Synthesis of mesoporous hydroxyapatite nanoparticles using a template-free sonochemistry-assisted microwave method

A facile template-free sonochemistry-assisted microwave method was successfully developed for the synthesis of mesoporous hydroxyapatite nanoparticles (MHN) in a short time. The prepared MHN were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms. TEM images showed a clear rod-like morphology with length of 50–100 nm and width of about 20 nm. XRD and FTIR indicated a typical hydroxyapatite phase with high crystallinity. N2 adsorption–desorption isotherms revealed an irregular mesoporous structure. Judging from the values calculated from N2 isotherms, the specific surface area and pore volume obviously decreased after the sintering process. In a typical example, the specific surface area, pore volume, and pore size of MHN before and after calcination were 79.74 m2/g, 0.46 cm3/g, 2.7 nm and 45.41 m2/g, 0.22 cm3/g, 2.8 nm, respectively. In addition, MHN could be synthesized in a period of time as short as 10 min. Further investigation indicated that microwave radiation played a dominant role in the emergence of mesoporous structure, while ultrasound irradiation acted as a supporting role. Based on the above results, a possible mechanism of formation of mesoporous hydroxyapatite has been proposed.