Currently, I am preparing the delamination of MXene (Ti3C2) with the Li cation intercalation. Originally, Ti3C2 was synthesized from in-situ HF etching which most author claimed that Li cation enlarge interspace of MXene and possibly enhance delamination by shaking or sonicating. By exposing MXene to longer sonication (approx. 20min to 1 hour), can the MXene sheet defect? For instance, If I sonicate multilayer MXene in DI water for 20 minute with 60% amplitude, can the large single sheet of MXene chop to smaller size? I am grateful if you could explain the phenomenon of the structural change in term of using sonication technique. Your suggestion and explaining are very crucial for my future work.
Well, ultrasonic treatment is a common technique to chop down nanotubes do certain lengths although below a certain size reasonable application becomes more and more limited. The mostly accepted mechanism is that the long tubes get twisted heavily under the sonic treatment and get torn apart at certain points depending on the conditions.
A sheet material of course behaves differently from a tube, but if we follow the analogy, it would be expectable that you cause fissures from the sheet rim by certain sonication conditions.
For MXene synthesis, there are a variety of factors that affect their size (and conductivity/stability). I will draw your attention to this article as a good reference: Article Ultralarge Flakes of Ti3C2Tx MXene via Soft Delamination
Herein, we show a method to produce 40+ micron Ti3C2Tx flakes. If you use shaking/centrifugation this by itself will reduce the flake size to 5-10 microns. If you want to decrease the flake size further, sonication (even simply bath sonication) will lead to a flake size reduction. Generally, if I want to produce smaller MXene flakes I will use probe sonication, as it will directly break the flakes. It will heat up the solution as well (and promote oxidation), so it needs to be cooled and cycled to minimize this.A few other factors that influence size are the etching methods (HF/HCl vs LiF/HCl for example), the way the MAX phase is produced, the delamination approach (LiCl leads to larger flakes than TMAOH or TBAOH for example). Getting the largest possible flakes is ideal for many applications, whether fundamental single flake studies or electronics, but smaller flakes are also useful if there are diffusion limitations or if you want to infiltrate fibers. It really depends on your goal.
Also, I do want to note that sonication can often increase your delamination yield. If the MAX is not fully etched, you break the flakes and increase the yield this way. The flake size will be smaller, of course.
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Sonication for longer times breaks the flake size of MXenes producing smaller flakes with defects. For some delamination, manual hand shaking is enough to get large size MXene flakes.
Sonication is required if the etching is made using HF and sonication is not required if etching is made using LiF and HCl as this itself cause swelling of MXene layers
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