Chem: Anhydrous Etching MXene-Polar Organic Solvent

【Research Background】

Since 2011 2D transition metal carbide (Ti ₃ C ₂ T _z since) MXene been found, until now, has been about 30 Zhong new MXene material it has been discovered. MXene‘s inherent chemical diversity, hydrophilicity, 2D morphology, and metal conductivity make it widely used in many fields, such as energy storage, electrochemical hydrogen evolution catalysis, gas sensors, seawater desalination, electromagnetic shielding, etc. .

Generally speaking, multilayer MXenes obtained by etching with HF acid are difficult to form stable, high concentration dispersions in water. To solve this problem, it is usually necessary to use organic molecular intercalation, such as dimethyl sulfoxide (DMSO), tetramethylammonium hydroxide (TMAOH), tetrabutylammonium hydroxide (TBAOH), and the like. In fact, water as a solvent will directly limit the potential value of MXene materials in some water-sensitive applications. For example, some polymerization reactions cannot be performed due to the presence of water. Similarly, some unique quantum dot materials cannot be combined with MXene performs compounding. The most important thing is that the trace amount of water contained in the material will affect the performance of the material in lithium or sodium ion batteries, especially when an organic solvent is selected as the electrolyte. Therefore, vacuum drying is usually required when preparing the negative electrode.

[Achievement Profile]

Recently, the team of Professor MichelW. Barsoum of Drexel University in the United States published an article titled 2D Ti ₃ C ₂ T _z MXene Synthesized by Water-free Etching of Ti ₃ AlC ₂ in Polar Organic Solvents in the top international academic journal Chem . Research paper, which uses an organic polar solvent, ammonium bifluoride (NH ₄ F ₂ ), to etch and intercalate MXenes materials in an anhydrous environment. High Ti ₃ C ₂ T _z nanosheets. In addition, the Ti ₃ C ₂ T _z material obtained by etching in propylene carbonate is also applied to sodium ion batteries. Compared with MXenes obtained by etching in a water environment, the electrochemical capacity is doubled, which is very useful value.

[Picture and text guide]

Figure 1. Schematic of etching and cleaning steps

Figure 2. XRD images ofTi ₃ C ₂ T _z etched in different organic solvents.

Figure 3. Micromorphological characterization of PC-Ti ₃ C ₂ T _z samples: SEM & TEM images.

Figure 4. XPS peaks of Ti 2p for PC-MX samples.

Figure 5. Electrochemical performance of PC-MX anodes for sodium ion batteries.

[Summary of this article]

     This study proved the feasibility of etching MAX in a certain amount of ammonium bifluoride organic polar solvent. This method is based on the assumption that ammonium bifluoride can decompose ammonium fluoride and hydrofluoric acid in polar solvents. Nevertheless, further research is needed to understand the etching mechanism of this etching method. Based on this work, it provides a new idea for the etching of other MAX materials. This etching method can be performed in a glove box if needed, which is completely different from the method using water as a solvent, because The latter cannot be operated in a glove box. This kind of MXenes material with high fluorine functional group content has been theoretically proven that it has very different optical, electrical and catalytic properties compared with the oxygen-rich functional group MXenes obtained by etching in water.

Literature link:

https://doi.org/10.1016/j.chempr.2020.01.019

Source: MXene Frontier