MXenes have been established as the substances of choice to be used in various applications due to their favorable properties. However, these materials face degradation problems.
Study: The combination of high pH and antioxidant improves the chemical stability of two-dimensional transition metal carbides and carbonitrides (MXenes) in aqueous colloidal solutions. Image Credit: Africa Studio/Shutterstock.com
To solve this problem, an article published in the journal Inorganic chemistry presents an innovative technique to improve the chemical stability of MXenes.
MXenes – What exactly are they?
MXenes have been widely explored over the past decade due to their remarkable electrical, thermal, optical and mechanical characteristics. These two-dimensional configurations of metal carbides and nitrides are often synthesized by water-based chemical etching via their MAX phase precursors.
MXenes are synthesized in colloidal form in aqueous environments, which is also a popular storage method due to these compounds having a high affinity for water.
The uniqueness of MXenes
The interesting mix of MXenes of high electrical conductivity and hydrophilicity (high affinity for water) and their ability to tolerate intercalants make them extremely useful for applications such as energy generation and storage, water purification water, detection and shielding against electromagnetic interference.
Nevertheless, little is understood about the chemical nature of these 2D materials, and even less about the effect of variables such as temperature, pH, and solution concentration on their reactivity.
Hydrolysis – The main contributor to the degradation of MXene
Previous research has demonstrated that hydrolysis is the main process contributing to the degradation of MXene in aqueous solutions. It has also been discerned that the surrounding pH level can have a dramatic impact on the rate of hydrolysis.
Although only a few papers on the subject have been published, the rapid degradation of MXene in basic media has been recorded and interpreted quite extensively, mainly the reaction between MXene and OH–.
These and many other conflicting results regarding the chemical stability of Mxene at the colloidal stage require further investigation. The direct identification of the byproducts of Mxene reactions offers a comprehensive technique for analyzing the reactivity of these materials in this respect.
Mxenes Current Research Base
In this work, researchers used direct examination of gas-based reaction byproducts using Raman spectroscopy and gas chromatography to assess the chemical stability of Mxenes over time in solutions. aqueous solutions at different starting pH values.
The examination is further complemented by observation of the concentration of Mxene in the solution by UV-vis spectroscopy, as well as electrical conductivity tests of Mxene sheets and a post-mortem study of degradation associated with solid products. of Mxene by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy.
To mitigate the impacts of counterions, which can inhibit the effects of pH level when an alkaline or acidic solution is used, the team used a pH-inert electrolyte.
Researchers have developed a synergistic method to suppress MXene degradation and extend shelf life by effectively blocking hydrolysis and oxidation.
The team predicted that the results would help design better storage techniques for aqueous solutions of MXene and lead to a better understanding of basic chemical processes.
The impact of the pH level of the aqueous solution on the degradation of MXene was studied by gas chromatography and Raman spectroscopy for evolved gases, as well as by visual observations and classification of solid reactive products using X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy.
The team pointed out that depending on the particular pH level, the degradation of MXene produces layered metalates. It has been revealed by experiment that the deterioration of MXenes within an aqueous solution is inhibited under basic conditions, in particular due to a slower rate of hydrolysis.
It has been suggested that the combination of a basic microenvironment with the introduction of a specific antioxidant is an effective technique to inhibit both the hydrolysis and the oxidation of MXenes in aqueous solutions, thus extending their lifespan. . The lifespan extension would be longer than would have been possible with either strategy individually.
The team concluded that these findings are essential for a deeper understanding of the chemistry associated with MXenes and are equally essential for the formulation of improved storage techniques.
Huang, S., and Mochalin, V. (2022). The combination of high pH and antioxidant improves the chemical stability of two-dimensional transition metal carbides and carbonitrides (MXenes) in aqueous colloidal solutions. Inorganic chemistryAvailable at: https://doi.org/10.1021/acs.inorgchem.2c00537
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