Hydrothermally controlled ZnO nanosheet self-assembled hollow spheres/hierarchical aggregates and their photocatalytic activities

We synthesized ZnO nano-micro structures, including microrods, nanosheets, a nanosheet self-assembled hollow sphere (NSHS), and a hollow hierarchical aggregate (HHA) by changing the concentration of trisodium citrate in a hydrothermal process. The NSHS was formed by the self-assembly of 2D nanosheets on the surface of a formaldehyde bubble, while the HHA was obtained by the self-assembly and hierarchical arrangement of NSHS. The photocatalytic activities of the ZnO structures were evaluated from the degradation of methylene blue under visible and black light irradiation. The NSHS showed better photocatalytic performance due to its excellent photon absorbance, low defect density and low emission quantum yield compared with the HHA. Furthermore, the size and number of the 2D nanosheets hydrothermally grown on the NSHS bubble template were controlled by changing the growth temperature.