TiO2 sol was prepared hydrothermally in an autoclave from aqueous TiOCl2 solutions as a starting precursor. Titanate nanotubes were obtained when the sol–gel-derived TiO2 sol was treated chemically with a 10 M NaOH solution and subsequently heated in the autoclave at 150 °C for 48 h. The samples were characterized using XRD, TEM, SEM, EDX, Raman spectroscopy, and a BET surface area analyser. The effect of post treatments, such as washing with and without hydrochloric acid and calcination, on the phase structure, shape and morphology, pore structures, and BET surface area of the titanate nanotubes was investigated. When a sample containing 7.08 wt% Na (after washing only with water) was calcined at different temperatures from 300 to 900 °C, it showed the formation of a mixture of sodium trititanates and sodium hexatitanates and was found to preserve the tubular morphology at higher temperatures. However, a sample containing 0.06 wt% Na obtained after prolonged washing with hydrochloric acid followed by heat treatment showed the formation of TiO2 anatase involving TiO2 (B) as an intermediate at lower temperatures and anatase was further transformed to the rutile phase when the temperature was raised. On the basis of different observations, a general formula NaxH2−xTi3O7·nH2O has been proposed for the trititanate nanotubes.

No abstract

No abstract

No abstract

Transition metal doped TiO2 (Ni, Fe, Cu) and nanocomposite TiO2 powders with rutile phase were synthesized by mechanical alloying and heat treatment, and were characterized by XRD, TEM, UV-DRS, and PL (Photoluminescence). Photocatalytic activity was also investigated with the degradation rate of 4-chlorophenol and measured by total organic carbon analyzer. TEMEDP and XRD patterns showed that the transition metal doped powders (only alloyed powder) were in the form of rutile phase with the particle size of 20-30 nm. The average grain size of transition metal doped powders was in the range of less than 10 nm. However, after heat treatment, the alloyed powder formed composite of the titanate and rutile phase. The UV-DRS and PL investigation showed that Ni doped 8 wt% nanocomposite TiO2 had the higher wavelength range (600-660 nm) (2.0-1.9 eV) than that of the commercial P-25 powder(380-400 nm) by Degussa Co. indicating that the Ni 8 wt% doped nanocomposite TiO2 shifted the absorption into the visible light region and thus, enhanced the photocatalytic activity. Further, these results agreed well with TOC investigation. Formation of titanate in transition metal doped TiO2 due to heat treatment was found to control the grain growth of nano-sized TiO2 and to enhance its thermal stability at high temperature.