This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: MXenes are two-dimensional nanomaterials first synthesized at Drexel University in 2011. They have been recognized by the International Union of Pure and Applied Chemistry as an emerging technology with "true potential to transform our world." But their widespread use has thus far been limited by the complicated process required to produce them.
In a recent paper, researchers from Drexel, with collaborators at the University of Pennsylvania and Murata Manufacturing Co. Ltd., show that a process called chemical vapor deposition can be tailored to produce the nanomaterials in a form, quality and quantity—and potentially at a lower cost—that could one day allow them to be used in electronic, environmental and quantum technologies. Since their discovery a decade and a half ago, MXenes have been tested for a range of uses, from energy storage to water filtration to electromagnetic shielding, but the process for making these two-dimensional materials has remained limited in several key ways.
The current process involves combining a precursor—a nanomaterial in powder form called a MAX phase—with a liquid etchant, such as hydrofluoric acid, repeatedly agitating the mixture, washing the product and then spinning it in a centrifuge multiple times to remove the reaction's byproducts. This produces MXene material in a form that requires further processing to turn it into an ink, coating or film, depending on how it will be used. According to the researchers, these steps—including the process of making the MAX phase precursor—all add cost and time to the process that have thus far slowed its progress toward more widespread commercial adoption.
In addition, the wet chemical etching process generates toxic waste and may lead to flaws in the surface of the MXene flakes. "While this process has been tailored to make MXenes of varying chemical compositions and scaled up to produce them in kilograms per day, it requires a separately synthesized precursor," said Yury Gogotsi, Ph.D., distinguished university and Bach chair professor in Drexel's Nick Howley College of Engineering and Computing, who led the research and is one of the Drexel researchers who discovered MXenes. "Being able to combine a solid metal source with abundant and inexpensive gaseous reactants to form MXenes directly opens a different manufacturing pathway." Their new approach, using a vapor-phase deposition process pioneered by researchers at the University of Chicago, was reported by Gogotsi and his collaborators in the Journal of the American Chemical Society.
It bypasses both the MAX phase synthesis and acid-etching steps. It also introduces lower-cost precursor materials: titanium tetrachloride, which is used to make titania—the white pigment in paint and sunblock—and methane, also known as natural gas. To do it, the researchers placed titanium powder in a quartz carrier tube, added methane and heated the mixture in a conventional tube furnace to trigger the reaction.
As the gaseous mixture cooled, a layer of MXene formed on the quartz substrate. "Being able to grow crystalline MXene directly from abundant precursors, without first making and etching extra precursor materials, is a significant development," said Hyunho Kim, Ph.D., a research professor at Sungkyunkwan University in South Korea, who is the first author of the paper and conducted the research as a postdoctoral assistant in Gogotsi's lab. "MXene inks made by selective etching remain valuable for coatings and printed devices, while vapor-phase synthesis gives us a complementary route to crystals with extremely low defect density for future electronics, optics and quantum technologies." Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly.
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