Eco-friendly Synthesis of Nano-hydroxyapatite from Biogenic Waste Via Mechanical Milling

The growing demand for sustainable and environmentally friendly materials has spurred interest in green synthesis approaches for bioactive compounds. In this study, nano-hydroxyapatite (nHA) was synthesized from fish scale biowaste via a top-down mechanical milling method. Fish scales, a renewable and calcium/phosphate-rich waste product, were first calcined to produce FsHA and then subjected to ball milling to produce nanoscale FsHA particles. The resulting material was characterized using particle size analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). FTIR analysis on ball-milled FsHA revealed the presence of HA peaks together with carbonate absorption bands, confirming the presence of B-type carbonate substitutions, indicating partial replacement of phosphate groups by carbonate ions. The presence of C-H groups indicates the potential for polyethylene (PE) contamination originating from the milling container. XRD analysis revealed a pronounced reduction in crystallinity and peak intensity, consistent with a reduction in crystallite size, lattice distortion, and partial amorphization induced by mechanical stress and carbonate incorporation. TEM and STEM imaging verified particle sizes in the 20–200 nm range but also revealed severe agglomeration and the presence of nanoplastic debris (4–5 nm), generated by abrasion of the PE container during milling. These results highlight the dual influence of milling conditions and container material on the purity, stability, and dispersion of biogenic nHA, emphasizing the importance of careful material selection in preventing unwanted contamination and preserving functionality for biomedical applications.