Controllable Synthesis, Characterization And Photocatalysis Application Of Magnetic Iron Oxides/Semiconductor Composite Nanomaterials

At present, nanoengineering of particle surfaces and functionalization have atrracted much attention because they display improved or new physicochemical properties. Surface functionalized magnetic iron oxide nanoparticles (NPs) and semiconductor NPs are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This dissertation focuses on the controllable synthesis and photocatalysis application of magnetic iron oxides/semiconductors composite nanoparticles.Firstly, Water-soluble hollow spherical magnetite (Fe3O4) nanocages (ca.100 nm) with high saturation magnetization are prepared in a one-pot reaction by sol-gel method and subsequent annealing to synthesise the maghemite (γ-Fe2O3) nanocages with similar nanostructures. The results indicated that glutamic acid played an important role in the formation of the cage-like nanostructures. Furthermore, we present a facile approach to the production of magnetic iron oxide short nanotubes (SNTs) employing an anion-assisted hydrothermal route by simultaneously using phosphate and sulfate ions. The size, morphology, shape, and surface architecture control of the iron oxide SNTs are achieved by simple adjustments of ferric ions concentration without any surfactant assistance. The result of a formation mechanism investigation reveals that the ferric ions concentrations, the amount of anion additive, and the reaction time make significant contributions to SNT growth. The shape of the SNTs is mainly regulated by the adsorption of phosphate ions on faces parallel to the long dimension of elongated hematite (α-Fe2O3) nanoparticles (c axis) during nanocrystal growth, and the hollow structure is given by the preferential dissolution along the c axis due to the strong coordination of the sulfate ions. Moreover, the as-synthesizedα-Fe2O3 SNTs can be converted to Fe3O4 and y-F2O3 ferromagnetic SNTs by a reducing atmosphere annealing process while preserving the same morphology. The structures and magnetic properties of these iron oxide SNTs were characterized by various analytical techniques. The original of coercivity ofγ-Fe2O3 SNTs have been also investigated. Additionally, the development of synthetic process for magnetic hollow silica materials is an issue of considerable topical interest. While a number of chemical routes are available and are extensively used, the diameter of magnetic hollow silica often large than 50 nm. We report on a facial route to synthesis ultrafine hollow silica nanoparticles (the diameter of ca.24 nm) with high surface area by using cetyltrimethylammmonium bromide (CTAB) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as co-templates and subsequent annealing treatment. When the hollow magnetite nanoparticles were introduced into the reaction, the ultrafine magnetic hollow silica nanoparticles with the diameter of ca.32 nm were obtained correspondingly.Then, titanium dioxide (TiO2) submicrospheres (SMs) have been successfully synthesized via a solvothermal method by hydrolysis of tetrabutyl titanate in ethanol solution with the CTAB presented. The SMs are composed of closely packed rod or tetragonal NPs, and the inner structure of SMs depends on whether the hexamethylenetetramine (HMTA) was introduced in the reaction or not. The surface and inner morphologies, structure, and optical properties of the SMs were investigated. Furthermore, we proposed a facile pathway to prepare three different types of magnetic iron oxides/TiO2 hybrid NPs by seed-mediated method. The hybrid NPs are composed of spindle, hollow and ultrafine iron oxide NPs as seeds and 3-aminopropyltriethyloxysilane (APTES) as link between the magnetic cores and TiO2 layers, respectively. The composite structure and the presence of the iron oxide and titania phase have been confirmed by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The hybrid NPs show good magnetic response, which can get together under an external applied magnetic field and hence it should become a promising magnetic recovery catalyst (MRC). Photocatalytic ability examination of the magnetic hybrid NPs was carried out in methylene blue (MB) solutions illuminated under Hg light in a photochemical reactor. About 50% to 60% of MB was decomposed in 90 min in the presence of magnetic hybrid NPs. The synthesized magnetic hybrid NPs display high photocatalytic efficiency and will find recoverable potential applications for cleaning polluted water with the help of magnetic separation.Thirdly, we report a systematic investigation of the growth of low-dimensional sub-100 nm SnO2 hollow nanostructures by a mild template-and surfactant-free hydrothermal route, aiming to achieve precisely controlling of morphology and size. The initial materials are potassium stannate and urea in an ethylene (EG)-H2O system, we found the size control of the SnO2 hollow nanospheres can be achieved by simply adjusting the urea concentration. By switching the solvent from EG-H2O to H2O or ethanol, the SnO2 nanostructures changed from nanospheres to ultrafine nanorods and nanoparticles. The formation mechanism of SnO2 hollow nanospheres is investigated, which reveal that the reaction time, urea concentration, and reaction temperature make significant contribution to the growth of hollow nanospheres. Based on the reaction parameters-dependent experiments, the oriented self-assembly and subsequent evacuation behaviours of Ostwald ripening are proposed to explain the formation mechanism of hollow nanostructures. Their size-dependent optical properties including UV-vis absorption spectra and room-temperature fluorescence spectra were also studied. Moreover, the studies of the photocatalytic property demonstrate that the fabricated hollow structures evinced a slight enhanced photocatalytic degradation activity for Rhodamin B (RhB) than that of solid SnO2 nanospheres under the same conditions. The synthesized tin oxide nanoparticles display high photocatalytic efficiency and potential applications for cleaning polluted water in the textile industry. Moreover, iron oxide/SnO2 magnetic semiconductor core-shell heterostructures with high purity were synthesized by a low-cost, surfactant-free and environmentally friendly hydrothermal strategy via seed-mediate method. The morphology and structure of the hybrid nanostructures were characterized by means of high-resolution transmission electron microscopy in details. The morphology evolution investigates reveal that the Kirkendall effect directs the diffusion and causes the forming iron oxide/SnO2 quasi-hollow particles. Significantly, the as-obtained iron oxides/Sn02 core-shell heterostructures exhibited enhanced visible light or UV photocatalytic abilities, remarkably superior to their a-Fe2O3 seeds and commercial SnO2 products, mainly owing to the effective electron hole separation at the iron oxides/SnO2 interfaces.Finally, connected zinc oxide (ZnO) nanoparticles were successfully synthesized by a simple solution-based chemical route in the presence of evaporation and concentration technology. The influences of processing parameters especially the evaporation and concentration time on the size and morphology of the nanoparticles have been investigated. The structure and optical properties were systematically characterized. It was found that the average diameter and morphology were strongly affected by the evaporation and concentration time. Additionally, the formation mechanism of the nanoparticles was also discussed. The studies reveal that the evaporation and concentration were important aggregation or nucleation processes for the ZnO growth, which leads to the macro-differences in morphology. The results provided some insights into the growth mechanism of ZnO nanostructures. The synthetic strategy developed in this study may also be extended to the preparation of other nanomaterials and promising applications in various fields of nanotechnology. More importantly, the photocatalysis ability of connect ZnO NPs for RhB is higher than the traditional P25. Furthermore, we demonstrated the preparation ofα-Fe2O3/ZnO core-shell composite nanoparticles by a seed-mediate method and a subsequently annealing treatment.The thicknesses of ZnO shells and morphologies were found to be dependent on the amount of the concentration of zinc precusor. The formation mechanism ofα-Fe2O3/ZnO core-shell heterostructures was speculated. The nanocomposites exhibit a high photocatalysis ability for RhB.