Synthesis, manufacturing and processing of ZIF-62 and derived glasses. a, crystal structure of ZIF-62 in the A direction. b, Photograph of an enhanced ZIF-62 synthesis with large crystals growing on the walls. c, photograph of 10 g of ZIF-62 (Zn) as synthesized from a single-batch synthesis and micrograph of a typical crystal. d, PXRD data of ZIF-62 and agZIF-62nP and simulated ZIF-zni and ZIF-62. e, Schematic of the in situ heating step for the optical microscope. f, DSC signal to determine Tm of batch ZIF-62 and cyclical analyzes of thermal capacity vsp with heating and cooling rates of 20°C min−1 determine Tg. g, Flowchart of the fusion processing applied to ZIF-62 in this study. ZIF-62 and derived materials are shown in red. Credit: Natural materials (2023). DOI: 10.1038/s41563-023-01738-3
Separating carbon dioxide molecules from gas mixtures requires materials with extremely fine pores. Researchers from the Friedrich Schiller University in Jena, in cooperation with the University of Leipzig and the University of Vienna, have found a new way of doing this.
They transformed crystalline compounds with an organometallic structure into glass. In doing so, they were able to reduce the pore size of the material to the point of making it impermeable to certain gas molecules. They reported their findings in the journal Natural materials.
Compressed metal-organic structures
“In fact, these glass-like materials were previously considered non-porous,” explains Dr. Alexander Knebel from the Otto Schott Institute at the University of Jena, who led this work. “The starting material, i.e. the crystalline framework compounds, have very clearly defined pores and also a large internal surface area. Therefore, they are also sought after as materials for the storage or separation of gases. However, this defined structure is lost during merging and compression. And we took advantage of that.”
“Compounds with a metal-organic structure consist of metal ions linked together by rigid organic molecules,” explains the head of the junior research group. “In the spaces of these three-dimensional, regular grids, gas molecules can move easily. During glass processing, we compressed the material. Simply put, we were able to shrink the pores to the desired size.”
Orderly disorder
Even though the overall structure of the crystal disappears during melting, some parts of the crystal retain their structure. “In technical terms, this means that in the transition from crystal to glass, the long-range order of the material is lost, but the short-range order is preserved,” explains Knebel.
Oksana Smirnova, a doctoral student at the University of Jena and lead author of the work, adds: “When we melt and compress this material, the porous interstices also change.” As a result, channels with bottlenecks or even dead ends are created and, as a result, some gases simply no longer pass through.
The group thus obtained pore diameters of 0.27 to 0.32 nanometers in the material, with precision to a hundredth of a nanometer. “For example: it is about 10,000 times thinner than a human hair and 100 times thinner than a DNA double helix. With this pore size, we were able to separate, for example, carbon dioxide ethane,” Knebel explains. “Our breakthrough in this area probably lies in the high quality of the lenses and the precise adjustment of the pore channels. And our lenses are also several centimeters long.”
“One of the goals of this work is to develop a glass membrane for environmental applications. Because separating carbon dioxide from gases is undoubtedly one of the great technological challenges of our time,” explains Knebel. “That is why I am also grateful… for the exceptional commitment of my doctoral student Oksana Smirnova, who contributed significantly to the success of this work.”
More information:
Oksana Smirnova et al, Precise control of gas transport channels in zeolite imidazolate framed glasses, Natural materials (2023). DOI: 10.1038/s41563-023-01738-3
Provided by Friedrich Schiller University Jena
Quote: Researchers create glass that sifts carbon dioxide (December 20, 2023) retrieved December 20, 2023 from
This document is subject to copyright. Apart from fair use for private study or research purposes, no part may be reproduced without written permission. The content is provided for information only.
