Formation Efficiency of One-Dimensional Nanostructured Titanium Oxide Affected by the Structure and Composition of Titanate Precursor: A Mechanism Study

The formation mechanism and atomic arrangement of one-dimensional (ID) nanostructured titanates have been systematically investigated with combinative spectroscopic and microscopic analyses. First of all, the influence of the interlayer distances of the lepidocrocite-type titanate precursor on the formation efficiency of ID nanobelts has been studied, clearly demonstrating that the increase of basal spacing upon the protonation does not promote the formation of 1D nanostructures. This finding did not support the previously proposed exfoliation mechanism of the layered titanate precursor. Of special interest is that the poor efficiency of the protonated titanate as a precursor could be enhanced by Fe substitution, underscoring the importance of precursor dissolution. According to time-dependent electron microscopic analyses, the hydrothermal alkali treatment initially gave rise not only to a decrease in the particle size of the precursor but also to the formation of ID titanate nanobelts with lepidocrocite structure, which was followed by the dissolution of the initially formed nanobelts, the appearance of bigger layer-shape crystallites, and their splitting into I D nanobelts with trititanate structure. This finding provided strong support for the dissolution/recrystallization model, in which the dissolution of the precursor plays a crucial role in the formation of ID nanostructured fitanate. Electron diffraction, Ti K-edge X-ray absorption near-edge structure, and micro-Raman spectroscopy clearly demonstrated that the ID nanobelts prepared by the extended hydrothermal treatment (i.e., 48 h) and layer-shaped intermediate commonly crystallize with trititanate-type structure, which is clearly distinguishable from the lepidocrocite structure of the precursor. On the basis of all the present experimental findings, we are able to conclude that the I D fitanate nanobelts with trititanate structure were produced via a splitting of intermediate layered crystallites formed from the dissolved species.