HYDROTHERMAL SYNTHESIS OF Fe(II)–SUBSTITUTED HYDROXYAPATITE

Abstract

For the synthesis of Fe(II)–substituted hydroxyapatite (HAp), iron needs to be introduced in anionic form. Conventionally, highly soluble iron chlorides or nitrates have been used as iron sources. However, the presence of chloride or nitrate ions during the reaction can result in the incorporation of these anions into the HAp lattice. Therefore, an iron compound that is free from such anions should be selected. In this study, FeO was investigated as an alternative iron source. Although FeO exhibits extremely low solubility and is generally unsuitable as an iron source, its dissolution was enhanced under hydrothermal conditions. Furthermore, the use of an aqueous formic acid solution facilitated the dissolution of FeO. Because formic acid decomposes upon heating to generate carbon monoxide, it provides a reducing environment. This reducing environment stabilizes iron in the Fe²⁺ state. As a result, Fe(II)–substituted HAp was successfully synthesized, and the chemical composition of the product was determined to be Ca_8.8Fe_0.6(PO₄)₆(OH)_0.8.