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

Abstract Nanosized CdS coupled TiO 2 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 TiO 2 materials consisted of uniform anatase TiO 2 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 (1 0 1) crystal planes of anatase and (1 1 1) crystal planes of CdS was observed in the HRTEM image. Ti 3+ signal was observed in the electron paramagnetic resonance (EPR) spectrum of CdS coupled TiO 2 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 TiO 2 . As expected, the nanosized CdS sensitized TiO 2 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 TiO 2 nanocrystals under visible light is also discussed.

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