MXenes are a family of two-dimensional (2D) transition metal carbides and nitrides with superior intrinsic properties such as high electrical conductivity, optical transparency, good mechanical strength and thermal stability. However, MXenes are subject to severe oxidative degradation relatively quickly, which causes their performance to deteriorate rapidly and limits their usefulness in most environments.
Hossein Alijani, a Ph.D. researcher, with the new anti-rust device. Image Credit: RMIT University
A recent study published in the journal Nature Communications addresses this question by exposing oxidized MXene films to very brief high-frequency electromechanical vibrations, leading to efficient removal of the oxide layer and recovering their electrical performance and electrochemical.
MXenes: why are they important?
MXenes are a new class of two-dimensional (2D) materials that have gained attention due to their unique properties and potential applications in various fields. MXenes are derived from a family of compounds called MAX phases, a class of ternary carbides and nitrides.
MXenes have a wide range of properties that make them useful for a variety of applications, including energy storage, electromagnetic interference shielding, and water purification.
MXenes have been found to have high conductivity, making them suitable for use in electronic devices. They also have a high specific surface area, which can be useful for adsorption and catalysis applications.
In addition, MXenes are very flexible and robust and have high thermal stability. These properties make MXenes a promising material for use in a variety of applications, including energy storage, electromagnetic interference shielding, and water purification. They are also being studied for use in biomedical applications, such as tissue engineering and drug delivery.
Challenges and Limitations Related to MXenes
MXenes have shown great potential in various applications; however, significant challenges still need to be addressed before they can be widely adopted. One of the major limitations of MXenes is their susceptibility to oxidative degradation when exposed to moist air or aqueous environments.
This causes them to degrade rapidly, limiting their applicability under most practical conditions and where longer term operation is desired. Additionally, once an oxide layer develops on the surface of the material, it can only be removed by strong acids, which also damage MXenes.
Therefore, efforts are needed to extend the shelf life of MXene to ensure its potential for translation into a marketable reality. So far, efforts have focused on increasing the oxidative durability of MXenes by prolonging their oxidation dynamics, either during preliminary synthesis or later during storage. However, there still exists a need for a simple and rapid method of recovering and restoring oxidized MXenes.
Highlights of the current study
The study was conducted using an array of Ti-based MXene samples synthesized using the liquid exfoliation method. The samples were exposed to moist air or aqueous environments, and their oxidative degradation was then monitored for several hours to several days.
The formation of oxides, such as titanium dioxide (TiO2) on the surface of the MXene samples, was also analyzed using various characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) .
To investigate ways to extend the shelf life of MXenes, researchers also evaluated various methods to improve the materials’ oxidative stability. This included storing MXene samples in sealed containers at low temperatures, as well as using various chemical treatments and annealing processes to retard oxidation kinetics.
The effectiveness of these methods was evaluated by analyzing the samples before and after treatment using these characterization techniques. Additionally, the team also attempted to recover and restore oxidized MXenes using various acid treatments.
Findings and future prospects
Current research results have demonstrated a simple and rapid method to recover and restore oxidized MXenes. The method consists of exposing the MXenes to a solution of hydrazine hydrate, effectively reducing the oxide layer on the surface of the material.
This results in a significant improvement in the electrochemical performance of MXenes and an extension of their shelf life. The researchers also found that the recovered MXenes maintained their structural integrity and showed no signs of damage or degradation.
In terms of future perspective, this research opens new possibilities for the use of MXenes in practical settings where longer-term operation is desired. The ability to recover and restore oxidized MXenes offers a potential solution to the problem of rapidly deteriorating performance and shelf life that previously limited their usefulness.
The researchers also suggest that this method could be extended to other transition metal carbides and nitrides, which could further expand the potential applications of MXenes.
A word from the researchers
“Surface oxide, which is rust, is difficult to remove, especially on this material, which is much, much finer than a human hair“, said Hossein Alijani, co-author of the study.
Current methods used to reduce oxidation rely on the chemical coating of the material, which limits the use of MXene in its native form. In this work, we show that exposing an oxidized MXene film to high-frequency vibration for just one minute removes rust on the film. This simple procedure recovers its electrical and electrochemical performance.
Hossein Alijani, co-author, Ph.D. Candidate, School of Engineering, RMIT
Reference
Ahmed, H. et al. (2023). Recovery of oxidized two-dimensional MXenes by high-frequency electromechanical vibration at the nanoscale. Nature Communication. Available at: https://doi.org/10.1038/s41467-022-34699-3
Source: RMIT University