Synthesis Of Fe₃O₄ Hollow Microspheres And Catalytic Properties Of Magnetic Titanium Silicalite Molecular Sieves

Magnetite(Fe3O4) hollow microspheres in nano/microscale have been widely used in catalyst, magnetic resonance imaging(MRI), drug delivery, bioseparation, lithium-ion batteries, and contamination separation due to their low density, high surface-to-volume ratio, good permeation and unique optical, electrical and surface properties. These unique properties and applications of Fe3O4 hollow microspheres make them a hot topic in recent years. Conventionally, one would use the template method to fabricate hollow structures and the templates can be generally divided into hard and soft templates. However, the high cost and tedious syntheses have impeded the scaling-up of many of these methods for large scale application. In addition, hollow structures as prepared suffer from the disadvantage of requiring removal of the template, which involves complicated processes and the inevitable drawbacks of product impurity. So, it remains a great challenge to explore simple and economical synthetic strategies to synthesize magnetite hollow nanostructures with desired morphologies and dimensions. In this paper, superparamagnetic mesoporous Fe3O4 hollow microspheres were synthesized by solvothermal method with trisodium citrate as an electrostatic stabilizer. The formation mechanism of Fe3O4 hollow spheres was explored and proposed as trisodium citrate-assisted Ostwald ripening. In addition, the Fe3O4@silica composite microspheres were prepared via a modified St?ber method by using Fe3O4 solid microspheres as nuclear magnetic and tetraethoxysilane as silica source. By diluting the TEOS with ethanol and controlling the amount of TEOS, we successfully obtained the monodisperse Fe3O4@Si O2 composite microspheres with uniform silica coating and good magnetic property. Finally, magnetic titanium silicalite molecular sieves were synthesized via the process of hydrothermal synthesis and solvent evaporation method by using tetraethoxysilane as silica source, tetrabutyl titanate as titanium source, tetrapropylammonium ammonium hydroxide as template agent and Fe3O4 hollow microspheres as magnetic nucleus. The as-prepared magnetic titanium silicalite molecular sieves were used in ammoximation of cyclohexane and its catalytic performance was investigated. The catalysts can be separated from liquid by the control of external magnetic field and used again, which resolves the separation and reuse problem of TS-1.