To photo-catalytically degrade RhB dye using solar irradiation, CeO₂ doped TiO₂ nanocomposites were synthesized hydrothermally at 700 °C for 9 hrs. All emission spectra showed a prominent band centered at 442 nm that was attributed to oxygen related defects in the CeO₂-TiO₂ nanocrystals. Two sharp absorption bands at 1418 cm⁻¹ and 3323 cm⁻¹ were attributed to the deformation and stretching vibration, and bending vibration of the OH group of water physisorbed to TiO₂, respectively. The photocatalytic activities of Ce-TiO₂ nanocrystals were investigated through the degradation of RhB under UV and UV+ visible light over a period of 8 hrs. After 8 hrs, the most intense absorption peak at 579 nm disappeared under the highest photocatalytic activity and 99.89% of RhB degraded under solar irradiation. Visible light-activated TiO₂ could be prepared from metal-ion incorporation, reduction of TiO₂, non-metal doping or sensitizing of TiO₂ using dyes. Studying the antibacterial activity of Ce-TiO₂ nanocrystals against E. coli revealed significant activity when 10 μg was used, suggesting that it can be used as an antibacterial agent. Its effectiveness is likely related to its strong oxidation activity and superhydrophilicity. This study also discusses the mechanism of heterogeneous photocatalysis in the presence of TiO₂.