Synthesis and Characterization of Hybrid Nanostructures

摘要

This thesis deals with the fabrication and manufacturing of novel hybrid nanostructures with enhanced functionality, particularly core-shell hybrid nanomaterials, 2D nanostructured materials and surfaces, and polymer nanocomposites.The study includes four parts; in the first part, core-shell hybrid nanocomposites composed of ZnO nanorods/Ag nanoparticles were prepared by a very simple chemical technique.ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of Ag nanoparticle by a cationic surfactant cetyltrimethylammonium bromide (CTAB) formed the ZnO nanorods/Ag coreshell nanocomposites and its morphological and optical properties have been investigated.The integration of semiconductor and noble metal nanoparticles with controlled structure at the nanoscale can effectively combine various effects specific to the different domains of the nanocomposite for better application versatility.This work demonstrates that Ag nanoparticles with an average diameter of 20 nm were coated onto the surface of hexagonal phase ZnO nanorods with a minimum amount of 0.09 mmol concentration of CTAB.The excitonic absorption band and surface plasmon absorption band of the ZnO NRs/Ag nanocomposites show red-shifts relative to pristine ZnO nanorods and metallic Ag nanoparticles.The coating of Ag nanoparticles onto the ZnO nanorods display red-shift in the near band edge luminescence spectra and a reasonable detraction in the deep level emission spectra compared with the pure ZnO nanorods.In the second part, palladium (Pd) octahedral and spherical nanocrystals were successfully synthesized on reduced graphene oxide (GO) by surface adsorption of H2 and CO in the presence of capping agent poly(vinylypyrrolidone) (PVP).Their comparative studies as anode material for direct methanol fuel cells (DMFCs) have been measured by hydrogen evolution reaction (HER) performance and methanol oxidation reaction (MOR) activity were studied in HClO4 acidic media.Pd octahedral nanocrystals have shown the low onset potential in the HER region and specific MOR activity of ca.4.3 mA cm-2 and mass activity of ca.5300 mA mg-1 Pd much higher than that of spherical nanocrystals.This result can be attributed to the abundance of (111) facets on the Pd octahedral shaped nanocrystals.Moreover, bimetallic PdPt nanoparticles of different compositions were anchored on graphene sheets through a novel and facile route and its electrocatalytic properties including methanol oxidation reaction (MOR), oxygen reduction reaction (ORR) and methanol tolerant oxygen reduction reaction (MORR) were evaluated in HClO4 solution.The as-synthesized GO/PdPt composites showed higher electrocatalytic activity, higher specific ORR activity and excellent poisoning tolerance for the methanol electro-oxidation compared with graphene supported monometallic catalyst, due to the combined effect of the composite with unique properties of graphene and alloying of Pd with Pt.In the third part, we developed a facile and novel hydrothermal route for the synthesis of 3D MoS2/GO-CNT hybrid nanostructure and explored their practical application in hydrogen evolution reactions.This new type of 3D networked structure was hydrothermally synthesized through an aqueous dispersion of GO and CNT, followed by the anchoring of MoS2 nanoparticles on the surfaces of GO-CNT.This ternary composite shows superior electrocatalytic activity and stability in the hydrogen evolution reaction (HER) with a low onset potential of only 35 mV, a Tafel slope of～38 mV/decade and an apparent exchange current density of 2.02× 10-4 mA.The superior hydrogen evolution activity stemmed from the synergistic effect of the MoS2 with electrocatalytically active edge sites and excellent electrical coupling to the underlying graphene and CNTs network.In the last and fourth part, bulk transparent polymer-inorganic nanocomposites were produced by a novel synthesis method and its optical and thermal properties have been investigated.Morphological study on the nanocomposite reveals that a homogenous dispersion of ZnO nanoparticles was achieved in the PMMA matrix.A reasonable increase in thermal and optical properties was also observed after loading a small amount of ZnO nanoparticles.Moreover, the PMMA/ZnO nanocomposites films were highly transparent and possess good absorption of light in the UV region which can strongly shield harmful UV light for human health.Comprehensive characterization of the hybrid materials synthesized in this work has been undertaken using a wide range of techniques; scanning electron microscopy (SEM) and field emission SEM (FESEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectrometry (XPS), UV-Vis and photoluminescence (PL), thermo gravimetric analysis (TGA), and differential scanning calorimetry (DSC).