Solution Synthesis Strategies For Hierarchical Nanostructures And Their Applications

The coupling and synergistic effects of the unique structure of multi-level, multi-dimension, and multi-components allow for the directed synthesis of hierarchical nanostructures and this field has attracted much interest recently. The hierarchical nanostructures exhibit unique physical and chemical properties derived from the unique and novel structure. Fabricate the novel nanoarchitectures with tailored morphologies and geometries, especially hierarchical nanostructures for some functional compounds in the solution-phase is still an interesting task not only in answering basic research questions but also in technological applications. The objective of this dissertation is to explore new avenue for the solution-phase fabrication of hierarehical nanostruetures and the investigation into their applications. Some simple and effective technologies have been developed for assembling highly ordered functional structures. The main points can be summarized as follows:1. Uncovering the reason for structure-dependent thermoelectric performance still remains a big challenge. We herein report a low-temperature and easily up-scalable strategy for synthesizing Bi2Te3nanostrings hierarchical structure through solution-phase reactions, during which there exists the conversion of "homo-hetero-homo" in Bi2Te3heteroepitaxial growth. Bi2Te3nanostrings are obtained through the transformation from pure Bi2Te3hexagonal nanosheets followed by Te-Bi2Te3"nanotops" heterostructure and to Bi2Te3nanostrings. The growth of Bi2Te3nanostrings appears to be a self-assembly process via a wavy competition process generated from the Bi3+and Te. The conversion "homo-hetero-homo" opens up new platforms to investigate the wet-chemistry of Bi2Te3nanomaterial. Furthermore, to study the effect of morphologies and hetero/homo structures especially in the smominge origin and uniform condition on their thermoelectric properties, thermoelectric properties of Bi2Te3nanostrings and Te-Bi2Te3heterostructure pellets fabricated by spark plasma sintering (SPS) have been investigated separately. 2. A facile solvothermal method to fabricate the hierarchical Bi2Te3nanoflowers assembled by2D thin nanosheets with defects has been proposed. Both the chemical growth process and mechanism of hierarchical Bi2Te3nanoflowers have been reasonably analyzed. Moreover, the as-fabricated Bi2Te3nanoflowers are shown to be promising thermoelectric materials with a ZT value as high as0.68. The work will open a new avenue to design thermoelectric materials with defects for obtaining high ZT values.3. The highly orietational CdS dendrite (HOCSD) has been successfully synthesized by a facile hydrothermal method. The gas-sensing characteristics of highly orietational CdS dendrite sensors were investigated. The results showed that HOCSD sensors exhibited excellent response and high response speed to HCOOH and N2H4, compared to HCHO and n-BuNH2. Such high performance of HOCSD sensors towards HCOOH and N2H4could be attributed to the two factors:the improved ability for diffusion and adsorption/desorption of CdS dendrites and the synergistic effect of the reduction ability and hydrogen bonds of detected gases. Moreover, it is believed that HOCSD sensors could be potentially applied to detect the HCOOH and N2H4with high response, fast response speed and good repeatability. To further validate the relationship between the reduction ability and hydrogen bonds of detected gases and the nanomaterial, the mesoporous SnO2has been sueeessfully synthesized via a low-cost ionothermal route using the commercial NH4Cl as the ionic liquid. The as-synthesized mesoporous SnO2have a higher area surface of292.7m2/g. Gas-sensing experiments demonstrate that the mesoporous SnO2exhibits an excellent sensing performance toward highly toxic reducing gases, and excellent selectivity for them.In summary, we presented some facile and environmentally friendly methods for the controllable synthesis of inorganic nanomaterials in this dissertation. It has been proved that the hierarehieal structure is favorable for the improved properties. Furthermore, it is hoped that this findings will aid in the design of new synthetic methodologies for preparation of inorganic materials with functional structure.