Characterization cyrstalinity, elements, and functional groups of hydroxyapatite shynthesized from sea urchin shell with annealing temperature variation

Abstract

This study aims to study the characteristics of hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) derived from sea urchin (Tripneustes sp.) shells via wet precipitation method with annealing temperature variations of 600°C (HAp600) and 900°C (HAp900). Raw materials used were calcium oxide (CaO) obtained from calcination of sea urchin shells at 1000°C as a calcium source, and diammonium hydrogen phosphate ((NH₄)₂HPO₄) as a phosphate source, with precipitation at 60°C and pH 10 followed by 24-hour aging. Characterization was performed using X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared (FTIR). XRD results confirmed hexagonal HAp phase formation consistent with JCPDS No. 09-0432, with average crystal sizes of 19.359 nm (HAp600) and 42.636 nm (HAp900), demonstrating significant crystal growth with increasing annealing temperature. A secondary β-tricalcium phosphate (β-TCP) phase was detected in the HAp600 sample, indicating incomplete HAp transformation. XRF analysis showed Ca/P ratios of 1.80 (HAp600) and 1.76 (HAp900), with the HAp900 sample approaching the ideal HAp stoichiometric value (1.67). The relatively high magnesium (Mg) content (5–6%) is a natural characteristic of magnesian calcite from sea urchin shells. FTIR spectra identified phosphate groups (PO₄^3-) at 1027–1028 cm^-1 and 558–603 cm^-1, and carbonate groups (CO₃^2-) at 1408–1412 cm^-1 indicating B-type carbonated hydroxyapatite formation.