Synthesis And Properties Of Ni - Based Nanomaterials

In this dissertation, some Ni-based binary metal nanocrystals (e.g. Ni-Ag alloy, Ni-Cu alloy) and Ni-based chalcogenide nanostructures (e.g. NiS quantum rods) have been successfully synthesized in non-aqueous system by choosing proper metal precursors and structure-directing reagents, respectively. Those Ni-based nanomaterials are characterized by powder X-ray diffraction (XRD), X-ray energy dispersive spectrum (EDS), X-ray photoelectron energy spectrum (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible absorption spectrum (UV-vis), photoluminescence spectrum (PL), and superconducting quantum interference magnetometer (SQUID). In addition, the physiochemical properties of the obtained Ni-based nanomaterials have been investigated. The main results are as follows:(1) By using trioctylphosphine (TOP) as solvent, oleic acid (OA) and dodecylamine (DDA) as surfactants, and acetylacetone nickel (Ni(acac)2) and silver nitrate (AgNO3) as source materials, the Ni-Ag alloy nanocrystals (NCs) have been successfully synthesized. Both EDS and XPS analysis show that there are only Ni and Ag two metal elements in the obtained products. XRD results exhibit that the diffraction peak positions of the obtained products are located in the middle of the face-centered cubic phase (fcc) Ni and fcc Ag, indicating that the obtained products are Ni-Ag alloy. TEM analysis reveals that the obtained alloy NCs are relatively uniform and their average diameters are about25nm. Corresponding HRTEM analysis shows clear lattice fringes and the lattice spacing is between the (111) plane of fee Ni and (111) facet of fcc Ag, further confirming that the obtained products are Ni-Ag nanoalloys and consistent with XRD results. The dark image of STEM and elemental mapping analysis reveal that the distribution of Ni and Ag elements in the alloy is relatively uniform. A series of control experiments demonstrate that the amount of TOP, the mole ratio of OA and DDA, the mole ratio of precursors and reaction temperature have great impacts on the size, shape and composition of the alloy NCs. Under optimized experimental conditions, by simply adjusting the mole ratio of solid precursors, the mole ratio of Ni and Ag in the obtained alloy NCs can be effectively controlled. Due to the presence of Ni component, the plasmonic resonance absorption peak of Ag in alloy NCs becomes broad and the intensity of the absorption peak turns weak. Furthermore, catalytic experimental results demonstrate the obtained Ni-Ag alloy NCs possess excellent catalytic performance for hydrogenation of2,6-dinitro toluene to produce corresponding amine derivatives. The selectivity of the catalytic product is found to correlate with the mole ratio of Ni and Ag in the alloys. With the increase of Ag concentration, the amount of dinitro hydrogenation product increases. When the mole ratio of Ni and Ag in the alloy NCs is1:3, the yield of dinitro hydrogenation product can reach96%, which is much higher than that of pure Ni NCs and comparable with that of pure Ag NCs.(2) The monodisperse polyhedral Ni-Cu alloy NCs with the average size of-15nm have been successfully synthesized by thermal treatment of Ni(HCOO)2and Cu(acac)2) solid precursors in1-octadecene (ODE), OA and DDA mixed solvents. The combination of OA and DDA is served as the structure-directing reagent. EDS analysis shows that only Ni and Cu two metallic elements exist in the obtained samples. The XRD results exhibit that the diffraction peak positions of the obtained samples are between that of fcc Ni and fcc Cu, indicating that the obtained samples are Ni-Cu alloys. Corresponding HRTEM analysis shows clear lattice fringes and the lattice spacing is between (111) plane of fcc Ni and (111) facet of fcc Cu, further confirming that the obtained samples are Ni-Cu alloy NCs and consistent with XRD analysis. The DF-STEM and elemental mapping analysis reveal that the distribution of Ni and Cu elements in the alloys is relatively uniform. A series of control experiments demonstrate that the mole ratio of OA and DDA, the mole ratio of precursors and reaction temperature have great impacts on the size, shape and composition of the alloy NCs. By adjusting the mole ratio of solid precursors and adding sequence, the mole ratio of Ni and Cu in the alloy NCs can be effectively controlled. Electrocatalytic experiments demonstrate that the obtained Ni-Cu alloy NCs can effectively catalyze oxidation of glucose. Furthermore, we find that the mole ratio of Ni and Cu in the alloy NCs have great impacts on the catalytic performance. These results imply that the obtained Ni-Cu alloy NCs can be served as a class of candidate materials to fabricate non-enzymatic glucose biosensor.(3) The highly monodisperse NiS quantum rods have been successfully synthesized by thermal treatment of Ni(acac)2solid precursors in the liquid mixture of dodecanethiol (DT) and1-octadecene (ODE) from room temperature to250℃and kept at250℃for a certain period. The key for obtaining high quality NiS quantum rods lies on controlling the molar ratio of Ni(acac)2and DT. The diameter of the obtained NiS quantum rods is about3.6-4.4nm and their length is about33-42nm. The aspect ratio of the obtained quantum rods is about8-10. HRTEM analysis shows that the lattice spacing that perpendicular to the rod growth direction is0.48nm, corresponding to the (110) planes of rhombohedra P-NiS. Thus, the growth direction of NiS quantum rod is along [110]. Corresponding XRD results reveal that the obtained quantum rods are the hexagonal and rhombohedra mixed phase NiS. EDS analysis exhibits that the main elecments in the obtained quantum rods are Ni and S and their atomic number ratio is close to1:1, further confirming that the obtained samples are pure NiS products. A series of control experiments demonstrate that the molar ratio of precursors, reaction time and heating rate have great impacts on the diameter, length, aspect ratio and phase structure of the obtained quantum rods. By using FT-IR and TEM analysis of the samples taken at different reaction temperature and ripening time, the possible formation process of the NiS quantum rods may be as follows:firstly, with the increase of reaction temperature, the Ni(acac)2is gradually reacted with DT to form intermediate compound C12H25-S-Ni-S-C12H25; subsequently, the intermediate compound is decomposed at high temperature to form NiS nanosheets; finally, the in-situ obtained NiS nanosheets are oriented aggregation during ripening stage and evolved into small quantum rods. Except for the strong absorption in ultraviolet region, an obvious and broad absorption peak centered at about559nm also can be observed from the Uv-vis absorption spectrum of the obtained NiS quantum rods. In addition, under the excitation of the light with the wavelength of295nm, the obtained NiS quantum rods exhibit a broad emission band in the ultraviolet region, which is splitted into two emission peaks centered at about332and343nm, respectively. Furthermore, the magnetic measurements demonstrate that the obtained NiS quantum rods possess superparamagnetic property.