Synthesis and crystallization of macroporous hydroxyapatite

Macroporous hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ was synthesized using ordered polystyrene sphere templates that were impregnated with a calcium phosphate precursor solution which was allowed to solidify followed by sintering from 500 to 1000 °C in flowing oxygen to remove the polymer and crystallize the phosphates. Using a combination of diffraction and imaging the face-centered cubic macroporous framework was shown to have pore diameters of 0.8-0.9 μm and to be composed of hydroxyapatite (80-98 wt%) and X-ray diffraction amorphous material (14-55%), the proportions dependent on the duration and temperature of heat treatment. At lower sintering temperatures the HAp is calcium deficient. Ion exchange of calcium by cadmium demonstrated the potential of this material for hazardous waste remediation.