Terbium adsorption onto polyhydroxyethylmethacrylate–hydroxyapatite composite and its modified composition by phytic acid

Abstract

Hydroxyapatite (Hap) was entrapped in poly(hydroxyethylmethacrylate) P(HEMA) by direct polymerization and P(HEMA–Hap) was obtained in aqueous solution. Phytate (phy) was immobilized by phytic acid (phy) modification onto the poly(hydroxyethylmethacrylate–hydroxyapatite), P(HEMA–Hap). The adsorptive features of P(HEMA–Hap) composite and its modified form P(HEMA–Hap)–phy, were investigated by using Tb analogues, rare earth elements (REE), by isotopic tracer method, ¹⁶⁰Tb was used as the radiotracer. It was observed that P(HEMA–Hap) composite had a higher affinity for Tb³⁺ than bare Hap, as well as its modified composition P(HEMA–Hap)–phy. Adsorption data obtained, fitted well to the classical Lagmuir, Freundlich, and Dubinin–Radushkevich (D–R) sorption models. Changes in enthalpy and entropy values showed that the overall adsorption process was endothermic (ΔH > 0), increasing entropy (ΔS > 0), and spontaneous (ΔG < 0), as expected. The adsorption kinetics following the pseudo-second order model indicated that the rate-controlling step was the chemical adsorption. Reusability of the adsorbent was also investigated and it was found that the adsorbent could be used at least for five times.

Keywords:

• Adsorption
• Composite
• Poly(hydroxyethylmethacrylate)
• Hydroxyapatite
• Terbium

Acknowledgment

This work was supported by The Research Fund of Cumhuriyet University (CÜBAP) to which the author is grateful.