Study on the synthesis of nano-hydroxyapatite assisted by sodium dodecyl sulfate significantly enhances the adsorption performance of rhodamine B

In this study, we synthesized sodium dodecyl sulfate modified hydroxyapatite (SDS-HAP) to enhance the removal efficiency of rhodamine B (RhB) dye. The SDS-HAP prepared using the sol-gel method exhibited a significantly higher adsorption capacity compared to pristine HAP. Various characterization techniques, including X-ray diffraction (XRD), N₂ adsorption-desorption isotherms, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM), were utilized to systematically investigate the morphological and structural changes. Batch experiments were conducted to evaluate the influence of RhB concentration, pH value, temperature, dosage, and contact time on the adsorption performance. Results indicated that the addition of SDS increased the specific surface area from 72.8 to 136.8 m² g^-1. The equilibrium adsorption capacity of SDS-HAP for RhB was approximately 3.3 times greater than that of pure HAP. Kinetic studies revealed rapid equilibrium following the pseudo-second-order model (<i>R</i> ² = 0.9999). The Freundlich isotherm model best described the experimental data, with a maximum adsorption capacity of 44.1 mg g^-1. Thermodynamic analysis confirmed that the adsorption process was spontaneous, endothermic, and driven by hydrogen bonding and electrostatic interactions between the dye molecules, PO₄ ^3-, Ca²⁺ and OH^-.