Time and temperature mediated evolution of CDHA from ACP nanoparticles in deep eutectic solvents: Kinetic and thermodynamic considerations

摘要

Abstract Calcium phosphate (CP) nanoparticles were synthesized in choline chloride-urea deep eutectic solvent (DES). The effect of synthesis time and temperature on crystallinity, particulate properties, and elemental/chemical purity of the CP nanoparticles were investigated by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infra-red spectroscopy. The results confirmed the formation of amorphous calcium phosphate (ACP) nanoparticles (at 25°C for 10min) with spherical morphology, mean diameter of 29nm, and high elemental-structural purity. The increase of synthesis time from 10min to 48h at 25°C had no significant influence on the phase transformation of ACP nanoparticle so that the nanoparticles showed high degree of amorphization after 48h. The crystallization of particles rapidly rose upon increase of the synthesis temperature so that the nanoparticles of calcium-deficient hydroxyapatite (CDHA) with percent crystallinity of ~97% were obtained in choline chloride-urea DES at 150°C after 24h. Kinetic and thermodynamic studies revealed that upon increase of temperature from 25 to 150°C, the rate constant and Gibbs free energy for growth of CP crystals in the DES rises from 8.70×10−4 to 1.37×10−3 min−1 and 3.22×10+2 to 4.57×10+2 KJ·mol−1, respectively. Graphical abstract Display Omitted Highlights • ACP and CDHA nanoparticles were synthesized in choline chloride-urea DES. • ACP nanoparticles with diameter of 29nm were synthesized at 25°C after 10min. • CDHA nanoparticles with crystalinity of 97% were obtained at 150°C after 24h. • ΔGcrystal growth increased from 3.2×10+2 (at 25°C) to 4.5×10+2 KJ·mol−1 (at 150°C). • SAXS analysis revealed the electrosteric stabilization of ACP nanoparticles by DES.