Synergistic Adsorption by Biomass-based Fe-Al (Hydr)oxide Nanocomposite of Fluoride and Arsenic

Fe-Al (hydr)oxide nano-/micro-particles were well grown and dispersed on a wheat straw template, which was characterized by a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and a vibrating sample magnetometer (VSM). The adsorption mechanism of the biomass-based Fe-Al (hydr)oxide nanocomposite was studied by the adsorption isotherms, which followed the Langmuir model better than the Freundlich and Temkin models. In particular, a synergistic adsorption by the mixed Fe-Al (hydr)oxide nano-/micro-particles based on the wheat straw was found, with higher maximum adsorption capacity (Q₀) than that of the material containing only Fe₃O₄ or Al(OH)₃ nano-/micro-particles, which was most obvious when the mole ratio of Fe to Al was 1:1. The degree of this unusual effect was reasonably determined by the departure between the experimental and calculated maximum adsorption capacity (Q₀-Q₀(cal)), which showed that the synergistic effect was most pronounced when the mole ratio of Fe to Al was approximately 1:1. The good adsorption capacity of the mixed Fe-Al (hydr)oxide nano-/micro-particles and the good dispersity by the wheat straw matrix were combined in the biomass-based Fe-Al (hydr)oxide nanocomposite. The nanocomposite material showed high adsorption capacity for both fluoride (F^-) and arsenic (As(Ⅲ) and As(Ⅴ)), and had the advantage of magnetic separation by tuning its compositions.