On the structure of one-dimensional TiO2 lepidocrocite

We recently reported on the synthesis of one-dimensional (1D) TiO2-based nanofilaments, (NFs) by reacting water insoluble, earth abundant, and non-toxic Ti-containing precursors, such as TiC, TiB2, and TiSi2, among others, with quaternary ammonium hydroxides, mostly tetramethylammonium hydroxide at near-ambient conditions. From selected area diffraction, X-ray diffraction, and Raman spectroscopy, we previously concluded that the NF's structure was anatase-based. Herein, using high-resolution scanning transmission electron microscopy, Raman spectroscopy, obtained using low laser power, and density functional theory modeling, we conclude that the actual structure is 1D titania lepidocrocite-based structure with minimal cross sections of ≈ 5 × 5 Å2. The NFs grow along [100] with a and c lattice parameters of 3.78 ± 0.01 Å and 3.04 ± 0.06 Å. They tend to self-assemble/stack in two directions, viz. along the b and c axes. And while in-plane and out-of-plane interfilamentous distances are functions of the nature of the cations surrounding the NFs, the band gap, at ≈ 4 eV, is not.