Synthesis of calcium phosphate nanoparticles in deep-eutectic choline chloride–urea medium: Investigating the role of synthesis temperature on phase characteristics and physical properties

Abstract A novel and green method based on precipitation of calcium phosphate reactants in a deep eutectic solvent (DES) was devised for the synthesis of calcium phosphate nanoparticles. The DES was prepared by simple mixing-heating of choline chloride and urea. The effect of synthesis temperature on particulate and structural properties of the synthesized calcium phosphate nanoparticles was examined by X-ray diffractometry, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and nitrogen adsorption techniques. Based on the results, increase of synthesis temperature from 25 to 150 °C was associated with the gradual evolution of calcium-deficient apatite phase, however with a poor degree of crystallinity. The particle size and Ca/P molar ratio of precipitated calcium phosphate particles were also dependent of temperature so that they increased from 25 to 85 nm and 1.10 to 1.27 when the synthesis temperature increased from 25 to 150 °C. The synthesized particles were mesoporous regardless of the synthesis temperature. Given the advantages of DESs from both environmental and chemical points of view, the present study can provide a new direction for DES-assisted synthesis of inorganic nanomaterials and particularly nanobiomaterials.