One-pot and sustainable synthesis of nanocrystalline hydroxyapatite powders using deep eutectic solvents

• HAp nanocrystals were synthesized in fresh and recycled choline chloride-urea DES.
• The size of HAp nanocrystals was calculated to be ~30 nm.
• The HAp nanocrystals showed a high degree of crystallinity above 85%.
• HAp powders synthesized in fresh and recycled DES didn’t show significant difference.
• DESs provide a green medium for the synthesis of nanocrystalline HAp powders.

Nanocrystalline hydroxyapatite (HAp) powders were synthesized by a facile and sustainable method based on precipitation of calcium and phosphate reactants in choline chloride-urea deep eutectic solvent (DES). Characterization of the powders by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and fourier transform infra-red spectroscopy revealed the formation of nanocrystalline HAp with average crystallite diameter of 33 nm, spherical morphology, Ca/P molar ratio of 1.64, and high elemental/structural purity. After synthesis, the DES was recovered successfully and re-used for the synthesis of HAp powders. Results on characterization of re-synthesized powders confirmed the synthesis of HAp nanocrystals with diameter of 30 nm, spherical to rod-like morphology, Ca/P molar ratio of 1.61, and high compositional purity. The findings of the present work endorsed the successful application of the DES as green, recoverable and affordable medium for the synthesis of nanocrystalline HAp.