Malate-Assisted Synthesis of ZnO Hexagonal Architectures with Porous Characteristics and Photoluminescence Properties Investigation

ZnO 3D hierarchical architectures with hexagonal shape and uniform size have been successfully synthesized with the assistance of sodium malate by a simple hydrothermal process. Scanning electron microscopy (SEM) images show that the hexagonal particles are composed of platelet-like nanoparticles that are orderly arranged to multilayer stacks. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analysis indicate that these nanoplatelets are single-crystal and grow perpendicularly to the c -axis of wurtzite ZnO. Nitrogen adsorption−desorption measurements reveal that the specific surface area of the sample can reach to 25 m 2 ·g -1, which is as high as that of 16 nm sized ZnO nanorods (aspect ratio of 1.6:1). The pore size distribution curve suggests the specific surface area improvement is due to the existence of small pores embedded in the 3D architectures. These small pores are attributed to the small gaps between these nanoplatelets. Malate ions have been found to play a key role in the formation of the porous 3D architectures. Room temperature photoluminescence measurements show that the porous architectures prepared in the presence of malate indeed exhibit intense ultraviolet exciton emission centered at 387 nm. The defects related yellow and green emissions have been greatly quenched, suggesting the sample is in high crystalline quality though it possesses porous characteristics.