The synergistic role of pH and calcination temperature in sol-gel titanium dioxide powders

Titanium dioxide (TiO2) nanoparticles were prepared by the sol-gel method starting from a volume of 1.5 mL of titanium tetraisopropoxide (TTIP) dissolved in 10 mL of ultrapure water milliQ grade (pH 5). The pH of the solution was adjusted by adding HNO3 and NaOH to reach an acidic and basic character of the sol, respectively. A wide pH range from 1 to 10 was explored. The prepared TiO2 nanopowders were annealed at three different calcination temperatures, 100, 450 and 800 degrees C for 3 h. The synergic effect of pH and calcination temperature on the structural and morphological properties of TiO2 nanoparticles was investigated by XRD and Raman analyses. At the lowest (100 degrees C) and highest (800 degrees C) calcination temperatures, we observed the dominance of anatase and rutile phases, respectively. A mixture of these phases was observed for the titania powders calcinated at 450 degrees C. In particular, the nanoparticles produced in strong acidic medium showed a coexistence of anatase and rutile with a dominance of rutile, whereas the anatase was the crystalline phase favored in alkaline medium environment.