An improved Stöber method towards uniform and monodisperse Fe3O4@C nanospheres

Abstract

Significant progress has recently been made in the synthesis of Fe₃O₄@C nanospheres with uniform, monodisperse and tunable carbon shells. Fe₃O₄@C nanospheres were obtained by directly carbonizing Fe₃O₄@polymer which was synthesized by a versatile and economical Stöber method with resorcinol and formaldehyde as precursors. The synthesis conditions in the formation of Fe₃O₄@polymer were systematically investigated. It was found that the yield of the Fe₃O₄@polymer is highly influenced by the concentration of ammonium hydroxide, and the monodispersity is mainly affected by the concentration of ammonium hydroxide and the citrate group sites outside the surfaces of the Fe₃O₄ nanospheres. Interestingly, carbonization of Fe₃O₄@polymer at high temperature makes the grain sizes of Fe₃O₄ in Fe₃O₄@C samples larger than those in the Fe₃O₄ sample, which makes the saturation magnetization value for the Fe₃O₄@C samples higher than those of common obtained materials. The adsorption performance of Fe₃O₄@C for anthracene was tested both in water and in cyclohexane solution; it shows fast adsorption rates (about 1 h to reach equilibrium in water and 3 h in cyclohexane solution) and high adsorption capacities (31.5 mg g⁻¹ in water and 2 mg g⁻¹ in cyclohexane solution), which are ascribed to its high uniformity and monodispersity. These make Fe₃O₄@C an ideal adsorption and enrichment material, especially for polycyclic aromatic hydrocarbons in water and in organic solvents.