Influence of Amorphous TiO2-x on Titania Nanoparticle Growth and Anatase-to-Rutile Transformation

Amorphous TiO2-x formed together with precursors and anatase nuclei, during TiCl4 hydrolysis at soft conditions, influences both crystal growth and phase stability. The highly defective nanoparticles of anatase grow by reaction of their basic hydroxyls with acidic ones of TiO2 precursor species. The growth of anatase crystals, however, is affected by their interactions with simultaneously formed amorphous TiO2-x which increasingly covers the particles hindering the anatase-precursor contact. The interactions among anatase and amorphous and precursor components have been studied by H-1-MAS (magic angle spinning) NMR spectroscopy. The interaction between acid and basic hydroxyls favors the formation of Ti-O-Ti bonds between' amorphous and anatase phases, increasing the agglomeration of anatase nanoparticles. These interactions destabilize anatase crystals and favor anatase-to-rutile transformation as the solution aging progresses