Construction Of Micro/Nanostructural Transition Metal (Fe/Mo) Oxide And Their Applications

In order to overcome the problems of environmental pollution and impending exhaustion of fossil fuels, we need to control pollution sources and to support the sustainable usage of green and clean energy sources, such as:nuclear energy, solar energy, chemical energy and so on. Transition metal oxides have been one of the most promising materials used as the photocatalysts or promising anode materials in lithium ion batteries, due to their excellent physical and chemical properties. However, to meet the requirements of practical applications, people had put forward higher requirements of the performances of the ransition metal oxides. It has reported that nano-scale materials with different morphologies, sizes and structures can greatly increase the performance of the metal oxide electrodes. Therefore, iron and molybdenum-based oxide with different structures and morphologies were obtained by different methods and used in photocatalysis and lithium ion battery areas. The main parts of this thesis including:Chapter1mainly described the research background, synthesis methods, development status and potential applications of iron and molybdenum-based oxide materials. Besides, the working principles of photocatalysis and lithium ion battery techniques as well as the improve method of the performance of the materials were included.In Chapter2, we provides a novel route for the preparation of α-Fe2O3nanocubes by a facile, one-step procedure through a noncovalent composite interaction between polyvinyl chloride (PVC, a polymer) and potassium ferrocyanide (PF, a coordination compound) with an initial molar ratio of20:1. Temperature-dependent sintering experiments proved that the α-Fe2O3nanocubes were derived from a structural transformation from nanoplates emerged at lower temperatures, suggesting condition optimization process of the2D plate structure to the3D cubic structure. A series of independent experiments including Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy and conductivity were performed to explain the presence of the composite interaction. Finally, our data indicate that the as-prepared α-Fe2O3nanocubes exhibited a higher lithium storage capacity and better cycling performance than the α-Fe2O3nanoparticles with irregular shapes.Chapter3discussed the Fe3O4nanomaterial with a highly symmetric octadecahedral nanobox structure was constructed by the addition of β-cyclodextrin as a protective agent. A series of composites (CM-1-CM-4) of polyethylene glycol (PEG) and the Fe3O4nanoparticles with different initial mass ratios were prepared through colloid chemistry processes. We found experimental evidence of the shape-dependence of the PEG composites on the amount of Fe3O4nanoparticles. In particular, the melting process of PEG is not only influenced by the presence of Fe3O4nanoparticles, but also directly associated with the amount of Fe3O4. Further, we noticed that the crystallinity of PEG is lowered upon compositing with Fe3O4nanoparticles, and becomes lower and lower with increasing Fe3O4nanoparticles with the exception of the composite CM-4. Moreover, our results indicate that the PEG composites present strong surface-enhanced Raman scattering for organic dyes, dependent on the amount of Fe3O4nanoparticles in the composites.In Chapter4, a variety of α-MoO3nanostructures, including1D nanobelts,2D nanolayers and3D nanoparticles, were prepared via three methods:sintering AMT, sintering aggregates of AMT with PEGs, and oxidating MoO2. Our results suggested that the surface structures of the α-MoO3crystals obtained can be controlled by preparation conditions, including sintering temperatures, sintering times and starting materials. Also, this work provided a paradigm for the structural regulation of α-MoO3crystals from3D to1D to2D. Further, the electron structures, photoluminescence performances and photocatalytic properties of the α-MoO3crystals were investigated. It was found that they were highly dependent on surface features of the α-MoO3crystals. Overall these results could be potentially useful for new crystal design and growth of inorganic nanomaterials.In Chapter5, a highly monodisperse Cu3Mo2O9micropompon structure was successfully created by an ethylenediaminetetraacetic acid (H4Y)-mediated hydrothermal route and a subsequent sintering process. We considered that H4Y, a strong competitive chelating ligand, played a significant role in prohibiting the formation of the intermediate (NH4)2Cu(MoO4)2, thereby not only producing a monodisperse structure of Cu3(OH)2(Mo04)2but also reducing the size of the structure by forming a stable complex:CuY. Our data demonstrated that the Cu3Mo2O9material exhibited excellent photocatalytic efficiency for the degradation of Congo red under visible light irradiation. Also, the time-dependent photoresponse of the Cu3MoO9gave a very high ratio of light current to dark current and a stable photocurrent density. Further, the material indicated good charge-discharge stability and high coulombic efficiency in lithium-ion batteries even during the100cycles. We believe that the present study represents a significant step in the development of transition metal molybdates.In Chapter6, we report on a new possibility of a controlled structural transition from ACM to CMOH by changing pH in water. A series of CMOH nanomaterials with different dimensions (from1D nanorods,2D nanobelts, to3D nanoparticles) were successfully constructed using dissolution/precipitation equilibrium between the two transition metal molybdates. Moreover, there are no significant structural and dimensional changes as a result of the transformation procedure from CMOH to CM. Further, two nanomaterials:CM-1nanorods and CM-2nanoplates were obtained through this transformation process and evaluated with respect to their possible application in LIBs. Our data provide strong evidence that the CM-2nanoplates exhibit greatly enhanced lithium storage properties, including very high storage capacity, extremely high coulombic efficiency and excellent cycling stability, compared to the other structures such us nanorods, microflowers and so on. It can be attributed to ultrafine particle size, very thin planar structure and large surface area.In Chapter7, leveling effects were found during the thermal decomposition of PEGs compositing with AMT. Three parameters:LS, LD and SD were proposed to estimate the span, intensity and dispersion of leveling effects. Leveling abilities of different inorganic salts to the thermal stability of three series of polymers (PEGs, PPGs and PVCs) were discussed and compared. Our result showed that there is a relatively strong interaction between ammonium salts and PEG chains to result in a change of the conformation of PEG chains from a folded state to an extended state. Also, this interaction greatly impaired the interaction between the PEG chains, leading to a change in the pyrolysis mode of the polymer. The two changes of PEG chains upon compositing are suggested to be the origin of leveling effects.In Chaper8, the works presented in the thesis are concluded and future research on construction of transition metal Fe/Mo oxide micro/nanostructures and their applications research are proposed.