Between the Fe 3O 4 core and outside surface TiO 2 layer, an SiO 2 layer is introduced to avoid the interaction between the two layers and inhibit photodissolution of the core. In this paper, a novel approach to synthesize three-layer core-shell nanoparticles is described. This has proved to be difficult due to the fact that the photocatalytic activity of the nanoparticles shows a decline when the magnetic cores experience photodissolution. The technical challenge here is coupling the Fe 3O 4 to SiO 2 with TiO 2 exposed as the outer surface to provide the catalytic sites and Fe 3O 4 as the core for magnetic separation and recovery. In this way, the superparamagnetism of nanoscale Fe 3O 4 particles makes it a suitable material. The magnetic composite photocatalyst can be magnetically agitated by an alternating magnetic field in a suspension system. One approach would be to introduce superparamagnetic properties and hence to recover the nanoparticles using magnetic fields. It is hence desirable to retain and recover the nanoparticles in such applications, particularly, in wastewater treatment. One of the main obstacles to the application of nanoparticles in industrial applications is the concern of the release and the fate of the nanoparticles in the environment. The properties of titania, which is well known for the high productivity of hydroxyl free radicals when exposed to ultraviolet light, low toxicity, and low cost make it a popular choice in wastewater treatment. Specifically titania can catalyse the decomposition of a wide range of chemicals such as azo dyes, aromatic compounds, and endocrine disruptors. One of these could be the treatment of chemicals and biological molecules in wastewater. Nanoparticles could find their uses in many important industrial processes. The particles were recovered after utilization, washing, and drying and the primary recovery ratio was 87.5%. The results showed that the introduction of the Fe 3O 4-SiO 2-TiO 2 functional nanoparticles significantly increased the decoloration rate so that an MO solution at a concentration of 10 mg/L could be decoloured completely within 180 minutes. The functionality of these particles was tested by measuring the photocatalytic activity of the decolouring of methyl orange (MO) and methylene blue (MB) under ultraviolet light and sunlight. These magnetic properties, large area, relative high saturation intensity, and low retentive magnetism make the particles have high dispersibility in suspension and yet enable them to be recovered well using magnetic fields. The results of characterizations showed that the encapsulated 700 nm Fe 3O 4-SiO 2-TiO 2 particles have a relatively uniform size distribution, an anatase TiO 2 shell, and suitable magnetic properties for allowing collection in a magnetic field. The Fe 3O 4 cores were then modified with SiO 2 and finally encapsulated with TiO 2 by the sol-gel method. The Fe 3O 4 cores which were mainly superparamagnetic were synthesized through a novel carbon reduction method. This paper describes a novel method of synthesizing Fe 3O 4-SiO 2-TiO 2 functional nanoparticles with the core-shell structure.
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