Eggshell-Derived Hydroxyapatite Coupled With Graphitic Carbon Nitride for High-Performance Adsorptive Removal of Pb (II) From Aqueous Solution

The hydroxyapatite–graphitic carbon nitride (HAp–GCN) nanocomposite was synthesized. The chemical structure, crystalline features, surface morphology, elemental composition, and textural properties of HAp–GCN were obtained using FTIR, XRD, FESEM, EDX, elemental mapping, and BET characterization techniques. HAp–GCN nanocomposite demonstrated quick adsorption kinetics and effective Pb(II) removal from aqueous solutions. Langmuir isotherm model provided the most suitable description of the equilibrium adsorption behavior, indicating predominantly homogeneous monolayer adsorption and yielding a maximum adsorption capacity of (227.7 ± 10.1 mg g⁻¹). The van't Hoff analysis of temperature dependent adsorption data revealed a positive standard enthalpy change (ΔH°= + 139.9 kJ mol⁻¹), indicating that Pb(II) adsorption onto HAp–GCN is an endothermic process. Desorption and recyclability studies performed using 0.5 M HCl over three successive adsorption-desorption cycles showed a gradual decline in desorption performance, however, the HAp–GCN nanocomposite retained appreciable Pb(II) adsorption efficiency. The result obtained confirms the potential of the material for effective remediation of Pb(II)-contaminated aqueous systems.