Magnetic modification of acid-activated kaolin: Synthesis, characterization, and adsorptive properties

Maghemite (gamma-Fe2O3) nanoparticles were synthesized onto the surface of acid-activated kaolin (AAK), prepared by calcination and acid activation of a coal bearing kaolin, by immobilizing an Fe-urea complex ([Fe(NH2CONH2)(6)](NO3)(3)) and subsequent calcination. The obtained samples were characterized by X-ray diffraction (XRD), N-2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetic measurements, and transmission electron microscopy (TEM). The results confirm the formation of ferromagnetic gamma-Fe2O3 nanoparticles, approximately 18 nm in size, onto the AAK surface. The obtained gamma-Fe2O3/AAK nanocomposite has a high Brunauer-Emmett-Teller (BET) surface area of 99.4 m(2)/g and possesses ferromagnetic characteristics with a maximum magnetization of 26.5 emu/g. The adsorption ability of gamma-Fe2O3/AAK nanocomposite was investigated using methylene blue (MB) as a typical pollutant. Owing to its high surface area, the gamma-Fe2O3/AAK nanocomposite showed higher removal efficiency for MB than for parent kaolin, with a maximum adsorption capacity of 50.2 mg/g. The adsorption kinetics of MB fit well with the pseudo-second-order kinetic model, and the equilibrium data can be well described by the Langmuir adsorption model. (C) 2014 Elsevier Inc. All rights reserved.