Synthesis of hydroxyapatite nanoparticles using an emulsion liquid membrane system

Hydroxyapatite (HAp) has been synthesized by various methods, such as co-precipitation, sol–gel, and microemulsion. However, particle size, particle size distribution and cost were drawbacks of those techniques. In this study, HAp nanoparticles were prepared by means of emulsion liquid membrane system (ELM) or water-in-oil-in-water system (W/O/W). The aim of the work was to evaluate the preparation of HAp nanoparticles using ELM consisting of Span 20 and Tween 80 as a mixture of biodegradable surfactant and caproic acid as an extractant. The effect of Ca/P ratio, reaction temperature, and calcination temperature on the characteristics of synthesized particles was investigated. The synthesized HAp particles were amorphous calcium deficient apatites. Ca/P molar ratio of the synthesized particle (Ca/Pp) increased with increasing initial Ca/P molar ratio (Ca/Pi) and reach maximum at Ca/Pp of 1.65. We found significant amount of β-TCP in the particles prepared with high initial Ca/Pi molar ratio of 2.00 at which the undesired reactions at high Ca2+ concentration occurred. Increasing of reaction and calcinations temperature resulted in the reduction of surface area. After thermal treatment at temperatures ranged from 450 to 750 °C, the specific surface area reduced from 227 to 58 m2/g. At temperature of 750 °C, we found that the morphology of microsized particles instead of nanosized ones.