Self-assembly of hydroxyapatite nanostructures by microwave irradiation

Hydroxyapatite (HAp) nanorods, bowknot-like nanostructures and flower-like architectures have been directly synthesized and assembled under microwave irradiation without the help of any templates. The uniform nanorods present an average diameter of about 40 nm and a length of up to about 400 nm. The as-prepared bowknot-like nanostructures consist of sword-like HAp nanorods with a typical width of 150 nm and lengths up to 1-2 mum. The flower-like architectures are composed of leaf-like flakes with typical diameters of 150-200 nm and lengths up to 1-2 mum. The SAED and HRTEM experiments imply that the sword-like HAp nanorods and leaf-like flakes are single crystalline in nature and preferentially grow along the [001] direction. It is found that the pH value and the complex reagent EDTA play important roles in synthesis of the final HAp nanostructures. The possible mechanism is discussed for the formation of the HAp nanostructures in the presence of EDTA under microwave irradiation.