Influence of Preparation Factors on Ca/P Ratio and Surface Basicity of Hydroxyapatite Catalyst

We aimed at precision control of the basicity of hydroxyapatite (Ca10(PO4)6(OH)2; HAP) and paid attention to four key factors in the synthesizing process—the solution's Ca/P ratio, pH, temperature and stirring time—and compared their influence on the Ca/P ratio and basicity of HAP. Among them, solution pH had the greatest influence on Ca/P ratio within the bulk of the catalyst. This was followed in order of influence by the Ca/P ratio of the solution (the ratio of raw materials), solution temperature and stirring time. In addition, we found that samples of HAP with the same Ca/P ratio had almost the same basic site density, even if they were synthesized using different combinations of preparation factors. This indicates that the basic site density of HAP prepared by the precipitation method depends only on the Ca/P ratio within the bulk of the catalyst.