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.