UChicago discovers efficient MXene recipe

Researchers from the University of Chicago have discovered the secret recipe for creating MXene. Much like a croissant with its individual layers painstakingly kneaded twixt generous amounts of butter, this breakthrough results in a beautiful flakey 2D material that could usher in a new era of electronics.

Until recently, MXenes (pronounced "max-eens") were as labor-intensive as good croissants in a French bakery. Involving several stringent chemical engineering steps, including heating the mixture to 3,000 degrees Fahrenheit (1,649 degrees Celsius) and then submerging it in a bath of hydrofluoric acid, MXenes presented a new realm of scientific discovery. For anything outside the scope of lab scale, however, this messy and energy-intensive process was impossible at best.

"This is fine if you're making a few grams for experiments in the laboratory, but if you wanted to make large amounts to use in commercial products, it would become a major corrosive waste disposal issue," said Dmitri Talapin, professor of chemistry at the University of Chicago and corresponding author of the paper published on their findings.

Discovered in 2011, MXenes made a lot of scientists very excited. Usually, when metal is shaved down, like gold or titanium, to create atomic-thin sheets, it no longer behaves like a metal.

But the unusually strong chemical bonds in MXenes allow them to retain the special abilities of metal, such as conductivity, and strongly at that.

Additionally, MXenes are also easily customizable, "You can put ions between the layers to use them to store energy, for example," said chemistry graduate student Di Wang and co-first author of the paper.

All of these advantages could make MXenes extremely useful for building new devices – such as energy storage or even for blocking electromagnetic wave interference. However, the issue of production had yet to be overcome, until now.

To design a more efficient and less toxic method, the team used a principle of chemistry called "atom economy," which seeks to minimize the number of wasted atoms during a reaction.

Published March 24 in the journal "Science," the UChicago team discovered new chemical reactions that allow scientists to make MXenes from simple and inexpensive precursors, and without the use of hydrofluoric acid.

Consisting of a single step, the process involves mixing several unnamed chemicals with whichever metal for its desired layers, then heating the mixture to 1,700 degrees Fahrenheit (927 degrees Celsius).

"Then you open it up and there they are," said Wang.

This new, easier, and less toxic method opens new avenues for scientists to create and explore varieties of MXenes for different applications – such as metal alloys or ion flavorings. The team tested the method with titanium and zirconium metals, but the researchers think that the technique can also be used for many other different combinations.

"These new MXenes are also visually beautiful," Wang added. "They stand up like flowers – which may even make them better for reactions, because the edges are exposed and accessible for ions and molecules to move in between the metal layers."

While flower-like when examined with a scanning electron microscope, upon closer examination, the layers resemble the flakey sections of a perfectly baked croissant – except unlike flour and butter, MXenes are metals and ions.

With this breakthrough in 2D materials, whether the university spurs a start-up or is put out to the academic community, a future made with MXenes is going to be one to look forward to.