Hierarchical porous hydroxyapatite microspheres: synthesis and application in water treatment

Hydroxyapatite (HA) microspheres with hierarchical porous structure were synthesized using a facile gas diffusion method. The morphology and structure of the as-synthesized products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and Brunauer–Emmett–Teller gas sorptometry analyses. Results showed that the change in pH resulting from ammonia diffusion provided the driving force for the formation of HA crystals. Under the cooperative influences of reaction time and reaction temperature, the nucleation and growth processes of HA nanocrystals were effectively controlled. Therefore, porous HA microspheres with large surface areas were produced at 60 °C for 24 h. On the basis of the time-dependent experiments, a possible formation mechanism of hierarchical porous HA microsphere was proposed. Moreover, hierarchical porous HA microspheres were investigated as adsorbent, and they exhibited a high adsorptive capacity for heavy metals Pb²⁺ and Cu²⁺ of approximately 213.58 ± 2.6375 and 59.68 ± 3.4436 mg/g, respectively. Therefore, hierarchical porous HA microspheres may be applied to heavy metal-contaminated water treatment.