Dynamically controlled synthesis of different ZnO nanostructures by a surfactant-free hydrothermal method

Abstract

To broaden the device applications of ZnO nanomaterials, various ZnO nanostructures have been fabricated by a “green” hydrothermal method. To achieve the dynamically controlled surfactant-free hydrothermal growth of ZnO, reactant solutions of zinc acetate dihydrate and hexamine were stirred or aged for a certain time beforehand. X-ray absorption fine structure analysis of intermediates in the disturbed solutions indicates that the coordination number of the Zn atoms varies with different pretreatments. The Zn–O bond length, which is sensitive to both the coordination number of Zn and the number of atoms comprising each agglomerate, also shows different values. Based on the fact that the total amount of Zn²⁺ in each reactant solution is constant, the formation of different ZnO nanostructures, from ZnO nanorods to nanotapers and rod-on-nanorod structures, can then be designed and understood from the standpoint of dynamic view by using agglomerates with different sizes and concentrations as building blocks. Particularly, ZnO nanopencils with excellent crystallinity and optical properties are obtained by this method. This rational engineering of building blocks in solutions not only provides a fundamental insight into the effects of physical disturbances on the structure of agglomerates and final ZnO products, but also presents a new idea for tunable and “green” fabrications of versatile ZnO nanostructures with the assistance of external force.