Facile solid-state synthesis of Fe3O4/kaolinite nanocomposites for enhanced dye adsorption

Synergistic metal oxide nanoparticles ​− ​kaolinite couplings have received much research attention as promising adsorbents because of their porous two-dimensional (2D) nanostructure and high adsorption ability. However, finding a simple method to prepare such a nanocomposite with high activity is still a big challenge. In this study, a novel and simple solid-state synthetic method of producing Fe3O4/kaolinite nanocomposites was developed for enhanced adsorptive removal of cationic (i.e., methylene blue, MB) and anionic (i.e., Congo red, CR) dyes. The obtained Fe3O4/kaolinite nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and nitrogen adsorption/desorption measurements. It was found that the amount of Fe3O4 nanoparticles formed in the kaolinite structure has a great influence on the properties and structure of Fe3O4/kaolinite nanocomposite. The sample containing 7 mass% Fe3O4 exhibited the best performance. The maximum adsorption capacity (mg g−1) increased from 13.4 to 42.3 for MB and from 14.3 to 138.5 for CR under neutral condition (i.e., pH: ~7.0), when the mass percentage of Fe3O4 in the nanocomposite was increased from 0 to 7, indicating that the dye-removal ability of kaolinite could be improved significantly by modification with moderate amount of Fe3O4. The adsorption of MB and CR could best be described by the pseudo-second-order equation, Langmuir adsorption model and Freundlich adsorption model. Schematic illustration for preparation of Fe3O4/Kaol nanocomposites and dye adsorption. [Display omitted] •A facile strategy for synergistic Fe3O4−kaolinite coupling was developed.•Highly active Fe3O4/kaolinite nanocomposite was successfully synthesized.•Fe3O4/kaolinite shows a higher removal efficiency for dyes than original kaolinite.•High concentration of methylene blue and Congo red can be rapidly removed by adsorption.•Combined function of Fe3O4 and activated kaolinite leads to high dye removal ability.