Self-assembly Of Nanocrystallites Research Articles

Direct synthesis of hollow polyhedral ceria nano powders via a template-free mixed solvothermal route

Novel mono-dispersed hollow polyhedral ceria nano powders with the average particle size of 250 nm were directly synthesized via a simple template-free mixed solvothermal method by using water-ethanol as the solvent. The formation of such hollow structure with the regular polyhedral particle shape was based on a solvent-controlled Ostwald ripening coupled self-templating process. The mixed solvent promoted the formation of the regular solid particles at the beginning of solvothermal reaction and drove the Ostwald ripening as the reaction went on. Owing to the Ostwald ripening and self-assembly of nano crystallites, ceria nano particles converted into the hollow structures with regular polyhedral shape during the solvothermal process just by increasing solvothermal reaction time. The as-synthesized hollow ceria nano powders exhibited strong absorptions in the UV-vis spectrum and the evaluated energy band gaps increased according to the shape evolution and size decrease of the nano particles, which demonstrated obvious blue shift effects.

Hydrothermal synthesis, characterization and formation mechanism of self-assembled mesoporous SrTiO3 spheres assisted with Na2SiO3·9H2O

Mesoporous SrTiO3 spheres were synthesized via the self-assembly of nanocrystallites in the presence of Na2SiO3·9H2O through a hydrothermal process. The as-prepared samples were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis and nitrogen gas sorption isotherms. The results revealed that the mesoporous spheres consisted of SrTiO3 nanocrystallites with an amorphous silicate shell and mesopores formed among them. Na2SiO3·9H2O played an important role in the formation of the mesoporous SrTiO3 spheres. Based on the experimental results a possible formation mechanism of the mesoporous SrTiO3 spheres was preliminarily proposed.

Magnetite hollow spheres: solution synthesis, phase formation and magnetic property

Polycrystalline magnetite hollow spheres with diameter of about 200 nm and shell thickness of 30–60 nm were prepared via a facile solution route. For the reaction, ethylene glycol (EG) served as the reducing agent and soldium acetate played the role of precipitator. In addition, polyvinylpyrrolidone (PVP) served as a surface stabilizer. The morphologies and structures were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The intermediate products at different stages were also studied to shed light on the evolution of phase formation. It revealed that the hollow structure formed via self-assembly of nanocrystallites (about 15 nm) using sodium acetate as mild precipitator. Evidences further pointed out that the Ostwald ripening process well explained the growth mechanism of the hollow structure. Magnetization measurements showed that the coercivity of magnetite hollow spheres at low temperature is about 200 Oe and the saturation magnetization is about 83 emu g−1, roughly 85% that of the bulk phase, close to the value of its solid counterpart. In addition, a freezing transition was observed at 25 K.