Solution growth of anatase TiO2nanowires from transparent conducting glass substrates

Abstract

Sol–gel reaction conditions that enable the growth of one-dimensional (1D) anatase titanium dioxide (TiO₂) nanostructures from fluorine-doped indium tin oxide (FTO) substrates are described. The generation of these linear nanostructures is achieved using acetic acid (HOAc) and titanium isopropoxide (Ti(OⁱPr)₄) in anhydrous heptane in the absence of an external bias or template. The procedure requires the functionalization of base-treated substrates with Ti-oxide nucleation sites, which serve as a foundation for the growth of linear Ti-oxide macromolecules. Calcination of these macromolecules at 450 °C under an ambient atmosphere produce uniform films of randomly oriented anatase TiO₂ nanowires. The nucleation and growth processes are both acutely sensitive to the relative molar ratio (R) of HOAc to Ti(OⁱPr)₄. Optimal surface coverage of the nucleation sites is observed when the R value utilized for the nucleation phase (denoted R_i) is equal to 1.3. The highest quality nanowire films were obtained when the R value employed during the gelation phase (denoted R_f) was held between 8.5 and 14. Characterization of the films by electron microscopy revealed a uniform film of disordered anatase TiO₂ nanowires with high aspect ratios. The dimensions of the nanostructures correspond to lengths of ca. 1–10 μm and widths of 54 ± 10 nm. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques demonstrate that the anatase nanowires are a linear arrangement of crystallites ranging in size from 13 to 19 nm. A systematic evaluation of how reaction conditions (e.g., solvent volume, stoichiometry of reagents, substrate base treatment) affect the generation of these TiO₂ films is presented.