... Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, JapanbDepartment of Energy and Material Sciences, Faculty of Engineering Sciences, ... formation of tubular TiO2 of 1 m and 50 nm in length and diameter, respectively, as shown in Fig. 1(c) and (d). With increasing the temperature of the hydrothermal treatment,the length of the ... resulted in slight sintering of TiO2aggre-gates and nanotubes obtained at 160 and 200◦C, respectively, asshown in Fig. 1(b’) and (c’).The nanostructures of the TiO2nanotubes calcined at...