Modification of Hydroxyapatite with Ion-Selective Complexants: 1-Hydroxyethane-1,1-diphosphonic Acid

Area of Science:

• Materials Science
• Inorganic Chemistry
• Environmental Chemistry

Background:

• Hydroxyapatite (HAP) is a key biomaterial and adsorbent.
• Modification of HAP can alter its surface properties and adsorption capabilities.
• 1-hydroxyethane-1,1-diphosphonic acid (HEDP) is a phosphonate known for metal chelation.

Purpose of the Study:

• To synthesize and characterize HEDP-modified HAP.
• To investigate the effect of HEDP modification on divalent metal ion binding.
• To determine the optimal conditions for HEDP incorporation onto HAP.

Main Methods:

• HAP synthesis from calcium hydroxide and phosphoric acid.
• HAP modification with HEDP under varying time and temperature.
• Characterization using FTIR, XRD, SEM, EDS, and BET surface area analysis.
• Metal ion binding affinity determined using nitrate solutions of transition metal ions.

Main Results:

• HEDP incorporation increased with higher initial HEDP concentration and optimal temperature/time.
• FTIR confirmed HEDP presence via new phosphonate bands; XRD showed improved crystallinity.
• SEM revealed new HAP-HEDP strands with high phosphorus content via EDS.
• Modified HAP exhibited high acid capacity and a metal ion affinity sequence: Pb(II) > Cd(II) > Zn(II) > Ni(II) > Cu(II).

Conclusions:

• HEDP modification significantly enhances the metal ion binding capacity of HAP.
• The modified HAP demonstrates selective binding for heavy metal ions, particularly Pb(II) and Cd(II).
• This HEDP-modified HAP presents a promising material for applications in metal ion removal and separation.