now changed. An international research team led by Joachim Sauer from the Humboldt University in Berlin has examined the processes in more detail with the help of X-ray crystallography and quantum mechanical calculations. Most important finding: Only the first water molecules actually stick to the solid structures. After that, chains of water molecules are formed first. This then becomes individual clusters and ultimately even a network of clusters. This understanding is of crucial importance in order to further advance the technology of extracting water from desert air.
Water molecules always behave a little differently
The way in which the water collects in the porous framework is important for the later water harvest. The researchers emphasize that the initial molecules must not stick too tightly to the organic structures. Because then it is harder to get them out later with the help of the sun. This explains why more water could be obtained with some materials and less with others. The knowledge also helps in the development of new organometallic materials. Because water molecules always behave a little differently depending on the humidity and temperature. So there will never be an organometallic material that works equally well all over the world. Instead, the researchers are now working on developing grid structures that are each optimized for specific locations. This should increase the amount of water obtained again.