Characterization and photocatalytic mechanism of nanosized CdS coupled TiO2 nanocrystals under visible light irradiation

Nanosized CdS coupled TiO2 nanocrystals were prepared by a microemulsion-mediated solvothermal method at relatively low temperatures. The prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), BET surface area analysis, X-ray diffraction (XRD), UV-vis absorption spectroscopy (UV-vis), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). It was found that the CdS coupled TiO2 materials consisted of uniform anatase TiO2 of 6-10 nm with highly dispersed cubic phase CdS nanocrystals. The prepared samples exhibit strong visible light absorption at about 550 nm. Meanwhile, they have high surface area in the range of 156-263 m(2) g(-1) and mesoporous character with the average pore diameter of ca. 5.0-6.5 nm. The coupling between the (101) crystal planes of anatase and (111) crystal planes of CdS was observed in the HRTEM image. Ti3+ signal was observed in the electron paramagnetic resonance (EPR) spectrum of CdS coupled TiO2 nanocrystals under visible light irradiation. It provided the evidence of an effective transfer of photo-generated electrons from the conduction band of CdS to that of TiO2. As expected, the nanosized CdS sensitized TiO2 nanocrystal materials showed enhanced activity in the oxidation of methylene blue in water or nitric oxide in air under visible light irradiation. The mechanism of photocatalysis on CdS coupled TiO2 nanocrystals under visible light is also discussed. (c) 2005 Elsevier B.V. All rights reserved.