Preparation, Morphology Control, Assembly Of Hollow Microspheres And Their Properties

Hollow micro/nanospheres have attracted tremendous interest in the past decades due to their well-defined morphology, low density, large surface area, functional characteristics and a wide range of potential applications, such as nanoscale chemical reactors, catalysts, drug delivery, pigments, photonic crystals, supercapacitors, lithium-ion batteries, gas sensors, pollutant removal and photodetection. Much effort has been made in developing new synhteisis methods, such as hard or soft templating, nanoscale kirkendall effect, galvanic replacement, and ostwalk ripening method. However, how to facilely synthesize hollow spheres having special structure and better properties is one of the biggest challenges. Another big challenge is how to obtain high-quality nanofilms of hollow spheres since two-dimensional or three-dimensional ordered suprestructures exhibit enhanced even novel properties and promising applications toward optical, electronic nanodevices. In this thesis, a general and facile method based on the in-situ polymer diffusion was developed for the fabrication of polymer/inorganic bilayer hybrid hollow spheres, which showed some special properties. This method was further used to synthesize meso-microporous Ta3N5hollow spheres with high efficient visible light-driven photocatalytic activity. We also use the Ta3N5hollow spheres as precursors to prepare uniform and well-defined single-crystal sodium tantalate cubes. Finally, high-quality multilayer Ta3N5hollow sphere-nanofilms were fabricated by combination of an oil-water interfacial self-assembly strategy and the controlled sol-gel reaction of precursors. The as-prepared Ta3N5hollow sphere-nanofilms exhibited enhanced photoelectrochemical water splitting ability. All the research content and results are summarized as follows:(1) A general and feasible method was developed for the fabrication of polymer/inorganic bilayer hybrid hollow spheres with inner shell rich of polymer and outer shell rich of inorganic components, such as PSAA/ZrO2, PSAA/Nb2O5, PSAA/Ta2O5and PSAM/TiO2. The formation process of these hybrid hollow spheres was studied in detail and an in-situ polymer diffusion mechanism similar to the Kirkendall effect was presented. Unlike pure inorganic and polymeric hollow spheres, the as-obtained hybrid hollow spheres showed tunable surface properties, high Vis-NIR reflectance, low thermal conductivity and good compatibility to polymers, which gives them some interesting applications like solar-reflective heat-insulating coatings.(2) Monodisperse meso-microporous Ta3N5hollow spheres have been synthesized by a feasible "one-pot" method based on an in-situ polymer diffusion mechanism and subsequent thermal nitridation. The unique meso-microporous shell structure, and the high specific surface area and pore volume of Ta3N5hollow spheres are also favorable for reagent adsorption and light harvesting through multireflection and scattering. Compared with TiO2(P25) and Ta3N5nanoparticles, the Ta3N5hollow spheres show much higher light-driven photocatalytic activity.(3) Uniform and well-defined single-crystal NaTaO3cubes were successfully synthesized through a solvothermal method using monodisperse meso-microporous Ta3N5hollow spheres as precursors. The structure and morphology of NaTaO3cubes were carefully investigated. The results show that the formation of NaTaO3cubes follows the dissolution-recrystallization mechanism, and use of monodisperse Ta3N5hollow spheres with a thin shell thickness as precursors is critical to obtain the uniform cube morphology of the products. The size of the NaTaO3cubes can be tunable by adjusting the ratio of ethanol to water. Due to the highly monodisperse size and shape, the cubes can be further self-assembled into a high quality monolayer nanofilm.(4) We presents the first successfully fabrication of multilayer Ta3N5hollow sphere-nanofilms with precisely tunable layer numbers based on an oil-water interfacial self-assembly strategy and by controlling the sol-gel reaction of precursors. The controllable polymer nanofilms, strong interactions between the surfaces of polymer colloidal particles and inorganic particles, and the relatively high hydrolysis and condensation rates of the tantalum precursors were found to be vital to the formation of high-quality hollow sphere multilayer nanofilms. The as-obtained Ta3N5hollow sphere-nanofilms exhibited significantly enhanced PEC water splitting efficiency, and the photoelectrochemical behavior strongly depended on the layer numbers and structures.