Sol–gel synthesis of TiO2 nanoparticles and photocatalytic degradation of methyl orange in aqueous TiO2 suspensions

Anatase TiO2 nanoparticles of about 16 nm in crystal size have been successfully synthesized via a sol–gel method. Thermal treatment of the precursor at 500–600 °C results in the formation of different TiO2 phase compositions. The samples were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Effects of the pH value of the solution, H2O2 addition, TiO2 phase composition and recycled TiO2 on the photocatalytic degradation of methyl orange (MeO) in TiO2 suspensions under ultraviolet (UV) illumination were primarily investigated. The results indicate that a low pH value, proper amount of H2O2 and pure anatase TiO2 will facilitate the photocatalytic oxidation of the MeO solution. The photodegradation degree decreases with increasing the pH value of the solution and varies with different amounts of H2O2. Pure anatase TiO2 shows better photocatalytic activity for MeO decolorization than biphase TiO2. The photocatalytic mechanism of the as-synthesized TiO2 nanoparticles was discussed.