Application of the statistical Taguchi method to optimize TiO2 nanoparticles synthesis by the hydrothermal assisted sol–gel technique

TiO2 nanoparticles were synthesized by hydrothermal assisted sol–gel technique. The preparation parameters including pH value, the amount of water, titanium tetra isopropoxide content, temperature and time of hydrothermal process were investigated by Taguchi statistical experiments to determine the influence of synthesizing variables on the optimal conditions and to realize the highest degree of crystallinity or smallest crystallite size. X-ray diffraction (XRD) analysis and direct band gap energy (Eg) values, measured via diffuse reflectance spectra (DRS), proved that all the samples consist of anatase as a unique phase. Transmission electron microscopy (TEM) and specific surface area values showed that the sample with the smallest crystallite size could exert more effective photoactivity confirmed by measuring the decomposition rate of methylene blue. The apparent photodegradation rate constant of the sample with the smallest crystallite size was about five times greater than that of commercial TiO2. A higher photoactivation performance of TiO2 nanoparticles could be achieved using 45 mL of water and 3.79 mL of titanium tetra isopropoxide in a sol with pH of 9 and passing hydrothermal process at 100 °C for 18 h.