Controlled Synthesis And Properties Study Of Graphene-Magnetic Spinel Ferrite Multifunctional Heteroarchitecture

In recent years, the arising of carbon nano-materials provides the potential to the application of more and more high efficient catalysts and good performance electrode materials. As a new carbon nano-material and a monolayer of carbon atoms packed into a dense honeycomb crystal structure, graphene has attracted extraordinary interest for fundamental studies as well as for potential applications. Due to the unique two-dimensional conjugated structure, exceptional physical and chemical properties, graphene based materials have shown promising applications in electronics, sensors, photocatalysis, supercapacitor and lithium-ion batteries, etc. In this dissertation, a series of graphene-magnetic spinel ferrite multifunctional heteroarchitectures were designed and prepared via a one-step hydrothermal method, and investigate their adsorption properties, photocatalytic performance under visible light irradiation and electrochemical behaviors for use as the anode in lithium-ion batteries (LIBs). Graphene and magnetic spinel ferrite composite can achieve complementary advantages between the two of them in performance, thus it is probable to develop high performance multifunctional heteroarchitectures based on such combinations. The main contributions of this dissertation are described as follows:1. The design and synthesis of graphene-magnetic spinel ferrite multifunctional heteroarchitecture.Graphene oxide (GO) is a widely used graphene derivatives with rich oxygen-containing groups like hydroxyl, carboxyl and epoxy, etc. Because of its good dispersibility in both water and many organic solvents, it is considered as an excellent substrate for constructing nanostructures. The functional groups can act as anchor sites and consequently make the in situ formed nanocrystals attach on the surface and edges of GO sheets. Graphene-magnetic spinel ferrite multifunctional heteroarchitectures can be controlled prepared via soft chemistry method, using metal (Fe, Zn, Co, Ni, Cu, Mn etc.) salts as metal sources and graphene as support material. Graphene-magnetic spinel ferrite multifunctional heteroarchitectures were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and nitrogen adsorptionedesorption isotherms techniques. The results showed that the graphene and magnetic spinel ferrite composite can effectively control the morphology, size and dispersion of magnetic spinel ferrite particles.2. The adsorption properties study of the graphene-magnetic spinel ferrite multifunctional heteroarchitectures.To investigate the adsorption of the graphene-magnetic spinel ferrite multifunctional heteroarchitectures, the usual contaminant methylene blue (MB) was selected as the model compound. The results showed that the graphene-magnetic spinel ferrite multifunctional heteroarchitectures have great potential as an effective absorbent for removing MB in water, due to its high adsorption capacity and convenient magnetic separation. At298K, the adsorption approached to equilibrium in1h. The adsorption kinetics investigation revealed that the adsorption of MB from aqueous solution over the graphene-magnetic spinel ferrite multifunctional heteroarchitectures followed pseudo-second-order kinetic model. The adsorption isotherms fitted well with the Langmuir equation, which can be explained as a monolayer adsorption.3. The photocatalytic performance and photodegradation mechanism study of the graphene-magnetic spinel ferrite multifunctional heteroarchitecture as photocatalyst under visible light irradiation.The photocatalytic activities of the graphene-magnetic spinel ferrite multifunctional heteroarchitecture and pure magnetic spinel ferrite photocatalysts were evaluated by the degradation of MB, methyl orange (MO), Rhodamine B (RhB) and active black BL-G under visible light irradiation. It is very interesting that the combination of magnetic spinel ferrite nanoparticles with graphene results in a dramatic conversion of the inert magnetic spinel ferrite into a highly active catalyst for the degradation of MB, RhB, MO and active black BL-G under visible light irradiation. The significant enhancement in photoactivity under visible light irradiation can be attributed to the remarkable synergistic effect of the combination of magnetic spinel ferrite and the graphene sheets, leading to the efficient separation of photogenerated electrons and holes in the graphene-magnetic spinel ferrite multifunctional heteroarchitecture. Hydroxyl radicals play the role of main oxidant in the graphene-magnetic spinel ferrite multifunctional heteroarchitecture and the radicals’ oxidation reaction is obviously dominant. Moreover, the graphene-magnetic spinel ferrite multifunctional heteroarchitectures themselves have a strong magnetic property, which can be used for magnetic separation in a suspension system.4. The storing electricity performance and mechanism study of graphene-magnetic spinel ferrite multifunctional heteroarchitecture as the anode material for lithium-ion batteries. The electrochemical behavior of the graphene-magnetic spinel ferrite multifunctional heteroarchitecture used as anode material for lithium ion batteries was studied. In contrast with pure magnetic spinel ferrite electrode, the reversible capacity, the cycle performanc and the rate capability of the graphene-magnetic spinel ferrite multifunctional heteroarchitecture electrode can be significantly improved. The superior electrochemical performance of the graphene-magnetic spinel ferrite multifunctional heteroarchitecture electrode can be attributed to its unique heteroarchitechture, leading to the remarkable synergistic effectt between magnetic spinel ferrite and the graphene nanosheets. The graphene-magnetic spinel ferrite multifunctional heteroarchitecture can provide a high electrode/electrolyte interface area and more lithiuminsertion/extraction sites, facilitating fast charge transfer between the active material and the electrolyte. The unique heteroarchitechture of graphene-magnetic spinel ferrite possesses good stability during the charge/discharge process due to the flexible two-dimensional network structure of graphene sheets, which could provide an elastic buffer space to accommodate the volume expansion/contraction of magnetic spinel ferrite nanoparticles, thus resulting in excellent cycling stability. The two-dimensional graphene nanosheets in the graphene-magnetic spinel ferrite multifunctional heteroarchitecture with excellent electrical conductivity can serve as the conductive medium between the magnetic spinel ferrite nanoparticles and the current collector. The charge carriers could be effectively and rapidly conducted back and forth from the magnetic spinel ferrite nanoparticles to the current collector through the highly conductive graphene nanosheets, resulting in good rate capability.5. The BiVO4-CoFe2O4-graphene heteroarchitecture catalyst and its high photocatalytic performance under visible light irradiation.Firstly, BiVO4-graphene heteroarchitecture was prepared by a facile one-step hydrothermal method and characterized by XRD, FTIR, Raman spectroscopy, XPS, EDS, TEM, and FESEM techniques. The results showed that the graphene sheets in this heteroarchitecture were exfoliated and decorated by leaf-like BiVO4lamellas with an average lamellas size of1-1.3μm and a thickness about15nm, while ruleless and hard aggregated BiV04particles were obtained without graphene oxide. Such results indicated that the graphene can play a role as a template which made BiV04crystals grow along certain directions, forming leaf-like lamellas. In comparison with the pure BiVO4catalyst, the BiVO4-graphene heteroarchitecture system revealed much higher photocatalytic activity for degradation of methyl orange (MO), methylene blue (MB), Rhodamine B (RhB) and active black BL-G in water under visible light irradiation due to the concerted effects of BiVO4and graphene sheets or their integrated properties. Secondly, BiVO4-CoFe2O4-graphene heteroarchitecture catalyst was prepared by a facile one-step hydrothermal method. The results show that BiVO4and CoFe2O4nanoparticles were loaded onto the surface of graphene sheets. In contrast with pure BiVO4and CoFe2O4, the BiVO4-CoFe2O4-graphene heteroarchitecture not only has a strong magnetic property, which can be used for magnetic separation in a suspension system, but also gave the higher photocatalytic activity.