Non-classical growth of brookite nanorods

To understand the growth processes of the brookite phase under hydrothermal conditions, several series of the samples were prepared, with varying temperatures, durations of the synthesis, precursor types and concentrations. A titanium lactate complex and amorphous hydrated titania were used as precursors. The samples were thoroughly characterized by XRD: integral intensities of the fitted peaks were used for the determination of the degree of crystallinity, phase composition and anisotropy of the particles. A series for which the duration of the synthesis was varied has shown that, at the initial stage, only amorphous and anatase phases were formed from the titanium lactate complex, while the brookite phase appeared after 4 hours of synthesis and its content grew with increasing synthesis time, at the expense of the anatase and amorphous phases. In all the cases when synthetic conditions allowed for brookite formation, the size of anatase crystallites was smaller than 19 nm, and the size of brookite particles was larger than 11 nm. A detailed HRTEM study of brookite particles has shown that they have pores and are built from several blocks. These results indicate that, under hydrothermal conditions, the formation of the brookite phase occurs due to a non-classical oriented attachment growth mechanism.