Conversion of waste eggshells to mesoporous hydroxyapatite nanoparticles with high surface area

The objective of this work was to convert waste eggshells to mesoporous hydroxyapatite (HAp) with high surface area by using a simple and inexpensive protocol without complexes. The eggshells were initially dissolved in concentrated nitric acid under vigorous agitation to form Ca(NO3)(2) solution, followed by the production of HAp nanoparticles through the addition of dilute phosphoric acid solution to the calcium solution at room temperature with a syringe pump. The HAp product possessed high surface area (212.4 m(2)/g), large pore size (16.8 nm) and small particle size ( < 10 nm) as shown by BET and small angle XRD analyses. Moreover, only about 8% of the HAp phase was converted to whitlockite at high temperature (950 degrees C), indicating its stability. (C) 2013 Elsevier B.V. All rights reserved.