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

• Calcination and acid treatment of raw kaolin produce porous acid-activated kaolin.
• γ-Fe2O3 nanoparticles were synthesized onto the surface of acid-activated kaolin.
• The γ-Fe2O3/AAK nanocomposite has high surface area and ferromagnetic properties.
• The γ-Fe2O3/AAK shows a higher removal efficiency for methylene blue than raw kaolin.
• High concentration of methylene blue can be rapidly removed by adsorption.

Maghemite (γ-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), N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetic measurements, and transmission electron microscopy (TEM). The results confirm the formation of ferromagnetic γ-Fe2O3 nanoparticles, approximately 18 nm in size, onto the AAK surface. The obtained γ-Fe2O3/AAK nanocomposite has a high Brunauer–Emmett–Teller (BET) surface area of 99.4 m2/g and possesses ferromagnetic characteristics with a maximum magnetization of 26.5 emu/g. The adsorption ability of γ-Fe2O3/AAK nanocomposite was investigated using methylene blue (MB) as a typical pollutant. Owing to its high surface area, the γ-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.

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