Researchers Propose Paradigm Shift in Making Mxenes

By Surbhi JainReviewed by Susha Cheriyedath, M.Sc.Jun 28 2022

In an article recently published in the journal Materials Chemistry and Physics, researchers discussed a paradigm shift in the synthesis of MXene through microwave-assisted rapid MAX phase etching and delamination.

Study: Microwave-assisted rapid MAX phase etching and delamination: A paradigm shift in MXene synthesis. Image Credit: Sergey Nivens/Shutterstock.com

MXenes: Exceptional 2D Materials

Among the two-dimensional (2D) families of materials, transition metal carbides, carbonitrides, and nitrides, collectively known as MXenes, have made notable strides. The MXene surface invariably ends with surface moieties after the selective etching (T_x, terminal groups). As a result, it is known as M_n+1X_nT_x, with T denoting the terminal group.

Due to their exceptional electrical conductivity, layered structure, hydrophilicity, and excellent transmittance, this new class of 2D materials have shown excellent potential in a variety of applications, including solar cells, batteries, hydrogen storage, supercapacitors, and catalysts, among others. It should be noted that there are significant environmental and time requirements for selectively etching the "A" element from the MAX phase.

In recent years, a number of initiatives have been made to lessen environmental risks. Although these procedures replaced HF solutions to lower operational risk, a reaction time of up to 48 hours continues to be a barrier to the mass manufacturing and use of MXenes. Therefore, creating a simple, quick, and environmentally friendly MXene production process is widely desired.

MXene Synthesis Using MAX Phase Etching and Delamination

In this study, the authors described the delamination of MXene sheets from the MAX phase as a unique and quick process. In the current approach, aluminum (Al) was etched from the MAX phase within two hours of processing, with a time reduction of up to 48 hours and a temperature reduction of 180 to 40 degrees Celsius.

The characteristics of the MXene were assessed using a variety of characterizations. The spectra typical of Ti₃C₂T_x derived from Ti₃AlC₂ after quick etching of Al were acquired in the X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) patterns. Scanning and transmission electron microscopy (SEM and TEM), ultraviolet (UV)-visible absorption spectra, and Brunauer–Emmett–Teller (BET) absorption-desorption curves were used to supplement these findings.

The team proposed a simple, brand-new, and quick way to make MXene. In a microwave synthesizer, the etching time was cut down to almost 30 minutes using LiF/HCl solution. Furthermore, during the microwave heating, the nucleation of Li atoms into the MAX phase's interlayer spacing Ti₃AlC₂ resulted in the washing process, which removed Al atoms from the Ti₃AlC₂ sites. The totally delaminated MXene sheets were created using this simple and creative process.

The researchers presented a new and substantially greener way of etching Al and MXene sheets delamination from the Ti₃AlC₂ MAX phase to address the complication of high temperature and extended time associated with traditional methods of Al etching.

To achieve this goal, Ti₃C₂T_x - MXene was created by rapidly etching Al from the MAX phase over the course of around two hours at a temperature of 40 degrees Celsius using a unique microwave-assisted hydrothermal technique.

High-quality MXenes in a Shorter Time

The creation of Ti₃C₂T_x was confirmed by XRD spectra, and XPS results on the surface composition supported the XRD findings. All of the elements commonly seen in the Ti₃C₂T_x MXene were visible in the deconvoluted XPS spectra for O 1s, Ti 2p, and C 1s. Additionally, the SEM, TEM, and associated element mapping studies demonstrated how high-quality MXene was produced from the MAX phase.

UV-visible absorption data and BET absorption-desorption curves supported the creation of high-quality MXene. As a result, in a notably shorter processing time, high-quality MXene with minor Al traces was created, which demonstrated the effectiveness of the approach used in the current work.

The proposed technique could yield a variety of 2D M_n+1Xn structures, which include carbides and nitrides of Zr, Ti, Nb, Ta, V, Cr, and Hf. Additionally, the discovered technology could open the door to a quicker, large-scale, and more environmentally friendly MXene production process that might be applied to other 2D materials as well.

Conclusions

In conclusion, this study elucidated the employment of a mixture of LiF/HCL to reduce the toxicity of the usual HF solution-based Al etching procedures. The analysis of the synthesized MXene showed that there was hardly any extraction of Al atoms, which supported the effectiveness of the current process for the simple, environmentally friendly, quick, and scaled-up synthesis of MXene.

The creation of high-quality MXene with barely detectable Al traces was shown in the results, which attests to the effectiveness of the current approach.

The authors believe that this study offers up new opportunities for the use of MXene in the industry, in addition to establishing a thorough approach for producing it quickly and in large quantities.

Reference

Numan, A., Rafique, S., Khalid, M., et al. (2022) Microwave-assisted rapid MAX phase etching and delamination: A paradigm shift in MXene synthesis. Materials Chemistry and Physics 126429. https://www.sciencedirect.com/science/article/pii/S0254058422007350?via%3Dihub

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