Influence of solvent and pH on the synthesis of visible light active titanium dioxide nano particles

Visible light active titanium dioxide (TiO₂) nano particles with high photocatalytic efficiency were prepared by sol gel method from titanium isopropoxide precursor by carefully controlling the synthesis conditions such as solvent and pH. Solvents used in this study are isopropanol, ethanol and methanol. The pH values considered are 1, 4 and 8. The products obtained were characterized using X-ray diffraction, UV–Visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). TiO₂ synthesized using methanol as a solvent at pH 1 showed a significant decrease in band gap (2.93 eV) when compared to that of anatase (3.2 eV) and rutile (3.0 eV). Visible light photocatalytic activity of the material with lowest band gap was determined by studying the photodegradation of methylene blue (MB) dye. The material showed a photodegradation efficiency of 84% after 180 minutes which is generally difficult to attain without doping or surface modification. We could achieve a high photocatalytic efficiency by band gap engineering which was done by changing the synthesis conditions.