Synthesis and characterization of calcium hydroxy and fluoroapatite functionalized with methyl phosphonic dichloride

The nature of apatite-organic molecule interaction was the subject of many investigations. Grafting the organic molecule onto the inorganic support may precede through either formation of covalent bonds or ionic interaction between superficial hydroxyl on the apatite surface and organic functions. The hybrid materials obtained by functionalization of apatite surfaces with phosphonate moieties are of interest for their potential applications such in catalysis, chromatography and biomedical domain. In this scope, calcium hydroxyl and fluoroapatite (CaHAp and CaFAp) were prepared in the presence of the methyl phosphonic dichloride (MPO), by contact method in organic solvent at 25 °C for 2 days. The products are rigorously characterized by chemical analysis, infrared (IR), MAS-NMR spectroscopies, powder X-ray diffraction (XRD), atomic force microscopy (AFM) and specific surface area (SSA). The X-ray powder analysis showed that the crystallinity was sensibly affected by the presence of organic moieties. The IR spectroscopy showed new vibration modes appearing related to phosphonate groups essentially at 2930, 1315, 945, 764 and 514 cm−1. The 31P MAS NMR spectrum for hydroxy and fluoroapatite exhibits a single signal at 2.8 ppm. After reaction with (MPO) the spectra show the presence of new signals, assigned to the formation of organic-inorganic bond between the superficial hydroxyl groups of the apatite (CaOH) and (POH) and methyl phosphonic dichloride. The SSA decreases with increasing phosphonate amount especially for CaHAp modified by (MPO). AFM indicated that the texture surface was changed by grafting.

► Surface reactivity of apatites toward methyl phosphonic dichloride is tested. ► Chemical analysis shows that hydroxyapatite is more reactive. ► NMR spectra show the formation of CaOPorg and PinorgOPorg bonds. ► AFM indicated that the texture surface was changed by grafting.