Large-Scale Synthesis of TiO2 Nanorods via Nonhydrolytic Sol−Gel Ester Elimination Reaction and Their Application to Photocatalytic Inactivation of E. coli

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Abstract
A simple method of synthesizing a large quantity of TiO2 nanorods was developed. A nonhydrolytic sol−gel reaction between titanium(IV) isopropoxide and oleic acid at 270 °C generated 3.4 nm (diameter) × 38 nm (length) sized TiO2 nanocrystals. The transmission electron microscopic image showed that the particles have a uniform diameter distribution. X-ray diffraction and selected-area electron diffraction patterns combined with high-resolution transmission electron microscopic image showed that the TiO2 nanorods are highly crystalline anatase crystal structure grown along the [001] direction. The diameters of the TiO2 nanorods were controlled by adding 1-hexadecylamine to the reaction mixture as a cosurfactant. TiO2 nanorods with average sizes of 2.7 nm × 28 nm, 2.2 nm × 32 nm, and 2.0 nm × 39 nm were obtained using 1, 5, and 10 mmol of 1-hexadecylamine, respectively. The optical absorption spectrum of the TiO2 nanorods exhibited that the band gap of the nanorods was 3.33 eV at room temperature, which is 130 meV larger than that of bulk anatase (3.2 eV), demonstrating the quantum confinement effect. Oleic acid coordinated on the nanorod surface was removed by the reduction of the carboxyl group of oleic acid, and the Brunauer−Emmett−Teller surface area of the resulting naked TiO2 nanorods was 198 m2/g. The naked TiO2 nanorods exhibited higher photocatalytic activity than the P-25 photocatalyst for the photocatalytic inactivation of E. coli.