Characterization of nanosized TiO2 synthesized inside a porous glass-ceramic monolith by metallo-organic decomposition process

This work reports the preparation of TiO₂ by decomposition of a metallo-organic precursor (MOD process) in the pores of an α-NbPO₅ glass-ceramic monolith (PGC-NbP) and the study of the TiO₂ anatase-rutile transition phase. The impregnation of titanium di-(propoxy)-di-(2-ethylhexanoate) in the PGC-NbP was confirmed by diffuse reflectance infrared spectroscopy. In the restrictive porous environment the decomposition of the metallo-organic compound exhibits a lower initial decomposition temperature but a higher final decomposition temperature, in comparison to the free precursor. The pure TiO₂ rutile phase is formed only above 700 °C when the titanium precursor is decomposed outside the pores. The TiO₂ anatase obtained inside the PGC-NbP was stabilized up to 750 °C and exhibits a smaller average crystallite size in comparison with the MOD process performed without PGC-NbP. Furthemore, the temperature of the TiO₂ anatase-rutile transformation depends on crystallite size, which was provided by XRD and Raman spectroscopy. The precursor impregnation-decomposition cycle revealed a linear mass increment inside PGC-NbP. Micro-Raman spectroscopy shows the presence of a gradient concentration of the TiO₂ inside the PGC-NbP. The use of the MOD process in the PGC-NbP pores has several advantages: control of the amount and the nature of the phase formed and preservation of the pore structure of PGC-NbP for subsequent treatments and reactions.