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Researchers Gain New Insights Into MXenes' Unusual Chemistry
February 5, 2019

2-D titanium carbide materials (MXenes) are one of the largest families of 2-D materials. They are a few atom-thick sheets with the structures of transition-metal carbides and nitrides. Their distinctive properties include high electrical conductivity and the ability to disperse in water, a unique combination which has earned them a nickname “conductive clays.”

MXenes’ reactivity toward water is shown in this experiment where a Ti carbide MXene survives longer in an oxygen-saturated, non-aqueous system, in contrast to the same MXene dispersed in argon-saturated water. Credit: Shuohan Huang.

Now, according to new information provided by Missouri University of Science and Technology (Missouri S&T), researchers have discovered that MXenes can react with water without the presence of other oxidizers. Their finding, detailed in a paper titled “Hydrolysis of 2D Transition Metal Carbides (MXenes) in Colloidal Solutions,” published recently in the American Chemical Society (ACS) journal Inorganic Chemistry, may lead to new insights into the unusual chemistry of MXenes and consequently, have impacts on MXenes’ storage and device manufacturing.

“Our new findings are important because now we know it is water itself rather than oxygen that MXenes need to be protected from during manufacturing and storage,” explained Shuohan Huang, a doctoral student in chemistry at Missouri S&T.

Researchers are excited about the potential use of MXenes in energy storage and harvesting applications such as batteries, supercapacitors and triboelectric nanogenerators, which convert wasted frictional energy into electricity, according to Dr. Vadym Mochalin, associate professor of chemistry at Missouri S&T, who is the principal investigator of this project.

“The reactivity of MXenes toward water we’ve demonstrated not only changes the common perception about resistance of titanium carbide to hydrolysis in ambient conditions, but also points out the striking differences in chemical properties between bulk and 2-D forms of the same material,” explained Prof. Mochalin.

To arrive at their “water-only” conclusion, Huang and Prof. Mochalin systematically tested the hydrolysis and chemical stability of MXenes Ti3C2Tx and Ti2CTx in water and non-aqueous colloidal solutions exposed to oxygen and/or inert gas environments in different combinations, as the example shown in the image.

“It seems that in their 2-D state, transition-metal carbides are quite reactive,” noted Prof. Mochalin. “With our result, we’re looking forward to follow-up studies of their rich chemistry in reactions with water and other molecules, including organic compounds, as well as studies into MXenes’ possible catalytic properties.”

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