Crystal structure modification of nano-hydroxyapatite using organic modifiers and hydrothermal technique

Hydroxyapatite (HAp) synthesis was achieved through a hydrothermal method involving orthophosphoric acid and calcium hydroxide. Different organic modifiers such as urea, naphthalene, and palmitic acid were applied in the reaction system to modify the crystallite size along with the morphology of HAp. The synthesized HAp was validated via X-ray diffraction (XRD) data, Fourier Transform Infrared (FTIR) spectra, Field Emission Scanning Electron Microscopy (FESEM) image, and optical bandgap energy (<6 eV) was determined through UV-vis spectrophotometry. Apart from that, different techniques such as Scherrer's method, Halder–Wagner model, Williamson–Hall method, size–strain plot, as well as Sahadat-Scherrrer's models were applied for calculating the crystal domain size, and some models also incorporated energy density, strain, and stress. The synthesized HAp has a crystal structure that falls within the permissible range of <100 nm, as established by analyzing the XRD data using established models. Nevertheless, the values for strain (from −0.0006 to 0.0062), stress (from −30 902 to 36 940 N m⁻²), as well as energy density (from 4 × 10⁻¹⁴ to 113.72 J m⁻³) were likewise computed for the synthesized HAp. The texture co-efficient analysis reveals that doped HAp is grown in the (202) and (112) planes, palmitic acid_HAp in (002), (112), and (202) planes, while all the synthesized HAp (pure HAp, urea, naphthalene) is grown in the (002) and (112) planes. Rietveld refinement was also performed to estimate the quantative phase percentage from XRD data.