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 (Fe 2 O 3 ) and the hydroxyapatite/iron oxide (Hap/Fe 2 O 3 ) composite to evaluate its potential for water purification applications. To achieve this goal, Fe2O3 and Hap/Fe 2 O 3 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 Fe 2 O 3 and Hap/Fe 2 O 3 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/Fe 2 O 3 composite demonstrated superior adsorption properties compared to pure Fe 2 O 3 , 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/Fe 2 O 3 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.