Surface modification of calcium fluoro and hydroxyapatite by 1-octylphosphonic dichloride

Abstract The reactivity of the surface of calcium hydroxyapatite (CaHAp) and fluorapatite (CaFAp) was tested and compared by grafting the 1-octylphosphonic dichloride (C 8 H 17 OPCl 2 ) using a molar ratio x = 2 or 4, x = n (organic)/ n (apatite). Successful synthesis was confirmed by different characterisation techniques such as X-ray powder diffraction patterns, IR spectroscopy, MAS-NMR ( 1 H and 31 P) and chemical analysis. The difference between their specific surface area (SSA: 57.46 for HAp and 12.09 m 2 /g for FAp), the percentage of carbon measured after treatment with (C 8 H 17 OPCl 2 ) and the intensities of IR bands attributed to the grafted moiety suggests that the surface of hydroxyapatite is more reactive than that of fluorapatite. The 31 P CP-MAS-NMR spectra of treated fluorapatite show a significant change in isotropic signal due to the protonation and deprotonation of superficial phosphate group. This can be explained by the difference in the nature of inorganic material.