Synthesis And Characterization Of Stimuli-responsive Fe₃O₄@Au Nanocomposites

The functionalization of nanomaterials has obtained immense research interest inrecent years, and multifunctional materials have various potential applications inpractical life. How to improve nanomaterials’ existing performance and to endowthem with new functionality is the basic research frame. Because of the capability ofdynamically changing their physical and chemical properties under exposure toexternal stimuli such as temperature, pH, magnetic field, illumination etc.,stimuli-responsive nanomaterials are also referred as smart nanomaterials. Amongthem, Fe₃O₄and gold nanomaterials have attracted a great deal of attention due totheir unique magnetic and optical properties respectively.Firstly, we have synthesized a dextran-based copolymer exhibiting temperatureand pH sensitivities by radical addition-fragmentation chain transfer （RAFT）polymerization. By using DEX-DMP as the macro chain transfer agent,thermo-sensitive monomer NIPAM and pH-sensitive monomer MAA werepolymerized in the side chain of dextran sequentially. Then self-assembly behavior ofthe aqueous nanogels and the temperature-induced phase transition behavior werestudied by a series of characterizations.With the aid of the dual sensitive copolymer, a quadruple-responsivenanocomposite that responds to temperature, pH, magnetic feld, andnear-infrared-spectroscopy （NIR） is obtained. Using the dextran-based copolymer as astable coating, Fe₃O₄nano-particles （NPs） were successfully prepared bycoprecipitation and incorporated into the smart network. NIR-sensitive gold nanorodswere embedded into the copolymer network through stable Au-S bonds. Thesefunctionalized nanocomposites with superior stability can respond to the four stimulimentioned above well. As evidenced by UV-Vis and TEM measurements, thetemperature-induced unusual blue-shift in the longitudinal plasmon band is possiblydue to the side-to-side assembly of gold nanorods. As a multifunctional smartnanomaterial, we can envision that these QNCs may possess many biomedicalapplications. In order to combine the properties of Fe₃O₄and gold nanomaterials, wesynthesized a kind of Fe₃O₄@Au core-shell nanostructure in a simple way by usingglucose as the green reducing agent. Fe₃O₄NPs were produced by thermaldecomposition of the metal–oleate precursors and transferred into water phase byoxidation of oleic acid. Fe₃O₄@Au core-shell nanostructure was made by usingglucose to reduce HAuCl4in the presense of Fe₃O₄at90℃. To verify the catalyticbehaviours of Fe₃O₄@Au, we subject Fe₃O₄@Au to a catalytic activity test by thereduction of4-nitrophenol to4-aminophenol. As expected, Fe₃O₄@Au shows wellcatalytic property. The magnetic separation of Fe₃O₄@Au is very easy, whichsuggests that Fe₃O₄@Au could be used as recoverable catalyst.