Taking 2D Materials to the MAX

Estimated reading time: 3 minutes

“Having the know-how to prepare good-quality MXenes is key to achieving excellent performance,” says Alshareef. To make the 2D MXene atomic crystals, the parent material, known as MAX phase, is first prepared using conventional ceramic processing technology. The M in MAX represents a transition metal, such as titanium; A is typically aluminum; and X is carbon or nitrogen. Solution processing methods are used to selectively remove aluminum to create two-dimensional crystals. These crystals are placed in suspensions that are then used to make films, gels, sheets and quantum dots of MXene.

The challenges in making MXenes is that temperatures as high as 1700 degrees Celsius are needed to make the parent MAX phase, and HF is needed to etch out the aluminum. “We are developing processes to simplify the synthesis protocols and to make them more environmentally friendly and energy efficient to prepare,” Alshareef says.

Developing New Devices

Recently, Alshareef and his group developed MXene-based soft, super-stretchy polymers called hydrogels. “We call it MXene smart skin,” Alshareef says. “It is stretchable by 3,400 percent, self-healing, soft and can sense just about anything—touch force, direction, speed, voice, pressure, temperature, humidity.” The team showed that a small piece of smart skin placed on the forehead could differentiate multiple facial expressions, while a piece placed on the skin over the voice box could differentiate each letter of the alphabet just by measuring voice box movement.

Sensor devices, which can capitalize on the large surface area and extraordinary conductivity of MXenes, are another promising avenue of research. Most recently, the team created a MXene-based wearable sweat sensor to monitor key biomarkers in perspiration. The stretchable sensor can simultaneously measure multiple parameters, including lactate, glucose, pH and zinc. “It measures and transmits directly to your phone—and it works,” Alshareef says. “Our prototype wearable sweat sensor is functioning well, and our future efforts will focus on miniaturization.”

Expanding MXene Research Across KAUST

Alshareef’s collaborations across the KAUST campus demonstrate the broad potential of MXenes. He has been working with Omar Mohammed to understand their fundamental optoelectronic properties and to fabricate MXene-based photonic and plasmonic devices; Peng Wang, from the Center for Water Desalination and Reuse, to develop osmotic power generators; and Xixiang Zhang to explore the two-dimensional nature of MXenes to grow two-dimensional ferroelectric, electro-optic and piezoelectric crystals that inherit the properties of MXenes.

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