Isolated effects of microwave radiation on the solid-liquid interface reactions between hydroxyapatite nanocrystals and silver ions

Abstract

The main objective of this work was to evaluate the effect of microwave radiation on the surface reactions and doping of as-synthesized hydroxyapatite (HA) nanocrystals with Ag+ ions. Our assays were based on wavelength-dispersive X-ray fluorescence, Rietveld refinement of X-ray diffraction data and Fourier transform infrared spectroscopy. The results demonstrated that the elemental and phase compositions of the as-synthesized HA nanocrystals were not affected by the microwaves. Conversely, the occupation of the PO43- and OH- sites of the HA nanocrystals by HPO42- and CO32- groups was strongly affected by the microwaves, as well as by the insertion of Ag+ ions into the structure. Consequently, the lattice parameters, crystallite size and aspect ratio of the as-synthesized HA nanocrystals were also affected. Furthermore, the microwaves were able to accelerate the reactions between the Ag+ ions and the HA surface as well as the rate of variation in HA cell unit volume. These findings indicate that microwaves are capable of significantly modifying not only the crystallographic features of HA nanocrystals but also the rate of Ag+ doping.