Abstract

Two effective types of superparamagnetic nano-scale adsorbents of bayerite/SiO2/Fe3O4 have been synthesized via three sequential steps: chemical precipitation of Fe3O4, coating of SiO2 on Fe3O4 using acidifying method, and further coating of bayerite (Al(OH)(3)) on SiO2/Fe3O4 adopting sol-gel (MASG) or homogeneous precipitation (MAHP) methods. The characteristics of MASG and MAHP were identified using the transmission electron microscopy (TEM) micrograph, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray powder diffractometer (XRD), and superconducing quantum interference device (SQUID).

Removal of fluoride from aqueous solution was examined to evaluate the adsorptive capacity of MASG, MAHP, and commercial activated alumina (CA), and the effects of enclosure of Fe3O4 with SiO2 for SiO2/Fe3O4, MASG, and MAHP particles. Among the adsorbents tested under the same experimental condition, MASG is the most effective adsorbent, of which the adsorption capacities are 38 g/kg (based on adsorbent mass of adsorption in terms of equilibrium constant q(L) of Langmuir isotherm), and can compete with CA even at a high pH value.

The innovative superparamagnetic adsorbents synthesized in this study possess physicochemical stability at pH range of 6-8 and great potential in the adsorption processes due to not only their high adsorption capacity but also the conveniently magnetic separation which can overcome the difficulty in solid-liquid separation for nano-particles in solutions