I am trying to synthesize MXenes (Ti3C2Tx), using the MILD etching method (in-situ formation of HF by reaction of LiF + HCl). I am taking equal amounts of LiF powder (Sigma Aldrich, >99.99% trace metals basis) and Ti3C2Tx powder with 10ml of 9M HCl. LiF and HCl are stirred for around 30 minutes, followed by a slow addition of MAX precursor. The etching is done at 35 deg Celsius at 300 rpm for 24 hrs. The product is then centrifuged 10 times (10 minutes each). The supernatant after the last centrifugation is collected, and its SEM micrographs (also EDS mapping) show very high traces of fluoride particles (~1 um) and a much lesser trace of Titanium. Why did fluoride particles remain undissolved or not removed in the decant of the first few centrifuges? Also, is it possible that Titanium is also getting etched out?
Note: 1) Traces of Aluminium are also present, even more than Titanium.
2) The mixture of LiF and HCl remained fuzzy even after 30 minutes of stirring at 300 rpm.
3) All these are done in ambient environment
LiF has poor solubility in water. Increase the number of washing cycles and try to use warm water to improve LiF solubility.
The presence of Al in EDS/SEM can indicate that the etching time was not sufficient. You can corroborate this with simple XRD analysis.
You do not specify the centrifugation parameters, but 3500-4500 rpm @ 5min should be sufficient to precipitate the impurities you have (Al, LiF, etc).
So:
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