Hydroxyapatite/superparamagnetic iron oxide nanoparticles nanocomposite for Congo red adsorption

Abstract

In this work, a nanostructural composite based on the superparamagnetic iron oxide nanoparticles (SPIONs) coated with hydroxyapatite (HAp) was demonstrated as an effective adsorbent for the removal of the Congo red (CR) from aqueous solutions. Prior to its application on the model pollutant, the morphology, crystallinity, specific surface area, chemical composition, and magnetic properties were characterized with several techniques, including scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett– Teller, and vibrating sample magnetometer. Amongst composites synthesized in different ratios of SPION’s weight, the composite containing 35 wt.% of SPION was chosen to adsorb CR. The magnetization saturation of the latter was about 20.39 emu·g –1 , still enough for magnetic separation. The effect of adsorbent mass, pH, initial concentration, temperature, and contact time on the adsorption efficiency and capacity of CR was evaluated using UV-Vis spectrometry. It was shown that the most effective results of CR removal were achieved for 0.10 g dosage of SPION/HAp to absorb 50 mL of CR solution of 50 mg·L –1 at pH 0 and a contact time of 4 h. The CR adsorption process on SPION/ HAp composite is matched with the pseudo-second-order kinetic model and the Langmuir model. The obtained thermodynamic parameters (Δ G ° > 0, Δ H ° = –39.02 kJ·mol –1 , Δ S ° = –0.134 kJ·mol –1 ·K –1 ) suggest that the adsorption of CR onto the composite is non-spontaneous, exothermic, with a rising of randomness at the adsorbate–adsorbent interface. The maximum CR adsorption capacity using the SPION/HAp adsorbent was determined to be 158.98 mg·g –1 , suggesting that the adsor-bent has a satisfactory potential to adsorb CR. The chosen composite can be easily separated using magnets, making it a promising material for wastewater treatment.