Shell Thickness Dependent Photocatalytic Properties of ZnO/CdS Core-Shell Nanorods

Core/shell nanorod arrays of ZnO/CdS have been synthesized with varying shell thickness and their shell thickness dependent photocatalytic properties have been investigated. Core/shell nanorod arrays of core diameter of 100 nm with variable shell thickness (10-30 nm) are synthesized by varying the concentration of the citric acid. XRD analysis reveals that tensile strain is obtained for ZnO nanorods and the compressive strain is obtained for core/shell nanorods. The UV-visible absorption spectra of the core/shell nanorod arrays show a red shift of the band edge of uncoated ZnO with shell growth. Steady-state photoluminescence (PL) spectra of the core/shell nanorod arrays show red shift of emission band with the increase in shell thickness. Decay kinetics indicate that the average lifetime (<tau >) of the core/shell nanorod arrays is larger than that of the uncoated ZnO nanorods due to charge separation. I-V studies show a 16-fold enhancement in current using the ZnO/CdS core/shell nanorod arrays having CdS shell thickness of 30 nm as compared to bare ZnO nanorods. The photocatalytic studies confirmed that the ZnO/CdS core/shell nanorod arrays exhibit improved degradation efficiency compared to bare ZnO and CdS under simulated solar radiation. The core/shell nanorods having shell (CdS) thickness of 30 nm displays the highest photocatalytic efficiency for the degradation of rhodamine B under simulated solar radiation, indicating efficient separation of electron-hole pairs. The mechanism of the photodegradation of RhB is given to elucidate the efficiency enhancement of ZnO/CdS photocatalysts. These results demonstrate that the ZnO/CdS core/shell nanorod arrays provide a facile and compatible frame for potential applications in nanorod-based solar cells and as efficient photocatalysts.