Three Dimensional ZnO Hierarchical Nanostructures:

Zinc oxide (ZnO) nanostructures have been studied extensively in the past years due to 12 the novel electronic, photonic, mechanical and electrochemical properties. Recently, more attention 13 has been paid to assemble nanoscale building blocks into three dimensional (3D) complex 14 hierarchical structures, which not only inherit the excellent properties of the single building blocks 15 but also provide potential applications in the bottom-up fabrication of functional devices. This 16 review article focuses on 3D ZnO hierarchical nanostructures, and summarizes major advances in 17 the solution phase synthesis, applications in environment, and electrical/electrochemical devices. 18 We present the principles and growth mechanisms of ZnO nanostructures via different solution 19 methods, with an emphasis on rational control of the morphology and assembly. We then discuss 20 the applications of 3D ZnO hierarchical nanostructures in photocatalysis, field emission, 21 electrochemical sensor, and lithium ion batteries. Throughout the discussion, the relationship 22 between the device performance and the microstructures of 3D ZnO hierarchical nanostructures 23 will be highlighted. This review concludes with a personal perspective on the current challenges 24 and future researches. 25