Novel preparation route of stable amorphous calcium phosphate nanoparticles with high specific surface area

Abstract

Novel and effective method for preparation of nanosized and stable calcium phosphates (CaPs) is developed. Amorphous or partially crystalline CaP nanoparticles are rapidly reprecipitated from synthesis solution due to fast change of pH. Basic steps of the proposed approach are: to dissolve CaP salt (e.g. hydroxyapatite) with acid and add base thus inducing reprecipitation of new CaP nanoparticles. It is well known that pH of synthesis medium has a significant effect in CaP precipitation, therefore we varied synthesis pH from 8 to 11. Study reveals impact of synthesis pH on chemical structure (FT-IR), phase composition (XRD) for as-synthesized and heat-treated (300–1100 °C) CaPs and specific surface area (BET). Partially crystalline CaPs form at pH 8 and pH 9, while amorphous calcium phosphate precipitates at pH 10 and pH 11. CaPs prepared by the novel technology have high specific surface area (133–154 m2/g). Their amorphous state corresponds to amorphous tricalcium phosphate with carbonate ion substitutions depending on pH of the synthesis. Effectiveness of technology is the use of conventional drying instead of lyophilisation.