I am using the HF acid etching technique to synthesize single layer Ti3C2 MXene flakes followed by LiCl intercalation. However, the etching process seems to have failed twice in a row whereas previously the process I used worked perfectly. The first time it failed was after the intercalation should have been completed; while rinsing away unreacted LiCl and large MXene flakes, the single layer MXene flakes were never freed up, and the centrifuge pellet got smaller and smaller as MXene flakes were rinsed away. The second time when rinsing off the HF acid the pellets got smaller and smaller, but no flakes were apparent in the waste.
Has anyone had a similar problem? How did you troubleshoot/solve it?
Thanks in advance.
Alyssa Grube
Which Concentration of HF was used? What is the etching time? and which temperature was the etching performed?
Kindly read through MXene Synthesis papers by Prof. Yury Gogotsi Research group.
Alyssa Grube, this is a common problem that many people run into during MXene synthesis when they first get started. There are many potential issues that can be occurring, and I'll try to go over the most common and their solutions. Before I go into the specific approaches, I recommend using the protocol listed in this article: Article Safe Synthesis of MAX and MXene: Guidelines to Reduce Risk D...
We go through every synthesis step, and in the SI, there are videos of every single step, as well as digital pictures of what every step should look like during synthesis. This includes the washing and delamination steps. I will refer to a number of characterization techniques, and I recommend using this article as a guide to understand what they should look like for successful MXene:Article Characterization of MXenes at Every Step, from Their Precurs...
For all of these, I recommend performing as much characterization as you can. The more pictures and XRD patterns you have, the easier it is to determine what step is going wrong. Since you don't observe swelling during delamination, I assume it has something to do with the etching or with LiCl becoming a hydrate, but it is hard to say without any additional information.
B. Srikanth Ragunath temperature 35 C in silicon oil bath, etching time 24 hours, HF conc is 38%
Christopher Shuck thank you for your detailed recommendations for trouble shooting; i have a few questions on some of your advice
where too large flakes leads to under etching, would MAX flakes that are too small lead to over etching and thus require a decreased etching time?
Alyssa Grube, yes. If the MAX crystals are small, shorter times work. Though, the procedure in the article I mentioned is for
Hello Alyssa,
thank you for sharing this very interesting technical problem with the RG community. I'm not going to answer the question directly. HInstead, my advice would be to avoid working with HF if at all possible! Please check all available information about the very serious health risks of working HF and then think about ways to replace it. Although HF is the most common etching fluid for MXenes, there are a few other reagents which can be employed. For example, please have a look at the followig relevant article:
Universal Strategy for HF-Free Facile and Rapid Synthesis of Two-dimensional MXenes as Multifunctional Energy Materials
Article A universal strategy for HF-free facile and rapid synthesis ...
Unfortunately this paper has not yet been posted by the authors as public full text on RG, I noticed that two of them have RG profiles. Thus it should be easily possible to contact one of them via RG and request the full text of the paper.
Yet another alternative, i.e. the use of ammonium bifluoride (NH4HF2) in organic solvents has been shown to be able to replace the hazardous hydrofluoric acid:
Article Synthesizing MXene Nanosheets by Water-free Etching
Here, too, you can request the full text of the paper directly from one of the authors. In any case I strongly suggest that your try to get away from working with really dangerous HF.
Good luck with your work and best wishes, Frank Edelmann
Christopher Shuck also about hydrated LiCl-how much more should be used? 10% more or higher? and thank you for responding to my questions
Alyssa Grube, I recommend heating the hydrated LiCl to determine how much water is in the LiCl, then adjusting it that way.
Christopher Shuck what HCl concentration for intermetallics testing? same as for the etching process?
Alyssa Grube, we use 6-9 M HCl. Make sure you have an open vessel and you add your powder slowly. This reaction can generate significant gas and is exothermic.
Acid etching was proved to have caused a reduction in mxene deposited, in most cases it etches the titanium atoms, leaving behind only carbon. To solve this, alkaline medium has been suggested using ammonium hydroxide, through electrochemical deposition of mxene, otherwise called anodic etching of aluminum from Max phase. This method was observed to achieve a preferred mass of mxene.
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