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Physical chemistry, Colloid chemistry
Anatase to rutile transition in an unmodified synthetic titania usually occurs at a temperature range of 600 – 700 °C. Various methods such as addition of metallic and non-metallic dopants and modifying the precursor have previously been reported to influence the anatase to rutile transition temperature. In the current study, the effect of addition of increasing amounts of silver to the extent of chelation of a formate group to a titanium precursor and the resulting effects on the transformation of anatase to rutile has been studied. The addition of silver (0, 1, 3 and 5 mol %) on the anatase to rutile transformation temperature has been systematically followed by FTIR, Raman, XRD, DSC and XPS. From the FTIR and Raman spectroscopy studies it was observed that the incorporation of silver caused a reduction in the intensity of the COO- stretches indicating that the titania – formate bridging complex is becoming weaker in the presence of silver. XRD studies indicated an early rutile formation for the silver doped samples. XRD of the samples calcined at 700 °C showed that 5 mol % Ag TiO2 contained both anatase (46 %) and rutile (54 %), whereas the undoped sample primarily consists of anatase (95 %). At 800 °C all silver doped samples converted to 100% rutile and the the un-doped TiO2 consisted of both anatase (55 %) and rutile (45 %). XPS analysis showed that Ag0 and Ag2O has been formed on the surface of the titania – formate complex, without calcination (> 100 °C) indicating that photo oxidation has occurred. FTIR, Raman and XPS studies confirmed that the presence of silver in the xerogel before calcination may be responsible for the reduction of the titanium – formate bridge. It was concluded that the presence of silver (Ag2O and Ag0) hindered bridging ligands, which resulted in a weakened titanium gel network. This structurally weakened gel network could easily be collapsed during calcination and it favors an early rutile formation.
Nolan, N., Seery, M., Hinder, S., Healy, L., Pillai, S.: A Systematic Study of the Effect of Silver on the Chelation of Formic Acid to a Titanium Precursor and the Resulting Effect on the Anatase to Rutile Transformation of TiO2. Journal of Physical Chemistry C, 114, 2010, 13026 - 13034.