Hydroxyapatite nanosheet-assembled microspheres: hemoglobin-templated synthesis and adsorption for heavy metal ions.

Hydroxyapatite (HAP) nanostructures have wide potential applications in many fields such as drug delivery, tissue engineering, bone repair, gas sensing, catalysis and water treatment. Inspired with the fact that HAP has a high affinity with proteins, we have designed and developed a new synthetic strategy for three-dimensional (3-D) HAP nanosheet-assembled microspheres (HAP-NMSs) by employing hemoglobin as a soft template. The as-prepared products are characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (SEM). The experimental results show that 3-D HAP microspheres are constructed by the self-assembly of HAP nanosheets as the building blocks. The influences of hemoglobin concentration, hydrothermal temperature and time on the morphology and crystal phase of the product are investigated. Based on the systematic investigation, a possible formation mechanism of HAP-NMSs is proposed. The as-prepared HAP-NMSs are explored for the potential application in water treatment. The experimental results indicate that the HAP-NMSs have a high adsorption capacity for heavy metal ions and selective adsorption activity for Pb(2+) ions in acidic solution, thus are promising for the application in wastewater treatment.