The hydrothermal method is a facile route for the synthesis of TiO 2 nanostructured materials, but it requires accurate process optimizations and adjustments to circumvent the undesirable morphology products. In this study, systematically controlled experimental studies are carried out under thermodynamic and kinetic considerations to understand the formation of well-aligned TiO 2 nanorods during the hydrothermal reaction. In this regard, TiO 2 nanorods are synthesized on various types of substrates, including single crystal TiO 2 and sapphire, fluorine doped tin oxide, and silicon. Variable growth parameters are classified and investigated for their effects on the morphological evolution of TiO 2 nanorods. The preferred morphology of TiO 2 nanorods with the {110} facet is confirmed based on the crystallographic results for TiO 2 nanorods acquired by extensive transmission electron microscopy studies during the entire growth processes. The presence of the seeds on the substrates is found to be mandatory for the formation, growth, and strong adhesion of TiO 2 on the applied foreign substrates. The results elucidate that the growth kinetics of the process is significantly governed by the amount of applied HCl concentration, which is highly influential on the morphology of the synthesized TiO 2 nanorods. Accordingly, the growth mechanism for the preferential growth maintaining the rod shape is derived.
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Hong et al. (2018) studied this question.