Chalcogen Compound-based Composite Nanostructures: Fabrication, Mechanism And Properties

Nanoscience and nanotechnology have attracted much attention of scientists in chemistry, physics, biology, and materials owing to its fascinating possible application, and have induced a research upsurge. In the field of nano-materials preparation, all dimensions of nanomaterials with the components almost throughout all the solid state species in periodic table of the elements with ever improving monodispersity and yield have been reported. Based on these developments, the focus of synthetic efforts appears to be shifting to creation of secondary structures of nanoobjects, even more hierarchical and complex nanosystem. The composite nanostructures combined two or more chemical distinct components in one single nanostructure, realize the combination of multifunction, and the effective interaction between nanoobjects will induce some unexpected physics, chemical properties. There is no doubt that this will bring new chance for the development of physics, chemistry, and materials. In this dissertation, we try to fabricate of chalcogen compound-based nanocomposite structures in solution, to develop new methods for preparation of sulfide, oxide-based nanocomposites, to explore the mechanism, and to study the related properties. The main results of this dissertation are outlined as follows:1. We established a one-pot route, successfully synthesized Ag2S-ZnS heterostructures, realized the semiconductor nancrystal Ag2S assistant growth of nanowires for the first time, discovered the catalyst mechanism of Ag2S nanocrystals, which is quite different from SLS mechanism by metal nanoparticle catalyst. The heteroepitaxial interface was carefully studied. The unique feature of this method is that formation of Ag2S and ZnS automatically separated in time. The advantages of this route are:(1) avoiding the separation and purifying of catalyst nanocrystals, (2) the ZnS exclusively grows on the Ag2S nanocrystals forming heterostructures. The length and diameter of ZnS nanowires can be easily controlled and adjusted by changing the reaction parameters. With similar method, cobalt-doped Ag2S-ZnS heterostructures were also synthesized and the magnetic properties were studied. The results indicate cobalt-doped semiconductor nanowires show enhanced saturation magnetic magnetization, the value of which at 2.0 K is up to 1.7 emu/g, and the coercivity up to 250 Oe.2. Ag2S-CdS heterostructures were synthesized by extension of the above method through tuning the reaction dynamics. It was found that the growth of CdS segment is along the direction of (110) crystal plane, the length of CdS segment can be finely tuned by the amount of CdS precursor. With the sequence addition of the precursors, three composition heterostructures (Ag2S-CdS-ZnS) were prepared, which is rare in the literature. The mechanism is discovered, and the interfaces of the corresponding heterostructure were carefully studied. Moreover, we also realized the assembly of the Ag2S-CdS heterostructures on graphene.3. A novel, source-catalyst-assistant "inward-taxial" growth route was developed to fabrication of Ag2S-AgInS2 heterostructured nanocrystals, in which Ag2S nanocrystals not only provide reaction space, but also guide the growth of AgInS2 nanocrystals. Ag2S, as one source for the generation of AgInS2, limits its growth into Ag2S nanocrystal, avoiding the self-nucleation. The morphology of heterostructures can be selectively prepared with different shaped Ag2S particles and reaction temperature. The concentration of the precursor In(dbdc)3 determines the growth location of AgInS2 on Ag2S nanocrystals, and obtained many kinds of shaped Ag2S-AgInS2 heterostructured nanocrystals.4. We demonstrated a chemical precursor route to fabricate vertical ZnO and Co-doped ZnO mesocrystalline nanowall arrays on usual p-Si plate. The obtained n-Zn1-xCoxO nanowall/p-Si heterojunction exhibits a well-defined and reliable rectifying behavior with a lower turn-on voltage tuned by Co2+ dopant concentration. The realization of n-type Zn1-xCoxO nanowall/p-type Si heterojunction will open up opportunities for low-cost and high performance optoelectronic devices based on these nanostructure arrays.5. Based on the electrostatic interaction, a facile and effective method for construction of the flexible composite membranes in solution has been developed. Monodispersived Fe3O4 nanoparticles are facilely assembled on both sides of reduced graphene oxide sheets floated in solution with controllable density. The obtained two-dimensional composite grain membranes exhibit superparamagnetic behavior at room temperature and considerable structure robustness, such as it can sustain supersonic and solvothermal treatments without nanoparticles falling off, also, can freely float in solution and curl into a tube. The composites membrane can be easily controlled by external magnetic field. The magnetic composite membrane exhibits an enhanced adsorption capability for microwave and is a promising absorption microwave materials, also, the large surface, high magnetization moment, and superparamagnetic properties make the grain sheets attractive for biomedical, environmental applications.6. The nanocomposites, Ag coated by Fe3O4 nanoparticles, were fabricated by a green assembly route. Fe3O4 nanoparticles can form a compact coating shell on Ag nanostructures. The obtained nanocomposites demonstrate superparamagnetic behavior. The blocking temperature shifts toward lower temperature owing to the strong interface interaction between Ag and Fe3O4. The Ag/Fe3O4 nanocomposites can be readily manipulated by an external magnetic field forming ordered arrangement. The antimicrobial activities of Ag/Fe3O4 nanocomposites are enhanced. These hydrophilic Ag/Fe3O4 nanocomposites would be suitable for biomedical, catalyst application.