Preparation of hydroxyapatite nanostructures with different morphologies and adsorption behavior on seven heavy metals ions.

Hydroxyapatite (HAP) nanostructures with different morphologies have been successfully synthesized in a facile method and the pH value of the solution has an important effect on morphology. Among them, the porous HAP nanospheres (NSs) with an average diameter of 76 nm were further employed as adsorbent to remove the heavy metal ions in solution. The BET surface area, pore size and pore volume of porous HAP NSs were 45.3 m2·g-1, 2.7 nm and 0.23 m3·g-1, respectively. The ICP results showed that the porous HAP NSs could remove effectively Pb2+, Cd2+, Cu2+, Co2+, Ni2+, Zn2+, Hg2+ ions and the maximum adsorption capacity reached 254.90 mg·g-1. Experimental equilibrium data were also analyzed by the Langmuir and Freundlich models and the best fit was obtained with the Langmuir isotherm equation. The kinetic study indicated that the adsorption of Pb2+ ions on porous HAP NSs was almost instantaneous and the maximum adsorption was reached within 20 min. Compared with the pseudo 1st order model, the adsorption kinetic data was well described by the pseudo 2rd kinetic model. In addition, the porous HAP NSs had a good stability and would be a promising nanoadsorbent for heavy metal ions.