Sol-gel synthesis of manganese and potassium substituted hydroxyapatite: Characterization and thermal behavior

This research focuses on improving the characteristics of hydroxyapatite (HA) for use in biomedical fields by creating nanoparticles of HA that are substituted with Mn and K through a water-based sol-gel technique. Mn nitrate tetrahydrate and K nitrate served as precursors for Mn 2+ , K+ ions, respectively, for the partial substitution of Ca 2+ ions in the HA structure, and the resulting nanopowders were heated at temperatures ranging from 800 °C to 1200 °C. The materials were analyzed using XRF, TEM, XRD, FTIR, DSC and TGA to examine their structural, morphological, and thermal characteristics. The findings validated effective ionic substitution, with nanoparticle dimensions varying between 6 and 12 nm and enhanced crystallinity was observed at elevated calcination temperatures. XRD analysis revealed that the nanopowders synthesized initially displayed a pure HA phase, whereas calcination resulted in a partial transformation into βtricalcium phosphate, with a maximum of 58.36 % β-TCP content observed at 1200 °C. FTIR spectra confirmed the presence of typical HA bands along with carbonate impurities, whereas Differential scanning calorimeter analyzer and thermogravimetric analysis were used for as-synthesized nanopowders to study thermal behavior. The as- synthesized 2 mol% substituted K hydroxyapatite (2KHA) nanopowder had a smaller size of the crystallite compared to the as-synthesized 2 mol% substituted Mn hydroxyapatite (2MnHA) nanopowders.The Ca/P ratio showed stability (~0.73), demonstrating structural integrity despite the development of non-stoichiometric compounds. This study emphasizes the potential benefits of substituting Mn and K to enhance the thermal and structural characteristics of HA, indicating the need for further refinement of synthesis conditions and scalable production methods to improve its biocompatibility and mechanical properties for biomedical applications.