Characterization of pore structure of mesoporous hydrogen titanium oxide hydrates Original Research Article

Mesoporous hydrogen titanium oxide hydrates have been synthesized by hydrothermal treatment of nano-sized titania powder (P-25) in a 10 M-NaOH aqueous solution in the temperature range of 90–210 °C for 24 h. XRD patterns of the as-synthesized powders confirmed that the crystalline phases were not TiO2 but hydrogen titanium oxide hydrates, such as H2Ti5O11·H2O or H2Ti4O9·H2O, and the SEM and TEM observations clearly revealed that the morphologies of the samples synthesized in the range of 120–150 °C were nanotube shapes and nanorod shapes above 180 °C. HRTEM photographs revealed that the wall thickness and inner diameter of the hydrothermally treated samples at 120 °C were estimated as about 1.73 and 3–4 nm, respectively. The specific surface area of the nanotube-shaped H2Ti4O9·H2O reached a maximum value of 395 m2/g, in contrast to below 50 m2/g for nanorod-shaped H2Ti5O11·H2O. Pore structure analysis by the BJH method, from N2 adsorption–desorption isotherm revealed that the structural change from the nanotube to nanorod shape resulted in rapid decrease in the pore volume and an increase in the peak pore size.