Effect of ZnS layers on optical properties of prepared CdS/TiO2 nanotube arrays for photocatalyst

The TiO2 nanotube arrays (TiO2 NTAs) prepared by re-oxidation were chosen as basement. The NTAs prepared through re-oxidation show smoother surface and more uniform tube mouth on large scale compared with the first as-grown one. We use successive ionic layer adsorption and reaction method to deposit quantum dots (ZnS and CdS) onto the sample successively. The findings reveal that two kinds of quantum dots (∼10 nm) distribute regularly and the nanotube mouth is open. From the UV–Vis absorption spectrum of samples, the red shift occurs after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650 nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency of 90.7% compared with bare TiO2 NTAs (52.9%) and just CdS QDs sensitized sample (65.8%). In the test of photocatalysis durability, the decay percentages of CdS/TiO2 NTAs and ZnS/CdS/TiO2 NTAs were 35.8 and 48.4%, respectively, which means that the ZnS passivation layer plays a crucial role in enhancing photocatalytic activities.