Eco-friendly Synthesis and Characterization of Eggshell-Derived Calcium-Deficiency Bone-Like Hydroxyapatite

Hydroxyapatite (HA) from eggshells is widely studied, yet no prior work has exploited the self-alkaline property (pH 10) of calcined eggshell powder to synthesize phase-pure HA without external NaOH/KOH or H₃PO₄ purification. In this study, reports first two-step thermal protocol: (1) calcination of eggshell powder at 900°C at 2 hours to generate CaO with intrinsic pH 10, (2) reaction with tricalcium phosphate (TCP) followed by secondary calcination at 900°C at 1 hour. The result is phase-pure hydroxyapatite with Ca/P ratio 1.627 to 1.636 (close to Calcium-Deficiency Hydroxyapatite (CDHA), not stoichiometric 1.67) and Scherrer crystallite size doubling from 21.7 nm to 54.1 nm preserving bioactive amorphous phase while enhancing mechanical stability. Unlike existing methods requiring chemical purification or > 1000°C sintering (which destroy CDHA bioactivity), We systematically characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR), and sustainable low-cost synthesis using only eggshell waste and technical-grade TCP. To our knowledge, this is the first report correlating self-alkaline synthesis with controlled crystallinity evolution in eggshell-HA, addressing a critical gap in scaling bioactive material exhibited bone-like characteristics, making it suitable for orthopedic and dental applications.