The Design Synthesis Of Multifunctionalnoble Metal Nanoparticles And Their Efficient Catalytic Properties

Noble metal such as gold（Au）, palladium（Pd） and bimetallic nanoparticles have attracted considerable attention due to their unique optical, electrical, and synergistic effects catalytic properties. Especially in catalystic field, to reduce costs and improve utilization, the design of reasonable structure and nano-catalyst for recycling become a hot focus in the field. In general, hollow structure or pore nano-materials can effectively save precious metal resources due to their high specific surface area, low density and low consumption of material. In addition, Fe₃O₄ NPs with small size, strong magnetic responsiveness, facilitate magnetic separation and recovery, so, to synthesize magnetic noble metal hollow structure nano-materials using superparamagnetism Fe₃O₄ NPs as supported material can improve the utilization of the materails. In this work, the fabrication of gold hollow nanospheres were carried out though one step method without any template. The design and synthesis of Fe₃O₄@Au hollow spheres and bimetallic Au-Pd magnetic hybrid nanoparticles were reported by using Fe₃O₄ as template. The morphology, composition and structure of sample were fully characterized by transmission electron microscopy（TEM）, high angle annular dark-field scanning TEM（HAAD-STEM）, scanning electron microscopy（SEM） with energy-dispersive X-ray spectroscopy（EDX）, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）, techniques. The reduction of 4-nitrophenol（4-NP） and potassium hexacyanoferrate（III）（K3Fe（CN）6） by sodium borohydride（Na BH₄） were chosen as model reaction for studying the catalytic performances of gold hollow nanospheres, Fe₃O₄@Au hollow spheres and Fe₃O₄@Au-Pd hybrid nanoparticles. The catalytic performance was mornitored by using UV-vis absorption spectrometry. The detailed experiments are as follows:（1） Gold hollow nanospheres（GHNSs） have been prepared by one step method using 2-mercaptothiazoline（2-MT） as both reductant and stabilizer. The as-synthesized GHNSs were observed exactly hollow spherical structure, size uniform, large specific surface area, outer diameter is about 120 nm, inner diameter is about 90 nm, exhibiting a wall thickness of 20-25 nm, composed of spherical shell of the Au NPs size of about 5 nm. The GHNSs exhibit excellent catalytic activity toward the reduction of 4-nitrophenol and potassium hexacyanoferrate（III） by sodium borohydride in water. GHNSs show good reusability for at least 5 successive cycles. The results indicated that GHNSs exhibited an excellent catalytic activity, good stability and reusability.（2） The Fe₃O₄@Au hollow spheres were designed and synthesis by porous Fe₃O₄ spheres as a template. The Au nanoseeds with diameter of 3.5 nm were stuck on the surface of the Fe₃O₄ hollow spheres. Based on Au nanoseeds, in the growth solution of gold, Au NPs in situ growth to about 6 nm, obtained Fe₃O₄@Au hollow spheres. The Fe₃O₄@Au hollow spheres have shown excellent catalytic activity towards the reduction of 4-nitrophenol and potassium hexacyanoferrate（III）. After recycled six times, as catalyst, the Fe₃O₄@Au hollow spheres still kept the catalytic activity. The results indicated that Fe₃O₄@Au hollow spheres exhibited an efficient catalytic activity, good stability and reusability.（3） The Fe₃O₄@Pd and Fe₃O₄@Au-Pd hybrid nanoparticles were synthesized by using Fe₃O₄ spheres as a template. The Fe₃O₄@Pd and Fe₃O₄@Au-Pd hybrid nanoparticles were characterized by TEM and SEM, and the result showed that the Pd NPs were about 20 nm and dispersed on the surface of the Fe₃O₄ hollow spheres. The Au@Pd bimetallic structure of Fe₃O₄@Au-Pd hybrid nanoparticles by HAADF-STEM characterized, the size of Au@Pd was 20-25 nm. The Fe₃O₄@Pd and Fe₃O₄@Au-Pd hollow spheres have shown excellent catalytic activity towards the reduction of 4-nitrophenol and potassium hexacyanoferrate（III）. The catalytic activity of Fe₃O₄@Au-Pd was higher than that of Fe₃O₄@Pd. In addition, the magnetic bimetallic heterogeneous nanocatalysts can be easily recycled which proved their good reusability, and the recycling with a conversion higher than 99 % was achieved after 6 cycles. The results indicated Fe₃O₄@Pd and Fe₃O₄@Au-Pd exhibited an efficient catalytic activity, good stability and reusability.