Solid-State Double Nuclear Magnetic Resonance Study of the Local Structure of Calcium Phosphate Nanoparticles Synthesized by a Wet-Mechanochemical Reaction

Calcium phosphate synthesized by a wet-mechanochemical reaction between Ca(OH) 2 and H 3 PO 4 is identified by X-ray diffractometry as an apparently single phase of hydroxyapatite (HAp). We examined more detail on the local structure of the product by high-resolution 1 H and 31 P solid-state double nuclear magnetic resonance (NMR) spectroscopy. Adsorbed and structural waters, as well as two kinds of OH groups in HAp, were observed in the inversion recovery 1 H magic angle spinning (MAS) spectra. HAp and other calcium phosphate were observed in 1 H→ 31 P cross polarization (CP)/MAS spectra. The 31 P differential cross polarization (DCP)/MAS and 1 H inversion recovery → 31 P CP/MAS measurements revealed different chemical interactions between 1 H and 31 P and, hence, could distinguish between ordered and disordered HAp. This micro-inhomogenity results from interiors and near-surface of nanoparticles as well as Ca 2+ -deficiency.