Phyto-Functionalization of Seashell-Derived Hydroxyapatite: Influence of Extract-Assisted Synthesis Strategy on Ciprofloxacin Adsorption

Phyto-functionalization offers a greener route to introduce surface functionality on inorganic materials instead of relying on synthetic organic modifiers. While green synthesis is widely reported, the influence of synthesis sequence on material properties remains underexplored. In this study, Vasticardium flavum seashell waste-derived hydroxyapatite (HAp) was functionalized with Lagerstroemia speciosa leaf extract using two approaches: leaf extract addition before (B-HAp) and after (A-HAp) HAp precursor mixing. A pure HAp sample produced from analytical-grade CaCO3 (P-HAp) was used as the control. Both functionalized samples showed improved adsorption of ciprofloxacin compared to P-HAp. B-HAp exhibited the highest adsorption capacity (28.80 mg g−1), followed by A-HAp (18.65 mg g−1), while P-HAp showed the lowest value (7.56 mg g−1). The superior performance of B-HAp is attributed to structural changes introduced when the extract was added before H3PO4 addition. Early interaction between extract molecules and Ca2+ limited crystal growth, producing smaller crystallites (5.01 nm) and reduced particle size (21 ± 11 nm). This also produced a much larger specific surface area (182.93 m2 g−1) compared to A-HAp (77.19 m2 g−1) and P-HAp (77.17 m2 g−1). Statistical analysis of the adsorption data, utilizing goodness-of-fit parameters (R2) and error functions, confirmed the validity of the experimental findings. These results show that green functionalization before Ca and P precursor mixing can tune the physicochemical properties of HAp and enhance its adsorption behavior. This simple approach provides a sustainable alternative to chemical surface modifiers.