KAIST develops 'asymmetric MXene' nanomaterial to pinpoint and remove radioactive contaminants

South Korean researchers have for the first time created an asymmetric two-dimensional structure that had previously existed only in theory — a breakthrough that could open the door to a range of functional materials for removing radioactive contaminants and shielding against electromagnetic waves.

KAIST announced Thursday that a research team led by professor Ryu Ho-jin of the Department of Nuclear and Quantum Engineering has experimentally synthesized an asymmetric layered ceramic — a ceramic with an asymmetric structure in which atomic layers are stacked in sequence — needed to produce asymmetric MXene, a next-generation functional nanomaterial in which the atomic compositions on each face differ from one another.

MXene is a two-dimensional nanomaterial known for its high electrical conductivity and surface reactivity, and has drawn significant attention across advanced technology fields including energy storage devices and sensors. Until now, however, all developed MXene materials have had symmetric structures, with identical atomic compositions on both faces, limiting the range of functions they could perform.

Asymmetric MXene, by contrast, has different atomic compositions on each face, allowing each side to perform distinct functions. This asymmetry enables properties that are difficult to achieve with conventional symmetric materials. The material is expected to find particular use in next-generation functional applications such as adsorption filters for removing radioactive nuclides and electromagnetic wave-absorbing and shielding materials.

Despite its promise, asymmetric MXene had largely been confined to computer simulations, with actual fabrication proving elusive because the necessary precursor materials could not be obtained.

To overcome this, the research team applied a high-entropy materials design strategy — an approach that combines multiple elements to achieve new properties. By simultaneously mixing six elements — titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), aluminum (Al) and tin (Sn) — the team found that differences in atomic size naturally caused the outer metal atomic layers to arrange themselves into stable asymmetric configurations. The team described this as a structural formation mechanism not previously reported in MXene precursor materials.

The asymmetric layered ceramic the team synthesized can serve as a precursor — a raw material for producing the final product — that, once subjected to selective chemical etching to remove specific atomic layers, can be converted into asymmetric MXene with differing atomic compositions on each face.

The achievement is considered significant because it lays the groundwork for realizing asymmetric MXene beyond the theoretical realm. It also points to potential applications across a broad range of advanced fields that were difficult to access with conventional symmetric materials, including radioactive nuclide capture, electromagnetic shielding, sensors and piezoelectric devices that convert pressure or vibration into electrical energy.

"This research demonstrates that asymmetric atomic structures, which were difficult to achieve through conventional crystallography, can be realized through high-entropy materials design," Ryu said. "We plan to expand this principle to various layered materials and develop it into a platform for exploring unexpected new structures."

The findings were published in the international journal Nature Communications on April 30.