Despite significant progress in the field of semiconductor photocatalysis has been made, it is still a great challenge to prepare low-cost photocatalysts with high activities. In our work, three dimensional (3D) flower-like ZnO hierarchical nanostructures assembled with numerous nanosheets were fabricated by a simple, template-free and one-step hydrothermal route. The products were characterized by XRD, UV-Vis, PL, SEM, TEM, HRTEM techniques. In the process, NH4F played a crucial role for the formation of ZnO hierarchical nanostructures, which was acted both as the alkali source and morphology director. Furthermore, the growth of ZnO involved a phase transformation from intermediate compound ZnF(OH) to ZnO. To further improve the photocatalytic activity, Ag-doped ZnO photocatalyst was also prepared. The photocatalytic results indicated that the Ag/ZnO exhibited higher photocatalytic activity than the pure ZnO. The great enhancement was mainly ascribed to their unique hierarchical nanostructures as well as the modification of Ag nanoparticles. Additionally, both ZnO and Ag/ZnO microspheres showed good recycling stabilities over several separation cycles in photodegradation. (C) 2015 Elsevier Inc. All rights reserved.