As I have used DMF for the synthesis process of HKUST-1, I had to activate it in the oven at 110 0C after solvent exchanging with ethanol, prior to applications. while it was in the oven the colour of HKUST-1 turned from light blue to dark blue. when it was cooled to room temperature dark blue turned to the lighter colour as before.
Is the change in color due to the loss of solvent molecules during the activation process ? or has the MOF dissociated during the activation step ? or are there any other reasons for the change of colour ?
The change of colour from light to dark is due to the removal of the axial ligand (ethanol, DMF or water) from the copper acetate lantern, then the dark to light colour change is due to atmospheric water binding onto this coordination site. I find it's a good way to visually identify whether the activated samples have been exposed to air.
At 110 degrees Celcius, HKUST-1 should not have degraded, but it is worth checking by PXRD anyway. I have never done this desolvation when the sample wasn't under vacuum, so I'm not sure whether the air interacts with HKUST-1 at these comparatively low temperatures.
Thanks for your answer. It helped me to confirm my theory. But are there any references to what you have told ? If there are any, please let me know. T
hanks again.
Mostly I speak from personal experience, but I found these Googling for dehydration of HKUST-1:
http://pubs.acs.org/doi/pdf/10.1021/cm052191g
http://pubs.rsc.org/en/content/articlehtml/2015/sc/c5sc01489a
http://science.sciencemag.org/content/343/6166/66.full
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