Highly efficient visible light TiO2 photocatalyst was prepared by the sol-gel method at lower temperature (<= 300 degrees C), and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). The effects of the heat treatment temperature and time of the as-prepared TiO2 on its visible light photocatalytic activity were investigated by monitoring the degradation of methyl orange solution under visible light irradiation (wavelength >= 400 nm). Results show that the as-prepared TiO2 nanoparticles possess an anatase phase and mesoporous structure with carbon self-doping and visible photosensitive organic groups. The visible light photocatalytic activity of the as-prepared TiO2 is greatly higher than those of the commercial TiO2 (P-25) and other visible photocatalysts reported in literature (such as PPy/TiO2, P3HT/TiO2, PANI/TiO2, N-TiO2 and Fe3+-TiO2) and its photocatalytic stability is excellent. The reasons for improving the visible light photocatalytic activity of the as-prepared TiO2 can be explained by carbon self-doping and a large amount of visible photosensitive groups existing in the as-prepared TiO2. The apparent optical thickness (tau(app)), local volumetric rate of photo absorption (LVRPA) and kinetic constant (k(T)) of the photodegradation system were calculated. (C) 2011 Elsevier B.V. All rights reserved.