Multiphase titanium dioxide (TiO2) nanoparticles were successfully synthesized using the hydrothermal method. The as-prepared nanoparticles were subjected to different annealing temperatures (Ta) to investigate their effects on the structural, morphological, and opto-chemical properties using X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Energy dispersive x-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and Ultraviolet-visible spectrometry (UV–Vis) techniques. As Ta is increased from 200 to 1200 °C, the TiO2 nanoparticles appear to have a stable tetragonal crystal structure throughout the various Ta. XRD measurements indicate an extended presence of mixed anatase-rutile phase composition with a slow phase transformation mechanism. The crystalline size of both the anatase and rutile phase increases from 19 to 38 nm and 18 -57 nm, respectively. The behaviour in the lattice parameter indicates that increasing Ta forces the crystalline structure in both phases to expand. Images from TEM and SEM micrographs reveal a similar morphology in agreement with XRD measurements. The micrographs reveal that increasing Ta increases material porosity and the dispersion of well-defined TiO2 nanostructure. The EDX spectroscopy confirms the successful synthesis of TiO2 nanoparticles with the absence of impurities after annealing. FT-IR confirms vibrational modes and bond behaviour associated with the expected titanium and oxygen elements with Ta. The UV–Vis spectroscopy characterizes changes in the multiphase TiO2 optical properties as the Ta is increased. An intense UV absorption is reported in the results section and its importance in solar cell applications is stated in the conclusion.
- Impurities and bandgap