| Nano-magnetic powders/graphene hybrids have been applicated in various fields, including environments, energy, biomedicine, catalysis and so on, owning to its stable chemical and physical properties. Therefore, the fabrication of nano-magnetic powders/graphene hybrids has attracted much attention in recent years. In the thesis, the achievements are as follows:1. Shape-cotrolled synthesis and magnetic properties of monodispersed Fe3O4nanoparticles through thermal decompositionMonodispersed hexagonal Fe3O4nanocrystals with high-energy facets were successfully synthesized through a facile modified thermal decomposition method using low-cost1,2-duodecanediol as reducing agent. The shape of the nanocrystals could be easily controlled among spherical, cubic and hexagonal shape by adjusting the molar ratio of surfactants. The hexagonal nanocrystals are proved to have a truncated octahedral shape by analyzing the HRTEM photographs of more than one hundred nanoparticles and STEM images of individual nanocrystals. The truncated octahedral nanocrystals have a large percentage of high-energy{100} and{111} facets exposed, which is thermodynamically unstable. Magnetic measurements show that the truncated octahedral nanocrystals behave ferromagnetic at room temperatures. These Fe3O4nanocrystals could self-assemble into two-dimensional and three-dimensional superlattices. The corresponding FFT patterns show that the super crystal is a bcc structure. Our work reveals that the non-spherical superlattice may be applied in a new generation of nanodevices.2. Fabrication of FeO4graphene hybrids and their magnetic properiesNovel Fe3O4graphene hybrids for applications including microwave-absorbing materials have been fabricated by a simple polyol method, and their morphology, chemistry and crystal structure have been characterized at the nanoscale. It is found that each Fe3O4graphene nanocomposite has a polycrystalline with an fcc spinel structure and an uniform chemical phase. It is suggested that individual Fe3O4nanoparticles chemically bond to the graphene sheets based on the analysis of Raman, FT-IR spectroscopy, thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Microwave absorption measurement shows that the light-weight Fe3O4/graphene hybrids/paraffins (50wt%) composites have a maximum RL value of-30.1dB at a1.48mm matching thickness and17.2GHz matching frequency, suggesting a good quality of electromagnetic wave absorption. Theoretical analysis using transmission line theory and quarter-wave principles is adapted to describe the microwave absorption behavior of the Fe3O4/graphene hybrids/paraffins (50wt%) composites.3. Fabrication of FeCo/graphene hybrids and their magnetic properiesFeCo/graphene hybrids have been fabricated by a simple polyol method followed by annealing in H2, and their morphology, chemistry and crystal structure have been characterized at the nanoscale. Microwave absorption measurement shows that the light-weight FeCo/graphene hybrids/paraffins (50wt%) composites are good quality of electromagnetic wave absorption in comparison with CoFe2O4and CoFe2O4/graphene hybrids. The reflection loss value is above-10dB in the frequency range of1.5-18GHz, when the thickness of the absorber was in the range of1.5-10mm. And the light-weight FeCo/graphene hybrids/paraffins (50wt%) composites have a maximum RL value of-40dB at a2.5mm matching thickness and9GHz matching frequency. Theoretical analysis using transmission line theory and quarter-wave principles is adapted to describe the microwave absorption behavior of the FeCo/graphene hybrids/paraffins (50wt%) composites.4. Fabrication of Fe/graphene hybrids and their magnetic properiesFe/graphene hybrids were prepared by a simple reduced method, and their microwave absorption properties were studied. Microwave absorption measurement shows that the light-weight Fe/graphene hybrids/paraffins (70wt%) composites are good quality of electromagnetic wave absorption. The light-weight Fe/graphene hybrids/paraffins (70wt%) have a maximum RL value of-43dB at a2.6mm matching thickness and2.5GHz matching frequency. Theoretical analysis using transmission line theory and quarter-wave principles is adapted to describe the microwave absorption behavior of the Fe/graphene hybrids.5. Fabrication of Fe3O4/graphene hybrids for lipase immobilizationGraphene decorated with magnetic Fe3O4nanoparticles are used to immobilize porcine pancreatic lipase for the first time. Fe3O4nanoparticles are found to be chemically bonded onto graphene sheets. Fe3O4/graphene hybrids show an excellent efficiency of immobilizing porcine pancreatic lipase, but, greatly dependent on the pH value, temperature and denaturant. The porcine pancreatic lipase immobilized on Fe3O4/graphene hybrids becomes recyclable and have a remarkable thermal-stability in comparison with a free porcine pancreatic lipase. Our work demonstrates that Fe3O4/graphene hybrids are high-quality and novel carriers for immobilizing lipase, which could be a good candidate for lipase immobilization. |
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