Interactions of Silver Ions with the Hydroxyapatite-Iron Oxide Composite Surface in Liquid

The study aims to investigate the adsorption of silver ions (Ag⁺) on iron oxide (Fe₂O₃) and the hydroxyapatite/iron oxide (Hap/Fe₂O₃) composite to evaluate its potential for water purification applications. To achieve this goal, Fe2O3 and Hap/Fe₂O₃ were synthesized by a co-precipitation method and characterized using X-ray diffraction (XRD), scanning electron microscopy, porosimetry, surface charge density, and zeta potential measurements. Batch adsorption experiments were then conducted to assess the effects of contact time, initial Ag⁺ concentration, pH, and temperature on adsorption efficiency. The results show that both Fe₂O₃ and Hap/Fe₂O₃ surfaces exhibit needle-like morphologies with numerous pores, while XRD confirmed the formation of hydroxyapatite and iron oxide phases. The zeta potential of the composite ranged from -25 to -7 mV, indicating surface charge behavior relevant to adsorption. The Hap/Fe₂O₃ composite demonstrated superior adsorption properties compared to pure Fe₂O₃, attributed to the high specific surface area and ion-exchange capacity of hydroxyapatite combined with the adsorption contribution of iron oxide. Kinetic analysis revealed that the adsorption followed the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Isotherm studies indicated that the Freundlich model best described the adsorption, reflecting the heterogeneous nature of the composite surface. Overall, the Hap/Fe₂O₃ composite exhibited high affinity for Ag⁺ ions, with adsorption efficiency strongly influenced by pH and contact time, confirming its potential as a promising material for removing heavy metals from aqueous solutions.