Terminal Groups Unlock MXenes' Versatile Potential

MXenes represent a novel class of 2D transition metal carbides and nitrides synthesized through selective etching of the metallic-bonded A layers from MAX phase precursors. In MAX phases, M (transition metal) and X (carbon/nitrogen) atoms form strong covalent bonds within M_n+1X_n layers, while the interleaved A layers (e.g., Al, Si) exhibit weaker metallic bonding with M atoms. During chemical etching, the preferential removal of A layers along the c-axis direction generates a layered structure of M_n+1X_n sheets. This process exposes reactive transition metal (M) atoms on the newly formed surfaces, which undergo spontaneous passivation through bonding with heteroatoms (e.g., -O, -F, -OH) to minimize surface energy. This surface atomic layer is a terminal group, denoted as T_x (where x indicates the uncertainty in its composition).。

However, the surface terminal groups of MXene significantly influence its properties. As Professor Peng-an Zong from Nanjing Tech University pointed out, "Tailoring the surface terminal groups to make specific MXenes suitable for targeted applications is a critical challenge that must be overcome for their practical implementation. For instance, existing studies have shown that for Nb₂CT_x MXene, when T_x is -S or -Se, it is a potential thermoelectric material; when T_x is -Cl, it exhibits clear superconducting properties; and when T_x is entirely -OH, Nb₂CT_x can serve as an excellent anode plate in aqueous energy storage devices, thanks to its low work function."

The review titled "Terminal Groups: The Key to Tunable and Versatile MXene Materials" systematically summarizes the structural characteristics and modification methods of MXene terminal groups, discusses their influence on electrical, optical, magnetic, and mechanical properties, and further elaborates on the immense application potential of MXenes under different conditions through the regulation of terminal group composition and distribution. It is worth emphasizing that, based on existing research, this review generalizes the fundamental principles of how specific terminal groups affect the properties of MXene materials and points out both the directions and challenges in tailoring these specialized terminal groups.

The team published their review in Nano Research on March 17, 2026.

Highlights of the Review:

1. Summarizes the common types of terminal groups in MXenes and their introduction methods.
2. Analyzes the influence of these terminal groups on the electrical, optical, and mechanical properties of MXenes.
3. Reviews the applications of MXene terminal-group modification in fields such as sensing, filtration membranes, and catalysis.
4. Provides insights into future development strategies for tailoring MXene terminal groups.

"Compared to existing research, there are still many unresolved mysteries in the strategies for modifying MXene terminal groups," the authors commented. "For example, a primary challenge in MXene theory is to establish robust criteria for identifying high-energy yet stable MXenes with multifunctional surfaces."

"Beyond predicting structural stability, investigating their properties is equally crucial," stated the corresponding author Professor Peng-An Zong, "Although the significant influence of surface terminations on the electronic band structure of MXenes is well-established, current analyses relying predominantly on computed band structures and DOS often yield only superficial and intuitive conclusions, failing to reveal universal governing principles. The modulation of MXene bands by terminal groups appears to be highly complex and non-intuitive. "

The review indicates that the tunability of terminal groups is the most prominent advantage of MXene materials compared to other two-dimensional materials. However, it is precisely the uncertainty of these terminal groups that has prevented MXenes from achieving definitive commercial applications. When terminal groups can be custom-tailored at will to meet specific requirements, MXenes will truly become the "universal material."

This work was supported by the The Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University.

DOI Link:

https://doi.org/10.26599/NR.2025.94908143

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.