Ammonia Effects In Nanomaterials Controlled Synthesis

Nanomaterials can be used in many fields such as information, energy, environment protection and medicine and have attracted great attentions due to their special physical and chemical properties. Since nanomaterials with different morphologies and different exposed faces have different properties, therefore, it is a research subject to controlled synthesize nanomaterials with different morphologies and different exposed faces.In this thesis, a series of namomaterials with different morphologies and different exposed faces such as α-Fe2O3, ZnSn(OH)6, CuO, Cu2O, Zn2SnO4/SnO2composites and the Prussian blue like Co3[Co(CN)6]2·xH2O were successfully synthesized through hydrothermal method by using NH3·H2O as alkali source, complex agent or eroding agent under different conditions. The growth mechanisms were discussed, and the properties of the as-prepared nanomaterials were studied, and we also discussed the relationship between the structure and the properties. The main contents of this thesis are summarized as follows:1. Ammonia and metal ions co-controlled synthesis in high-index faced α-Fe2O3nanocrystals:High-index facets usually have higher surface energy and more adatoms, vacancies and kinks, which makes the high-index facets have better activities in photo-and electro-catalysis and have special applications in optical, electrical, sonic, and magnetic devices. However, during the crystal growth, high-index facets usually have fast growth rates due to the high surface energy and ultimately disappear. In this chapter, a-Fe2O3nanostructures with different sets of high-index facets were controlled synthesized by applying different metal ions as structure-directing agents and excessive NH3H2O as alkali source and coordination agent. The growths of the a-Fe2O3nanostructures with high index facets were induced by metal ions and well-defined quasi-cubic, dodecahedral, oblique parallelepiped and hexagonal planar a-Fe2O3nanocrystals could be obtained separately in high yields controlled by Ni2+Zn2+, Cu2+, Mg2+and Al3+, respectively. Magnetic studies uncover that these four forms of iron oxide have distinct differences. The hexagonal bipyramid iron oxide nanocrystals might be spin-canted ferromagnetically controlled at room temperature and the ferromagnetism disappears at temperatures lower than TM. The quasi-cubic, the oblique parallelepiped and the hexagonal planar nanocrystals have a splitting between FC curve and ZFC curve from the highest experimental temperature and no Morin transformation occurs, indicating that some degree of spontaneous moment exists over the entire temperature range and defect ferromagnetically controlled at room and low temperature.2. Synthesis and properties of ZnSn(OH)6and Zn2SnO4/SnO2hollow spheres: Hollow multi-cation metal oxides nanomaterials or multifunctional nanocomposites have attracted a great deal of interests due to their large reaction surface area and multi-bandgap, which would make them have great application potentials in many fields such as robust catalysts/carriers, gas sensors, electrodes in dye-sensitized solar cells and Li-ion batteries. In this chapter, uniform ternary compound ZnSn(OH)6hard spheres were successfully prepared through a simple hydrothermal method with a water-soluble biopolymer sodium alginate as crystal growth modifiers and ammonia as basic source. The hollow ZnSn(OH)6hard spheres were obtained by eroding the ZnSn(OH)6spheres with ammonia under hydrothermal conditions, while the hollow Zn2Sn04/SnO2spheres were obtained by calcining the hard ZnSn(OH)6spheres in air at600℃. Gas sensor tests demonstrated that the hollow ZnSn(OH)6spheres have a better response to ethanol than that of the hard ZnSn(OH)6spheres. As electrode material of dye-sensitized solar cells, hollow ZmSnO4/SnO2spheres have a very good efficiency of4.52%, exceeding the highest efficiency reported for Zn2SnO4(3.8%) fabricated and much higher than that reported for SnO2(1.2%). Maybe in the composite system, multi-bandgap or multi-junction semiconductor materials can absorb a greater portion of sunlight to enhance the efficiency of the solar cells.3. CuO hollow spheres synthesis by ammonia eroding and photocatalytic properies:With a direct band gap of1.2eV, CuO can be used as ultraviolet and visible-light photocatalyst for photo-degradation of dyes in wastewater treatment. In this chapter, the monodisperse CuO spheres were successfully fabricated with the assistance of the water soluble biopolymer sodium alginate in NH3·H2O solution. The hard CuO nanospheres can be corroded by ammonia to form hollow CuO nanospheres under hydrothermal conditions. Their visible-light photocatalytic activities were investigated and the results show that both of the hard and the hollow CuO spheres have great visible-light photocatalytic abilities for the photodegradation of dyes. Especially, it only takes1min for50mg of CuO hollow spheres to photodegrade100mL of50mg/L Methyl Blue (MB) solution by using the solar light and without the assistance of any equipment, while for50mg of P25(TiO2), it takes more than30min even under UV irradiation.4. Three-dimensional network nanomaterials synthesis by ammonia eroding:In favor of electron conveying, three-dimensional networks, can be used in many fields such as electro-or photo-catalysis, energy storage. With the assistance of the water soluble biopolymer sodium alginate and NH3-H2O as alkali source and eroding agent, we successfully synthesized three-dimensional network Cu2O microspheres. With NH3-H2O as eroding agent, we also prepared three-dimensional network the Prussian blue like Co3[Co(CN)e]2·xH2O octahedral microcrystals.