(Left) A schematic showing the crystallization of a 2d ZIF film by dipping a crystalline substrate in ultradilute precursor solution at room temperature. (Right) Crystal structure of the 2d ZIF, where white, blue and red spheres represent carbon, nitrogen and zinc atoms respectively. Image: Qi Liu, EPFL.Metal-organic frameworks (MOFs) are a class of materials with nano-sized pores that give them record-breaking internal surface areas. This makes them extremely useful for a number of applications, including separating petrochemicals and gases, mimicking DNA, producing hydrogen, and removing heavy metals, fluoride anions and even gold from water.
In the gas-separation domain, MOFs are of particularly interest for separating hydrogen from nitrogen, which is crucial for clean energy production, fuel cell efficiency, ammonia synthesis and various industrial processes. Hydrogen-nitrogen separation also has several environmental benefits, making it integral to advancing sustainable technologies and industrial practices.
Now, a team of researchers led by Kumar Varoon Agrawal from the School of Basic Sciences at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland has developed a MOF film with the smallest possible thickness that can perform record levels of hydrogen-nitrogen separation. They report their work in a paper in Nature Materials.
The researchers worked with MOFs known as a zeolitic imidazolate frameworks (ZIFs), which have garnered considerable attention for their potential in molecular separations, sensing and other applications. To make the films, they employed an innovative crystallization method that capitalizes on the precise alignment of ultra-dilute ZIF precursor mixtures with an underlying crystalline substrate. By carefully controlling precursor concentrations and interactions with the substrate, the team were able to suppress out-of-plane growth – a common problem in making thin films.
This approach paid off. Within a matter of minutes, and at room temperature, the scientists were able to fabricate macroscopically uniform two-dimensional (2D) ZIF films with unprecedented thickness – just one structural unit, measuring 2nm. The scientists also showed that this process is scalable, preparing thin films with area of hundreds of square centimeters. In contrast, conventional methods can only fabricate ZIF films with a thickness down to 50nm, making widespread use difficult.
This novel ZIF film has a unique configuration: nanometer-thick with a uniform array of hydrogen-sieving six-membered zinc-imidazolate coordination rings. “This allows for an exceptional combination of hydrogen flux and selectivity, holding immense potential for highly efficient gas-separation applications,” says Agrawal.
This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.