Synthesis Of Iron Oxide/noble Metal Composites And Their SERS Properties

With the development of nanotechnology, iron oxide micro/nanostructures have displayed wide applications in chemical sensor, biotechnology/biomedicine, environmental treatment, magnetic fluids and data store due to their unique physicochemical properties. Especially, Fe3O4nanoparticles (NPs), which possess high saturation magnetization, low toxicity and good biocompatibility, have been comprehensively studied for a range of applications in biotechnology and biomedicine. Likewise, noble metal (Au, Ag) NPs can produce unique local surface plasmon resonance effect under the action of laser, which effectively improves the development of surface enhanced Raman spectroscopy (SERS). Nowadays, SERS technology has realized extreme sensitive detection and unwonted single molecular detection. It is easy to see that combination of magnetic NPs with noble metal NPs would endow possibilities for the development of interesting advanced composites as a result of bring together rapid separation, target and unique SERS effect. Not only can so advanced composites tract targeted analyte, also analyze them in time. In this dissertation, we reported some iron oxides and iron oxide/noble metal composites, mainly investigated their application in SERS detection and treatment of organic dyes. The main contents are included:1. Uniform mesoporous hematite superstructures (～2μm) have been obtained via an oleic acid-assisted one-pot solvothermal route. The as-obtained products were characterized by XRD, XPS, Raman, SEM, TEM, FT-IR, TG-DSC and N2absorption-desorption isotherm. These results indicate that hematite superstructures self-assembled by using large number of NPs have high surface area (78.3m2/g) and mesoporous structures. Some factors (reaction time, surfactant, the amount of surfactant and precursor) influencing the phase, crystallinity and morphology of the products were systematically investigated. Based on the experimental investigation and analysis, we mainly discussed the formation mechanism of mesoporous hematite superstructures, phase transition (magnetite-hematite-maghemite) induced by reaction time and gave a proper explaination. The magnetic study reveals a surprising phenomenon that the mesoporous. hematite superstructures exhibit a unique superparamagnetic behavior with a high saturation magnetization (28.9 emu/g) at room temperature, which is seldom reported thus far for. hematite micro/nanostructures. The Zero field cooled-field cooled (ZFC-FC) measurement verified the existence of superparamagnetic blocking temperature (Tb=158K), which further approves the superparamagnetic behavior of the mesoporous superstructures at room temperature.2. Fe3O4/Au, Fe3O4Ag and Fe3O4@Au composites with different Au content were obtained by phase-liquid assembly of Au, Ag NPs and further growth on Fe3O4supports. UV-visible absorption spectroscopy and magnetic measurements demonstrate not only do the obtained composites inherit local surface plasmon resonance effect of noble metal NPs, also keep excellent magnetic response behavior. Taking Rhodamine6G (R6G),4-mercaptopyridine (4-Mpy) model molecules for example and normal dispersed Au, Ag NPs for reference, a magnetic-induced idea was introduced to adjust aggregated states of above-mentioned composites and research their SERS performances. It indicates that magnetic-induced aggregated states of composites concentrate the adsorbed probe molecules, and create more "hot spots", which cause superior SERS performances. Especially, Fe3O4@Au composite microspheres with well-defined structures can be considered as candidates for track and analysis of special tissue and cell.3. Water-dispersive Au-loaded Fe3O4@C composite microspheres were controllably synthesized by a simple and efficient chemical liquid-phase route. The amount of Au loading can be effectively tuned (0.95%-5.93%atomic percent) by altering the feeding amounts of solution Au NPs or further growth. The obtained Au-loaded Fe3O4@C composites exhibit both superior SERS sensitivity and catalytic degradation activity for organic dyes. The SERS signal intensity of R6G, crystal violet (CV) and methylene blue (MB) distinctly enhance with the increase of Au loading. Furthermore, the catalytic experiments of the Fe3O4@C@Au composite microspheres with a5.93%of Au loading demonstrate that the model organic dye of MB solution (1.0×10-5M) could be degraded within10min and the catalytic activity could be recovered without sharp activity loss in six runs, which indicate their superior catalytic degradation efficiency (98%) and rate (0.331min-1). These results indicate that Au-loaded Fe3O4@C composite microspheres could be served as promising materials in wastewater treatment.