Why does Ti 2p binding energy, determined by XPS, using Al Kα monochromatized anode, shift to lower values when the hydrothermal reaction time increases from 24 to 72 hours?
A 3 days hydrothermal experiment should undercome a reduction of your titanium species. Maybe do you get reducer agents in the media which lower the oxidation state of titanium (after thermal activation)?
Thank you for the answer. After hydrothermal treatment, it followed the acid washing only (0.1N HCl), but it was similar for all samples (from 24 to 72 hours). Alkaline media and time should be responsible for titanium 4+ shifting. No Ti3+ was detected (yet!).
Are you using Titania or titanium metal. If it's the former, what are you using as your reference point? If there is no evidence of reduced states, then it could be that using the adventitious carbon as a reference is not that reliable here since the nature of the surface carbon is changing. We have seen this depending on reaction conditions and times on a number of metal oxides, so one must always be careful and look.
It may be worth recording the Ti Auger peak also and calculating the Auger parameter. If this value is equal in both cases, then there is a good probability that there is no change and it is a case of charge referencing.
Titania was used as a precursor. There is no shifting, as you both correctly said. It was a reference issue. Thank you both!
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