Self-assembly of hierarchically ordered CdS quantum dots-TiO₂ nanotube array heterostructures as efficient visible light photocatalysts for photoredox applications

In recent years, much attention has been focused on the preparation of CdS-TiO₂ nanotube array (CdS-TNTA) hybrid nanomaterials. Nevertheless, it is still challenging to synthesize hierarchically ordered CdS-TNTA heterostructures as efficient photocatalysts via a facile and simple approach. In this work, tailor-made negatively charged CdS quantum dots (QDs) are evenly deposited on a hierarchical framework of TiO₂ nanotube arrays, consisting of periodically ordered nanorings on the surface and nanotubes underneath, by modulating the surface charge properties of the constituents. It has been demonstrated that the CdS-nanoporous TiO₂ nanotube array (CdS-NP-TNTA) hybrid nanostructures exhibit promising visible-light photoactivity towards the photooxidation of organic dye pollutants and the photocatalytic reduction of nitrophenol derivatives as a result of the monodisperse deposition of CdS QDs on the well-defined NP-TNTA scaffold. Photoelectrochemical investigations have shown the significantly enhanced separation efficiency of photogenerated electron-hole charge carriers in the CdS-NP-TNTA heterostructure under visible light irradiation. Furthermore, the self-assembled CdS-NP-TNTA heterostructure demonstrates improved photostability. Our work should provide a new paradigm to prepare hierarchically ordered narrow band-gap semiconductor/one-dimensional semiconductor nanomaterials for efficient visible light-driven photocatalysis. © 2013 The Royal Society of Chemistry.