How to put as much gas as possible in a given volume? The theory tells us that a simple solution exists. It is enough to increase the pressure: twice as much thrust causes about twice as many molecules to enter it. But not all gases like to be pressurized, and some can even explode. This is the case of acetylene, a fairly simple gas, widely used for flame welding which, at room temperature, can detonate at only twice atmospheric pressure.
To solve this problem, Air liquide and academic partners (CNRS, Chimie Paris Tech, Kyoto University), collaborating within the international laboratory Smolab, have just proposed, in Nature Chemistry, a new solution thanks to a rather amazing material. “Some say he’s breathing”, indicates David Farrusseng, research director at the CNRS at the Institute for Research on Catalysis and the environment (Lyon) and director of the Smolab, but who did not participate in this study.
This “breathable” molecule belongs to the third generation of a family developed in the early 2000s, the metallo-organic networks, or MOF (in English, metal-organic framework). They are crystalline solids that are porous and regular, unlike sponges, foams or other activated carbons, which are more disordered. Their skeleton consists of metal “nodes” (zinc, copper, …) connected by ligands consisting of fairly long organic molecules. The first generation could trap gases, but the building would break apart when the gas left. The second was rigid, with cavities of fixed dimensions. And the third, which appeared in the mid-2000s, is flexible, modular, flexible or therefore “breathable”, according to various qualifiers. The links of the network indeed slide into each other according to the applied stimuli, chemical, electrical, luminous…
Several problems solved
This time, the team of researchers shows that this “breathing” depends on pressure. Their molecule has two states, “open” and “closed”, with larger holes in the first state than in the second. The molecule thus solves several problems. In general, porous materials capture gases well, but struggle to release them, because if the gas has entered it is because it has a good affinity for its congeners, which it is not ready to let go. Up to 50% of the introduced gas can remain there and therefore be lost, possibly recoverable by heating, which requires energy and increases costs.
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