We report the synthesis of anatase TiO2 nanoparticles of average size 12 nm (determined by field emission scanning electron microscope and high resolution transmission electron micorscope) and the degradation of Orange II, Methyl Orange and Rhodamine B dyes using ultraviolet (UV) light source. The TiO2 nanoparticles are well crystalline having anatase phase as confirmed by X-ray diffraction technique. The indirect and direct band gaps of TiO2 nanoparticles were measured to be about 3.09 eV and 3.74 eV, respectively. The increase in the band gap from its bulk value may be accounted for the quantum confinement effect. After UV exposure, the Orange II (20 min), Methyl Orange (25 min) and Rhodamine B (150 min) concentrations were found to degrade more than 99%, 98% and 99%, respectively. Furthermore, the synthesized TiO2 nanoparticles are efficient photocatalyst in comparison to the other reported TiO2 nanostructures and composites (with other materials) due to its small volume/less electron-hole recombination, oxygen vacancy and good crystallinity. The LDA, CA-PZ functional and ultrasoft pseuodopotential were used to find the band gap of anatase TiO2 theoretically. The PDOS signifies the formations of excitons are mainly in between O 2p and Ti 3d orbitals. (c) 2012 Elsevier B.V. All rights reserved.