MXens have been established as the main substances to be used in various applications due to their favorable properties. However, these materials face problems when it comes to degradation.
Study: The combination of high pH and an antioxidant improves the chemical stability of two-dimensional transition metal carbides and carbonitrides (MXens) 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?
MXens have been extensively explored for the past ten years due to their remarkable electrical, thermal, optical, and mechanical characteristics. These two-dimensional configurations of metal carbides and nitrides are often synthesized by hydrated chemical etching using their MAX phase precursors.
MXens are colloidally synthesized in aqueous environments, which is also a popular storage method because these compounds have a strong affinity for water.
The uniqueness of MXenes
The interesting combination of MXenes of high electrical conductivity and hydrophilicity (strong affinity for water) and their ability to tolerate intercalants make them extremely useful for applications such as energy production and storage, water purification, the detection and shielding of electromagnetic interference.
However, little is understood about the chemical nature of these 2D materials, much 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 shown that hydrolysis is the main process that contributes to the degradation of MXene in aqueous solutions. It has also been found that the surrounding pH level can significantly affect the rate of hydrolysis.
Although only a few articles have been published on the subject, the rapid degradation of MXene in basic media has been recorded and interpreted quite thoroughly, mainly the reaction between MXene and OH-.
These and many other contradictory findings on the chemical stability of Mxene in the colloidal stage require further research. The direct identification of the by-products of Mxene reactions offers a comprehensive technique for analyzing the responsiveness of these materials in this regard.
Bases of Current Mxenes Research
In this work, the researchers used a direct examination of the by-products of the gas-based reaction by Raman spectroscopy and gas chromatography to evaluate the chemical stability of Mxenes over a period in aqueous solutions at different initial pH values.
The examination is complemented by the observation of the concentration of Mxene in the solution by UV-vis spectroscopy, together with tests of electrical conductivity of Mxene sheets and post-mortem study of the degradation associated with Mxene solid products by ray diffraction. X, X-ray photoelectron spectroscopy, and Raman spectroscopy.
To mitigate the impacts of contractions, which can inhibit the effects of pH level when using an alkaline or acidic solution, the team used an electrolyte that was inert to pH.
The researchers devised a synergistic method to suppress MXene rupture and extend shelf life by efficiently blocking hydrolysis and oxidation.
The team anticipated that the findings would help design better storage techniques for MXene aqueous solutions and lead to a better understanding of basic chemical processes.
Study results
The impact of the pH level of the aqueous solution on the degradation of MXene by gas chromatography and Raman spectroscopy for advanced gases was investigated, as well as visual observations and classification of reactive solid products by X-ray diffraction, photoelectron spectroscopy X-ray and Raman spectroscopy.
The team noted that, depending on the particular pH level, the breakdown of MXene produces layered metals. The experiment revealed that the deterioration of MXens within an aqueous solution is inhibited under basic conditions, especially due to a slower hydrolysis rate.
It was suggested that combining a basic microenvironment with the introduction of a specific antioxidant is an efficient technique to inhibit both the hydrolysis and oxidation of MXens within aqueous solutions, thus extending their shelf life. The extension of the useful life would be longer than would have been possible with any strategy individually.
The team concluded that these findings are critical for a deeper understanding of the chemistry associated with MXenes and are equally critical for the formulation of improved storage techniques.
Reference
Huang, S. and Mochalin, V. (2022). The combination of high pH and an antioxidant improves the chemical stability of two-dimensional transition metal carbides and carbonitrides (MXens) in aqueous colloidal solutions. Inorganic Chemistry, available at: https://doi.org/10.1021/acs.inorgchem.2c00537
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