New Process for Making MXenes Via Vapor-Phase Synthesis Could Expand Its Technological Applications

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New Process for Making MXenes Via Vapor-Phase Synthesis Could Expand Its Technological Applications

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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 it takes 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, PhD, 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, PhD, 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."

The researchers also found they could tailor the resulting material by increasing the exposed titanium surface area and confining the reaction within a narrow carrier tube.

Under these conditions, MXene formed on the quartz substrate without direct contact with the solid titanium source. It also self-organized into rounded structures, called "spherulites," which formed a porous nanocrystal network.

As the synthesis time increased, the researchers observed continuous lateral growth into larger flakes. Individual spherulites expanded and merged with neighboring structures, producing swirl-like crystalline domains containing flakes tens of micrometers across.

This discovery shows that crystalline two-dimensional MXene can be synthesized directly via a gas-to-solid growth process. And their continued lateral growth suggests it may be feasible to produce large-area and wafer-scale MXene crystals using this process.

"Scalability and control are long-sought-after goals in materials manufacturing," Gogotsi said. "This process has important similarities to the chloride route used for industrial titania production. Both use titanium tetrachloride as a high-temperature vapor precursor; conceptually, methane supplies carbon in the MXene process, while oxygen is used to form titania. Because titanium chloride is already handled on a very large industrial scale to produce millions of tons of titania, the same engineering principles could ultimately be adapted to produce inexpensive MXene powder in ton-scale quantities."

According to the researchers, continued control over nucleation and lateral growth could eventually enable large-area, low-defect MXene crystals and even wafer-scale conducting films for use in electronics, optical communication and quantum computing technologies.

In addition, the group sourced its precursor material from a titanium sponge rather than the high-purity titanium foil used in the University of Chicago study that reported the first synthesis of MXene using the chemical vapor deposition process. This was an important development because titanium sponge is an abundant industrial product that is substantially less costly than high-purity titanium.

The next step in this research will involve refining the process to ensure structural uniformity, increase flake size, and achieve precise control over the surface chemistry of the MXenes produced. The team will also continue to adjust the process to produce MXenes with other compositions for various applications.

In addition to Gogotsi, Jongyoun Kim and Teng Zhang, from Drexel University; Yasunori Hioki, of Murata Manufacturing Co., Ltd.; and Swarnendu Das and Eric A. Stach, from the University of Pennsylvania, also contributed to this research.

This research was supported by the U.S. National Science Foundation, U.S. Department of Energy, and Murata Manufacturing Co., Ltd. Authors declare the following competing financial interest(s): Hyunho Kim, Yasunori Hioki and Yury Gogotsi are inventors of a patent application related to this work, filed by Murata Manufacturing Co., Ltd. on 06/20/2025, application number: 63/827303. The authors declare no other competing financial interests.

Read the full paper here: https://pubs.acs.org/jacsat/article/doi/10.1021/jacs.6c10774/5260618/Vapor-Phase-Synthesis-of-Ti2CCl2-MXene

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