Application of statistical strategies to process optimization of sol-gel-derived SiO2 modification of TiO2

Commercial TiO2 is modified by combination with a sol-gel-derived SiO2. Statistical experimental methods are employed to find the optimal preparation conditions for achieving high photoactivity. Of the five variables studied, TiO2 weight percentage (TiO2/(SiO2 + TiO2)) and water/Si molar ratio are the key variables affecting photoactivity. Also, calcination temperature is a significant variable, with final temperatures from 300 to 450 degreesC having a large positive influence on photoactivity. Interaction effects of nitric acid concentration and water/Si molar ratio, and TiO2 weight percentage and nitric acid concentration, are significant when compared with the other two-factor interaction effects. A quadratic form fit by using the central composite design is established to correlate the experimental data with the theoretical ones from the statistical model. The test statistics, F distribution, and multiple correlation coefficient R-2 confirm the adequacy of the model.