Study On Preparation And Properties Of Core-Shell Structure Nanoparticles

The preparation of nanocomposite particles is a great challenge in the fields ofsynthetic chemistry and materials science, because nanocomposite particles haveunique structural, mechanical, electronic, magnetic and optical properties. Variousnano-and micro devices were built up based on nanocomposite materials. Here, wefirst report on a synthetic route to prepare new material which is nanometer-sizemetals M (M=Ni, Co, stainless steel) particles coated with uniform silica layerutilizing wire electrical explosion technique and St?ber method. The method wasbased on the use of silane coupling agent 3-mercaptopropyltrimethoxysilane(HS-(CH2)3Si(OCH3)3, MPTS) as a primer to render the metal surface vitreophilic,thus rendered metal surface is compatible with silica. The product wascharacterized by XRD, XPS, TEM and TG-DTA spectroscopy. Measure resultsindicate that the metal/SiO2 nanocomposite particles have the core-shell structureand the thickness of SiO2 coating layer increases with the increasing reaction time.Result of the thermogravimetric analysis (TGA) and differential thermal analysis(DTA) indicate that the thermal stability of metal/silica is better than the pure metalnanoparticles. We suggest that the SiO2 shell is quite uniform and compact coatedon the surface of metal nanoparticles. Magnetic properties of these powders havebeen evaluated. These metal/silica core–shell nanoparticles can be utilized asprecursors for making property-tunable magnetic nanoparticles, thin films, andmultilayered core–shell structure nanocomposites. Core-shell structure Ni/Fe3O4nanocomposites were prepared by wire electrical explosion method andco-precipitation method. Ni/Fe3O4 nanocomposite powders with different mol rate wereuniformly dispersed in to the bakelite, respectively. The saturation magnetizationvalues (Ms) of Ni/Fe3O4 nanocomposites increased with increasing the concentrationof Ni. Ni/Fe3O4 nanocomposites showed higher values than coercivity concentrationof Ni and Fe3O4 because of the effects of shape anisotropy and exchange bias. Thebakelite resin comprised with 75 vol % Ni/Fe3O4 (3:1, 2:1, 1:1 vol %) powdersprovided good microwave absorption performances in ranges of 6-12, 8-13, and9-14GHz over the absorber thickness of1.5mm. The reflection loss (RL) valuesupper than14dB dB were obtained in the 9.5GHz with absorber thickness of 1.5mm, this values better than the RL values pure Ni(5.3 dB,8.7GHz) and pureFe3O4(6.5dB,18GHz). Spinel CoFe2O4 coating shell on the surface of hollow glassmicroballoon was synthesized by co-precipitation method and the shell thickness is 200nm.The produces were characterized by X-ray powder diffraction(XRD),energy dispersivespectrometer (EDS) and scanning electron microscopy (SEM), The as-synthesized powdermaterials were uniformly dispersed in the phenolic cement,then the mixture was painted onmetal plate with the area of 200mm×200mm as the test board. The test of microwaveabsorption was carried out by the RAM reflectivity far field RCS method. The results indicatethat notable microwave absorption performance have been obtained when the microwavefrequency is above 16GHz. This performance is much better than the pure CoFe2O4nanoparticles under the same condition. Ferrite/TiO2 (Ferrite=SrFe12O19, BaFe12O19, CoFe2O4and MnFe2O4) composite nanoparticles with core-shell structure have been obtained. In whichM type hexaferrites SrFe12O19 and BaFe12O19 nanoparticles were synthesized by citrateprecursor technique, spinel CoFe2O4 and MnFe2O4 were synthesized by co-deposition method,and then the shell TiO2 nanocrystals were derived via sol-gel technology. The presence of asmall quantity of polyethyleneimine (PEI) on the surface of the strontium ferrite nanoparticlesfacilitates this coating process. The morphology, crystalline structure, particle size and sizedistribution of ferrite/TiO2 composite nanoparticles were characterized by transmission electronmicroscopy (TEM), X-ray powder diffraction (XRD) and 3000HSA analyzer (MALVERN),respectively. Energy-dispersive spectroscopy (EDS) was utilized for the element analysis of theproducts. The as-prepared composite particles can be utilized as a magnetic photocatalystwhich can be fluidized and recovered by an applied magnetic field enhancing both separatingand mixing efficiency for recyclable fluids. Magnetic properties and photocatalytic activities ofthese powders have been evaluated. The results of the experiments show that the saturationmagnetizations of ferrite/TiO2 nanoparticles decrease with increasing the thickness of thetitania coating, while the coercivity does not show any change after coating. Photocatalyticactivities of these powders increase with increasing the thickness of TiO2 coating layer. As thethickness of TiO2 increases, the influence of the SrFe12O19 rapidly decreases and in the end thephotocatalytic activity of the composite never changes with increasing the thickness of TiO2.When the content of TiO2 is 30 % and there is enough UV illumination (5 h in our experiment)the photodegradation ratio of Procion Red MX-5B by the composite of TiO2/SrFe12O19 is 98 %similar to that of pure TiO2...