How to put as much gas as possible in a given volume? Theory tells us that a simple solution exists. All you have to do is increase the pressure: twice as much thrust brings in about twice as many molecules. 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 the 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 breathes”indicates David Farrusseng, director of research at the CNRS at the Institute for Research on Catalysis and the Environment (Lyon) and director of Smolab, but who did not participate in this study.
This “breathing” molecule belongs to the third generation of a family developed in the early 2000s, metal-organic networks, or MOFs (in English, metal-organic framework). They are crystalline solids which are porous and regular, unlike sponges, foams or other activated carbons, which are more disorderly. Their skeleton is made up of metal “knots” (zinc, copper, etc.) linked by ligands made up of fairly long organic molecules. The first generation could trap gases, but the building broke 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, supple or therefore “breathable”, according to various qualifiers. The links of the network indeed slide into each other according to the stimuli applied, chemical, electrical, light…
Several issues fixed
This time, the research team shows that this “breathing” depends on the 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 means that it has a good affinity for its fellows, that it is not ready to let go. Up to 50% of the gas introduced can remain there and therefore be lost, possibly recoverable by heating, which requires energy and increases costs.
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