Synthesis, characterization and investigation of catalytic properties of metal-substituted (M = Mg2+, Zn2+ and Na+) calcium hydroxyapatite

Abstract

Calcium hydroxyapatite (Ca10(PO4)6(OH)2,CHAp) has unique characteristics and can be used as artificial material for the recovering of bones and teeth, for drug delivery systems, as adsorbent and catalyst. The specific chemical, structural and morphological properties of calcium hydroxyapatite are highly sensitive to the changes in chemical composition and processing conditions. Various kinds of transition metal and other cations can be readily accommodated into the apatite framework based on their large cation exchangeability. The traces of metal ions introduced in apatite structure can affect the lattice parameters, crystallinity, dissolution kinetics and other physical properties of apatite. The aim of this study was to find more economically accessible metal-substituted calcium hydroxyapatite–based catalyst. In this paper, the sol-gel and co-precipitation synthesis methods were used for the preparation of metal-substituted (M = Mg2+, Zn2+ and Na+) calcium hydroxyapatite (Ca10(PO4)6(OH)2, CHAp) samples. The synthesized powders were characterized by powder X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and gas chromatography-mass spectrometry (GC-MS). The CHAp:M samples prepared by co-precipitation method were almost single-phase at different concentrations of substituents, while the sol-gel-derived CHAp:M specimens contained additional impurity phases. Metal-containing CHAp samples were tested as catalysts in a solvent-free synthesis of 2-adamantylidene(phenyl)amine. It was demonstrated that the zinc-containing CHAp improved the yield of Schiff base.