This scanning electron microscope image reveals the beautiful, flowery shapes of tiny structures known as MXenes. Image: Di Wang.
This scanning electron microscope image reveals the beautiful, flowery shapes of tiny structures known as MXenes. Image: Di Wang.

The secret to a perfect croissant is the layers – as many as possible, each one interspersed with butter. Similarly, a new material with promise for novel applications is made of many extremely thin layers of metal, between which scientists can slip different ions for various purposes. This makes them potentially very useful for future high-tech electronics and energy storage.

Until recently, these materials – known as MXenes, pronounced ‘max-eens’—were as labor-intensive to make as good croissants in a French bakery. But in a new breakthrough, researchers at the University of Chicago have shown how to make MXenes far more quickly and easily, with fewer toxic by-products.

The researchers hope that their advance, reported in a paper in Science, will spur new innovation and pave the way towards using MXenes in everyday electronics and devices.

When they were discovered in 2011, MXenes made a lot of scientists very excited. Usually, when you shave a metal like gold or titanium to create atomic-thin sheets, it stops behaving like a metal. But unusually strong chemical bonds in MXenes allow them to retain the special abilities of metal, like conducting electricity strongly.

They’re also easily customizable: “You can put ions between the layers to use them to store energy, for example,” said chemistry graduate student Di Wang, co-first author of the paper along with postdoctoral scholar Chenkun Zhou.

All of these advantages could make MXenes extremely useful for building new devices – for example, to store electricity or block electromagnetic wave interference. However, the only known way to make MXenes involves several intensive chemical engineering steps, including heating the mixture at 3000°F followed by a bath in hydrofluoric acid.

“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,” explained Dmitri Talapin, professor of chemistry at the University of Chicago, joint appointee at Argonne National Laboratory and corresponding author of the paper.

To design a more efficient and less toxic method, the researchers utilized the principles of chemistry—in particular ‘atom economy’, which seeks to minimize the number of wasted atoms during a reaction.

In this way, they discovered new chemical reactions that allow them to make MXenes from simple and inexpensive precursors, without the use of hydrofluoric acid. It consists of just one step: mixing several chemicals with whatever metal you wish to make layers from and heating the mixture at 1700°F. “Then you open it up and there they are,” said Wang.

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

This story is adapted from material from the University of Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.