| Magnetic nano-catalysts, a kind of new nano-catalyst with favorable magnetic recovery and high catalytic activity, have wide application prospects.in liquid phase catalysis, such as photocatalysis, organic synthesis catalysis, and biocatalysis. Particularly, the magnetic core/shell nano-composites composed by a Fe3O4core and a specific shell have been regarded as one kind of desirable catalysts carrier to prepare magnetic nano-catalysts because of their good chemical stability and surface properties, uniform particle size, and favorable liquid dispersion performance.In this dissertation, the magnetic nano-catalysts based on Fe3O4nanoparticles were systematically researched. Fe3O4nanoparticles were prepared by solvothermal method and surfactant modified solvothermal method. Then, Magnetic core/shell microspheres were prepared by coating mesoporous SiO2and mesoporous aluminum oxides on Fe3O4nanoparticles. Finally, Pd/mmso-SiO2@Fe3O4, Pd/y-AlOOH@Fe3O4and Pd/y-Al2O3@Fe3O4catalysts were synthesized by supporting Pd nanoparticles, and TiO2/SiO2@Fe3O4photocatalysts were prepared by coating TiO2. All magnetic supporters and catalysts were characterized by XRD, N2adsorption-desorption, TEM, VSM, and SEM. The Heck reaction catalytic acivity and reusability of Pd/meso-SiO2@Fe3O4, Pd/γ-AlOOH@Fe3O4and Pd/γ-Al2O3@Fe3O4magnetic core/shell nano-catalysts were studied. Meanwhile, the catalytic performances of TiO2/SiO2@Fe3O4catalysts for photocatalytic degradation dyestuffs (RhB, methyl orange, and methylene blue) were evaluated. The main work of the dissertation was as follows:1. Cetyltrimethyl ammonium bromide (CTAB) was used, for the first time, as modifier to improve the solvothermal synthesis of Fe3O4microspheres. CTAB molecules played the roles of capping agent, crystal growth oriented agent, and dispersant. When the CTAB concentration was0.102mol/L and the solvothermal time was12h, obtained Fe3O4microspheres exhibited favorable superparamagnetism and monodispersion, and the particle size distribution was about230nm-250nm. Meanwhile, the Fe3O4microspheres without any other treatment or pre-coated could be coated by mesoporous SiO2and y-AlOOH. The obtained SiO2@Fe3O4and y-AlOOH@Fe3O4microspheres presented obvious core/shell structure and superparamagnetism. Thereinto, the SiO2shell showed abundant of worlike pores with2.1nm of average pore size, and the y-AlOOH shell with2:0nm-5.0nm of mesopores was composed of many near nanosheets. The CTAB molecules could serve as nucleation seeds for precipitation of mesoporous shells and act templates for the formation of mesoporous structure during the coating process.2. Monodispersed meso-SiO2@Fe3O4microspheres were rapidly synthesized (30min) by ultrasonic-assisted method, and the microspheres exhibited uniform core/shell structure with obvious mesoporous shell. During the preparation process, the morphology and dispersion of microspheres and mesoporous structure of silica shell were significantly influenced by initial concentration of CTAB (CCTAB),ultrasonic irradiation power (P) and ultrasonic irradiation time (T). Under the best preparation condition (CCTAB=6.86mmol/L, P=150W and T=30min), the BET surface area and BJH pore volume of microspheres were468.6m/g and0.35cm/g, respectively. The acceleration effects of ultrasonic were mainly manifested in three aspects: accelerating the hydrolysis-condensation process of TEOS, accelerating the coassembly of hydrolyzed precursors and templates, and accelerating the deposition of silica oligomers on the magnetic particles.3. For the Pd/meso-SiO2@Fe3O4(E) catalysts, Pd nanoparticles were loaded on the surface of meso-SiO2@Fe3O4(E) supporters and into the mesopores of SiO2shell. The sizes of Pd nanoparticles were4nm-6nm and2nm～3nm, respectively. In the Heck reaction of bromobenzene and butyl acry late, the conversion of bromobenzene over5.32%Pd/meso-SiO2@Fe3O4(E) catalyst reached about100%under condition of120℃of reaction temperature,0.01mol%of Pd mole content, and12h of reaction time. Compared with the other supported Pd catalysts reported in literatures, Pd/meso-SiO2@Fe3O4(E) catalysts exhibited higher catalytic performance. Furthermore,5.32%Pd/meso-SiO2@Fe3O4(E) catalyst presented excellent magnetic recycling and reusability. After recycled for8times, the conversion of bromobenzene was above92%, the loss of catalyst was below5%, and the Pd loading was about5.15wt%. The catalyst kept uniform core/shell structure and the Pd nanoparticles with2nm～4nm of particle size kept highly dispersed state.4. For the Pd/γ-AlOOH@Fe3O4and Pd/γ-Al2O3@Fe3O4catalysts, the monodispersed Pd nanoparticles with6nm-8nm of particle size were loaded on the γ-AlOOH sheets of Pd/γ-AlOOH@Fe3O4, but the Pd nanoparticles on the latter exhibited obvious aggregation. In the Heck reaction of bromobenzene and styrene, both kinds of catalysts showed higher catalytic activity than the other supported Pd catalysts reported in literatures. Thereinto, the conversion of bromobenzene over4.5%Pd/γ-AlOOH@Fe3O4catalyst reached about100%under condition of120℃of reaction temperature and12h of reaction time. After recycled for8times, the conversion of bromobenzene was above90%, the recovery of catalyst was above93%, and morphology and Pd loading of catalyst were kept well.5. For the50%TiO2/6%SiO2@Fe3O4magnetic core/shell photocatalysts, the thickness of the homogeneous anatase TiO2layer was about8nm-10nm, and the BET surface area and the BJH pore volume were495.3m2/g and0.54cm3/g, respectively. The50%TiO2/6%SiO2@Fe3O4microspheres exhibited the best photocatalytic performance. The conversion of RhB achieved up to98.1%after60min UV irradiation. After recycled for8times, it also maintained high degradation rate and catalyst recovery. In addition, the photocatalysts received visible-light reponse after structure optimization. Two kinds of dyes (methyl orange and methylene blue) were completely degradated by9%TiO2/6%SiO2@Fe3O4catalyst after60min irradiation of high-pressure mercury lamp. Meanwhile, the catalyst exhibited favorable recovery and reusability. |
PDF Full Text Request