Structural characterization and optical property of TiO2 powders prepared by the sol–gel method

The structural characteristics and optical property of TiO2 powders with different phases are studied by various techniques in this paper. Butyl titanate and oxalic acid were used as Ti source and catalyst, respectively, for sol–gel synthesis of TiO2 powders. The synthesized products were characterized by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis and photoluminescence techniques. X-ray diffraction patterns confirm TiO2 phase transformation from amorphous to anatase and rutile with the increase in calcination temperatures from 200 °C to 700 °C. Two exothermic peaks at 275 °C and 485 °C on the differential scanning calorimetry curve are responsible for the decomposition of the oxalate groups, which can enhance TiO2 phase transformation from amorphous to anatase and rutile. The crystalline sizes of the synthesized TiO2 powders are in the range of 20–65 nm. The coherent phase boundary between (200) crystal plane of anatase and (11−2) crystal plane of rutile is determined first time, based on the Fourier transform analysis. The near band edge emission peaks of anatase at 396 nm and rutile at 419 nm, and four peaks of the different defects in TiO2 crystals can be identified on the photoluminescence spectra of the synthesized TiO2 powders. The activation energies for the grain growths of anatase and rutile were calculated, indicating that the surface chemistry may be a critical parameter to control grain growth. Based on the experimental results, the mechanism for the formation of anatase and rutile TiO2 is discussed.