To photo-catalytically degrade RhB dye using solar irradiation, CeO 2 doped TiO 2 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 CeO 2 -TiO 2 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 TiO 2 , respectively. The photocatalytic activities of Ce-TiO 2 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 TiO 2 could be prepared from metal-ion incorporation, reduction of TiO 2 , non-metal doping or sensitizing of TiO 2 using dyes. Studying the antibacterial activity of Ce-TiO 2 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 TiO 2 . Solar energy is uniquely poised to solve major energy and environmental challenges that are being faced by humankind. As such, it is important to develop a suitable environmentally-friendly technology that permits the full range of the solar spectrum to be used for simultaneously solving energy and environmental challenges. It has been proposed that it is possible to address these challenges using nanocomposite materials that are capable of solar photocatalytic conversion 1,2 . Nanocomposite materials have a mixture of different chemical compositions and have received wide interest from fundamental and applied science researchers. The physical properties of these materials can be combined to produce materials that have desirable characteristics. Optical or biological characteristics can change with decreasing particle sizes, which is a major reason for interest in nanocomposite materials 3 . For example, metal oxide nanocomposites have excellent physical properties, such as high hardness and melting points, low densities and coefficients of thermal expansion, high thermal conductivities, good chemical stabilities. They also have improved mechanical properties, such as higher specific strengths, better wear resistance and specific modulus, and have wide potential for various industrial fields 4,5 .

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