Hi!

No it's not essential to activate them. For the most of them you got the almost same peaks.

Dear Fatemeh Shekofteh thank you for sharing this very interesting technical question with the RG community. To the best of my knowledge there is no need for any "activation" of MOFs prior to XRD analysis. Actually, it is not really clear to me what you mean by "activation". Quite often such MOFs are prepared by hydrothermal syntheses, and, if you are lucky, these syntheses yield crystalline materials right away. Thus it only depends on whether you have crystalline or amorphous materials to decide if an XRD analysis is possible. For some general information about this topic, please have a look at the following very instructive literature reference:

Crystallography of metal–organic frameworks

Article Crystallography of metal–organic frameworks

Fortunately this review article has been posted by the authors as public full text on RG. Thus you can freely download it as pdf file. Also please note that numerous other potentially useful research papers about MOF crystallography can easily be found and accessed by searching the "Publications" section of RG.

I hope this helps answering your question. Good luck with your research and best wishes, Frank Edelmann

https://journals.matheo.si/index.php/ACSi/article/viewFile/2610/1016,kindly check this link.

https://www.researchgate.net/figure/a-TG-analysis-of-MOF-crystals-b-SC-XRD-analysis-crystal-structure-and-cell_fig1_325717575,u can follow this link.

https://mdpi-res.com/d_attachment/nanomaterials/nanomaterials-08-00650/article_deploy/nanomaterials-08-00650-v2.pdf,u can check this link.

https://pubs.acs.org/doi/10.1021/acsami.1c07268,kindly check this link.

Dear Dr Fatemeh Shekofteh . See the following useful RG link: Article Crystallography of metal–organic frameworks

Kindly see also the following useful RG link: Article A Chemical Route to Activation of Open Metal Sites in the Co...

Also check please the following useful RG link: Article Synthesis of metal–organic frameworks (MOFs) MIL-100(Fe) fun...

The following RG link is also very useful: Chapter Synthesis Methods and Crystallization of MOFs

Many thanks to all of you. So why in XRD patterns of my MOF powders, the signal-to-noise ratio of the peaks is so low. I mean, the patterns are not smooth at all.

Someone told me that when the amount of powder is low, XRD is noisy and not good. I think this reason should not be true and I should look for a more logical reason.

Dear Fatemeh Shekofteh ,

apart from details with respect to the structure of MOFs and their production,

there are in general some reasons for low signal to noise ratios (i.e. large noise compared to the net expected signal) in XRD pattern:

a) of course, a too low amount of material on the sample stage will give low signal and thus high noise; you may share the estimated thickness of your powder sample; because the x-ray penetration depth is in the order of some µm, the sample thickness should be in the order of at least some µm;

b) low acquisition time will also result in low counts signal S in the XRD pattern combined with quite large noise N: N=S1/2 ; so signal to noise is S/N=1/N1/2; a way out is to increase the acquition time.

c) low crystallinity; in case of very low crystallinity of your sample material you will have only tiny 'crystalline' peaks. They compete with the noise of the 'amorphous' background.

d) low crystallite size; you know that the crystallite size affects the peak width; low crystallite size will cause peak broadening und thus peak height reduction...

You may share an example of your XRD pattern as well as the estimated sample thickness...

Best regards

G.M.

Dear Fatemeh Shekofteh thank you again for sharing your interesting problem with other RG members. I think that Gerhard Martens has already provided an excellent and rather comprehensive answer. Personally I assume that low crystallinity is the most common reason for the problem which you encountered, i.e. that you have too much amorphous material in your sample. If you prepared your MOF sample by hydrothermal synthesis, chances are that you can obtain a better crystalline material by slower and more controlled cooling of your reaction mixture.

P.S. Unfortunately it has become a common bad habit to provide multiple answers suggesting readily available links without any further comments, according to the motto "See this, check that!". Quite often the respected RG members don't even care about reading previous answers. So, dear Aref Wazwaz please note that the RG link Article Crystallography of metal–organic frameworks

Honestly, what if all the respectable RG researchers gave "multiple answers" ?

https://www.researchgate.net/post/Honestly_what_if_all_the_respectable_RG_researchers_gave_multiple_answers

Thank you and best wishes, Frank Edelmann

Thanks Gerhard Martens & Frank T. Edelmann

I have two patterns related to almost similar samples. One is noisy and the other is good (following image). The operator told me she used different detectors. Now according to your descriptions, can I know with these two patterns that only different detectors result in this two different patterns?

Dear Fatemeh Shekofteh thank you for your kind response and for sharing the XRD patterns. Please note, however, that we are synthetic inorganic chemists. Thus I will better leave the answer to Gerhard Martens as he is a proven expert in this field. With best wishes, Frank Edelmann

Dear Fatemeh Shekofteh ,

thanks for feed back and sharing your XRD pattern.

When comparing your pattern, three things show up to me:

a) the countscale in the green pattern is much stronger than in the red one;

b) the peak widths in the green pattern are much smaller compared to those of the red one; and

c) the background of the green pattern is much stronger than that of the red one.

This (green case) background is quite large compared to the peak heights and is flat throughout the pattern without any significant structure. My conclusion is that this background is mainly not due to any amorphous phase contribution to the x-ray pattern, but is due to fluorescence of the metal atoms of the MOFs, excited by the Cu K-alphas of the x-ray tube.

Fatemeh Shekofteh , you may share what kind of metal atoms are involved in your sample.

In order to reduce this background one has to use a) another anode material of the x-ray tube, or b) one has to 'monochromatize' the input radiation of the detector.

Monochromatization is correlated with a strong decrease of photon flux; this decrease has to be compensated either by increasing the acquisition time or by increasing the net aperture of the detector, i.e. opening/widening the slits in front of the detector. However, in this case, the angular resolution of the XRD set up is degraded, with the consequence, that the so-called instrumental (peak) broadening is significanly increased, Thus we 'see' broad peaks in the red pattern.

This peak broadening, combined with the nevertheless quite low count scale, leads to the impression, that the series of quite small peaks around 30° are not sticking out of the noise in the case of the red pattern. But, apart from this noise aspect, from my bird's perspective, both pattern show the same overall behaviour of the diffraction pattern.

So my impression is, that there has not only a change in the detector happened, but also a change in the beam handling and shaping on the detector side.

Best regards

G.M.

Thanks very much @Gerhard Martens

The metal node in two samples is Cobalt.

Thanks for the info, Fatemeh Shekofteh

So you have a lot of Co K fluorescence radiation in the background of your 'green coloured' XRD pattern...

Co K-edge is at 7,709keV ; Cu K-alpha is at 8,048keV & 8,027keV;

thus Cu K-alpha is able to excite the Co K-shell...