Magnetic properties and dye adsorption capacities of silica–hematite nanocomposites with well-defined structures prepared in surfactant solutions

• Surface of silica particles was modified with hematite in cationic surfactant solution.
• Morphology of nanocomposite was influenced by concentrations of Fe salt and surfactants.
• Magnetic properties of hematite were improved by hybridization with silica.
• Adsorption efficiency of MB dye was largely dependent on their surface areas.

Silica–hematite (α-Fe2O3) nanocomposites were synthesized by addition of aqueous solution containing ferrous ions (Fe2+), cetyltrimethylammonium bromide (CTAB) as a surfactant and tert-butanol (t-butanol) as a cosurfactant into colloidal silica solution. At alkaline atmosphere, silica surface with negative charges electrostatically attracts positively-charged iron hydroxide nuclei or particles which are stabilized by cationic CTAB molecules, and then silica–iron compound composites could be formed. Finally, the silica–hematite composite particles were obtained after calcination at 800 °C for 4 h. Through these processes, two types of composites having “core–shell type” or “decorated type” could be achieved. Morphology, BET surface area, crystallinity and magnetic properties of samples were analyzed by using TEM, BET, XRD and VSM, respectively. The “decorated type” composites had larger BET surface area and better magnetization. Also, to estimate the application in water treatment, adsorption properties of composites were studied through methylene blue (MB) adsorption which was characterized by UV–vis spectroscopy, involving collection of composites with neodymium magnet.

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