Role of Ti−O Bonds in Phase Transitions of TiO2

Abstract

A phase transition was achieved from TiO2 particles to titanate nanotubes by the breakage of Ti-O bonds without using expensive precursors, high temperatures, high chemical concentrations of alkaline solutions, and long synthesis times. The controlled preparation of one-dimensional nanostructures of titanates (H2Ti4O9.nH2O) has been conducted at a very low concentration of alkaline solution (1 M NaOH), and in a very short time (12 h) using TiO2 anatase and TiO2 P-25 (precursors) and a microwave enhanced soft chemical process. Temperature was used as a variable, and only low process temperatures (100-110 degrees C) were used. A combination of anatase nanoparticles/hydrogen tetratitanate nanotubes was synthesized using TiO2 (anatase) and a temperature of only 100 degrees C. When TiO2 (P-25) was used with the same concentration of alkaline solution (1 M NaOH), the same processing time of 12 h, and a higher temperature at 110 degrees C, only hydrogen tetratitanate nanotubes were observed. The linkages of "Ti-O" play a very important role in the structural features of different phases. X-ray diffraction (XRD) showed two crystalline phases (tetragonal and monoclinic) in the case of TiO2 (anatase) and one crystalline phase (monoclinic) for products of TiO2 (P-25). The role of Ti-O linkages is obvious in the Raman spectra as revealed by a shift in peak positions for a layered structure of the hydrogen tetratitanate and a nanosphere structure of the resulting TiO2. An X-ray photoelectron spectroscopy (XPS) study showed a shift to a lower binding energy of the 2p peaks (2p1/2, 3/2) in the Ti region for titanate and confirmed the formation of titanate nanostructures. Transmission electron microscopy (TEM) revealed nanotubes of hydrogen tetratitanates (H2Ti4O9.nH2O) in the form of bundles. High-resolution TEM (HRTEM) data supported findings of X-ray diffraction results of the products of TiO2 (anatase) and TiO2 (P-25).