Synthesis And Photocatalytic Activity Of Magnetic-separable Fe₃O₄@TiO₂Composite Microstructures

TiO2is widely used in semiconductor photocatalysis due to itsexcellent features. However, TiO2particles with nanoscale size isdifficult to separate and recycle after employing for thephotocatalytic reactions. Magnetic separation and recoverytechnology can be used to recovery TiO2nanoparticles in thesolution because of the high saturation magnetization of Fe3O4orγ-Fe2O3. Therefore, TiO2composite structures with magnetic cores,not only can improve the photocatalytic activity, but also canrealize magnetic recovery.In this thesis, we successfully synthesized the Fe3O4@SiO2@TiO2three-layer composite structures with different size, in which themagnetic Fe3O4nanoparticles are used as the cores, coating withSiO2and TiO2layers. On this basis, we prepared theFe3O4@SiO2@TiO2and γ-Fe2O3@SiO2@TiO2magnetic nanocompositestructures with special chain-like structure through improving thecoating methods. The photocatalytic activity and magneticrecycling property of chain-like γ-Fe2O3@SiO2@TiO2photocatalystwere evaluated by photodegrading rhodamine B (RhB) solutionunder Xenon lamp. A variety of characterization methods are usedto study the structure, composition, morphology and magneticproperties for these structures. The main results are as follows: (1) Fe3O4nanoparticles with small size and large size weresynthesized by the coprecipitation and the hydrothermal methods,respectively. The dispersion of the large Fe3O4nanoparticlesis moreuniform and the saturation magnetization is stronger than that ofthe small Fe3O4nanoparticles. The surface morphology of Fe3O4particles can be adjusted by different dispersing agents. Fe3O4magnetic particles with sodium polyacrylate as dispersing agentshow the best uniform dispersion and particle integrity. The roughsurface for the particled is favaroble for the following coating ofSiO2and TiO2. Therefore, the synthesis method and dispersingagent play important roles in controlling the microstructure andmorphology of Fe3O4.(2) The preformed monodisperse Fe3O4magnetic microspheresare used as templates to grow sequential SiO2coupling layer bySt ber method and subsequent TiO2photocatalysis layer by sol-gelreactions, leading to the Fe3O4@SiO2@TiO2composite structureswith different sizes. In contrast, the large composite structuresexhibit better coating uniformity, dispersion, and high saturationmagnetization, which is more benefit for the magnetic recovery andreuseof the photocatalysts.(3) The γ-Fe2O3@SiO2@TiO2composite nanoparticles with specialchain-like structure synthesized by modified sol-gel method, whichhas good photocatalytic performance and excellent magneticrecovery property. The chain structure formation mechanism isrevealed by analyzing the structures and magnetic properties.In conclusion, we synthesized Fe3O4@SiO2@TiO2compositestructures with different sizes and chain-like γ-Fe2O3@SiO2@TiO2 composite structures by hydrothermal, St ber and modified sol-gelmethods. Especially, the γ-Fe2O3@SiO2@TiO2composite structureshave good photocatalytic performance and excellent magneticrecovery property. Relevant research results have greatsignificance in designing and synthesizing other multi-functionalphotocatalysts in field of magnetic recovery.