I tried to synthesise different morphologies by adjusting the ratio of DMF to methanol. When the DMF and ethanol ratios were 9:1 and 7:3, the XRD images of the samples showed a diffraction peak not belonging to MIL-125 at around 8°. When the DMF and ethanol ratios were 5:5, The XRD of the sample is completely different from MIL-125. I can't determine the composition of the sample.
Why is this happening?
What is the composition of a 5:5 sample？
I'd appreciate it if someone could respond.
Although I am not familiar with the structure of MIL-125, I will comment from a crystallographic standpoint. The peaks at 2θ around 10 degrees and around 6.5 degrees in the chart on the left seem to match the MIL-125 pattern searched online. The peak around 8 degrees between them is not due to its structure. Therefore, it can be determined that it originates from a different crystal structure. On the other hand, in the chart on the right, the peak around 8 degrees grows significantly, and the peak derived from MI L-125 disappears. Therefore, it seems that we are observing a completely different crystal structure. Many peaks can be seen on the higher angle side, but these cannot be determined unless the crystal structure is completely determined. The easiest to understand is the peak on the low angle side, which represents the longest period structure. It is easiest to judge by focusing on each individual.
For your reference.
If two traces overlapped on the same scale of 2theta, would help compare to conclude. I never worked on IMF-125. From my experiences with polymorph screening and ID the physical forms of API in solid/semisolid/suspension formulations and medicine products, it looks like to me there are some issues regarding the physical forms, eg morphology or polymorph, or kind of solvates. Some of the peaks in the traces were enhanced whilst the others not observable or reduced to lumps at the scale of baseline noise, suggesting the MIL-125 surface structure were modified differently under the different wet conditions and hence, probably became 1) favoured in some orientations, 2) bonded with solvent molecules at different ratios and 3) combinations of those described in 1) and 2).
I would be able to provide further advice per sample preparations, characterizations and/or determinations of your materials, please show overlapped, no matter shifted in y-axis or not, if applicable.
The overlapped traces are much better for comparison and showed two completely different crystalline structures. In addition, the crystallinity of the one in colour was much lower than the other and may contain much higher amorphous content.
Interestingly, both showed the diffraction peak at about 8deg, as you said, not belonging to that of MIL-125, indicating potential impurities in your two samples.
If you don't have other techniques to characterise your samples, you could run more xrd on your samples after different treatment of your samples, such as drying in oven and/or purging with nitrogen gas, in short and longer time; or simply grinding gently and coarsely, to see the changes in xrd if applicable.
BTW, xrd is not the technique to define the materials composition but only their crystallinity, i.e. crystalline structyres and amorphous content. Having said that though, it is good to spot on different polymorph if applicable and impurities.