Revisiting the hydrothermal synthesis of titanate nanotubes: new insights on the key factors affecting the morphology

Abstract

Recently, titanate nanotubes have attracted a significant deal of interest, but the mechanism of formation as well as some structural aspects of these materials is still under debate. In this context, the main goal of the present study is to identify the key factors affecting the morphology of the titanate nanostructures during hydrothermal synthesis in order to increase the homogeneity and control, as finely as possible, the dimensions of the nanotubes. Previous studies also analyzed the influence of synthesis conditions but, unlike other works, the simultaneous assessment of the influence of parameters such as the phase and crystal size of the TiO₂ used as precursor, and the time and temperature of the hydrothermal treatment has been now analyzed under the same experimental context. The characterization of the prepared materials by means of TEM, XRD, N₂ adsorption isotherms and Raman spectroscopy was performed to establish correlations between the structural features and the preparation conditions. In this research, special attention has been paid to study the non-washed materials, which most of the previous studies have excluded from characterization. After hydrothermal treatment amorphous particles with different morphologies are isolated before acidification, which seems to be a crucial stage in controlling nanotube formation. Besides, the obtained data indicate that some characteristics of the nanotubes, such as the degree of conversion, the homogeneity and crystallinity of the structures or the aspect ratio, can be easily selected by adjusting the synthesis parameters.