Fabrication and Characterization of Magnetic Hydroxyapatite Entrapped Agarose Composite Beads with High Adsorption Capacity for Heavy Metal Removal

Magnetic hydroxyapatite entrapped agarose composite beads (M-HAP/Agar composite beads) have been successfully synthesized by emulsification of magnetic HAP nanoparticles with agarose suspension. In the process, the magnetic HAP nanoparticles served as the main resource for high adsorption performance, which were constructed by surface modification of Fe₃O₄ with <i>N</i>-(phosphonomethyl)­iminodiacetic acid (PM-IDA) and followed by coating with HAP. This strategy integrates the distinct advantages of large-size beads and magnetic response for easy recovery as well as nanoparticles for high adsorption capacity. The resulting M-HAP/Agar composite beads display large specific surface area (90 m² g^–1) and uniform spherical shape (150 μm). These magnetic hydroxyapatite nanoparticles in beads can provide more adsorption sites due to their suitable porous structure. As a result, the adsorbent exhibits excellent performance in adsorption of Pb²⁺, Co²⁺, and Cu²⁺, showing maximum binding capacities as high as 842.6, 105.1, and 71.6 mg g^–1, respectively. All these results suggest that these magnetic nanoparticles entrapped in beads have a positive effect on improving the adsorption capacity. Moreover, the beads possess superparamagnetism and large size, allowing them to be easily recovered from solution. Therefore, this work provides a promising approach for the design and synthesis of multifunctional hydroxyapatite composite beads for highly efficient removal of heavy metals in the field of wastewater treatment