Controllable Synthesis, Magnetic And Catalytic Properties Of Micro-/Nano-structures Of Binary Alloys Based On Fe, Co And Ni

Magnetic alloys materials are very important functional materials, which have attracted extensive attention because of their special physical, chemical properties and their potential applications in ferrofluids, magnetic resonance imaging, biotechnology, biomedicine, data storage, catalytsis, and environmental remediation, etc., and which strongly depended on their size, morphology, composition, and structure etc. In this thesis, we focused on developing different methods to synthesize magnetic binary alloys micro-/nanostructures based on Fe, Co and Ni with different morphologies, sizes, and compositions. At the same time, their formation mechanism, magnetic properties, and catalytic applications in reduction of 4-Nitrophenol were studied. The main contents and major results are given as follows:1. Uniform-sized, monodisperse, and single crystalline 3-dimensional NiCo₂ dendritic microstructures were successfully synthesized in high yield by a simple and facile solution phase route in presence of CTAB. By adjusting the experimental parameters NiCo alloys nanostructures with different morphologies, sizes, and compositions were controllable synthesized, at the same time, the formation mechanism was investigated. While NiCo₂ alloys micro-structure with shapes of sphere-like and flower-like were prepared by hydrothermal and solvothermal methods, respectively. Magnetic measurements revealed that all of the NiCo₂ alloys obtained are ferromagnetic at room temperature. The saturation magnetization value of the Ni_33.8Co_66.2 dendrites (163.55 emu/g) is lower than that of the Ni_32.3Co_67.7 spheres (212.29 emu/g) and Ni33.4Co66.6 flower-likes (195.79 emu/g), but the Ni_33.8Co_66.2 dendritic structures exhibit an enhanced coercivity value. NiCo₂ alloys with different shapes (Ni_33.8Co_66.2 dendrites, Ni33.4Co66.6 flower-likes and Ni_32.3Co_67.7 spheres) have been used as reusable heterogeneous catalysts to reduce 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) by NaBH4. From the average reaction rate constants at three different temperatures, we determined the activation energy, the entropy of activation, and the pre-exponential factor for each shape of NiCo₂ alloys. The kinetic data indicate that Ni_33.8Co_66.2 dendrites are catalytically more active than that of both the Ni33.4Co66.6 flower-likes and Ni_32.3Co_67.7 spheres probably due to its largest surface-to-volume ratio and surface areas.2. The Ni-based metals, such as Ni, and FeNi alloy nanostructures with different shapes were synthesized by solvothermal method in polyol system. The reaction parameters such as reaction time, the concentration of NaOH, temperature, solvent, and the initial concentration of metals ions that affected the morphology of FeNi alloys were investigated systematically. When we changed the type of solvents, the Ni nanostructures with chain-like were obtained, and the possible formation mechanism was also discussed. Magnetic data show that all of the Ni and FeNi2 alloys obtained are ferromagnetic at room temperature. The saturation magnetization value of the Fe34.8Ni65.2 spheres with size of ca. 300 nm (174.62 emu/g) is higher than that of the Fe34.1Ni65.9 spheres with size of ca. 230 nm (166.71 emu/g) and Fe_33.5Ni_66.5 spheres with size of ca. 170 nm (160.05 emu/g), but the Fe_33.5Ni_66.5 spheres (ca. 170 nm) exhibit an enhanced coercivity value. The saturation magnetization value of the chain-like Ni nanostructures (68.3 emu/g) is lower than that of flower-like Ni nanostreutures (84.9 emu/g), but all higher than that of the bulk nickel (55 emu/g). Especially, the flower-like Ni nanostructures exhibit an enhanced coercivity value (ca. 204.81 Oe). At last, the FeNi2 alloys with three different sizes were applied to reduce the 4-Nitrophenol to 4-Aminophenol by NaBH4 in aqueous solution, and the reaction rate constants were obtained. The kinetic data indicate that Fe_33.5Ni_66.5 nanospheres (ca. 170 nm) are catalytically more active than that of both the Fe34.1Ni65.9 nanospheres (ca. 230 nm) and Fe34.8Ni65.2 nanospheres (ca. 300 nm) probably attribute to its smallest size, which induces the largest surface-to-volume ratio and surface areas. The BET3. Crystalline FeCo alloys (Fe59Co41, Fe37Co63) nanoparticles in diameter of 6?12 nm were synthesized by reduction of FeCl3 with hydrazine under ultrasonic wave, which is a simple, low-cost, surfactant-free route, and may stimulate technological interests. The reaction parameters such as temperature, the total concentration of [Fe3+] + [Co₂+], and the initial ratio of Fe3+/Co₂+ that affected the FeCo sizes and morphologies were investigated systematically. As-synthesized Fe59Co41 nanocrystallite shows excellent soft magnetic behaviour with high saturation magnetization up to 216.2 emu/g that is comparable with that of bulk Fe and Fe60Co40 alloy, and could have applications in catalysis, biotechnology, and magnetic storage devices.4. The metals/r-graphene and alloys/r-graphene hybrid materials, such as Ni/r-graphene, Co/r-graphene, Cu/r-graphene, NiCo/r-graphene, FeCo/r-graphene, FeNi/r-graphene, CoCu/r-graphene and NiCu/r-graphene hybrid materials were successfully synthesized by a fiacle two steps method used hydrazine as reduction reagent. The samples were characterizated by SEM, TEM, HRTEM, XRD, EDX, and ICP, respectively, the results shown that the nanoparticles were uniform dispersed on the surface of the graphene sheets. The reaction parameters such as reaction time, the concentration of metals ions, the modified of graphene, and the added sequence of the materials that affected the formation of hybrid materials were investigated systematically, based on which possible formation mechanism for the hybrid materials was proposed. The room temperature magnetic properties were characterizated by SQUID (MPMS XL-7), the metal or alloy/r-graphene hybrid materials exhibited an enhanced saturation magnetization or coercivity. At last, the reduction of 4-NP to 4-AP were carried out used five different materials as catalysts. The rate constants of the five catalysts is 5.82×10-3 S^-1(S1, Ni/r-graphene), 4.63×10-3 S^-1(S2, Ni/r-graphene), 4.95×10-3 S^-1(S3, Ni/r-graphene), 2.60×10-3 S^-1(r-graphene), 3.50×10-3 S^-1(Ni nanoparticles), 4.15×10-3 S^-1(the mixture of Ni nanoparticles and r-graphene), respectively. Here, the r-graphene shows a good catalytic property for this reduction reaction, which was needed further investigation.