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Visible light photocatalysis via nano-composite CdS/TiO2 materials Sesha S. Srinivasan, Jeremy Wade and Elias K. Stefanakos Clean Energy Research Center, College of Engineering, University of South Florida, Tampa, FL 33620 ABSTRACT Nano-structured colloidal semiconductors with heterogeneous photocatalytic behavior have drawn considerable attention over the past few years. This is due to their large surface area, high redox potential of the photogenerated charge carriers and selective reduction/oxidation of different class of organic compounds. Nano-structured TiO2 is widely used as a photocatalyst for the effective decomposition of organic compounds in air and water under UV radiation. On the other hand, the development of visible light activated photocatalysis, for utilizing the available solar energy remains a challenge and requires low band gap materials as sensitizer. Among the various inorganic sensitizers, bulk CdS with an Eg of 2.5 eV and an energetically high-lying conduction band has been identified as a potential candidate. This can be coupled with a large band gap semiconductor (TiO2 with Eg ~ 3.2 eV) for visible light photocatalysis and solar energy conversion. In the CdS sensitized TiO2 nano-composite system, charge injection from the conduction band of the semiconductor sensitizer to that of TiO2 can lead to an efficient and longer charge separation by minimizing electron-hole recombination. In the present paper, we have carried out a systematic synthesis of nano-structured CdS/TiO2 via reverse micelle process. The structural and microstructural characterizations of the asprepared CdS/TiO2 nano-composites are determined using XRD and SEM-EDS techniques. The visible light assisted photocatalytic performance is monitored by means of degradation of phenol in water. INTRODUCTION Environmental pollution on a global scale will probably be the greatest problem for the chemical scientists in the 21st century. Photocatalytic nanomaterials, a new kind of eco materials, are widely used for desalination/disinfection and air/water purification applications. Anatase TiO2 is the most widely used semiconductor photocatalyst for an effective decomposition of organic compounds in air and water under UV light irradiation with wavelength shorter than 387 nm [1, 2]. The major problem is that only about 4% of the solar spectrum falls in this UV range. The efficient use of sunlight becomes an appealing challenge for developing photocatalysts [3]. One approach for achieving this objective is to sensitize TiO2 by using a narrow band gap semiconductor with a higher conduction band than that of TiO2. CdS with a band gap of 2.5 eV is almost invariably used as the sensitizer for large band gap semiconductors because of the ideal position of its conduction and valence band edges. CdS alone, however, shows little or no signs of photoactivity because of its instability and rapid Electron-Hole Pair (EHP) recombination rates. Studies have proven that with the appropriate particle interaction, CdS/TiO2 nanocomposites can efficie