Study On Ionic Liquid-Assisted Synthesis Of Fe₃O₄ Nanomaterials And Preparation Of Core-Shell Magnetic Composite Catalysts

Nanostructured magnetic materials have drawn much attention due to their unique physical and chemical properties and extensive applications in biomedicine, catalysis, environmental protection and magnetic recording materials. For the first time, coralloid Fe₃O₄ nanoclusters have been prepared via ionic liquid-assisted solvothermal method in this work, and the nanoclusters have been applied to catalyze the degradation of phenol in water. Besides, Pd-loaded core-shell magnetic composite catalyst has been synthesized without extra reducing agent and the catalytst performance has been tested by Suzuki coupling reaction.First, coralloid Fe₃O₄ nanoclusters stacked by nanosheets were successfully synthesized using ferric nitrate as the precursor, ethylene glycol as the solvent and reducing agent and the ionic liquid?[Dmim]Cl? as the structure-directing agent. In comparison, spherical Fe₃O₄ nanoclusters assembled by nanospheres were synthesized in the absence of ILs. The measured BET surface areas and saturation magnetization of coralloid nanoclusters were 23.8 m2g-1 and 50.1 emu×g-1 respectively, which were both higher than those of spherical nanoclusters?14.5 m2g-1 and 40.2 emu×g-1respectively?. The mechanism for ionic liquids-induced oriented crystal growth has been in depth proposed based on the interaction between ILs and Fe₃O₄ crystal planes. Moreover, the products have been applied to the degradation of phenol in the water under UVA irradiation. The result shows that coralloid Fe₃O₄ nanoclusters have higher catalytic activity than that of spherical nanoclusters and can promote the degradation efficiently. The degradation rate of phenol reaches 99.07% after 3 h reaction.For the synthesis of core-shell magnetic composite catalyst, firstly, Fe₃O₄@RF has been synthesized via extend Stober method. The core-shell magnetic composite catalyst Fe₃O₄@C-Pd with uniform Pd dispersionwere successfully prepared by the carbonization of resorcinol–formaldehyde shell and no additional reducing agents are employed for the reduction of Pd2+. The size of Pd nanoparticles increased with the increase of the carbonization temperature and the size of Pd nanoparticles, loading capacity and saturation magnetization of Fe₃O₄@C-Pd catalyst carbonized at 550 °C were 10 nm, 8.73% and 54.90 emu×g-1 respectively. Suzuki coupling reactions have been chosen to test the activity of the magnetic composite catalysts. Fe₃O₄@C-Pd catalyst carbonized at 550 °C showed the highest performance and great substrate applicability. Especially, the yield of biphenyl could reach 100% in 30 min for the coupling reaction of iodobenzene. The core-shell magnetic catalyst with high saturation magnetization could be recycled easily and has excellent reusability. The yield of biphenyl remained high at 90.68% and the loss rate of Pd was only 9.16% after ten cycles.