H2O-controlled synthesis of TiO2 with nanosized channel structure through in situ esterification and its application to photocatalytic oxidation

Abstract

TiO2 with a characteristic nanosized channel structure was synthesized by the sol–gel reaction of a titanium precursor with water produced from the in situ esterification of acetic acid and polymers containing hydroxyl groups. Several polymers including polyethylene glycol, Pluronic P123, and Tween 20 were used in these reactions to optimize the resulting surface area and pore size. The prepared samples were characterized by X-ray diffraction, N2 adsorption, thermogravimetric analysis, infrared spectroscopy, and field emission-scanning electron microscopy, and evaluated for photocatalytic decomposition of two hazardous compounds. Contrary to the anisotropic structure of TiO2 when prepared with considerable amounts of water, TiO2 synthesized through in situ esterification had a relatively large and regular channel structure that originated from the inorganic–organic network that formed between template molecules and Ti species. This inorganic–organic network seemed to be induced by hydrolysis of the Ti precursor with the small amount of H2O produced from the esterification reaction. The effect of the type and quantity of polymer on the structural properties of the synthesized TiO2 was also elucidated. The relationship between the structural properties and the photocatalytic activities of the TiO2 was investigated by studying the photodecomposition of probe materials with various molecular sizes. Photodecomposition of 2-isopropyl-6-methyl-4-pyrimidinol, a pyrimidine derivative, was limited by the TiO2 channel size because its large molecular size restricted its diffusion into the TiO2 channel. On the other hand, cyanide, with its relatively small molecular size, was effectively decomposed by TiO2 photocatalysis, and the decomposition activity was proportional to the TiO2 surface area regardless of the channel size.