Hydroxyapatite (HAp) is a bioceramic material highly valued for its excellent biocompatibility, bioactivity, and close resemblance to the mineral phase of natural bone. In this study, defunct coral reefs were repurposed as a natural calcium precursor for the sustainable synthesis of hydroxyapatite. The coral samples were calcined at 800 °C, 900 °C, and 1000 °C to produce calcium oxide (CaO), among which calcination at 900 °C yielded the highest CaO content (84.09 %). The obtained CaO was subsequently utilized for hydroxyapatite synthesis under sintering temperatures of 800 °C, 900 °C, and 1000 °C. X-ray diffraction (XRD) analysis confirmed the successful formation of phase-pure hydroxyapatite, exhibiting distinct diffraction peaks consistent with the standard HAp pattern. Fourier Transform Infrared Spectroscopy (FTIR) identified the characteristic vibrational bands of phosphate (PO₄³⁻), hydroxyl (OH⁻), and carbonate (CO₃²⁻) groups, while Scanning Electron Microscopy (SEM) revealed the typical porous morphology of hydroxyapatite. The sample sintered at 900 °C showed superior crystallinity, structural homogeneity, and well-distributed porosity. The synthesized HAp showed a Ca/P molar ratio of 2.18–2.34, crystallite size of 23–45 nm, and porosity of 29–33 %, confirming phase purity and a biomimetic microstructure. These quantitative features emphasize the temperature-dependent structural changes and support 900 °C as the best processing condition. These findings demonstrate that defunct coral reefs can be effectively converted into high-purity hydroxyapatite, underscoring their potential as a sustainable and eco-friendly raw material for bio-ceramic and biomedical applications such as bone grafts, coatings, and tissue engineering scaffolds.
Dahlan et al. (Wed,) studied this question.