So, in XPS measurements you have obtained shifted peaks of Ti2p and O1s to lower binding energies, and no additional peaks? Have you measured the same for the samples which were not calcinated? What are the differences? If there is no additional peaks, only shifted peaks appear, you have to answer the question - is it possible to reduce all Ti+4 to Ti+3? Why are you not observing the peaks for Ti+4? It is also not clear for me, why the peak for O1s is shifted too. What are the binding energy values obtained by you? Are there any differences for the samples calcinated in lower and higher temperatures? Maybe the peaks appear at lower binding energies due to the formation of rutile after calcination in 600 oC? In the paper enclosed by you the authors wrote "Under normal conditions, high temperature treatment of titania in an oxygen deficient atmosphere always results in the formation of oxygen vacancies. During the high temperature treatment, the Ti-O-Ti network weakens and this facilitates the Ti-O bond breaking and a consequent structural rearrangement to a thermally more stable rutile phase (...). The loss of lattice oxygen atoms at a higher temperature weakens the Ti-O-Ti bonds, which can be the reason for lowering of O1s binding energies." So, are you perfoming the calcination in oxygen deficient condictions?

Hi,

Find the article in the attachment related to Oxygen vacancy.

Find another article in the attachment.

Find one supporting article. Hope it will help you.

Thank you.

Dear Dinesh,, many thanks for your response. Dear i have read these articles. These have good info about oxygen vacancy but still they are not enough to support my statement..

Further i am doing calcination in air atmosphere.

Ti+3 centers absorb light at 780 nm - if you have reduced form of Ti you should see it - the color of sample should be blue (between grey and blue rather). Are you samples colored after calcination? Also, please remember that Ti+3 centers are kinetically unstable at room temperature. After calcination in 600 oC you should obtain rutyl phase of TiO2. Please, find enclosed manuscripts - maybe you will find the answer there.

And next one

Dear All, I think the attached article support my statement...

Yes, in the paper enclosed by you, the authors reported receiving the high temperature stable, oxygen rich anatase phase. So, calcination in 600 oC do not caused the transformation of anatase into rutile in their samples. Maybe, also in your case it is true. You should check it for example by XRD. The presence of oxygen vacancies may be shown in the PL measurements. XPS also should help - you may check the formation of Ti+3 under illumination. The presence of additional peaks for Ti2p at lower energy binding due to the formation of Ti+3 in irradiated sample should be identified - as you wrote above in the question. By XPS you may check the formation of oxygen vacancies upon irradiation. Still, there is no evidence of formation Ti+3 as a result of calcination - are you suggesting the presence of Ti+3 only due to the calcination?

Dear Elżbieta Świętek, Beside formation of Ti+3 after calcination in XPS data, there is also a shift of Ti2P and O1s to lower energy values observed in my case.So what i was asking, is that also possible that Ti2P and O1s shifted to lower energy values after calcination also because of oxygen vacancy?.

And i think in the given article they also suggested that the shift of Ti2P and O1s to lower energy values is because of oxygen vacancy.

So, in XPS measurements you have obtained shifted peaks of Ti2p and O1s to lower binding energies, and no additional peaks? Have you measured the same for the samples which were not calcinated? What are the differences? If there is no additional peaks, only shifted peaks appear, you have to answer the question - is it possible to reduce all Ti+4 to Ti+3? Why are you not observing the peaks for Ti+4? It is also not clear for me, why the peak for O1s is shifted too. What are the binding energy values obtained by you? Are there any differences for the samples calcinated in lower and higher temperatures? Maybe the peaks appear at lower binding energies due to the formation of rutile after calcination in 600 oC? In the paper enclosed by you the authors wrote "Under normal conditions, high temperature treatment of titania in an oxygen deficient atmosphere always results in the formation of oxygen vacancies. During the high temperature treatment, the Ti-O-Ti network weakens and this facilitates the Ti-O bond breaking and a consequent structural rearrangement to a thermally more stable rutile phase (...). The loss of lattice oxygen atoms at a higher temperature weakens the Ti-O-Ti bonds, which can be the reason for lowering of O1s binding energies." So, are you perfoming the calcination in oxygen deficient condictions?

I think, the above mentioned paper answers your basic question :)

Dear Elżbieta Świętek, Here is my attached XPS results... I am doing calcination in air atmosphere.

Thank you! I checked your results. The shift is about 0.34 eV for the value of binding energy of O1s and Ti2p1/2 and 0.32 eV for Ti2p/3/2. I think in your case the formation of rutile may occur after calcination (I supppose - partially) - please, compare with XPS data from:

http://www.nature.com/nmat/journal/vaop/ncurrent/fig_tab/nmat3697_F3.html.

You may try to calcinate the samples at higher temteratures and see what happens in XPS after that.

Dear Elżbieta Świętek, yes there is a partial formation of rutile also after calcination and is evident from XRD. But what i need to confirm is that these band shift of Ti2P and O1s is because of oxygen vacancy or not???

In my opinion this shift is due to the oxygen vacancy (it can be explained that the oxygen atoms were lost)

Thank you Elżbieta Świętek

You're welcome :)

Just a doubt. If calcination has caused Oxygen vacancies on the very surface of your sample, that seems to involve the "whole" surface (or better, the whole 2-3 nm deep selvedge). In other words, the overall stoichiometry of your material surface should have been changed. Insteda, I would expect at most some peak enlargement / asymmetry, witnessing the appearance of a small population of oxygen-deficient sites in your surface layers.

Can you exclude any work-function difference between spectra on pre-calcination sample and spectra on post-calcination ones? Carbon 1s peaks are identical and perfectly aligned?

Sorry for the appearant over-simplifying suspicion, but you know that sometimes XPS data may be not that easy to be analyzed, above all when low-conductive or insulating surfaces are probed.

Please, I have a peak in XPS at 836 ev, Is that TiO 

Please, after air plasma treatment, is the amount of oxygen in the composite(TiO/Fe2O3) increased? And what does oxygen vacancy mean? Does it mean that oxygen was decreased? After treating my composite with air plasma, I noticed, I took the EDS analysis and noticed that the untreated composite had less weight percent of oxygen.

In my opinion Olaniyan Ibukun XPS will be in the best position to give you accurate result, because EDS can only give you the percentage composition of selected region which you map in your analysis which may vary when you choose another position on your sample. Oxygen Vacancy is the creation of oxygen defect in a material lattice by lost of oxygen atom which can serve as an active site on which oxidation or reduction take place during photocatalytic activity or a trapping site which can inhibit and reduce the activity of your sample .