Removal of methylene blue with a highly effective hydroxyapatite-silica nanocomposite

Two Hydroxyapatite-silica nanocomposite adsorbent (HApS220 and HApS230) were successfully synthesized using sol-gel technique. The samples were characterized by powder X-ray diffraction (XRD), Infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), which confirmed the formation of a Hydroxyapatite-silica nanocomposite. The synthesized powders were then used for adsorption of methylene blue (MB). Both compounds possessed high absorption capacities, the adsorption equilibrium time is around 10 min. HApS230 sample shows higher adsorption capacity compared to HApS220. Furthermore, isotherm studies show that the adsorption used is an ion exchange process and that Temkin isotherm describes the adsorption better compared to the Langmuir and Freundlich and Dubinin-Radushkevich isotherms. Kinetics studies confirm that the adsorption follow the pseudo-second order model and chemisorption mechanism. Thermodynamics' studies confirm that the adsorption of MB on HApS samples is a spontaneous endothermic process. The average removal effectiveness of MB reached about 89.02% (6.389 mg/g adsorption capacity) and 91.36% (6.55 mg/g adsorption capacity) for HApS220 and HApS230 respectively.