I am synthesizing a material and thus far based on other scans I thought that it was a metal oxide at all stages but it has been suggested that the as-synthesized compound might be a metal hydroxide which after I anneal becomes a metal oxide. I am trying to determine a way to tell the difference between the two.
I have done the standard characterization on the as-synthesized compound (XRD, Raman, EDS, XPS) and trying to determine if something in one test will show up if it is a hydroxide and be absent for the metal oxide form.
I saw that Raman might have some OH bonding out near 3200-3500 cm-1 that might not appear in the metal oxide version. In previous Raman tests I did not attempt to scan out that far. If that is true will scanning the higher wave numbers help me determine the difference or is there another method that might be easier and more certain to differentiate between the two materials? Thanks for any help.
Tim Ritter
Before annealing, you had hydroxides. They had to be watched by Raman at 3200-3500 cm-1. During annealing, usually all hydroxides decompose with the release of oxide and water vapor. If you have a 3200-3500 cm-1 band, then it should disappear with more prolonged heating. If it does not disappear and you are interested or interfered with by the presence of a small amount of hydroxyl groups, then you can investigate your composite in more detail.
Hello!
What kind of metal? And the synthesizing steps? Is you oxide was in water at any point of course it would form and hydroxide. After annealing the hydroxide becomes an oxide againg.. just use FTIR before and after annealing, the spectra would be quite different in both cases
Transition metals for the most part. They are being synthesized in water as well.
I looked into FTIR and it looked like the metal oxide and hydroxide papers I found had similar peaks for the OH bonding. If there is a big enough difference with FTIR then maybe I can run that as well.
For Raman the OH doesn't have to be completely gone but I would need to be able to show a large decrease in the OH to prove it is an oxide.
The heat treatment (annealing) was at 800C which is why I expect there to be a difference because the hydroxide should decompose at that temperature.
If you calcine transition metal hydroxides at 800°C, then no hydroxyl groups will definitely remain. Another thing is that some oxides, during long-term storage, can absorb water from the air, again forming hydroxides, but this is typical only for alkali and alkaline earth metals.
I think thermogravimetry may give the answer. Because generally if hydroxides are heated in presence of oxygen, water should be given out and will have signal in TGA
If you are using XRD, a very simplistic approach is to see if you have an amorphous or crystalline phase in the scan. If amorphous, you are generally a hydroxide. If it is crystalline, it will be an oxide and should show a diffraction pattern.
You can differentiate between metal hydroxide and metal oxide by comparing their corresponding XRD ICDD data or you also check crystallinity of the corresponding sample as #William Wiseman said and you can calcinate you sample to remove hydroxide group as#Vadim Verlotski said, if you haven't know the calcination temperature please take TGA as #Sunil Kulkarni said. Raman spectra can also be useful for the determination of hydroxide group.
I performed Raman all the way out to 4000 cm-1 and I observed a possible small peak at 3649 cm-1. Does anyone know how the peak intensity might compare with other peaks such the M-O peaks that appear earlier?
Trying to determine if what I see is hydroxide proof or if it is just some surface effect or even background at the moment and nothing. Thanks for the help.
Yuri Mirgorod , Is the only region that the hydroxide signal in Raman shows up in the 3200-3500 cm-1 band? A broad band from ~1250-1550 cm-1 isn't associated with OH- bonding is it?
Tim Ritter
I can only say about water. It only has a very small peak at 1525nm-1. Although there is a strong hydrogen bond in water.
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