Assembly of a CdS quantum dot–TiO2 nanobelt heterostructure for photocatalytic application: towards an efficient visible light photocatalyst via facile surface charge tuning

Abstract

In recent years increasing efforts have been devoted to synthesizing hybrid semiconductor nanocomposites; however, it still poses a challenge to fabricate well-defined semiconductor based heterostructures. In this work, a well-defined TiO₂ nanobelt functionalized with a CdS quantum dot (viz. TiO₂ NB–CdS QD) binary nanostructure has been fabricated by an efficient self-assembly approach based on a facile surface charge tuning. A collection of techniques including X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), field emission scanning electron microscopy (FESEM), transmission scanning electron microscopy (TEM), and X-ray photoelectron spectra (XPS) was utilized to characterize the structure of TiO₂ NB–CdS QD binary heterostructure. It was found that the as-constructed TiO₂ NB–CdS QD heterostructure exhibits significantly enhanced photocatalytic performance for the degradation of organic pollutants under visible light irradiation in comparison with blank TiO₂ NBs and randomly mixed counterparts. The significantly enhanced photocatalytic performance of the TiO₂ NB–CdS QD heterostructure can be attributed to the synergistic contribution from the enhanced light absorption intensity of the hybrid nanocomposite and intimate interfacial contact between CdS QD and TiO₂ NB ingredients afforded by the electrostatic self-assembly buildup, which remarkably facilitates charge separation and lengthens the lifetime of photogenerated electron–hole pairs under visible light irradiation. Moreover, it was demonstrated that the TiO₂ NB–CdS QD heterostructure shows favorable photostability on account of intrinsic protection by a surface ligand of CdS QDs. In addition, the possible photocatalytic mechanism was tentatively proposed and predominant active species during the photocatalytic process were unambiguously determined.