Biological/organic Molecules Assisted Liquid-phase Synthesis And Properties Of Nano-materials

The synthesis and design of nanometerials is the most promising research area for nanoscience, and it is also the base of the application and future development of nanotechnology. Due to the unique properties, small size effect, surface effect and quantum size effect, etc, which are different from their bulk substances, nanomaterials have great potential applications in the fields such as catalysis, environmental protection, bio-medicine, etc. The size and shape of the inorganic micro-nanomaterials have great influence on their physical and chemical properties. Thus, the synthesis and properties characterization of inorganic nanomaterials with controllable size, distribution, morphologies and structures are very important for the basical and applied research of new nanomaterials. In this dissertation, several different synthesis methods have successfully developed for synthesizing nano-structured materials with controlled morphology. By adjusting the reactant concentration, reaction time, reaction temperature and reactant ratio, we synthesize oxide (SnO₂), two carbonate (BaCO₃, SrCO₃) and NiFe₂O₄ nanocrystals@graphene composite with controllable morphology and size. The morphology, structure and components of the obtained products are characterized and analyzed by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM) /high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-visible absorption spectroscopy (UV-Vis), etc. The formation mechanisms of the as-synthesized nanostructures are discussed and their properties are also investigated. The main results and innovative achievements are summarized as follows:1. SnO₂ nanocrystals were prepared by using a biomolecule (L-lysine)-assisted hydrothermal method. The as-synthesized products were characterized by XRD, Raman, FT-IR and TEM/HRTEM. The reaction parameters, including the concentrations of biomolecule or the ratio of the SnCl4/L-lysine, reaction temperature and time, had little effect on the size and shape of the as-synthesized SnO₂ nanocrystals. This synthesis route led to almost monodisperse products with particle sizes below 10 nm. The L-lysine functioned as both a source of alkali and a chelating agent. The as-synthesized nanocrystalline SnO₂ had excellent phtotcatalytic degradation of RhB under UV irradiation which was attributed to the more oxygen vacancies on the surface of the nanocrytalline SnO₂. The photocatalytic activity of the SnO₂ nanocrystalline was optimized. Under the basic condition(pH=8), SnO₂ nanocrystals synthesized at 180℃held the best catalytic property activit with the degradation of RhB, close to 100% within 150 min.2. Shape-controlled crystallization and self-assembly of high-ordered BaCO₃ architectures were synthesized by using dextran as the structure directing agents in aqueous solution. The phases, morphologies and structures of the products were characterized by XRD, SEM, TEM, HRTEM and FT-IR spectrophotometer. Dendrite-like, dumbbell-like, and spherical BaCO₃ complex nanostructures were obtained by tuning the experimental parameters such as the concentration of dextran, the concentration of Ba2+ cations and reaction time. The formation of dendrite-like, dumbbell-like, and spherical complex nanostructures could be explained by a rod-dumbbell-sphere (RDS) self-assembly growth mechanism. The surface properties of BaCO₃ crystals were successfully modified to be superhydrophobic using fluorosilane as modifier. The superhydrophobicity of BaCO₃ complex nanostructures was attributed to the combination of chemical composition and the textured topography. The superhydrophobic properties of as-resulted products may have potential applications as filler in composite materials.3. We reported the biomineralization in vitro of SrCO₃ complex nanostructures obtained by using glucosan as the modifier in the dimethyl formamide (DMF)-deionized water (DIW) mixed solvents. Rod-, dendrite-, dumbbell-, and sphere-like SrCO₃ nanostructures were achieved by tuning the volume ratio of DMF/DIW, reaction time, and concentrations. The phase, structure, and morphology of the as-obtained products were characterized by XRD, SEM, TEM, HRTEM, FT-IR spectroscopy, and Bunauer-Emmett-Teller (BET) analysis. The possible formation mechanism of SrCO₃ complex nanostructures follows the rod-dumbbell-sphere growth process. Both higher DMF/DIW ratios (i.e., more DMF molecules) and larger glucosan concentrations in the mineralization process were in favor of the self-assembly process, due to more hydrogen bonds may formed in the system,which led to the formation of dumbbells and spheres. The as-synthesized SrCO₃ complex nanostructures had excellent adsorption properties and superhydrophobicity, which may open up a wide range of potential applications in environmental protection.4. NiFe₂O₄ nanocrystals@graphene composite (NFGC) was synthesized via a simple chemical deposition method by using graphene oxide as a precursor. The as-synthesized product was systematically characterized by XRD, FT-IR, Raman,TEM, HRTEM, XPS, respectively. The magnetic property of the NiFe₂O₄ nanocrystals@graphene composite was also investigated. The results shown that the NiFe₂O₄ nanocrystals homogeneously anchored to the graphene sheets were well-crystallized particles, with an average size of 10-15 nm. Magnetic measurement reveals the NiFe₂O₄ nanocrystals@graphene composite was superparamagnetic with a saturation magnetization of 46.2 emu·g^-1, a coercivity of 11.2 Oe and remanence effect of 0.583 emu·g^-1.