Study of preparation of mesoporous TiO₂-B nanofibers from mesoporous anatase TiO₂ and interaction between CH₃I and TiO₂-B

Anisotropically grown TiO₂-B with a textural porosity and a high specific surface area has been prepared, characterized, and used to catalyze the thermal and photochemical decomposition of CH₃I. The fibrous TiO₂-B is fabricated by the reaction of mesoporous anatase TiO₂ at 90 °C, followed by addition of 0.1 M HCl solution into the reaction precipitate to reach pH 1. Addition of 0.1 M HCl solution for other pH values of 6, 9, and 12 is also carried out to investigate the pH effect on the elemental composition and morphology of the reaction products, which provides some mechanistic clues for the formation of the TiO₂-B nanofibers. XRD patterns, Raman and reflectance UV-Vis spectra, and SEM and TEM images are used to characterize the material. The TiO₂-B fibers, ∼10 nm in width and several hundred nanometers in length, grow along the [frac(1, 2) 0 1] direction of the monoclinic structure, as suggested by the observation of the (2 0 1) fringes which are normal to the axial direction and have a neighboring distance of 0.37 nm in the TEM images. The TiO₂-B nanofibers aggregate into cotton-like particles with a size similar to that of the original anatase particles, forming mesopores with an average diameter of 4.5 nm and a high BET area as much as ∼600 m²/g which is much larger than those reported previously for titanates and TiO₂-B with morphologies of tube or fiber. The TiO₂-B material has an experimentally-determined bandgap energy of 3.3 eV. Its thermal and photochemical reactivities toward CH₃I decomposition are demonstrated by infrared spectroscopic investigation in a gas-solid system.