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 °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 °C) and highest (800 °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 °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.