Morphology and Band Gap Modulation of CdS Quantum Dots Deposited on Reoxidation TiO2 Nanotube Arrays

Highly ordered TiO2 nanotube arrays (TiO2-NTAs), with uniform tube size around 100 nm in diameter and 10 mu m in length, were obtained by means of reoxidation and annealing processes. CdS quantum dots (QDs) were assembled onto the TiO2-NTAs by sequential chemical bath deposition (SCBD). The composition, microstructure, optical and photocatalytic properties of the CdS QDs sensitized TiO2-NTAs were investigated in detail. Compared with the one step oxidation, reoxidation is beneficial to the improvement of morphology of TiO2-NTAs. As the SCBD cycles increase, the band gap of CdS QDs sensitized TiO2-NTAs shifts from 3.09 eV (bare TiO2-NTAs) to 2.81 eV (CdS QDs sensitized TiO2-NTAs with five SCBD cycles). CdS QDs sensitized TiO2-NTAs deposited with five SCBD cycles show the best uniformity of size, space distribution and highest absorbance, and show higher photocatalytic effect comparing with pure TiO2-NTAs under UV-light irradiation.