Solvothermal Synthesis Of Selenide And Oxides Nanocrystallines And Their Assembly Into Nanocomposites

Nanocrystallines have the unique quantum size effect, surface effect, macroscopic quantum tunneling effect, and other physical characteristics. They also exhibit a variety of uncommon thermal, magnetic, optical, electrical properties that are not displayed by the macroscopic structures in the conventional materials. For this reason, nanocrystallines are expected to find important applications in optoelectronic devices, sensor materials, information technology, biomedical and chemical industry in future. This has driven the rapid development of the synthesis and application of nanocrystallines that have been the hot issue in the past two decades. However, before the full realization of their practical applications, a number of obstacles has to be overcome. Among these is the synthesis of monodisperse and controllable size nanocrystallines that are needed for most functional devices. In this paper, we address this key issue, and studied the synthesis of selenium compounds and oxides nanocrystallines by solvothermal reactions. As a further step towards devices of the synthesized qantum dots, we developed the heterogenous structures of carbon nanotubes-quantum dot and investigated their optical properties.First, we synthesized CdSe, TiO2 and SnO2 nanocrystallines by the solvothermal method. By this, we achieved monodispersed CdSe semiconductor nanocrystallines of 5-6 nm in diameters using the synthesis temperature of 300°C. The nanocrystallines displayed excellent behavior of self-assembly in ordered structures. The nanocrystallines thus produced emitted strong fluorescence at room temperature.Second, uniform and monodispersed spherical titanium dioxide nanocrystallines were synthesized by the nonhydrolytic solution-based reactions using TOPO as solvent and TiCl4 as the precursor. By adding surfactant oleic acid in the reaction, we obtained the rod-like TiO2 nanocrystallines of two different sizes, both of which exhibited nanocrystalline effective photocatalytic activities. The system of the oxide nanocrystallines was further extended to producing tin oxides in use of SnCl4 as precursor in replace of TiCl4 along the similar route. The produced monodispersed and uniform tin oxides emitted super strong nanocrystalline blue fluorescence that was even visible to naked eyes.Third, based on the synthesized nanocrystallines and as a step closer to functional devices of the nanocrystallines, we studied the assembly of the CdSe dots and TiO2 nanocrystallines on one-dimensional nanostructures, including carbon nanotubes and silica nanofibers. We achieved excellent assemblies of the CdSe nanocrystallines on the double-wall carbon nanotubes with the ordered linear arrays across 300 nm in length. Furthermore, well dispersed nanocrystallines were loaded onto SiO2 nanofibers.Finally, loading TiO2 nanocrystalline onto acid or alkali processed multi-walled carbon nanotubes generated the nanocomposite structures of granular and lamellar TiO2, respectively, which are completely different from those in use of CdSe. Moreover, introducing TiO2 into the nitrogen-doped bamboo-shaped carbon nanotubes could led to insert of some TiO2 nanocrystallines inside the bamboo units, with the remainder left on the CNT surfaces either in the form of coatings or in discrete particles.