Comparative study of the TiO.sub.2 nanopowders prepared from different precursors and chemical methods for heterogeneous photocatalysis application

A comparative thermal analysis study was realized by the thermogravimetric and thermodifferential analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) on TiO.sub.2 system. This study is to establish the influence of the preparation method on thermal behavior of powders obtained by different methods as follows: the sol-gel (SG), microwave-assisted sol-gel (MW) and hydrothermal (HT) methods. Titanium (IV) ethoxide, titanium (IV) isopropoxide and titanium (IV) butoxide were used as TiO.sub.2 precursors, as well as the parental alcohol as solvent, and the hydrolyzing agent (ammonia containing water) was added drop by drop to obtain a solution with pH 10. Based on TG/DTG/DTA results, the temperature of 450 °C was chosen for the processing of powders in air. Morphology and structure of the calcinated powders were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images show spherical nano-sized particles and X-ray diffractograms for all samples calcinated at 450 °C show crystallization in a single phase of TiO.sub.2 (anatase). According to the activation energy, E.sub.a, values calculated by Kissinger and Ozawa methods, amorphous-to-anatase transition is facilitated in the microwaved-assisted samples in comparison with the sol-gel derived samples. The photocatalytic activity of the TiO.sub.2 samples toward the degradation of methyl orange (MO) was evaluated, the sample denoted Ti-Bu-SG being the most effective removing a total of ~99% of the dye in 180 min, while Ti-Bu-MW presented the lowest degradation efficiency, about 82%.