Structural and optical characterization of the crystalline phase transformation of electrospinning TiO₂ nanofibres by high temperatures annealing

The electrospinning technique has been used to synthesize TiO₂ nanofibres, which by annealing at high temperatures achieves the crystalline phase transformation of anatase to rutile passing through the anatase-rutile mixed. The investigated temperature range was 0-1000^°C. The TiO₂ nanofibres surface morphology and chemical stoichiometry were obtained by Scanning Electron Microscopy and Energy Dispersive Spectrometry. The annealed nanofibres diameter was ranged from 137.0 to 115.3 nm in the investigated temperature range. The influence of the annealing temperature on the structure and crystalline phase quality of the TiO₂ nanofibres has been investigated by X-ray diffraction and Raman scattering. Clear evidence have been obtained of the structural transformation of TiO₂ nanofibres from pure anatase to pure rutile, including the almost amorphous and anatase-rutile mixed structural phases by X-ray diffraction and confirmed by Raman scattering. By X-ray diffraction was found that the TiO₂ nanofibres crystalline phases presented as preferential growth direction (101) for anatase and (110) for rutile. The Raman spectroscopy exhibits the anomalous behavior for band broadening and shifting of Raman bands with increasing crystallite size that forms the nanofibres. The room-temperature photoluminescence presents radiative bands whose dominant band redshifts from 2.56 to 1.32 eV, as the crystalline phase is transformed by annealing at high temperature.