Fe-modified hydroxyapatite with regulated surface properties for enhanced Mn²⁺ adsorption: Structural evolution and...

Area of Science:

• Materials Science
• Environmental Chemistry
• Adsorption Science

Background:

• Hydroxyapatite (HAp) is a promising adsorbent for heavy metal removal.
• HAp's adsorption performance is limited by its surface chemistry and structure.
• Optimizing HAp for enhanced heavy metal adsorption requires surface modification.

Purpose of the Study:

• To synthesize and evaluate pristine hydroxyapatite (P-HAp), Fe-modified hydroxyapatite (Fe-HAp), and Ti-modified hydroxyapatite (Ti-HAp) for Mn²⁺ removal.
• To investigate the impact of metal modification on HAp's adsorption behavior and capacity.
• To elucidate the mechanisms underlying enhanced Mn²⁺ adsorption in modified HAp materials.

Main Methods:

• Synthesis of P-HAp, Fe-HAp, and Ti-HAp.
• Batch adsorption experiments to determine Mn²⁺ uptake under varying pH conditions.
• Adsorption isotherm and kinetic modeling (Langmuir, Freundlich, pseudo-second-order).
• Material characterization using BET, XPS, and DFT calculations.

Main Results:

• Fe-HAp exhibited the highest Mn²⁺ adsorption capacity (16.44 mg g^-1) at pH 5, outperforming P-HAp (13.25 mg g^-1) and Ti-HAp (11.55 mg g^-1).
• Freundlich model best described adsorption for Fe-HAp and Ti-HAp, indicating heterogeneous adsorption sites.
• Pseudo-second-order kinetics dominated all materials, suggesting surface chemical interactions are key.
• Fe modification improved pore characteristics and altered surface chemistry, facilitating Mn²⁺ coordination.

Conclusions:

• Metal modification is an effective strategy to enhance HAp's adsorption properties.
• Fe incorporation significantly improves Mn²⁺ removal by optimizing structural and surface chemical features.
• Synergistic effects, particularly surface coordination, drive the enhanced adsorption of Mn²⁺ onto Fe-HAp.