A microwave-assisted rapid route to synthesize ZnO/ZnS core-shell nanostructures via controllable surface sulfidation of ZnO nanorods

We demonstrate a new strategy for preparation of ZnO/ZnS core-shell nanorods via microwave-assisted in situ surface sulfidation of ZnO nanorods. This is a facile and rapid process, requiring only a low level of microwave irradiation (400 W), through which a conformal ZnS nanoparticle layer is deposited onto the ZnO nanorods, while retaining the uniformity of the original ZnO nanorods in the as-prepared ZnO/ZnS hybrid structures with excellent fidelity. Furthermore, the thickness and nanoparticle size of the ZnS shell can be conveniently varied or controlled by the concentration of the organo-sulfur source thioacetamide (TAA). The as-prepared products exhibit narrowed band gap and strong orange luminescence at 621 nm, due to the interstitial oxygen ion defect present in hydrothermally grown ZnO. However, the PL intensity gradually decreases with the increase of the thickness of ZnS shell, indicating charge transfer between the two components of the ZnO/ZnS hybrids. Further investigation has revealed that the hybrid nanostructures possess significantly higher visible light photocatalytic activity which is twice that of the original ZnO nanorods. The mechanisms of the optimal ZnS shell thickness to reach the maximum photocatalytic activity in the ZnO/ZnS core-shell hybrid are proposed and discussed. It is believed that this facile, rapid microwave-assisted strategy is scalable and its application can be extended synthesize other oxide/sulfide (MO_x/MS_y) core-shell nanostructures for different applications.